Search Results (113)

Natural bentonite, dominated by montmorillonite-type layered aluminosilicates, is increasingly considered as an inexpensive and environmentally acceptable support or catalyst for the thermochemical conversion of waste carbon streams. Its relevance to catalysis arises from a combination of cation-exchange capacity, swelling behavior, hierarchical porosity after modification, and the possibility of generating Brønsted, Lewis, redox and metallic active sites. This review critically evaluates bentonite modification strategies—acid activation, alkaline and sodium exchange, inorganic oxide pillaring, transition- and noble-metal impregnation, organosilane or surfactant functionalization, and carbon-based hybridization—with emphasis on their consequences for texture, acidity, thermal stability, metal dispersion and catalytic behavior. The review then connects these structure–property relationships with the emerging application of modified bentonites in plastic-waste thermocatalysis and hydrogen-rich product formation. The recent literature indicates that acid-modified bentonite can substantially improve liquid hydrocarbon formation from polyethylene, binder-free bentonite pellets can operate at kilogram-batch scale for drop-in fuels, and Ni-, Fe- or Ni–Fe-modified bentonite-type catalysts can promote tar cracking, reforming and gas upgrading. However, direct evidence for high hydrogen yields from plastic waste over bentonite remains narrower than the evidence for liquid-fuel production, biomass pyrolysis or model-compound reforming. Therefore, this article distinguishes between direct plastic-waste evidence and transferable evidence from biomass, acetic acid, tar and hydrocarbon reforming studies. The analysis identifies Ni-impregnated acid-activated or pillared bentonite, Ni–Fe/bentonite, and La/Ca-promoted Ni/bentonite as the most promising routes for plastic-derived hydrogen-rich syngas, while acid activation alone is best regarded as a pretreatment rather than a complete catalyst design. Key limitations include catalyst deactivation by coke, metal sintering, chloride poisoning from PVC, inconsistent reporting of gas yields, and insufficient life-cycle and techno-economic analysis. A roadmap is proposed for designing reproducible, scalable bentonite catalysts for circular plastic-waste valorization. Full article

Ammonia (NH₃) is a compelling carbon-free hydrogen carrier. Its catalytic decomposition to produce a hydrogen/nitrogen (H₂/N₂) gas stream is central to the “NH₃-H₂” clean energy cycle, provided that residual NH₃ is removed to fuel-cell-grade purity downstream. This review integrates advances from the past five years across four major catalytic NH₃ decomposition pathways, encompassing conventional thermocatalysis, plasma-catalytic, photo(thermal), and electrically driven catalysis, within a unified mechanistic and practical framework, distinguishing it from existing single-pathway reviews. Noble metal catalysts, particularly Ru-based systems, achieve superior low-temperature activity through support engineering, promoter effects, and active-site construction. However, our analysis reveals that non-noble metal (Fe, Co, Ni) catalysts and their alloys, nitrides, and carbides have made substantial progress, with certain Co-based and bimetallic systems approaching Ru-level performance via interfacial oxygen vacancy engineering and electronic structure modulation. Emerging non-thermal routes effectively overcome thermodynamic barriers, enabling operation at temperatures 200–300 °C below conventional thermal requirements, though each faces distinct challenges in energy efficiency, stability, and scalability. Key challenges remaining across all pathways to practical implementation, including residual NH₃ removal and H₂ purification, catalyst deactivation and stability, heat management and energy efficiency, start-up/shut-down dynamics, as well as system integration and economics, are critically assessed. This review provides theoretical guidance and practical recommendations for developing scalable, low-temperature NH₃ decomposition technologies. Full article

