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Review

Heteroatom Doping of Transition Metallic Compounds for Water Electrolysis

by
Xiaoyan Zhang
1,†,
Xueqing Pan
1,†,
Xiaoyi Wu
1,2,
Yufang Xie
3,
Yin Yin
1 and
Xinchun Yang
1,4,*
1
School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, China
2
Institute of Industrial Economics, Jiangsu University, Zhenjiang 212013, China
3
School of Physics and Electronic Engineering, Jiangsu University, Zhenjiang 212013, China
4
Institute of Technology for Carbon Neutrality, Shenzhen Institutes of Advanced Technology (SIAT), Chinese Academy of Sciences (CAS), Shenzhen 518055, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Energies 2025, 18(16), 4223; https://doi.org/10.3390/en18164223
Submission received: 28 May 2025 / Revised: 30 July 2025 / Accepted: 4 August 2025 / Published: 8 August 2025
(This article belongs to the Special Issue Catalytic Hydrogen Production and Hydrogen Energy Utilization)
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Abstract

With high storage capacity and zero emissions, hydrogen energy stands as a favorable replacement for fossil fuels. Therefore, earth-abundant electrocatalysts have attracted significant research interest. Particularly, a heteroatom doping strategy demonstrated exceptional capability in precisely modulating the electronic structure of transition metal-based catalysts while optimizing their local coordination environments, thereby representing a new paradigm for intrinsic catalytic activity enhancement. This review provides a systematic overview of recent advances in heteroatom doping strategies for transition metal catalysts. It is particularly focused on elucidating the fundamental mechanisms through atom dopants, which can efficiently regulate electronic configurations and catalytic behavior. By comprehensively analyzing structure–activity relationships and underlying catalytic principles, this work will establish a framework for precise doping strategies to engineer high-performance electrocatalysts.

1. Introduction

Sustainable transformation of the energy system requires the development of efficient and cost-effective renewable energy technologies [1,2,3,4,5,6,7,8,9,10,11,12]. Hydrogen serves as a sustainable energy carrier that reduces fossil fuel dependence while addressing environmental challenges [13,14,15,16,17,18,19,20]. Up to now, industrial-scale hydrogen generation is largely dependent on steam natural gas reforming as well as coal gasification, whereas these technologies are intensively energy-consuming, thereby, resulting in gray hydrogen with massive pollutant/carbon emissions [21,22]. Recently, green hydrogen derived from biomass, as well as solar energy production technologies, are gaining much attention. In particular, electrocatalyzing water splitting into high-purity hydrogen represents a promising hydrogen production technology at scale. Water electrolysis for hydrogen production achieves zero carbon emissions through the simultaneous anodic oxygen evolution reaction (OER) combined with the cathodic hydrogen evolution reaction (HER) [23,24,25,26].
However, sluggish reaction kinetics and high overpotentials constrain this process, highlighting the need for superior electrocatalysts to lower the reaction energy barriers and accelerate kinetics [27,28,29,30,31,32]. Although noble metal-based catalysts exhibit excellent catalytic activity, their scarcity and high cost restrict their large-scale application. In recent years, due to their unique electronic structures and earth-abundant resources, transition metal-based electrocatalysts have attracted widespread attention [27]. Nevertheless, their catalytic performance remains restricted by inadequate active site exposure and challenges in precisely tuning intermediate adsorption energetics.
Heteroatom doping engineering has been regarded as a transformative strategy for improving the catalytic performance of the host material. The introduced heteroatoms can significantly enhance catalytic activity by reconstructing the coordination environment of transition metals, inducing charge redistribution, and modulating the electronic structure [33,34,35,36]. In detail, heteroatom dopants can induce lattice strain and distortion of the lattice surrounding the metal atoms due to differences in the atomic radius as well as electronegativity in the dopant–host atom system. Moreover, the electronegativity difference induced by doping heteroatoms drives charge redistribution, facilitating the electron transfer kinetics of the atom doping catalytic system. Furthermore, electron transfer as well as orbital interactions between the dopant atoms and the transition metals significantly modulate the position of the d-band center in transition metals. In detail, this modification not only enables electron transfer and orbital interactions in the heteroatom doping catalytic system but also has a greater impact on the d-band center of transition metals, consequently adjusting the adsorption energy of reaction intermediates. The introduction of heteroatomic elements (N, P, S, and B) has been proven to significantly improve the performance of transition metal electrocatalysts through electronic structure modulation, increased active site density, and optimized adsorption energetics [37,38,39]. Furthermore, in addition to mono-dopants, the heteroatom doping strategy includes dual-doping and multi-doping approaches, which introduce synergistic effects for further catalytic activity and stability enhancement. Experimentally, many studies have been focused on heteroatom doping in transition metals through various synthetic methods, such as electrochemical deposition [35], thermal treatment [40,41], low-temperature ammonium carbonate treatment [42], hydrothermal/solvothermal synthesis [37,43,44], gas–solid phase reactions [34], and the interfacial diffusion approach [35,45]. As a result, the obtained heteroatom doping catalytic performance enhancement is due to the multi-atom synergistic effect [46,47,48].
This review summarizes the understanding of the heteroatom doping strategy for transition metals and their compounds in HER applications. Additionally, this work discusses the effect of dopants on catalytic mechanisms and identifies challenges and opportunities for future research. By exploring the structure–activity relationships of these materials, we will establish a framework for the rational design of next-generation electrocatalysts that combine high performance with economic and environmental sustainability.

