Recent Advances and Techno-Economic Prospects of Silicon Carbide-Based Photoelectrodes for Solar-Driven Hydrogen Generation

Abstract

Silicon carbide (SiC) has attracted increasing attention as a robust photoelectrode material for solar water splitting due to its exceptional chemical stability, mechanical strength, and resistance to photocorrosion. Recent advances in nanostructuring—particularly the development of nanoporous SiC architectures—have dramatically improved light absorption, charge separation, and charge transport in this material. This review summarizes current strategies to enhance the PEC performance of SiC, including hierarchical nanostructuring, defect engineering (e.g., doping to tailor band structure), heterojunction formation with co-catalysts, and incorporation of plasmonic nanoparticles. Remaining challenges are discussed, notably the wide band gap of common SiC polytypes (limiting visible-light utilization) and rapid charge-carrier recombination. In addition, we examine the techno-economic prospects for SiC-based PEC systems, outlining the efficiency and durability benchmarks required for commercial hydrogen production. Finally, we propose future research directions to achieve efficient, durable SiC photoelectrodes and to guide the development of scalable PEC water-splitting devices. This review uniquely integrates material design strategies with techno-economic evaluation, providing a roadmap for SiC-based PEC systems.

1. Introduction

Hydrogen produced from water using solar energy is a promising route towards a carbon-neutral energy system. It represents a central pillar of the emerging hydrogen economy, providing a means to store intermittent solar power in a chemical form with high gravimetric energy density. Recent analyses emphasize that “green” hydrogen, produced via renewable-driven water splitting, can decarbonize industrial sectors such as ammonia synthesis, steelmaking, and long-distance transportation [1,2]. Two related approaches exist: photocatalytic (PC) water splitting, where suspended photocatalyst particles simultaneously generate H₂ and O₂ in a single chamber, and photoelectrochemical (PEC) water splitting, where photoelectrodes (PE) are immersed in an electrolyte and spatially separate the oxidation and reduction half-reactions. PEC devices offer better control over product separation but require uniform and highly structured coatings on conductive substrates [3,4]. Despite significant progress, the fabrication of photoelectrodes remains technologically demanding, as uniform thin films must be deposited directly on conductive substrates while maintaining strong adhesion and optimized band alignment.

PEC processes employ photoabsorbents such as semiconductors, polymers and dyes to harvest light, generate excitons, and activate reduction–oxidation (redox) reactions [5,6]. Generally, the semiconductor must absorb a photon with energy equal or more to its band gap to generate excitons. Once excitons are generated, electrons and holes must be separated and transported to the PE surfaces. Understanding charge carrier transport mechanisms is essential for the development of advanced PE and efficient PEC devices [7]. Moreover, large-scale (LS) implementation depends on process reproducibility and accuracy, which need to establish standards and protocols. To move to large-scale hydrogen production in PEC plants, it is first necessary to overcome threshold indicators: achieving efficiency above 10% and ensuring stable operation for several thousand hours [8].

This review critically surveys recent progress in SiC-based PEC water splitting. We begin by summarizing synthesis routes and nanostructuring strategies for producing porous and one-dimensional SiC photoelectrodes. Next, we discuss defect engineering and doping approaches used to tailor the band structure and carrier concentration. We then examine heterojunctions and co-catalysts—both inorganic and plasmonic—that improve catalytic kinetics and extend light absorption. Finally, we highlight current challenges, including scalability, cost, and long-term stability, and outline future research directions aimed at realizing efficient and durable SiC-based PEC systems.

2. Fundamental PEC Principles

In semiconductors-based PEC processes, photoabsorbents immersed in an aqueous electrolyte must possess suitable band edge positions with respect to water redox energies (Figure 1). Ideally, PEC water splitting requires a significant energy input to overcome Gibbs free energy of 237 kJ/mol, with theoretical minimum energy equal to 1.23 eV per electron required. In real conditions, H₂ production is accompanied by energy losses due to charge recombination and inefficient light absorption. Moreover, aqueous electrolytes absorb light, particularly in the near-infrared range, posing challenges for multilayer PE with a bandgap below 1.5 eV. Reducing the electrolyte thickness decreases light absorption but simultaneously increases voltage losses due to hindered ion transport. Therefore, an optimal balance between light absorption efficiency and ionic conductivity is important. The optimal water layer thickness for a silicon-based PEC cell is calculated to be about 5 mm [9]. Therefore, to design an efficient PEC reactor several key stages need to be considered:

(1)

Photon absorption by the semiconductor (hv ≥ Eg), leading to exciton generation.

(2)

Charge separation and migration of photoinduced electrons and holes to the semiconductor–electrolyte interface.

(3)

Surface redox reactions at the photoanode and photocathode.

(4)

Optimization of electrolyte properties, including pH, concentration, and thickness, to balance ionic transport and optical transparency.

The main and possible side reactions occurring in PEC water splitting are summarized in series of equations (Scheme 1).

(1)

Overall reaction—2H₂O(I) → 2H₂(g) + O₂(g)—Overall water splitting reaction requiring ≥ 1.23 eV per e⁻

(2)

Photoanode (oxidation)—2H₂O → O₂ + 4H⁺ + 4e⁻—Oxygen evolution reaction (OER) driven by photogenerated holes (h⁺)

(3)

Photocathode (reduction)—4H⁺ + 4e⁻ → 2H₂—Hydrogen evolution reaction (HER) driven by photogenerated electrons

(4)

Intermediate step 1—H₂O + h⁺ → •OH + H⁺—Formation of hydroxyl radicals as reaction intermediates

(5)

Intermediate step 2—2•OH → H₂O₂—Recombination of hydroxyl radicals leading to H₂O₂ formation

(6)

Side reaction (undesired)—H₂O₂ + 2h⁺ → O₂ + 2H⁺—Oxidation of hydrogen peroxide causing reduced Faradaic efficiency

(7)

Surface oxidation (SiC)—SiC + 2h⁺ + 2OH⁻ → SiO₂ + C + H₂O—Possible surface oxidation under strong anodic bias

(8)

Recombination—e⁻ + h⁺ → heat or luminescence—Non-productive recombination reducing PEC efficiency

The photoanode facilitates the oxygen evolution reaction (OER), while the photocathode performs the hydrogen evolution reaction (HER). The overall PEC water-splitting process is illustrated schematically in Figure 2. The energy band diagram indicates that SiC polytypes (4H-SiC, 6H-SiC, 3C-SiC) possess favorable band-edge positions straddling the redox potentials of water (0 V and +1.23 V vs. RHE), enabling spontaneous water splitting without external bias.

Scheme 1. Operational principle of PEC water splitting with two semiconductor electrodes (with permission from MDPI, 2023 [10]).

Scheme 1. Operational principle of PEC water splitting with two semiconductor electrodes (with permission from MDPI, 2023 [10]).

SiC’s unique combination of chemical inertness, high thermal stability, and tunable conductivity makes it suitable for both photoanode and photocathode roles [11,12]. Nevertheless, possible side reactions (e.g., peroxide formation or surface oxidation) must be carefully managed through surface passivation, co-catalyst deposition, and band-edge engineering.

Additionally, external factors such as magnetic and electric fields can assist charge separation, while nanostructuring, doping, and heterojunction formation can enhance charge transport efficiency.

If sufficient energy is provided to overcome the barriers, the water redox reaction proceeds to generate H₂ and O₂. Figure 1 presents the energy diagram with band edge positions of various semiconductors.