Developing earth-abundant photocatalysts that operate efficiently under visible light remains a central challenge in sustainable aerobic oxidation chemistry. We synthesized a binuclear cobalt(II) structure (Co₂) in which two redox-active metal centers are bridged by a polypyridine scaffold to integrate light-harvesting and catalytic functions within a single low-nuclearity unit. The complex exhibits a strong absorption band below 450 nm, undergoes facile charge separation upon photoexcitation, and channels molecular oxygen (O₂) toward superoxide radical anion (O₂^•–) under blue-light irradiation. Spectroscopic and mechanistic studies indicate that the polypyridine framework governs photon capture and excited-state delocalization, whereas the proximal Co(II) sites mediate the subsequent single-electron transfer to O₂. Driven by this dual-site synergy, Co₂ selectively oxidizes a broad scope of thioethers to the corresponding sulfoxides in yields exceeding 95%, with no over-oxidation to sulfones detected. The catalyst retains its structural integrity over five successive runs without measurable activity loss. By confining complementary photophysical and redox functions within a discrete bimetallic unit, this work establishes a design strategy for noble-metal-free, visible-light-driven organic transformations. Full article

In this work, ternary Mo–Ni–X (X = Al, Co, Cr, Cu, Fe, W) thin films with nominal composition Mo₈₀Ni₁₀X₁₀ (at. %) were prepared by magnetron sputtering and evaluated as electrocatalysts for the hydrogen evolution reaction (HER) in alkaline media. The influence of alloy composition, substrate type, and deposition temperature on catalytic performance was systematically investigated. Electrochemical screening revealed a strong dependence of HER activity on both substrate conductivity and ternary alloying, with Al-, Cr-, and W-containing systems showing the best performance on glassy carbon substrates. This highlights the importance of interfacial charge-transfer efficiency in determining catalytic behavior. The Mo₈₀Ni₁₀Cr₁₀/GC system was selected for detailed analysis. Deposition temperatures ≥ 500 °C resulted in enhanced HER activity, reaching an overpotential of η₁₀ = −222 mV at j = −10 mA cm⁻². The improved performance is attributed to temperature-induced microstructural optimization and electrochemically driven surface reconstruction, leading to the formation of a Ni-enriched active interface. AFM analysis confirmed surface restructuring during operation, with roughness increasing from ~1 to ~3 nm, indicating the formation of additional electrochemically accessible active sites. XPS results suggest partial depletion of Mo during cycling, while Cr mainly contributes to structural stabilization of the evolving thin film. Overall, the results demonstrate that HER performance is governed by the coupled effects of alloy composition, substrate-dependent charge transport, and in situ surface reconstruction. This work highlights magnetron sputtering as a scalable approach for designing homogeneous noble-metal-free thin-film electrocatalysts with tunable activity. Full article

Due to the scarcity and high cost of precious metals, development of a noble metal-free, low-cost catalyst for hydrogen generation via water splitting is crucial. To develop an efficient HER catalyst, Ti, the ninth most abundant metal in Earth’s crust, was engineered systematically. The pristine transition metal titanium cannot drive an electrocatalytic hydrogen evolution reaction (HER) with an efficient rate in an acidic medium (0.5 M H₂SO₄). However, in situ growth of TiO₂ film on Ti surface achieves HER activity, showing an overpotential for 10 mAcm⁻² at 671.4 mV with a Tafel slope of 163.69 mV dec⁻¹. The electrocatalytic performance was further boosted by immobilizing CuO particles onto the as-developed TiO₂/Ti film, which shows 10 mA cm⁻² overpotential at 543.7 mV with a Tafel slope of 101.09 mV dec⁻¹. The CuO–TiO₂/Ti heterostructured electrode exhibited remarkable long-term stability, with the current density increasing by 36% over 25 h of continuous operation, suggesting gradual electrochemical activation while maintaining robust catalytic performance. In this research, detailed structural, surface, and electrochemical investigations, including SEM–EDX, EIS, OCP, and XPS analyses, verified the optimized formation of the TiO₂ layer and CuO incorporation, underscoring the positive impact of heterointerface engineering on HER enhancement. Full article