2. Mechanism of Hydrogen Evolution from Electrolytic Water

A simple water electrolysis system is shown in Figure 1 [49], and electrocatalytic water splitting demands a voltage of 1.23 V in theory. The process of water electrolysis includes the cathodic HER and the anodic OER [50]. The electrochemical splitting of water under alkaline conditions involves multi-electron transfers, facing high overpotentials, as well as slow reaction rates.
The HER possesses three primitive steps: the Tafel step, Heyrovsky step, and Volmer step.
The HER in acid media involves the following basic steps:
Tafel: M + H2O + e− → M–H* + OH−
Heyrovsky: M–H* + H2O + e− → M + H2 + OH−
Volmer: M + H2O + e− → M–H* + OH
M refers to the catalyst’s active site, while M–H* represents hydrogen adsorption at active sites.
The HER’s progress undergoes the Volmer, Heyrovsky, and Tafel steps. Firstly, water molecular is dissociated to form an intermediate species at the Volmer step. For the Heyrovsky step, another H2O is sustainably combined to M–H* and is followed by a reaction with a second electron, yielding H2 and OH−. Finally, in the Tafel step, two adjacent M–H* react with each other to form H2. The overall HER process undergoes either the Volmer–Tafel or Volmer–Heyrovsky pathway, comprising three sequential stages: water dissociation, intermediated H* adsorption, and H2 formation [51].
Conventionally, the free energy of hydrogen adsorption M–H* (ΔGH*) is employed as a key metric. Under an optimum ΔGH* of zero, ideal HER kinetics are achieved, which is deemed a guide for constructing HER electrocatalysts with high performance. Additionally, the water adsorption energy associated with the activation energy of water dissociation presents HER behavior. Strong water adsorption energy represents stronger water–catalyst binding affinity, while activation energy directly correlates with the water dissociation rate. Therefore, an optimized electronic configuration of active sites is necessary for the complex reactive steps to cooperate and achieve high-performing HER progress.
Theoretically, overpotential (η) serves as a crucial metric for assessing a catalyst’s performance. In detail, the corresponding overpotential at cathodic current densities of 10 mA cm−2 and 100 mA cm−2 is defined as η10 and η100, respectively, and a smaller η denotes superior electrocatalytic activity. Typically, the reaction pathway or mechanism for the HER can be explored directly by the Tafel slope (TS) from the corresponding polarization curve. This approach provides valuable insight into the electrocatalytic behavior and allows for the evaluation of the dominant steps involved in the reaction.
The formula for Tafel is shown as follows:
η = a + b log (j)
The dependence of overpotential (η) on current density (j) is quantified using the Tafel equation. Here, b corresponds to the Tafel slope, a key parameter of electrochemical reaction kinetics. A lower b value reflects an accelerating reaction kinetics. Additionally, the electrochemical surface area (ECSA) is used to study electrochemical processes occurring on the electrode surface. Impedance spectroscopy (EIS) provides information on the resistance within the circuit. In addition, stability serves as another crucial criterion for evaluating an electrocatalyst’s industrial viability. Electrocatalyst stability is commonly evaluated using chronopotentiometry or chronoamperometry at fixed current densities, with minimal variations in overpotential or current density corresponding to more robust stability.