Figure 1. The bandgap and band position of semiconductors investigated for solar conversion with the water redox potentials (red dotted) (with permission of WILEY-VCH Verlag GmbH&Co. KGaA 2020 [13]).

Figure 1. The bandgap and band position of semiconductors investigated for solar conversion with the water redox potentials (red dotted) (with permission of WILEY-VCH Verlag GmbH&Co. KGaA 2020 [13]).

The energy levels of band edges of some semiconductors align with either oxidation or the reduction potential, making them suitable exclusively as photoanodes or photocathodes. However, certain materials can exhibit both n-type and p-type conductivity under specific modifications or doping [14].

The bandgap diagram (Figure 1, green-yellowish bars) highlights SiC as a promising material for PEC water splitting due to its favorable band alignment and versatility. Displayed SiC polytypes 4H-SiC, 6H-SiC, and 3C-SiC (Figure 1) straddle the water redox potentials (0 V and 1.23 V vs. RHE—Reversible Hydrogen Electrode), enabling unassisted PEC water splitting, distinct Cu₂O (2.2 eV), which aligns only for reduction, or TiO₂ (3.2 eV), which struggles with visible light absorption [15,16]. Notably, 3C-SiC smaller bandgap allows better visible light utilization, achieving a solar-to-hydrogen (STH) conversion efficiency of 0.38%, outperforming wide-bandgap materials while narrow-bandgap materials such Si (1.14 eV) misaligned for oxidation. Therefore, SiC is a strong candidate for both photoanode and photocathode material in PEC systems and tandem structures.

Various methods are being investigated to improve the efficiency of charge separation. In addition to developing new materials [17], external influences are being tested. Since electrons and holes can recombine without participating in chemical reactions, external bias, auxiliary redox reagents, or external fields employed to facilitate separation. The external electric fields enhance electron–hole separation, while magnetic fields influence charge trajectories, improving transport efficiency. As a result, both magnetic and electric fields reduce energy barriers [18,19]. However, since reliance on external magnetic and electric fields may limit practical applicability, the scientific community is particularly interested in materials capable for efficient exciton separation and rapid charge transportation without additional external inputs. Traditionally, PEC systems are classified as: (1) single light absorber based on either photocathode, or photoanode; (2) hybrid tandem cells based both the photoanode and photocathode [20] or based on single PE integrated with photovoltaic cells [21].

In single-PE reactors, the counter electrode is typically platinum (work function: 5.3–5.6 eV) or a cost-effective alternative such as Cu₂S/brass [22], which facilitates electron transfer, minimizing charge recombination. Tailoring the size of semiconductor materials, modifying band structure, leveraging pyroelectric, piezoelectric, and ferroelectric effects, and incorporating intermediate layers further enhance charge separation and transport efficiency [23]. Advances in nanotechnology and nanoengineering enable the fabrication of PE layers with precisely controlled geometries [24]. Attachment of as-prepared low-dimensional particles onto PE offer increased surface area and flexible structural tuning. However, such strategies faces challenges, including weak adhesion to the substrate or matrix, and limited stability during prolonged operation [25]. To improve the contact between PC layers and substrate, research exploited the strategy of forming nanostructures directly on PE surfaces via an aerosol-assisted vapor-phase deposition [26], laser interference lithography and hydrothermal synthesis [27], controlled electrical field exposure on ferroelectric material layers to create regions with alternating polarization [28], pulsed Joule heating [29], arc-plasma irradiation [30], combustion synthesis [31], electrospinning [32], anodization [33], etc. Direct deposition techniques, post-treatment [34,35], incorporation of co-catalysts (Figure 2A), buffer layers, and donor-acceptor doping (Figure 2B) or two-step PC systems employment (Figure 2C) are well-proven methods overcoming PEC challenges [36]. Figure 2 depicts energy diagrams for PEC water splitting (A) semiconductor with a co-catalyst uses UV light to excite electrons from valence band; co-catalyst facilitates rapid charge separation; (B) semiconductor with impurity levels absorbs visible light, exciting electrons from the impurity level to the conduction band; (C) Z-scheme with two semiconductors employs visible light for stepwise excitation, enabling efficient redox reactions.

Since polarons and defect states hinder charge conductivity, while oxygen vacancies introduce defect states within the bandgap, enhancing light absorption but promoting charge recombination [37], the managing of lattice structure is important. Lei et al. in [38] highlighted surface defects as promotive better charge separation, whereas bulk defects lead to charge recombination. Nevertheless, surface treatments and defect passivation have proven effective in suppressing recombination. Surface defects passivation reduces charge losses and improves separation [39]. Wei et al. [40] demonstrated that passivating defects by depositing a thin layer of protective coating based on perovskites significantly reduces recombination and enhances charge separation. In SiC, polarons can form due to the interaction of charge carriers with the polar lattice, as SiC has a partially ionic character. Defect states in SiC, such as those from silicon or carbon vacancies or impurities, introduce energy levels within its bandgap. These states can act as recombination centers, competing with the desired redox reactions. Oxygen vacancies in oxidized SiC, thin SiO₂ film formation, introduce defect states that enhance conductivity by providing additional electrons.

Figure 2. Energy diagrams for photoelectrochemical water splitting. (A) Wide-bandgap semiconductor with co-catalysts, enhancing charge separation. (B) Wide-bandgap semiconductor with impurity energy levels, modifying band structure. (C) Z-scheme using two narrow-bandgap semiconductors for efficient redox reactions (with permission from MDPI, 2024 [41]).

Figure 2. Energy diagrams for photoelectrochemical water splitting. (A) Wide-bandgap semiconductor with co-catalysts, enhancing charge separation. (B) Wide-bandgap semiconductor with impurity energy levels, modifying band structure. (C) Z-scheme using two narrow-bandgap semiconductors for efficient redox reactions (with permission from MDPI, 2024 [41]).

Practical PEC operation requires thermal stability at temperatures that may exceed 80 °C during sunlight exposure, far above the electrolyte’s freezing point [42]. Temperature of PEC enhances charge carrier transport and reaction efficiency; however, prolonged thermal exposure can cause structural changes and performance degradation in materials, emphasizing the importance of thermal management [43,44,45]. SiC exhibits exceptional thermal and mechanical stability, enabling it to withstand extreme temperatures up to 2258 K without degradation, ensuring reliability in reaction environments, even in solar thermochemical reactors [46,47,48] and nuclear waste storage systems [49].

Compared to the different semiconductors for PEC, distinctive characteristics of SiC include a unique combination of properties that makes it a promising candidate for water-splitting. Consequently, SiC is exploited as a protective layer for PC semiconductors, such as a-Si/a-SiGe, to enhance stability in alkaline electrolytes [50]. Compared to toxic materials, SiC is more environmentally friendly and resistant to photocorrosion in long-term application.

This review explores recent advancements in nanostructured SiC PE, focusing on design, performance improvements, and potential applications in PEC water splitting. By examining recent developments and comparing SiC with other materials, we aim to underscore promise and suggest future research directions to optimize efficiency and stability.

3. Silicon Carbide PEC Water Splitting

In recent years, SiC has emerged as a material of great interest due to its high chemical stability, environmental friendliness, mechanical strength, and thermal stability under extreme conditions [13]. However, rapid charge carrier recombination limits exploitation of SiC in PEC reactions. To overcome the limitations, various strategies have been proposed, including selection of optimal SiC polytypes, implementation of nanostructuring, structural modifications, and development of composites. Although SiC (even 3C-SiC) is limited in visible light absorption, several strategies (such as nanostructuring and co-catalyst integration) have been investigated to improve PEC performance [51].