Ammonia decomposition over non-precious metal thermos-catalysts offers a viable and cost-effective pathway for sustainable hydrogen production. In this study, LaCeO₃ perovskite was synthesized using a citric acid complexation method and employed as a support for mono- and bimetallic catalysts prepared by incipient wetness impregnation, maintaining a total metal loading of 10 wt%. Structural and surface properties were systematically investigated using BET, XRD, H₂-TPR, SEM, TEM, and CO₂-TPD. Among the monometallic catalysts (Ni, Co, and Fe), 10%Ni/LaCeO₃ exhibited the highest activity, which is attributed to its enhanced reducibility and optimal surface basicity, facilitating NH₃ activation. Bimetallic systems (Ni-Co, Ni-Fe, and Co-Fe) with equal metal loadings (5 wt% each) showed better activity compared to their monometallic counterparts following the order: 5%Ni–5%Co/LaCeO₃ > 5%Ni–5%Fe/LaCeO₃ > 5%Co–5%Fe/LaCeO₃. The improved performance of the Ni-Co system is due to structural interactions between Ni and Co, which promote hydrogen desorption and accelerate N–H bond cleavage, while suppressing nitrogen recombination as the rate-limiting step. Further systematic optimization of the Ni/Co ratio showed that 8%Ni–2%Co/LaCeO₃ had the highest catalytic activity with consistent performance over 50 h. This optimal composition provides a balanced distribution of active metallic sites and moderate-to-strong basic sites, enhancing NH₃ adsorption and intermediate transformation. These findings show that LaCeO₃-supported Ni-Co catalysts are promising candidates for efficient hydrogen production from ammonia without using noble metals. Full article

The development of sustainable, noble-metal-free photocatalytic systems for acceptorless dehydrogenation (ADH) of cyclic amines remains a significant challenge. Herein, we report a novel heterogeneous photocatalyst constructed by covalently grafting a cobaloxime-based proton reduction catalyst onto a photosensitive covalent organic framework (PT-COF). The tailored PT-COF scaffold, featuring a donor–acceptor architecture and uncondensed amino groups, serves as both an efficient visible-light harvester and a porous support for cobalt active sites. The resulting Co-PT-COF hybrid exhibits excellent photocatalytic activity for the ADH of a wide range of cyclic amines, affording the corresponding N-heteroarenes in 62–95% yields under an Ar atmosphere at 28 °C with blue LED irradiation for 12 h in water. Notably, the catalyst demonstrates outstanding recyclability over five consecutive cycles with minimal loss of activity or cobalt leaching. Comprehensive photoelectrochemical and spectroscopic studies reveal that enhanced charge separation and efficient electron transfer from the photoexcited COF to the cobalt centers underpin the superior performance. Mechanistic investigations, including in situ EPR spectroscopy, confirm the involvement of α-amino radical intermediates in the catalytic cycle. This work establishes a sustainable platform for solar-driven dehydrogenation chemistry and provides a versatile blueprint for integrating molecular catalysts with photoactive frameworks. Full article

The oxygen reduction reaction (ORR) is a key process in electrochemical energy conversion technologies such as fuel cells and metal–air batteries; however, its sluggish kinetics and reliance on precious metal catalysts limit large-scale application. This review provides a comprehensive overview of recent advances in non-precious nanoscale electrocatalysts for ORR in alkaline media. Particular emphasis is placed on reaction mechanisms, including dominant pathways, kinetics, and key intermediates, as well as the advantages of alkaline electrolytes over acidic systems. The performance of various catalyst classes is systematically discussed, including transition metal-based materials (Fe, Co, Zn, Cu, and bimetallic systems) and metal-free carbon-based electrocatalysts. Special attention is given to heteroatom-doped carbon materials, carbon nanostructures, and emerging hybrid systems such as MXene-based composites. Comparative analysis highlights the relationship between catalyst composition, structure, and electrochemical performance metrics, including half-wave potential, onset potential, Tafel slope, number of electron transfer, and operational stability. Overall, non-precious catalysts demonstrate promising activity and durability, approaching that of noble metals under alkaline conditions. The insights summarized in this review guide the rational design of efficient, cost-effective ORR electrocatalysts and support the development of sustainable energy technologies. Full article