3. Heteroatom Doping of Transition Metallic Alloy

Due to the difficulty in adjusting the binding strength with reaction intermediates, transition metal catalysts often suffer from poor electrocatalytic HER activities. Heteroatom doping engineering is increasingly deemed as a promising strategy, which not only maintains the intrinsic composition of host materials but also enhances the catalytic performance of transition metal-based electrocatalysts via modulating charge redistribution and accelerating electron transfer [48]. For instance, Zhang et al. synthesized P-doped Ni-Mo bimetallic aerogels (Ni-Mo-P) by employing NaH2PO4 for in situ phosphorus doping. The material exhibits an impressively low overpotential (1.46 V) at a 10 mA cm−2 current density. The P dopant can accelerate the charge transfer for enhanced HER kinetics. The DFT results confirm that the P-induced effect enables optimal H* binding strength with active sites [52]. Han et al. demonstrated the successful preparation of a novel 3D Co-P nanosheet structure (Co-P/FTO) under alkaline conditions. The induction of that P dopant results in abundant active sites to improve HER performance, with an overpotential of 125 mV and a Tafel slope of 54 mV dec−1 [53]. Recently, a series of nitrogen-modified transition metal electrocatalysts (N-Ni, N-Fe, et. al) [42] was obtained through ammonium carbonate treatment at a controlled temperature. Multiple physicochemical characterization reveals that surface nitrogen functionalization maintains the pristine composition of the metallic framework. As shown in Figure 2, the nitrogen modification induced a localized electron-rich environment and polarized the electron distribution at the catalyst surface due to higher electronegativity compared to transition metals. Furthermore, boron-doped transition metal nickel (B-Ni) is also proven by the Rao group via a controlled boronizing method [54]. The enhanced HER property primarily originated from the B dopant, which both facilitates electron transfer and lowers the d-band center of Ni. In addition, robust stability is observed, and a chronopotentiometry test at −100 mA cm−2 was carried out for at least 100 h. Such a novel electronic configuration will weaken the binding strength of intermediates (H*) on active sites and adjust their charge and spin densities. Therefore, this electronic reconfiguration optimizes the adsorption/desorption energetics of intermediates, resulting in a low Gibbs free energy barrier and affinity OH* thermal neutral behavior, thereby accelerating Volmer–Heyrovsky kinetics.
Furthermore, the introduction of non-metal dopants optimizes the d-band center of host catalytic sites, leading to improved hydrogen evolution activity. Mono- or dual-heteroatom doping efficiently adjusts the d-band center of Ni-based active sites for superior HER catalytic activity in alkaline solutions. N withdrew electrons from Ni, while phosphorus donated electrons, resulting in a balanced charge distribution [46]. As confirmed by the DFT results, this synergistic effect favors the d-band center of active sites closer to the Fermi level. The optimized thermal–neutral behavior benefits water dissociation and hydrogen desorption. Overall, the electronic configuration of transition metal catalysts can be precisely tuned through heteroatom doping, thereby optimizing adsorption/desorption properties, as shown in Table 1. As a result, heteroatom-doped transition metal-based catalysts demonstrate improved HER activity enabled by their low energy requirements.
In addition, heteroatom-doped carbon material-supported nanocatalysts exhibit promising catalytic performance toward electrocatalytic HER [55,56]. For supported nanocatalysts, these heteroatom dopants ingeniously tune the electronic configuration of the carbon matrix, giving rise to the excellent conductivity and stability of the carbon support. Liu et al. [57] synthesized Ni3Cu1@NG-NC nanocatalysts through controlled calcination. It is reported that the encapsulation of Ni-Cu alloy nanoparticles in N-doped graphene layers is derived from a porous N-doped carbon matrix, as shown in Figure 3. The Ni3Cu1@NG-NC catalyst shows superior HER activity, delivering 10 mA cm−2 at 122 mV (alkaline) and 95 mV (acidic), with corresponding Tafel slopes of 84.2 mV dec−1 and 77.1 mV dec−1. The enhancement stems from synergistic effects between the bimetallic core and graphene shell, which collectively optimize electronic configuration and promote efficient electron transport. The unique porous architecture also increases active sites and improves mass transport. The catalyst demonstrates remarkable stability over 80 h of continuous operation.
Table 1. Catalytic properties of heteroatom-doped transition metallic alloy in HER.
Table 1. Catalytic properties of heteroatom-doped transition metallic alloy in HER.
CatalystElectrolyteη10
(mV)		Tafel Slope
(mV dec−1)		StabilityHeteroatom ElementsREF
N-Nineutral6410620 mA cm−2 for 18 hN[42]
B-Nialkaline (1.0 M KOH)16012210 mA cm−2 for 100 h
100 mA cm−2 for 100 h		B[54]
N-P-Nialkaline (1.0 M KOH)25.83430 mV for 50 h
1000 cycles		N, P[46]
S–CoFe@NCneutral373462 mV for 50 hS[58]
Amorphous Ni-S-Mn alloyalkaline (30% KOH)92(η200)282 mV200 mA cm−2 for 100 hS[59]
Ni-Mo-Palkaline (1.0 M KOH)69108.440 hP[52]
Co-P/FTO (2)alkaline (1.0 M KOH)12554140 mV for 10 hP[53]
P-Mo-Nacid (0.5 M H2SO4)1054310,000 CV cyclesP, N[60]
Co-Ni-S-P/Graphenealkaline (1.0 M KOH)1178510,000 CV cycles
10 mA cm−2 for 50 h		S, P[61]
S-AuPbPtacid (0.5 M H2SO4)1217.75000 cyclesS[62]
Ni3Cu1@NG-NCalkaline (1.0 M KOH)12284.210, 20, 30, and 40 mA cm−2 for 80 hN[57]

4. Heteroatom Doping of Transition Metal Compounds

Transition metal compounds (TMCs), such as transition metal oxides, phosphides, sulfides, and nitrides, have garnered much interest due to their substantial reserves, structural diversity, and adaptable catalytic properties. However, they often suffer from sluggish catalytic kinetics due to the complex modulation of their electronic structure on catalytic sites. Multiple engineering approaches have been developed to enhance the HER kinetics of diverse TMC electrocatalysts. In contrast to other methods, heteroatom doping has been considered to optimize the electronic micro-environment of TMC active sites and improve the reactive kinetics of hydrogen evolution over TMC electrocatalysts.