The fabrication of SiC coatings for PE requires strict control over quality, uniformity, and adhesion to the substrate. Processes such as chemical vapor deposition [52,53,54], molecular beam epitaxy [55,56], ion beam synthesis of SiC on Si [57], and the coordinated atomic substitution (CAS) method [58] are the dominant techniques for synthesizing thin SiC films. Listed methods provide high purity and crystal quality but require complex equipment and stringent control over process parameters such as temperature, pressure, and reaction environment. The CAS method enables the sequential replacement of Si atoms with C atoms in the near-surface layer while preserving the crystalline structure of the substrate. SiC is formed through the chemical interaction of CO with Si at temperatures up to 1410 °C, leading to the substitution of Si atoms with C atoms in the crystal lattice [59]. However, the unit cell volume of SiC is roughly half that of Si, so the CAS method faces several challenges. Beyond 200 nm of SiC layer thickness, the adhesion between SiC and the Si substrate deteriorates, resulting in poor interfacial contact [60]. Since charge transfer in the water splitting reaction is an important parameter, contact between the synthesized layers is vital. Peng et al. [61] investigated SiC/CdS heterostructure synthesized via both hydrothermal deposition and wet chemistry. Hydrothermal deposition yielded a more compact SiC/CdS interface compared to the wet-chemistry method. A proper interfacial contact led to a higher hydrogen evolution rate (363 μmol h⁻¹g⁻¹) and an extended lifetime of photogenerated electrons (3.13 ns) [61].

Advancements in material science enabled the controlled synthesis of SiC with tailored sizes, morphologies, and porosities [62]. Controlling the morphology of SiC films allows for regulation of charge accumulation and transport [63]. According to Kulkarni, SiC coatings classified into two main types—non-porous α-SiC and porous β-SiC. Generally, non-porous α-SiC synthesized at high temperatures (1700–2400 °C) via a solid-state reaction between Si and C. The resulting product has a very low surface area (<1 m²/g) and is suitable only as a diluent in catalytic reactions. Porous β-SiC exhibits either random porosity (surface area > 200 m²/g, with micro-, meso-, and macropores) or ordered porosity, such as mesoporous structures (pore size 2–50 nm) and hierarchical forms with bi- and tri-modal porosity which are good for catalysis, as catalytic supports, and in energy storage systems (Figure 3) [64]. Li et al. in [65] reported that nanoporous SiC photoanodes outperformed planar ones by a factor of 342 facilitated by the increased surface area (Figure 4) [65]. Similarly, Jian et al. achieved a photocurrent density of 2.30 mA/cm² at 1.23 V vs. RHE—3.3 times higher than planar SiC—with light absorption efficiency exceeding 93% and charge injection efficiency reaching 91% [66].

Control the level of porosity or formation nano structures onto surface of as-prepared SiC perform through plasma treatment. Plasma etching of SiC surfaces significantly increases surface area, reduces electron–hole recombination, and tunes the band gap, therefore improves physicochemical properties. The ensuing strategy of mitigation recombination is creation charge retention sites or reservoirs. Hole storage medium formed by deposition C layer on SiC prevents rapid recombination with electrons. Xu et al. [67] demonstrated that C coating reduces electrical resistance of SiC photoanode allowing achieve STH to 2.67% [67]. Similarly, C nanostructures deposited onto SiC improve conductivity and facilitate electron transport, achieving a hydrogen evolution rate of 3160.2 μmol/g/h, significantly outperforming unmodified SiC [67].

As water molecule adsorption is highly dependent on surface and PE composition [68], the semiconductor-electrolyte interface is crucial for reaction kinetics [69,70]. High reaction rate facilitates photocurrent densities, whereas slow oxidation reaction kinetics lead to self-oxidation of the material [5,71], reducing stability. Adjusting pH of the electrolyte significantly impacts the PEC properties and employs to tune bandgap energy of SiC. Zhao et al. demonstrated a shift in photoluminescence from the blue to the green region due to pH variations in 3C-SiC nanocrystals. The photoluminescence shift is associated with surface states that influence charge recombination and enhance the hydrogen evolution efficiency on the surface [72]. In alkaline conditions, the flat band potential shifts negatively, favoring cathodic processes. Conversely, in acidic conditions, the potential shifts positively, promoting anodic processes. Notably, SiC shows greater corrosion resistance in alkaline media. Conversely, acidic environments degrade its stability: under anodic polarization, SiC undergoes electrochemical oxidation, where Si–C bonds are broken, leading to the formation of intermediate silicon oxides (SiO_x) and carbonaceous species on the surface. These oxides subsequently dissolve or hydrolyze, releasing gaseous CO and CO₂ as final products. The corrosion process proceeds through oxidation of surface Si atoms to SiO₂, accompanied by carbon oxidation, resulting in gradual thinning and roughening of the SiC layer. For n-type SiC, the flat-band potential shifts linearly with pH (~52 mV per unit for 3C-SiC). Alkaline conditions, by contrast, enhance charge separation and electrode stability due to the formation of a passivating SiO₂ layer, although the more negative flat-band potential may slightly reduce the driving force for anodic reactions. Meanwhile, acidic conditions favor anodic charge transfer but compromise long-term stability due to continuous oxide dissolution and carbon gasification [73,74,75,76,77,78,79,80,81,82].

Table 1. PEC water splitting with electrode material based on SiC in various electrolytes.

№	Electrode Material/Type/Band Gap	Light Source/Electrolyte	Bias	Photocurrent Density	Source
Na2SO4 electrolyte
1	6H–SiC and 3C–SiC s/n-type/6H–SiC has a band gap of 3.0 eV, and 3C–SiC has a band gap of 2.3 eV	Monochromatic light of 410 nm wavelength (30 mW cm−2)/0.5 M Na2SO4 solution at pH 6.8	Onset potential of 0 V vs. RHE for the Si-face, and photocurrent measurements reaching a maximum at 0.4 V	The Si-face of 6H–SiC produced a photocurrent density of 1.01 mA/cm2 at 0.4 V	[77]
2	4H-SiC nanohole arrays/n-type 4H-SiC/2.61 eV	AM1.5G (100 mW/cm2)/0.5 M Na2SO4 aqueous solution (pH ~6.8)	1.23 V vs. RHE	3.20 mA/cm2	[79]
3	SiC core–TiO2 shell nanoarrays/type-II heterojunction/2.3–3.2 eV	100 mW/cm2/1 M Na2SO4 solution buffered to pH 6.8	1.4 V vs. Ag/AgCl	3.62 mA/cm2	[80]
4	4H-SiC nanohole arrays integrated onto a SiC wafer substrate/n-type 4H-SiC/2.61 eV for the SiC nanohole arrays, 2.65 eV for the original 4H-SiC	350 W Xe, AM 1.5 G, 100 mW/cm2/ 0.5 M Na2SO4 aqueous solution (pH 6.8)	0.016 V vs. RHE 1.23 V RHE	3.20 mA/cm2 at 1.23 V vs. RHE	[81]
5	SiC@g-C3N4 core–shell NW/n-type/3C-SiC—2.4 eV, g-C3N4—2.6 eV	300 W Xe (includes UV and visible light)/0.1 M Na2SO4 solution	−0.6 V vs. Ag/AgCl	−0.62 mA cm−2 at −0.6 V vs. Ag/AgCl	[75]
6	3C-SiC/n-type/2.36 eV	AM1.5G (100 mW/cm2)/1 M NaOH solution	0 V vs. RHE	10 mA/cm2	[76]
7	Nanoporous 3C-SiC photoanodes/n-type/2.36 eV	AM 1.5G 100 mW/cm2/1.0 M NaOH solution	1.23 V vs. RHE	2.30 mA/cm2	[66]
8	3C-SiC/n-type/2.36 eV (cubic SiC)	AM 1.5G (100 mW/cm2)/1.0 M NaOH solution	0 V vs. RHE (onset potential ~0.40 V RHE)	0.5 mA/cm2 at 1.0 V RHE (for NiO/3C-SiC)	[83]
9	Epitaxial 3C-SiC/p-type/2.5 eV	A 150 W Xe lamp with a UV filter (λ > 420 nm)/0.5 M H2SO4	1.0 V vs. Ag/AgCl	20 mA/cm2	[84]
10	Epitaxially grown 4H-, 6H-, and 3C-SiC/p-type/2.3 eV (3C-SiC), 2.9 eV (6H-SiC), 3.2 eV (4H-SiC)	1 W/cm2/1 M H2SO4	Self-driven	3C-SiC 20 mA/cm2	[85]
11	a-SiC based/from 2.0 eV (PEC1) to 1.7 eV (PEC3)	AM 1.5 spectrum, 1000 W/m2/1 M H2SO4 with pH 3	0 V vs. RHE for PEC3	50 µA/cm2	[86]
12	SnO2/SiC nanowire/n-type/SiC 2.4 eV, SnO2 3.6 eV	A 300 W Xe/1.0 M H2SO4	0.6 V vs. Ag/AgCl	62.0 mA/cm2, 6.9 times higher than pristine SiC NW	[74]