4.1. Heteroatom Doping of Transition Metal Phosphide

In transition metal phosphides, Liang et al. [63] demonstrated a non-precious S-doped MoP nanoporous layer (S-MoP NPL) with high performance for hydrogen evolution in universal pH electrolytes (Figure 4). S-MoP NPL exhibited a low overpotential of 86 mV to stably produce an HER current density of 10 mA cm−1 in an acidic solution. DFT computations revealed that S-doping decreased the free energy of hydrogen adsorption, as well as binding energy, enhancing electron transfer and catalyst–electrolyte interactions. The porous structure facilitated proton transport and hydrogen adsorption. S-MoP NPL demonstrated superior HER activity across all pH levels due to its unique electronic properties and structural advantages.
Furthermore, Zhao’s group [64] utilized a B,V co-doping strategy for Ni2P, creating B,V-Ni2P with markedly improved alkaline hydrogen evolution activity, as demonstrated in Figure 4. The synergistic effect of dual dopants in B,V-Ni2P efficiently reduces the Tafel slope to 57 mV dec−1, indicating an HER process governed by the Volmer–Heyrovsky pathway. By virtue of its flexible oxidation states and atomic radius similar to nickel, a vanadium dopant can engineer a lattice distortion, as well as the redistribution of electron density, thus facilitating water dissociation. At the same time, boron, as an electron-deficient non-metal dopant, can modulate the electronic structure of nickel phosphide. The combination of amorphous and crystalline domains creates more active sites while promoting efficient ion diffusion and electron conduction. Moreover, the synergistic effect between B and V co-doping optimally tunes hydrogen intermediate adsorption, where the optimized ΔGH* significantly boosts HER performance. Additionally, dual doping substantially reduces the energy barrier for water dissociation and shifts the d-band center, thereby promoting the desorption process.
Incorporating additional carbon nanostructures can further enhance the catalytic kinetics of heteroatom-doped transition metal phosphides through synergistic effects (Table 2). Cao et al. [65] demonstrated the fabrication of boron-incorporated cobalt phosphide nanoparticles supported on CNT (B-CoP/CNT). As shown in Figure 5, the obtained B-CoP/CNT exhibits enhanced HER kinetics with broad pH applicability. The B-CoP/CNT catalyst exhibits superior HER performance, requiring remarkably low overpotentials of 39 mV (acidic), 79 mV (neutral), and 56 mV (alkaline) to achieve 10 mA cm−2 current density. Furthermore, HER activity shows negligible decay after 5000 CV cycles and 100 h of continuous HER, as well as 30-day ambient air storage in pH-universal media. Based on Bader charge analysis, the introduction of B species induces distortion in the adjacent Co atoms arising from the optimized electronegativity of the B atom. The B-CoP structure results in a diminished electron donation from Co to both P and B neighboring sites for electron delocalization. The enhanced electron delocalization in the Co atoms increases the conductivity of the host active sites, achieving high electrical conductivity. DFT calculations further indicate that B doping optimizes the H adsorption energy with thermoneutral behavior on the CoP surface and the Co d-band’s downward displacement relative to the Fermi level for fast HER kinetics.
Additionally, Li et al. [66] presented a template-free strategy to fabricate nitrogen-doped hollow carbon spheres (MoP@NC), where MoP nanoparticles are embedded within N-doped hollow carbon matrices for efficient alkaline HER. The MoP@NC-250 catalyst demonstrates exceptional HER performance, with a low overpotential of 96 mV at 10 mA cm−2, combined with a favorable Tafel slope of 53 mV dec−1, attributed to the hollow structure, high pyridinic-N content, and interfacial synergy between MoP and the N-doped carbon matrix. Theoretical calculations indicate that pyridinic N atoms adjacent to MoP can optimize the electronic structure, weaken Mo-Hads bonds, and enhance HER performance. Additionally, pyridinic N plays a key role in adsorbing H2O and preventing OH* adsorption, accelerating water splitting. Furthermore, Tabassum et al. [67] designed a novel B/N co-doped graphene nanotube (CoP@BCN) architecture, featuring cobalt phosphide nanoparticles embedded in B/N-enriched carbon nanotube matrices for efficient electrochemical HER across all pH values. The B/N co-doping enhances electron transport and prevents the agglomeration of CoP nanoparticles, while the 1D nanotube structure provides a large surface area and improved mass diffusion pathways. As shown in Figure 5, with superior catalytic efficiency, the CoP@BCN architecture delivers current densities of 10 mA cm−2 at minor overpotentials (87 mV in acid, 215 mV in base, and 122 mV in neutral media) and sustains stable operation for 8 h.
Introducing atomically dispersed alloying additives into catalysts [68] can achieve breakthrough enhancements in catalytic performance by precisely modulating the local electronic structure along with geometric reconfiguration of active sites. Song et al. [69] developed an innovative Ru1CoP/CDs composite featuring single-atom Ru-doped CoP nanoparticles anchored on carbon dot-spliced ultrathin nanosheets, achieving exceptional HER performance, with overpotentials of 49 mV (acidic) and 51 mV (alkaline) at 10 mA cm−2. The catalytic nanosheets represent a minimal polarization curve shift after 2000 CV cycles in both alkaline solution (1.0 M KOH) and acidic solution (0.5 M H2SO4). DFT calculations demonstrate that atomically dispersed Ru sites substantially reduce the activation energy for both water dissociation and H2 formation, thereby accelerating overall HER kinetics.
Table 2. Catalytic properties of heteroatom-doped transition metal phosphide in HER.
Table 2. Catalytic properties of heteroatom-doped transition metal phosphide in HER.
CatalystElectrolyteη10
(mV)		Tafel Slope
(mV dec−1)		StabilityHeteroatom ElementsREF
B-CoP/CNTacid (0.5 M H2SO4)39505000 CV cycles
100 h		B[65]
alkaline (1.0 M KOH)5669B
neutral (1.0 M PBS)7980B
B,V-Ni2Palkaline (1.0 M KOH)148(η100)5760 h@100 mA cm−2
1000 CV cycles		B, V[64]
3.4 at% S-MoPacid (0.5 M H2SO4)863430,000 s@10 mA cm−2S[63]
N-CoP/CCalkaline (1.0 M KOH)39581000 cycles
30 h		N[70]
neutral (1.0 M PBS)7469
acid (0.5 M H2SO4)2549
N−Co2P/CCneutral (1.0 M PBS)42683000 cycles
120,000 s@10 mA cm−2		N[71]
acid (0.5 M H2SO4)2745
alkaline (1.0 M KOH)3451
S-CoP NPsalkaline (1.0 M KOH)17577/S[72]
S-CoP@NGalkaline (1.0 M KOH)14660S
S-CoP@CCalkaline (1.0 M KOH)1215720 h@130 mVS
S-CoP@NFalkaline (1.0 M KOH)10979S
MoP@NC-250alkaline (1.0 M KOH)96531000 CV cyclesN[66]
CoP@BCN-1acid (0.5 M H2SO4)87462000 CV cyclesB, N[67]
alkaline (1.0 M KOH)21552
neutral (1.0 M PBS)12259
Ru1CoP/CDs-1000alkaline (1.0 M KOH)5173.42000 cyclesRu[69]
acid (0.5 M H2SO4)4951.6