summarizes the main PEC characteristics of SiC-based photoelectrodes in different electrolytes”.

Among the more than 250 known SiC polytypes, the most widely studied β-SiC (3C-SiC, cubic) and α-SiC (4H-SiC, 6H-SiC hexagonal and 15R-SiC rhombohedral). PEC application of pentagonal p-SiC with band gap 2.35 eV and high charge mobility (up to 2500 cm²/V·s) investigated rarely. But it is known that the valence and conduction bands of p-SiC are well-suited for PEC reactions; furthermore, isotropic strain tuns band gap allowing adjustments tailored properties for different PC applications [87].

As summarized in Table 1, SiC-based photoelectrocatalysts exhibit remarkable versatility depending on crystal phase, morphology, and surface modification. Among these, 3C-SiC stands out as the most efficient polytype for PEC hydrogen generation due to its favorable band gap (~2.36 eV), visible-light absorption capability, and relatively long charge-carrier diffusion length [88]. However, its overall activity is limited by charge recombination and sluggish water oxidation kinetics. Recent research therefore focuses on nanostructuring and heterojunction engineering to overcome these issues. For instance, ultrathin 3C-SiC nanocrystals (<8 nm) demonstrate efficient photocatalytic water splitting due to the autocatalytic behavior of Si surface sites, facilitating water dissociation into Si–H and Si–OH with minimal energy barriers. Experiments in 0.5 M Na₂SO₄ (pH 6) show that nanocrystals sized 3.0–3.6 nm exhibit a low onset potential and high activity compared to larger particles (~20 nm) [72]. On the other hand, among SiC polytypes 3C-SiC exhibits the highest conversion efficiency (0.38%) due to the ability to absorb part of the visible light and the prolonged charge carriers diffusion in epitaxial samples [88]. In

Table 2. Comparative characteristics of SiC polytypes used in PEC hydrogen generation.

SiC Polytype	Bandgap (eV)	Carrier Concentration (cm−3)	Carrier Mobility (cm2V−1s−1)	Typical Photocurrent Density (mA cm−2)	Optimal Electrolyte (pH)
3C-SiC	2.08–2.38	1 × 1017–1 × 1018	800–1000	1.5–2.5	Neutral or weakly alkaline
4H-SiC	3.26	1 × 1016–1 × 1017	900–1200	2.0–3.2	Alkaline (pH ≈ 13)
6H-SiC	3.02	5 × 1015–1 × 1017	500–700	1.0–2.0	Neutral
15R-SiC (α-SiC)	3.10	1 × 1016–1 × 1018	400–600	1.0–1.8	Neutral to weakly alkaline
p-SiC (pentagonal)	2.35	~1 × 1017	up to 2500	2.5–4.0	Neutral (pH ≈ 7)
a-SiC (amorphous)	1.4–2.0	1 × 1018–1 × 1020	10–50	0.3–1.0	Acidic (pH ≈ 4–6)

, the photoelectrochemical performance of SiC polytypes, which is strongly influenced by their crystal symmetry and band structure, is summarized. The presented parameters are based on generally accepted fundamental data reported in the literature. Despite 3C-SiC suitable for both cathodic and anodic water-splitting processes, efficiency is significantly higher in cathodic mode for hydrogen evolution [89]. Plasma treatment of 3C-SiC nanowires (NW) reduces the band gap from 2.38 eV to 2.08 eV [90]. Wang et al. reported an increase in photocurrent density to 78.8 mA/cm² for plasma treated SiC PC layers, compared to 4.6 mA/cm² before treatment. Furthermore, the lifetime of photogenerated charges increased from 0.32 to 1.18 s, reducing recombination [91].

To further enhance the separation of photogenerated charges, heterostructure design has emerged as a key strategy. In this context, Zeng et al. [92] reported the fabrication of a Ni(OH)₂/Co₃O₄/3C-SiC composite, which introduces a built-in electric field promoting charge separation and extending carrier lifetime. In this configuration, Co₃O₄ serves as a hole-extraction layer transferring holes to Ni(OH)₂, an OER co-catalyst that accelerates oxygen evolution by lowering the kinetic barrier. XPS and XAS analyses confirmed Ni–O–Co bond formation, high-spin cobalt states, and enhanced electron delocalization, all of which contribute to improved OER activity. XANES and EXAFS confirm increased electron delocalization and Co-O bond elongation due to CoO₆ distortion, while Ni K-edge spectra validate Ni(OH)₂ structure. Figure 5 depicts spectroscopic characterization of Ni(OH)₂/Co₃O₄/3C-SiC photoanodes: (a) Raman spectra confirm Ni(OH)₂ and Co₃O₄; (b) Co 2p XPS shows a binding energy shift, reflecting electronic interaction; (c) Ni 2p XPS verifies Ni²⁺ in Ni(OH)₂; (d) O 1s XPS reveals Ni-O and Co-O bonds with a Ni-O-Co shift; (e) XAS at Co and Ni L-edges indicates cobalt’s high-spin state and confirms Ni(OH)₂ structure [92].