4.2. Heteroatom Doping of Transition Metal Sulfide

Wang et al. [73] proposed that non-metal dopants lower the Volmer step energy barrier, significantly enhancing the HER kinetics of Ni3S4 in alkaline environments. They systematically employed B, N, O, and F dopants to precisely tune both the adsorption energy and electronic configuration. The optimized F-Ni3S4 demonstrates remarkable electrocatalytic performance with minimal overpotentials (η10 = 29 mV, and η100 = 92 mV). The Tafel slope of F-Ni3S4 is 46.2 mV dec−1, suggesting the rate-determining step of F-Ni3S4 as the Heyrovsky step rather than water dissociation (the Volmer step). The results indicated that varying electronegativities of heteroatoms can modify the electronic structure, along with spatial redistribution of Ni and neighboring S atoms, leading to changes in charge transfer energy (Figure 4). DFT calculations elucidated that the adsorption energies of H2O and OH intermediates correlated with the d-band center (εd) of Ni, whereas ΔGH* depended on the p-band center (εp) of S. Fluorine doping (F-Ni3S4), which optimally balanced these parameters by elevating εp closer to the Fermi level, thereby weakening H–OH bonds and reducing ΔGH* to near-thermoneutral values while simultaneously lowering εd to enhance H2O/OH adsorption. This dual-site modulation significantly accelerated the Volmer step and optimized H2 formation. Furthermore, Pan’s work [74] demonstrates that doping V into Ni3S2 can facilitate the formation of Ni3S2 nanowires at lower temperatures while also enhancing HER catalytic activity. The observed enhancement arises from the doping-mediated elevation of charge carrier concentration around the Fermi level, thereby promoting a faster charge transfer, as shown in Figure 6.
Heteroatom engineering can also synergize with other strategies to enhance catalytic activities. MoS2, as a promising catalyst, has attracted significant research interest, as shown Table 3. Xie et al. [75] first combined atom doping with controlled disorder engineering and successfully achieved precise control of structural disorder in O-MoS2 ultrathin nanosheets via a hydrothermal method. Under incomplete crystallization, the obtained catalyst exhibited a poor degree of disorder, balancing active site density and conductivity. As shown in Figure 7, disorder engineering generated abundant unsaturated sulfur edge sites, while oxygen doping enhanced intrinsic conductivity through Mo-S orbital hybridization, lowering hydrogen adsorption free energy and accelerating charge transfer. Electrochemical tests revealed a superior HER performance, characterized by an onset potential of 120 mV and a high HER current density of 126.5 mA cm−2 at 300 mV overpotential, with favorable reaction kinetics (Tafel slope = 55 mV dec−1), due to the synergistic optimization of active sites and interdomain electron transport. Stability tests confirmed durability over 3000 cycles, highlighting induced defects and corrosion resistance for efficient HER catalysis. Ye et al. [76] fabricated nitrogen-incorporated FeS2 nanoparticles (N-FeS2), demonstrating effective HER. The introduction of nitrogen adjusted the electronic states and band structure of FeS2, reducing the electron density around S atoms. Therefore, more electrons were formed on the N-FeS2 surface, lowering the S-H interaction and promoting H2 formation. Electronic structure engineering coupled with optimized hydrogen adsorption energy resulted in a durable electrocatalyst with high-performance HER characteristics (η10 = 126 mV).

4.3. Heteroatom Doping of Transition Metal Oxide

In recent years, abundant transition metal oxides (TMOs) on Earth, such as CoO, Co3O4, NiO, MnO2, MoO, and ZrO2, have been widely used for the hydrogen evolution reaction (HER). The incorporation of heteroatoms with TMOs can cause subtle lattice distortions, regulate the oxidation states of active centers, and increase the number of active sites, further enhancing the active properties of TMOs. Wang et al. [81] synthesized free-standing N-doped nickel oxide nanosheet array (N-NiO) HER electrocatalysts via a hydr–thermal–nitrogen doping method. Doping engineering efficiently enhanced the conductivity of NiO and supplied a large number of active sites, as depicted in Figure 8. Additionally, N,S-co-doped CoMoO4 was successfully fabricated on nickel foam substrates via chemical vapor deposition [82]. As shown in Figure 9, co-doping with N and S atoms facilitated water molecule activation by reducing the dissociation energy barrier, resulting in outstanding HER performance with a mere 58 mV overpotential at −10 mA cm−2 current density. Additionally, the N, S-CoMoO4/NF400 electrode demonstrated stable operation at a cathodic HER current density of 10 mA cm−2. Zhang reported [83] a phosphorus-doped Co3O4 nanowire array (defined as P-Co3O4/NF) with exceptional performance toward electrocatalyzing HER. P-Co3O4/NF achieves an HER current density of 10 mA cm−2 at a low overpotential of 97 mV and a Tafel slope of 86 mV dec−1 in 1.0 M KOH, significantly outperforming undoped Co3O4/NF (165 mV). More importantly, after 1000 continuous cyclic voltammetry scans, no obvious degradation was observed. Doping reduces the charge density around Co sites, enhances the molar ratio of Co3+/Co2+ species, and optimizes H adsorption and the Volmer step. Enhanced electrical conductivity and reduced charge transfer resistance result in improved HER activity. Sun et.al [84] fabricated novel electrocatalysts as sulfur-doped CoO epitaxial layers on mesoporous Co3O4 (S-CoO/Co3O4). At a current density of 10 mA cm−2, S-CoO/Co3O4 achieves an overpotential of 181 mV, lower than that of pristine Co3O4 (513 mV). The S dopant significantly reduces the charge transfer resistance with a Tafel slope of 64 mV dec−1 for fast HER kinetics. XPS and TEM analyses confirm that sulfur doping not only decreases the surface Co3+/Co2+ ratio but also introduces the S species, which optimizes the electronic structure and charge transfer. The S-CoO surface layer functions as an effective protective barrier, can preserve the structural integrity of the Co3O4 core, and demonstrates exceptional durability, with 95% activity retention over 20 h of continuous operation, which suggests that an interfacial synergistic effect plays an important role in determining HER kinetics [85,86,87,88,89], Table 4.