6H-SiC possess significant potential for application in self-powered PEC water splitting cells due to its semiconductor properties; however, the slow water oxidation kinetics requires surface modification, crystallographic orientation tuning or cocatalysts [93]. Surface modification of 6H-SiC is achieved by ion implantation or post-annealing methods. Ion implantation forms bubbles and ripples on the surface, which enhance optical absorption and improve charge separation by changing the morphology. Annealing, in turn, creates defects such as vacancies or impurity levels, which improve optical absorption, but, on the other hand, serve as recombination centers [94]. Xu et al. in [78] demonstrated that the Si- faces of 6H-SiC exhibits superior OER kinetics and lower charge recombination than the C-polar. On Si- faces, O-H bond cleavage occurs without significant energy barriers. In contrast, on the C-face, the primary limiting factor is O-H bond cleavage, which leads to higher recombination rates. Figure 6 presents water oxidation kinetics on C- and Si-faces under 410 nm light [78] (Figure 6). In 6H-SiC, the generated electrons and holes migrate to different facets due to differences in their energy levels. The Si-(0001) facets, rich in Si atoms, attract electrons, whereas the {10-10} facets, containing Si and C, collect holes due to differences in the surface structure and electronic properties of the facets. DFT calculations by Wang et al. [95] show that Si-(0001) has a lower electron density (−1.2 e/ų near Si) compared to {10-10} (up to 3 e/ų near C), which creates a potential difference that drives electrons to Si-(0001) and holes to {10-10}. Mott–Schottky analysis confirms that the conductivity level of Si-(0001) is 0.28 eV higher and the valence band is 0.42 eV lower than that of {10-10}, enhancing charge separation [95]. In 4H-SiC polytype on Si-terminated surface (0001) PEC process begins with the adsorption of a water molecule (H₂O) on a Si atom. This adsorption induces structural rearrangements, increasing the distance between neighboring Si atoms by 0.25–0.40 Å, which is a reasonable range for surface relaxation due to the interaction with H₂O. The first hydrogen atom from H₂O dissociates without an energy barrier, forming a Si-H bond (with a bond length of 1.48 Å, typical for Si-H bonds) and a Si-OH group (with a bond length of 1.66 Å, consistent with Si-O bonds in hydroxyl groups). The second dissociation step, splitting the OH group, requires overcoming an energy barrier of 0.65 eV, resulting in two Si-H bonds and a Si-O bond. The final step, desorption of two hydrogen atoms to form H₂, has a high energy barrier of 3.04 eV, which limits the overall reaction kinetics—a common bottleneck in PEC water splitting due to the stability of Si-H bonds [96].

4. Co-Catalysts and Metallic Modifications

Co-catalysts such as Ni, CoPi, NiO_x, etc. can accelerate specific reaction steps, facilitate oxygen evolution [1], and shift the photocurrent onset potential [97]. Ni gained significant attention as a co-catalyst due to its ability to reduce overpotential, making the reaction more energy efficient. Coating 3C-SiC with Ni significantly increases the photovoltage up to 0.82 V, ensuring that the majority of charge carriers participate in the H₂ evolution reaction, which demonstrates a high efficiency with minimal side reactions [98]. The addition of Ni/Ni–Mo catalysts onto amorphous SiC surfaces further reduces overpotential and increases photocurrent density, enhancing charge transfer rates and PC activity in alkaline environments [99]. A NiO_x/SiC/CNOs PC with a band gap of 2.4 eV achieved a hydrogen evolution rate of 3160.2 μmol/(g·h) when 1.0% NiO_x was added. The addition of NiO_x enhances charge transport and reduces electron–hole recombination, as evidenced by decreased photoluminescence intensity [100].

Table 3. Co-Catalysts assisted PEC water splitting by SiC Electrode Material.

№	Electrode Material/Type/Band Gap	Light Source/Electrolyte	Bias	Photocurrent Density	Source
1	SiC WR with Ni NP/2.36 eV	300 W Xe/1 M KOH aqueous solution	1.4 V vs. Ag/AgCl	−32.4 mA/cm2, significantly higher compared to pristine SiC NW (−3 mA/cm2)	[101]
2	a-SiC, Ni/Ni-Mo catalysts/2 eV	AM1.5 450W Xe (100 mW/cm2)/1 M potassium hydroxide (KOH) solution (pH 14)	0 V vs. RHE	−14 mA/cm2	[99]
3	(a-SiC(Al))/p-type	AM 1.5 at 1000 W/m2/1 mol/L sulfuric acid (H2SO4) solution with pH 0	−2 V	−17 mA/cm2 at −1.75 V for the 600 °C annealed sample, while the 700 °C sample achieved about −1 mA/cm2	[102]
4	Nanostructured NiO and 3C-SiC/p–n heterojunction/ 3C-SiC 2.36 eV, NiO 3.52 eV	AM1.5G, 100 mW/cm2/1.0 M NaOH solution	0.55 V RHE, with onset potential at 0.20 VRHE	1.01 mA/cm2 at 0.55 VRHE /IPCE 31% under 410 nm LEDs at 1.0 mW/cm2	[82]
5	Nanoporous 6H-silicon carbide (6H-SiC) with a conformal coating of Ni-FeOOH nanorods as a water oxidation cocatalyst/n-type/3.02 eV	AM1.5G illumination at 100 mW/cm2/1.0 M NaOH solution	1 V_RHE	0.684 mA/cm2/IPCE 25% at 410 nm and 12% at 450 nm	[65]
6	N-doped 4H-SiC/n-type/1.416 eV	300 W Xe lamp with an AM1.5, 100 mW/cm2	1.4 V vs. Ag/AgCl	6.50 mA/cm2 at 1.4 V (vs Ag/AgCl), 50.1% enhancement over non-piezoelectric conditions	[103]
7	Nanoporous 3C-SiC photoanode + Ni:FeOOH OER cocatalyst/Transition-metal oxyhydroxide/2.36 eV	AM 1.5G (100 mW cm−2)/1.0 M NaOH	1.23 V vs. RHE	2.30 mA cm−2	[66]
8	Nanoporous 6H-SiC photoanode + Ni–FeOOH coating/Transition-metal oxyhydroxide/3.0–3.2 eV	AM 1.5G (100 mW cm−2)/alkaline	Onset ≈ 0 V vs. RHE 1.0 V vs. RHE	0.684 mA cm−2 @1.0 V vs. RHE	[65]
9	3C-SiC photoanode with Ni(OH)2/Co3O Conversely, acidic environments dual-interface modifier/Transition-metal hydroxide and oxide	AM 1.5G/alkaline	1.23 V vs. RHE	1.68 mA cm−2	[92]

summarizes recent progress of PEC performance by co-catalysts assisted SiC semiconductors.

The application of metal nanoparticles (often termed plasmonic particles) has become widespread [104]. Plasmonic particles interact with light at specific frequencies, inducing collective oscillations of electrons on the metal surface [105,106,107]. The introduction of such nanoparticles enhances the radiation (light field) during energy conversion, which leads to enhanced generation and separation of photogenerated carriers [108]. Additionally, metal nanoparticles offer high stability and corrosion resistance in acidic environments [109]. Plasmonic effects occur when the size of metal nanoparticles is smaller than the wavelength of light, resulting in unique optical, electrical, and catalytic properties (Figure 7). For n-type semiconductors, a Schottky contact forms at the metal interface, which enhances charge separation and improves photocatalytic efficiency (Figure 7A). In general, plasmonic enhancement arises due to localized surface plasmon resonance (LSPR), leading to the generation of hot electrons and holes in the metal, which are subsequently transferred to the semiconductor, boosting photocatalytic performance (Figure 7B). Furthermore, resonant energy transfer via near-field enhancement increases photocatalytic efficiency if the LSPR energy matches the semiconductor band gap (Figure 7C) [41].