5. Conclusions and Outlooks

This review summarizes our current understanding of recent progress in the regulation of transition metal-based catalysts through heteroatom surface engineering. In addition, it summarizes the catalytic properties of heteroatom-doped transition metal electrocatalysts, as shown in Table 1, Table 2, Table 3 and Table 4. In summary, the enhancement of HER catalytic performance through heteroatom doping can be attributed to several factors. Firstly, the electronic environment around the active sites can be modified through heteroatom doping, leading to a redistribution of charges in the surrounding regions. This, in turn, accelerates charge transfer and improves the material’s conductivity. Secondly, non-metal doping can introduce vacancies or defects that cause lattice distortion, effectively multiplying active sites for boosting kinetic active metrics. Thirdly, a heteroatom dopant can optimize the adsorption/desorption balance of intermediated species, tune the free energy of H*, and ultimately improve the overall efficiency of water splitting.
Although catalysts prepared through heteroatom doping have shown excellent catalytic performance, there are still opportunities and challenges for their future development. The insights presented below offer valuable design principles for developing advanced catalyst systems with enhanced performance:
  • Water electrolysis still faces some challenges, such as the high cost of electricity, the low efficiency of the electrolysis process, and the poor stability of electrodes in harsh conditions. In addition, the combination of hydrogen and oxygen in electrolytes will cause a possible explosion risk. When gas crossover occurs, the mixed hydrogen and oxygen may explode in some cases. This concern is especially relevant under high-pressure conditions. Therefore, advanced control systems with high-performance and stable catalysts are necessary, which not only efficiently produce high-purity hydrogen but also manage gas pressure and electrolyte flow.
  • In the domain of catalyst design and synthesis, the challenge of regulating the active sites of heteroatom-doped transition metal-based catalysts persists as a significant hurdle. The limitations of mono-doping in meeting the escalating demands necessitate a shift towards more sophisticated strategies. These include multi-atom doping, metal and non-metal co-doping, and the construction of heterogeneous structures, which hold promise in enabling the precise regulation of the catalyst’s architecture. In addition, more efforts are needed to explore straightforward, eco-friendly, and cost-effective synthesis methods, which can produce catalysts with high performance and robust stability, for large-scale applications.
  • The exploration of changes in electronic structure and catalytic reaction mechanisms is still insufficient. It is crucial to combine theoretical calculations with characterization techniques to establish more reliable models. These models can provide a solid theoretical foundation for catalyst development, particularly in understanding reaction intermediates and reaction kinetics. Furthermore, they can serve as valuable tools for assisting in the design of next-generation catalysts, thereby advancing hydrogen energy development.

Funding

This work was supported by funds provided by the National Natural Science Foundation of China (22201294, 12304143, 12274182), the Innovation/Entrepreneurship Program of Jiangsu Province (JSSCTD202146 and JSSCRC2021538), the High-level Talents Program of the CAS (E344021001, E3G0561001), the Guangdong Basic and Applied Basic Research Foundation (2023A1515012370), the Shenzhen Science and Technology Program (KQTD20221101093647058), the Clean Energy Joint International Laboratory (E3G1041001), and the SIAT Innovation Fund for Excellent Young Scientists (E3G0071001).

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. A diagrammatic representation of an alkaline/neutral water electrolysis configuration. Reproduced with permission from [49], Copyright 2019, Wiley.
Figure 1. A diagrammatic representation of an alkaline/neutral water electrolysis configuration. Reproduced with permission from [49], Copyright 2019, Wiley.
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Figure 2. (a) Schematic diagram of water adsorption on N–Ni(111). (b) The current densities for Ni, N–Ni framework, and Pt/C at varying overpotentials. Scale bars: 500 μm (b); 3 μm inset of (b); 3 nm (c); Reproduced with permission from [42], Copyright 2017, ACS. (c) SEM and (d) HRTEM images of B-Ni. (e) Mechanistic illustration of B-doped catalyst for improved hydrogen evolution. Color code: green (Ni), blue (B), white (H), red (O). Reproduced with permission from [54], Copyright 2021, ACS.
Figure 2. (a) Schematic diagram of water adsorption on N–Ni(111). (b) The current densities for Ni, N–Ni framework, and Pt/C at varying overpotentials. Scale bars: 500 μm (b); 3 μm inset of (b); 3 nm (c); Reproduced with permission from [42], Copyright 2017, ACS. (c) SEM and (d) HRTEM images of B-Ni. (e) Mechanistic illustration of B-doped catalyst for improved hydrogen evolution. Color code: green (Ni), blue (B), white (H), red (O). Reproduced with permission from [54], Copyright 2021, ACS.
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Figure 3. (a) A schematic representation of the synthesized Ni3Cu1@NG-NC. SEM images of (b) Ni4Cu0@NG-NC and (c) Ni3Cu1@NG-NC. (d) Comparison of the overpotentials η10 and Tafel slopes, as well as the mass activities of various samples. (e) The stability test of Ni3Cu1@NG-NC recorded at 10, 20, 30, and 40 mA cm−2. Reproduced with permission from [57], Copyright 2019, Wiley.
Figure 3. (a) A schematic representation of the synthesized Ni3Cu1@NG-NC. SEM images of (b) Ni4Cu0@NG-NC and (c) Ni3Cu1@NG-NC. (d) Comparison of the overpotentials η10 and Tafel slopes, as well as the mass activities of various samples. (e) The stability test of Ni3Cu1@NG-NC recorded at 10, 20, 30, and 40 mA cm−2. Reproduced with permission from [57], Copyright 2019, Wiley.
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Figure 4. (a) Structure of S-doped MoP. Color code: green (Mo), red (P), and yellow (S). (b) Cross-sectional SEM image of NPL after anodization. (c) Top-view SEM images of 3.4 at% S-MoP NPL. Scale bar: 200 nm. (d) Overpotential and Tafel slope of 3.4 at% S-MoP NPL. (e) The electrochemical stabilities of HER with constant current density of 10 mA cm−2 in different conditions. Reproduced with permission from [63], Copyright 2019, ACS. (f) Synthetic route and (g) SEM of B,V-Ni2P. (h) iR-compensated LSV curves obtained for B, V-Ni2P, and control samples in 1 M KOH. (i) Comparison of exchange current density (pink) and ECSA (blue) properties between B,V-Ni2P and benchmark catalysts in 1 M KOH. (j) Comparison of voltages to attain current density of 100 mA cm−2 for overall water splitting across NiFeOOH||B, V-Ni2P, and another nickel-based electrolyzer. Reproduced with permission from [64], Copyright 2023, Wiley.
Figure 4. (a) Structure of S-doped MoP. Color code: green (Mo), red (P), and yellow (S). (b) Cross-sectional SEM image of NPL after anodization. (c) Top-view SEM images of 3.4 at% S-MoP NPL. Scale bar: 200 nm. (d) Overpotential and Tafel slope of 3.4 at% S-MoP NPL. (e) The electrochemical stabilities of HER with constant current density of 10 mA cm−2 in different conditions. Reproduced with permission from [63], Copyright 2019, ACS. (f) Synthetic route and (g) SEM of B,V-Ni2P. (h) iR-compensated LSV curves obtained for B, V-Ni2P, and control samples in 1 M KOH. (i) Comparison of exchange current density (pink) and ECSA (blue) properties between B,V-Ni2P and benchmark catalysts in 1 M KOH. (j) Comparison of voltages to attain current density of 100 mA cm−2 for overall water splitting across NiFeOOH||B, V-Ni2P, and another nickel-based electrolyzer. Reproduced with permission from [64], Copyright 2023, Wiley.
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Figure 5. (a) Synthetic route of B-CoP/CNT. (b) HRTEM results of B-Co3O4/CNT hybrid. (c) iR-corrected polarization curves for HER in 0.5 M H2SO4 electrolyte. Inset: overpotential (η10) required to achieve 10 mA cm−2 current density. (d) iR-corrected HER polarization curves recorded in 1.0 m PBS and 1.0 m KOH, respectively. (e) DFT results of B-CoP for HER. Reproduced with permission from [65], Copyright 2020, Wiley. (f) Schematic route for synthesis and (g) FESEM result of MoP@NC hollow microspheres. (h,i) Comparison of catalytic performance. (j) DFT results of various catalytic sites. Reproduced with permission from [66], Copyright 2021, Elsevier. (k) Schematic synthesis of CoP@BCN nanotubes. (l–n) HER properties of CoP@BCN-1 in various electrolytes before and after 2000 CV cycles. Insets: chronoamperometric curves. Reproduced with permission from [67], Copyright 2017, Wiley.
Figure 5. (a) Synthetic route of B-CoP/CNT. (b) HRTEM results of B-Co3O4/CNT hybrid. (c) iR-corrected polarization curves for HER in 0.5 M H2SO4 electrolyte. Inset: overpotential (η10) required to achieve 10 mA cm−2 current density. (d) iR-corrected HER polarization curves recorded in 1.0 m PBS and 1.0 m KOH, respectively. (e) DFT results of B-CoP for HER. Reproduced with permission from [65], Copyright 2020, Wiley. (f) Schematic route for synthesis and (g) FESEM result of MoP@NC hollow microspheres. (h,i) Comparison of catalytic performance. (j) DFT results of various catalytic sites. Reproduced with permission from [66], Copyright 2021, Elsevier. (k) Schematic synthesis of CoP@BCN nanotubes. (l–n) HER properties of CoP@BCN-1 in various electrolytes before and after 2000 CV cycles. Insets: chronoamperometric curves. Reproduced with permission from [67], Copyright 2017, Wiley.