Au, Ag, and Cu possess energy levels suitable for exciting surface plasmons in the visible and near-infrared regions, making them promising for photocatalytic applications [110,111,112]. However, each metal presents distinct advantages and limitations. Kwon et al. [113] showed that Ag nanoparticles outperform Au nanoparticles in light absorption within the 400–500 nm range. Conversely, a hierarchical ZnO/CuO/Au nanostructure demonstrated greater stability and a twofold increase in photocurrent compared to a ZnO/CuO/Ag structure, highlighting Au superior stability in such systems [113]. The incorporation of noble metals-based composites significantly enhances PC activity by improving charge transfer and reducing recombination. Metals such as Pt, Ag, and Au act as charge carrier “bridges”, facilitating efficient electron–hole separation [114]. SiC serves as a stable support for Pt, preventing chemical degradation in corrosive environments, ensuring uniform distribution of the active metal, and maintaining catalytic activity at high temperatures [115]. Incorporating Pt into SiC increased the hydrogen production rate by 175 times compared to pure SiC, achieving a hydrogen evolution rate of 2980 μmol·g⁻¹·h⁻¹ [29]. Wang et al. [116] investigated an Au–Pt–SiC composite where Pt, deposited on the Si-(0001) face, forms a Pt–Si chemical bond. This bond creates a channel for rapid transfer of photogenerated electrons from SiC to Pt for proton reduction (H⁺ to H₂). Au, via localized surface plasmon resonance (LSPR), absorbs light in the 400–700 nm range, broadening the absorption spectrum and generating high-energy electrons that enhance catalytic activity. The LSPR effect in Au induces an electron deficiency, lowering its Fermi level and increasing the work function to ~7.0 eV compared to 5.4 eV for Pt. This creates an additional electric field in the Au–Pt structure, facilitating directional electron transfer from SiC through the Pt–Si bond to Au, where they participate in reduction reactions. The synergy between Au’s LSPR and the Pt–Si bond minimizes recombination, yielding a quantum efficiency of 2.2% at 420 nm [116].

Similarly, Ag nanoparticles enhance light absorption and quantum efficiency in SiC-based systems. Incorporating 3% Ag into a SiC/g-C₃N₄ heterostructure extends the absorption range to 463 nm and increases the apparent quantum efficiency (AQE) to 7.3% at 420 nm. This improvement, driven by enhanced charge transfer and reduced exciton recombination, is evidenced by high stability in cyclic experiments and a hydrogen evolution rate of 2971 μmol·g⁻¹·h⁻¹ [117].

Table 4. Plasmonic assisted PEC water splitting by SiC Electrode Material.

№	Electrode Material/Type/Band Gap	Light Source/Electrolyte	Bias	Photocurrent Density	Source
1	n-type 3C-SiC with Au or Pt nanoparticles deposited on the surfaces/2.3 eV	AM 1.5G (1 kW/m2)/1 M KOH	Reduced from −1.64 V vs. SCE to −1.40 V and −0.76 V after incorporation Au and Pt, respectively	38 mA/cm2 with Pt	[118]
2	Au nanoparticles (NPs) decorated on SiC NW/3C-SiC having a bandgap of 2.3 eV and 6H-SiC having a bandgap of 3.3 eV	300 W Xe/0.5 M Na2SO4	0.5 V vs. Ag/AgCl	The apparent quantum efficiency 2.12% at 365 nm	[77]
3	p-SiC with Pt metal islets/3.0 eV	50 mW/cm2 Xe/0.5 M H2SO4		0.135 mA/cm2 was obtained for the p-SiC/Pt system. The self-driven p-SiC/n-TiO2 system showed a maximum photocurrent density of 0.05 mA/cm2	[119]
4	Pt-loaded SiC photocathode/2.4–2.5 eV	AM 1.5G/borate buffer solution (pH 9.1)	−0.6 V vs. Ag/AgCl	0.62 mA cm−2	[120]

summarizes resent progress of PEC performance by plasmonic assisted SiC semiconductors.

5. Data-Driven Technoeconomic Assessment of SiC-Based PEC Systems

Recent comparative techno-economic (TEA) analyses highlight that the levelized cost of hydrogen (LCOH) via PEC water splitting is highly sensitive to factors such as reactor configuration, STH efficiency, and system lifetime. For example, authors in [121] evaluated the PEC approach alongside photovoltaic-electrolysis under realistic operation scenarios, incorporating factors such as fluctuating irradiance, material cost, and device degradation rates. In addition to efforts aimed at improving device performance, recent TEA studies have also explored system-level hybridization strategies. One particularly promising direction involves coupling PEC water splitting with simultaneous hydrogenation reactions to co-produce higher-value chemicals. A comprehensive assessment of a 1000 kg H₂/day PEC plant integrated with seven different hydrogenation reactions showed that such hybridization can substantially improve economic metrics [122]. These findings underscore that integration strategies can bolster the economic viability of PEC hydrogen production, complementing improvements in the PEC device itself. Among all parameters considered in techno-economic models, the plant lifetime, capital expenditure (CapEx per m² of collector area), and capacity factors, which depend on solar availability and device uptime/efficiency, have the greatest impact on LCOH variability. Sensitivity analyses indicate that achieving STH efficiencies above 10% and device lifetimes beyond 10 years are necessary to reach LCOH targets below ~USD 10 per kg H₂. A probabilistic TEA of medium-scale PEC plants (producing ~1 kg H₂ per day) further reveals that even under optimistic assumptions (e.g., 10% STH efficiency and USD 500/m² CapEx), the LCOH is highly uncertain—typically in the range of USD 5–20 per kg H₂ depending on plant lifetime and assumed learning-by-doing cost reductions [123]. These analyses illustrate the substantial gap between current PEC capabilities and economic targets, guiding researchers on which parameters most urgently need improvement. Depending on the maturity level of a PEC system, different modeling approaches may be chosen for TEA. In early-stage or conceptual systems, simplified scenario-driven analytical models can offer sufficient fidelity while accommodating high uncertainty [124]. For more mature or well-defined systems, detailed process modeling (e.g., Aspen Plus-based simulations) can be employed to capture component-level complexities. In this review, we adopt a parameterized analytical TEA approach, leveraging a Machine Learning (ML) [125] predicted photocurrent density as an input to estimate LCOH. This framework enables rapid scenario analysis and sensitivity evaluation across a range of device areas, lifetimes, and capital cost values—an approach well-suited for the early-stage evaluation of SiC-based PEC architectures. To explore the cost-efficiency potential of SiC PEC systems, we conducted a combined analysis using ML and techno-economic assessment. This data-driven approach uses experimental performance data along with ML predictive modeling to estimate the LCOH under various operating scenarios. The present assessment follows the U.S. Department of Energy’s H2A Analysis methodology as standardized framework for hydrogen production economics. The H2A model provides common assumptions for financial parameters (e.g., 8% real internal rate of return, 25.7% tax rate), depreciation (MACRS schedule), and discounted cash flow analysis. All costs in our study are reported on an LCOH basis (USD per kg H₂) to facilitate comparison across different hydrogen production pathways [126].

5.1. Machine Learning for Photocurrent Prediction

To explore the key factors influencing PEC performance in SiC-based systems, we compiled a dataset of more than 20 photoelectrode configurations from the literature (Table 1, Table 2 and Table 3), encompassing various SiC polytypes (3C, 4H, 6H, and amorphous SiC) and multiple surface modifiers or co-catalysts (Pt, Au, Ni, FeOOH, g-C₃N₄, TiO₂, etc.). Each record included the semiconductor bandgap (1.4–3.2 eV), modifier type, illumination source (AM 1.5G solar simulator or Xe lamp), electrolyte composition and pH, applied bias (V vs. reference), and photocurrent density (mA cm⁻²).

Prior to model training, potential multicollinearity among the input features (modifier, bias, material, pH, bandgap, electrolyte, and light source) was examined through pairwise correlation analysis. No strong linear correlations (|r| > 0.8) were detected, indicating acceptable feature independence. These variables were selected as they represent the principal physicochemical and operational parameters governing PEC water splitting. Nevertheless, weak nonlinear dependencies may still exist due to data aggregation from diverse experimental setups.

A Random Forest regressor was trained to predict photocurrent density from the materials and operational parameters. The model achieved a mean absolute error (MAE) of 13.2 mA cm⁻², which is reasonable considering the limited and heterogeneous dataset. Feature-importance analysis (Figure 8a) indicated that surface modifier, applied bias, and electrolyte pH are the dominant factors influencing PEC activity, while the bandgap and illumination source play a secondary role within the studied range.

This exploratory ML analysis highlights the crucial role of catalytic and interfacial engineering in enhancing photoelectrode performance. We emphasize that the present model is not intended for accurate prediction but rather for identifying promising parameter combinations and guiding future high-throughput PEC studies.

Although the dataset has been expanded as much as is currently possible, the scarcity of consistent experimental data on SiC-based PEC systems remains a limitation. Further accumulation of standardized datasets will enable more robust, statistically representative ML modeling in the future.

5.2. Baseline Technoeconomic Estimation

Accurately estimating the capital costs of PEC modules is challenging at this early stage of technology, due to the lack of commercial-scale fabrication data. Existing techno-economic studies often must rely on assumed or prototype-level cost figures, which can vary widely with device design and materials. For instance, reported estimates in the literature range from approximately USD 500/m² for relatively simple single-junction PEC panels to about USD 3500/m² for advanced tandem devices that incorporate nanostructured absorbers and precious-metal catalysts. Given this variability and the absence of market data, most analyses adopt indicative cost values rather than exact figures, acknowledging the high uncertainty in CapEx projections for PEC hydrogen systems [127]. According to Schneidewind et al. [128], achieving an LCOH below ~USD 2/kg H₂ (comparable to the cost via state-of-the-art PV-EC systems) with PEC water splitting is only possible under very optimistic conditions: specifically, the PEC system would need an STH efficiency in the 20–25% range, a CapEx below ~USD 300/m², and an operational lifetime of at least 10 years (while incurring minimal O&M costs). Current PEC prototypes, by contrast, typically operate at <10% STH efficiency and have module costs well above USD 1000/m², leading to LCOH values greater than USD 10/kg H₂. This comparison underscores the dual challenge facing PEC technology: (1) breakthroughs in photoelectrode materials to boost efficiency and durability, and (2) manufacturing scale-up to drive down CapEx (for example, via learning-by-doing and economies of scale). Without concurrent progress on both fronts, it will be difficult for PEC pathways to economically compete with the established PV-EC route. Nonetheless, the PEC approach offers a compelling opportunity by integrating light absorption, charge separation, and catalysis in a single monolithic device—potentially simplifying the overall system and infrastructure if performance and stability targets can be met. It is worth noting that more than 60% of the projected PEC system cost stems from the fabrication of the photoelectrode modules and their protective layers [129]; thus, advances in scalable, low-cost, and robust electrode architectures are essential for future cost reduction. Encouragingly, recent experimental advances have started to close the gap between laboratory PEC demos and the requirements for economic viability. Notably, Butson et al. [130] reported a tandem PEC device (with dual light absorbers) that achieved an impressive 20.8% STH efficiency under AM 1.5G illumination, without any external bias. The device operated stably at photocurrent densities above 13 mA/cm², producing roughly 305 mL of H₂ per hour over a 25 cm² active area. This result represents a significant step toward the efficiency and stability needed for scale-up in PEC hydrogen production. From a techno-economic perspective, the authors projected that if such a device could be scaled and operated continuously for 25 years—with capital costs around USD 800/m² and sustained performance above 15% STH—then the LCOH could drop below ~USD 4/kg H₂. This would approach, or even undercut, the U.S. Department of Energy’s target range for competitive green hydrogen costs. While these projections are optimistic, they highlight the critical interplay between device efficiency, durability, and scalable fabrication in determining the economic viability of PEC systems. Using the top-performing photoelectrode configuration identified in our dataset (a Pt-decorated 3C-SiC photoanode, which achieved a photocurrent of 38 mA/cm² under benchmark conditions), we developed a baseline TEA model for a notional SiC PEC device. The major assumptions such as 100 cm² photoactive area per device; 8 h of sunlight-driven operation per day, 300 days per year; 5 years of operation before replacement; 90% of generated charge goes to hydrogen; capital cost USD 0.5 per cm²; operational costs USD 20 per device per year in operations and maintenance (O&M) expenses for were used this baseline scenario.

Using these baseline parameters, we calculated the LCOH for the single 100 cm² device over its lifetime. The results indicated a very high cost per kilogram of H₂, owing largely to the small scale. To put this in perspective, consider that a PEC cell operating at a modest photocurrent density of ~10 mA/cm² (under the same 8 h/day, 300 days/year schedule) and having an active area of only 0.01 m² (10 cm × 10 cm) would produce only about 5.5 g of H₂ in 5 years. Such a tiny output leads to an exorbitant LCOH (on the order of >USD 97/kg H₂ in this toy scenario). While no one would build a PEC system at such a small scale for commercial hydrogen production, this calculation highlights the extreme sensitivity of hydrogen cost to device area. It justifies why scalability is a primary focus: as the active area increases, the amount of H₂ produced rises proportionally, dramatically lowering the LCOH. As shown in Figure 8b, increasing the photoelectrode area from 0.01 m² to 1 m² (with other factors held constant) would be expected to reduce the LCOH from roughly USD 97 to ~USD 11 per kg H₂.

5.3. Scenario-Based Analysis of LCOH

To better understand which variables offer the greatest leverage for cost reduction, we conducted a scenario analysis, varying one factor at a time from the baseline while holding others constant. Three independent scenarios were examined:

Scaling up PEC Area: Increasing the PEC cell area from 0.01 m² to 1 m² (with baseline photocurrent density and a 5-year lifetime) reduces the LCOH from approximately USD 97/kg to about USD 11/kg H₂ (Figure 8b). This dramatic improvement underscores the dominant role of scale—larger devices or modules produce far more hydrogen over their lifetime, diluting the capital and fixed costs per kg of fuel.

Extending Device Lifetime: Increasing the device operational lifetime from 1 year to 10 years (with baseline 0.1 m² area and ~10 mA/cm² photocurrent) yields an LCOH reduction from over USD 140/kg (at 1 year) down to under USD 20/kg H₂ (at 10 years), as shown in Figure 8c. This highlights the importance of material durability and system stability. Here, SiC’s intrinsic corrosion resistance is a valuable attribute, suggesting that SiC-based devices might achieve the longer lifetimes needed if engineering challenges (seals, contacts, etc.) are solved.

Enhancing Photocurrent (Performance): Boosting the photocurrent density five-fold, from 10 mA/cm² to 50 mA/cm² (for a baseline 0.1 m² area and 5-year life), decreases the LCOH from about USD 135/kg to roughly USD 28/kg H₂ (Figure 8d). This confirms that performance improvements do help lower hydrogen costs—but their impact is less pronounced than scaling or longevity. In other words, even a very high photocurrent device must still be large and long-lived to approach economic viability.