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Figure 6. (a) Diagram of preparation pathway for electrocatalysts. (b,c) Comparison of HER performance in 1.0 M KOH. (d) Optimized models during catalytic water splitting of F-Ni3S4. Reproduced with permission from [73], Copyright 2020, Wiley.
Figure 6. (a) Diagram of preparation pathway for electrocatalysts. (b,c) Comparison of HER performance in 1.0 M KOH. (d) Optimized models during catalytic water splitting of F-Ni3S4. Reproduced with permission from [73], Copyright 2020, Wiley.
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Figure 7. (a) SEM and (b) structure results of V-Ni3S2 catalyst. (c,d) Comparison of HER performance over V-Ni3S2-based catalyst. Reproduced with permission from [74], Copyright 2017, ACS. (e,f) DFT result of optimal MoS2 model. (g) SEM result of the O-MoS2 ultrathin nanosheets. Scale bar: 100 nm. (h) The modeled structure of an O-MoS2 nanodomain and the associated HER mechanism at active centers. Reproduced with permission from [75], Copyright 2013, ACS. (i,j) Schematic crystal structures of FeS2 and N-FeS2. Reproduced with permission from [76], Copyright 2021, Elsevier.
Figure 7. (a) SEM and (b) structure results of V-Ni3S2 catalyst. (c,d) Comparison of HER performance over V-Ni3S2-based catalyst. Reproduced with permission from [74], Copyright 2017, ACS. (e,f) DFT result of optimal MoS2 model. (g) SEM result of the O-MoS2 ultrathin nanosheets. Scale bar: 100 nm. (h) The modeled structure of an O-MoS2 nanodomain and the associated HER mechanism at active centers. Reproduced with permission from [75], Copyright 2013, ACS. (i,j) Schematic crystal structures of FeS2 and N-FeS2. Reproduced with permission from [76], Copyright 2021, Elsevier.
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Figure 8. (a) Synthetic route, (b) SEM, (c) HRTEM, and (d) comparison of HER property of N-NiO synthesis. Reproduced with permission from [81], Copyright 2021, Springer Nature. (e) Tafel plots. Reproduced with permission from [81], Copyright 2021, Springer Nature.
Figure 8. (a) Synthetic route, (b) SEM, (c) HRTEM, and (d) comparison of HER property of N-NiO synthesis. Reproduced with permission from [81], Copyright 2021, Springer Nature. (e) Tafel plots. Reproduced with permission from [81], Copyright 2021, Springer Nature.
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Figure 9. (a) SEM result and (b) HER properties of N, S-CoMoO4/NF400. Reproduced with permission from [82], Copyright 2022, Springer Nature. (c) SEM result of P8.6-Co3O4/NF and (d) its LSV compared with other controlled samples toward HER in 1.0 M KOH. Reproduced with permission from [83], Copyright 2018, ACS. (e) Synthetic route of S-CoO/Co3O4 catalyst. Reproduced with permission from [84], Copyright 2018, Elsevier.
Figure 9. (a) SEM result and (b) HER properties of N, S-CoMoO4/NF400. Reproduced with permission from [82], Copyright 2022, Springer Nature. (c) SEM result of P8.6-Co3O4/NF and (d) its LSV compared with other controlled samples toward HER in 1.0 M KOH. Reproduced with permission from [83], Copyright 2018, ACS. (e) Synthetic route of S-CoO/Co3O4 catalyst. Reproduced with permission from [84], Copyright 2018, Elsevier.
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Table 3. Catalytic properties of heteroatom-doped transition metal sulfide in HER.
Table 3. Catalytic properties of heteroatom-doped transition metal sulfide in HER.
CatalystElectrolyteη10
(mV)		Tafel Slope
(mV dec−1)		StabilityHeteroatom ElementsREF
F-Ni3S4alkaline (1.0 M KOH)2946.275 h@200 mA cm−2F[73]
B-Ni3S4alkaline (1.0 M KOH)5156.8/B
N-Ni3S4alkaline (1.0 M KOH)5478.6V
V-Ni3S2-NWalkaline (1.0 M KOH)6811212 h@91 mVV[74]
O-MoS2 (S180)acid (0.5 M H2SO4)120553000 CV cyclesO[75]
N-FeS2alkaline (1.0 M KOH)12612420 h@126 mVN[76]
N-MoS2acid (0.5 M H2SO4)14(0.5)77–95/N[77]
N-NiMoSalkaline (1.0 M KOH)68863000 CV cycles
1000 h@100 mV		N[78]
N-a-MoSxacid (0.5 M H2SO4)143571000 CV cyclesN[79]
Ni/Ni3S2/SC NSAsalkaline (1.0 M KOH)908112 h@220 mVS[80]
Table 4. Catalytic properties of heteroatom-doped transition metal oxide in HER.
Table 4. Catalytic properties of heteroatom-doped transition metal oxide in HER.
CatalystElectrolyteη10
(mV)		Tafel Slope
(mV dec−1)		StabilityHeteroatom ElementsREF
N-NiOalkaline (1.0 M KOH)1549010 h@1.089 VN[81]
N, S-CoMoO4/NF400alkaline (1.0 M KOH)5848.681000 cycles
16 h@10 mA cm−2		N, S[82]
P-Co3O4/NFalkaline (1.0 M KOH)97601000 CV cyclesP[83]
S-CoO/Co3O4alkaline (1.0 M KOH)1816410 h@10 mA cm−2S[84]
S-NiFe-oxide NFsalkaline (1.0 M KOH)1771141000 cyclesS[90]
S-NiFe-oxide MPsalkaline (1.0 M KOH)187122
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Zhang, X.; Pan, X.; Wu, X.; Xie, Y.; Yin, Y.; Yang, X. Heteroatom Doping of Transition Metallic Compounds for Water Electrolysis. Energies 2025, 18, 4223. https://doi.org/10.3390/en18164223

AMA Style

Zhang X, Pan X, Wu X, Xie Y, Yin Y, Yang X. Heteroatom Doping of Transition Metallic Compounds for Water Electrolysis. Energies. 2025; 18(16):4223. https://doi.org/10.3390/en18164223

Chicago/Turabian Style

Zhang, Xiaoyan, Xueqing Pan, Xiaoyi Wu, Yufang Xie, Yin Yin, and Xinchun Yang. 2025. "Heteroatom Doping of Transition Metallic Compounds for Water Electrolysis" Energies 18, no. 16: 4223. https://doi.org/10.3390/en18164223

APA Style

Zhang, X., Pan, X., Wu, X., Xie, Y., Yin, Y., & Yang, X. (2025). Heteroatom Doping of Transition Metallic Compounds for Water Electrolysis. Energies, 18(16), 4223. https://doi.org/10.3390/en18164223

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