5.4. Implications and Future Work

The above findings demonstrate that while advances in photocurrent performance (through materials discovery and design, possibly guided by ML) are important, the critical economic levers for SiC-based PEC hydrogen production are scalability and durability. In practical terms, this means research should prioritize strategies that enable larger-area PEC devices and extend their operational lifetimes. ML can assist in this endeavor by screening for promising SiC-based heterostructures or co-catalyst modifications that might yield durable performance, while TEA can guide where to focus engineering efforts at the system level (for instance, improving module encapsulation to prolong life, or developing cheaper manufacturing techniques to allow scaling up area). In our TEA, we assumed a 20-year project horizon with financial parameters aligned to H2A standards (8% IRR, etc.), and we benchmarked cost inputs against analogous PEC and PV-EC systems reported by DOE and industry studies. Even with these standards, the modeled LCOH for our lab-scale SiC PEC device came out to ~USD 90–USD 100/kg H₂, far above the commercial target of <USD 2/kg. The order-of-magnitude gap is primarily due to the small device area, suboptimal STH efficiency, and limited lifespan in current setups. This conclusion is qualitatively consistent with previous benchmark studies [131], which show that the cost of PEC hydrogen is overwhelmingly influenced by the photoabsorber panel cost, the materials (and their replacement frequency), and the device lifetime. For example, DOE-led analyses of hypothetical PEC reactors report a wide LCOH range (~USD 1.6–USD 10.4 per kg H₂) depending on system configuration and assumed efficiency [131]. Yet, even in the more optimistic cases, long-term economic viability would require highly scalable designs and robust, long-lived materials. Our analysis reinforces this point: incremental improvements in current density or efficiency must be paired with breakthroughs in scale and stability to make PEC water splitting competitive. Future work in this area may benefit from multi-objective optimization and comprehensive uncertainty analysis. For instance, techno-economic optimization could be performed where both the device design (materials, structure) and system aspects (plant size, operations strategy) are varied simultaneously to find Pareto-optimal solutions balancing efficiency, lifetime, and cost. Uncertainty quantification (e.g., Monte Carlo simulations on key parameters) would also help identify which uncertain factors (such as future capital cost reductions or longevity improvements) most strongly affect the viability of PEC technology. Finally, an important next step is experimental validation at scale: implementing and testing SiC-based PEC modules of larger area and longer duration, to verify that the promising attributes of SiC indeed translate to practical, long-lasting performance in real-world conditions.

6. Outlooks

Silicon carbide (SiC) has emerged as a robust and versatile platform for solar water splitting; however, several scientific and technological challenges must be overcome to realize its full potential. Future research directions can be grouped into four main categories.

6.1. Materials and Structural Design

Continued innovation in SiC nanostructuring and heterostructure engineering is essential. Hierarchical morphologies combining macro-, meso-, and microporosity may enhance light absorption and mass transport. Core–shell and multilayer architectures can integrate catalytic or protective coatings to overcome SiC’s limited visible-light response. Moreover, coupling SiC with narrower-bandgap semiconductors or stable co-catalyst layers can extend absorption into the visible range and improve interfacial charge transfer.

6.2. Performance and Stability Challenges

Despite its intrinsic chemical durability, the long-term stability of SiC photoelectrodes under realistic operating conditions remains insufficiently explored. Addressing issues such as oxidative degradation, surface fouling, and catalyst detachment will require robust passivation strategies (e.g., TiO₂, carbon, or conductive polymer over-layers) and systematic lifetime testing. At the same time, improving efficiency demands approaches that combine bandgap tuning, defect and polytype engineering, and optimized junction design to minimize recombination and enhance carrier extraction [132].

6.3. Scalability and System Integration

Most studies to date involve small-scale demonstrations. Future efforts should focus on scalable fabrication of large-area SiC electrodes with consistent quality using low-cost techniques (such as roll-to-roll deposition or solution-based growth). System-level challenges—including light management, gas flow distribution, and electrode replacement—must also be addressed to achieve practical PEC modules.

6.4. Data-Driven and AI-Assisted Optimization

Integrating computational modeling with machine learning (ML) can accelerate materials discovery and device optimization. ML can identify correlations between structure, composition, and performance, while “digital twins” of PEC systems can predict degradation and guide real-time optimization. Such data-driven approaches will be essential to shorten development cycles and bridge laboratory and industrial scales.

In summary, the transition of SiC-based photoelectrochemical systems from laboratory prototypes to efficient, durable, and scalable devices will require a multidisciplinary strategy combining advanced materials design, stability engineering, scalable manufacturing, and intelligent data-driven optimization. With sustained progress in these directions, SiC-based PEC water splitting could evolve into a viable technology within the coming decade.

7. Conclusions

Silicon carbide (SiC) continues to stand out as a durable and chemically stable semiconductor for solar-driven water splitting. Recent advances in nanostructuring and surface engineering have significantly improved its light-harvesting and charge-separation capabilities. High-surface-area and porous SiC electrodes exhibit enhanced photocurrent densities and excellent resistance to photocorrosion, underscoring SiC’s suitability for harsh electrochemical environments. Further optimization through hierarchical pore networks, core–shell architectures, and integration of co-catalysts (such as metal nanoparticles or OER catalysts) can further extend its photoresponse into the visible region and boost activity.

Despite these achievements, several critical challenges remain. The wide bandgap of common SiC polytypes (2.0–3.0 eV) restricts visible-light absorption and limits solar-to-hydrogen (STH) efficiency. Promising strategies to overcome this include controlled doping, introduction of mid-gap states, and formation of SiC-based alloys or composites that broaden spectral utilization. Another persistent limitation is charge-carrier recombination, even in well-engineered SiC nanostructures. Addressing this issue will require optimized heterojunctions, efficient co-catalysts, and precise junction engineering to promote charge separation and extraction.

From a practical standpoint, stability and scalability are essential for real-world applications. Long-term operation under intense illumination and in corrosive electrolytes must be validated, including the stability of co-catalysts and conductive layers. Strategies such as protective over-layers (TiO₂, carbon, or conductive polymers) and regenerative operating modes (self-cleaning or reactivation) may be required. Moreover, the fabrication of large-area SiC photoanodes and their integration into PEC modules remain engineering challenges. Developing cost-effective synthesis and deposition techniques will be key to lowering production costs while maintaining performance.

Economic analyses consistently show that current SiC PEC devices are not yet competitive, with hydrogen production costs still several times higher than commercial targets. Our techno-economic evaluation indicates that scale-up and lifetime extension will have an even greater impact on cost reduction than incremental efficiency improvements. Figure 9 to date hydrogen production rates (in μmol g⁻¹ h⁻¹ of H₂) reported for selected SiC-based PEC systems: SnO₂/SiC nanowire photoanodes [74], SiC@g-C₃N₄ core–shell nanowires [75], planar 3C-SiC photoelectrodes [76], and Au-nanoparticle-decorated SiC nanowires [77]. These examples highlight the performance range of SiC photoelectrodes in recent studies. (Higher bars indicate greater hydrogen generation rates, which correlate with better PEC performance.)

Nevertheless, combining materials innovation, engineering scale-up, and data-driven optimization provides a realistic pathway to closing this gap. If high-efficiency, long-lived SiC photoelectrodes can be manufactured affordably and deployed at scale, SiC-based PEC water splitting could become a key component of the clean hydrogen economy. Continued interdisciplinary collaboration—linking materials science, surface chemistry, and techno-economic modeling—will be essential to transform the promise of SiC photocatalysis into sustainable hydrogen production in the near future.