Photocatalytic water splitting for hydrogen (H₂) evolution is a critical sustainable energy strategy, and cadmium sulfide (CdS) is a promising visible-light photocatalyst due to its suitable band gap. However, the practical application of pure CdS is severely hindered by rapid charge-carrier recombination and significant photocorrosion. In this work, we constructed a CdS/vanadium carbide (VC) photocatalyst via a simple ultrasonic method. The structural, morphological, optical, and photoelectrochemical properties of the composites were systematically investigated. Under visible light (λ ≥ 420 nm) and with 0.35 M Na₂S-0.25 M Na₂SO₃ as the sacrificial agent, the optimized composite featuring a CdS:VC mass ratio of 10:1 (denoted CV-10) achieved a remarkable hydrogen evolution rate of 3485.6 μmol g⁻¹ h⁻¹. This rate represents a 60-fold enhancement over pure-phase CdS and significantly surpasses that of a conventional Pt/CdS catalyst. Furthermore, the CV-10 composite demonstrated excellent stability, showing no activity decay after 16 h of cycling. Spectroscopic and electrochemical analyses revealed that the metallic VC can function as an efficient cocatalyst, accelerating charge separation and transfer while suppressing electron–hole recombination. This work demonstrates that noble-metal-free VC is a highly effective and low-cost cocatalyst, providing a new pathway for designing efficient and stable CdS-based photocatalysts in solar hydrogen production. Full article

The rational configuration of electronic band structures through deep-seated structural disorder remains a formidable challenge in sustainable solar-to-fuel conversion. Herein, we report a transformative kinetic strategy to “freeze” an extraordinary density of non-equilibrium structural defects within an integrated Cu₄MgO₅/ZnO nanocomposite. Synthesized via a chitosan-assisted coordination-combustion route followed by rapid thermal quenching, the material preserves a record crystallographic dislocation density of 1.09 × 1015 m⁻² and significant lattice microstrain (1.04 × 10⁻³). This engineered structural disorder induces a profound reconfiguration of the electronic landscape, generating a continuous manifold of sub-bandgap “tail states” that narrow the optical bandgap to a remarkable 1.34 eV. Consequently, the defect-rich architecture facilitates unprecedented dual-channel photocatalytic performance under simulated solar irradiation in an aqueous solution containing 5 vol% triethanolamine (TEOA) as a sacrificial electron donor; the catalyst achieved a hydrogen evolution rate of 17,700.0 µmol g⁻¹ h⁻¹ and a methane production rate of 172.50 µmol g⁻¹ h⁻¹—representing a 36.3-fold and 43.1-fold enhancement over commercial ZnO, respectively. With an apparent quantum yield of 8.42% at 420 nm and robust photostability—maintaining 95.3% of its activity over five consecutive cycles (25 h total)—this noble-metal-free ternary system bypasses the limitations of traditional heterojunctions. Our findings establish a new benchmark for defect-engineered catalysts, providing a scalable blueprint for high-efficiency carbon neutrality and solar fuel production. Full article

Electrocatalytic water splitting powered by renewable energy is a promising route for sustainable hydrogen production. Rather than developing separate catalysts for HER and OER, recent efforts focus on multifunctional electrocatalysts that can efficiently drive both reactions, simplifying system design and improving efficiency. A major limitation of conventional water splitting is the high overpotential and low-value oxygen production in OER. To overcome this, hybrid water splitting replaces OER with more valuable oxidation reactions, such as pollutant degradation or organic upgrading, enhancing overall energy and economic efficiency. This review covers the fundamentals of water splitting and highlights key physicochemical techniques for probing electrocatalyst activity, particularly structural reconstruction under operating conditions. It evaluates noble-metal, nonprecious-metal, and metal-free nanocarbon catalysts in both acidic and alkaline media, with emphasis on their roles in alternative anodic reactions. Finally, it outlines current challenges and future directions for developing efficient, durable, and sustainable electrocatalysts for advanced hydrogen production systems. Full article

Water electrolysis has emerged as a strategically appealing route for the sustainable production of green hydrogen (H₂) via the hydrogen evolution reaction (HER), though the sluggish kinetics of the oxygen evolution reaction (OER) remains a bottleneck hindering large-scale practical applications. In this regard, an attractive solution is offered by the integration of the ethanol oxidation reaction (EOR) into hybrid water-splitting systems, favorably reducing anodic overpotentials. Nonetheless, an open challenge is related to the fabrication of eco-friendly and economically viable catalysts free from noble metals, combining efficiency and stability. Herein, we explore nickel-oxide-based nanostructures grown onto porous Ni foam scaffolds by a scalable hydrothermal (HT) approach as EOR electrocatalysts. Material properties arising from modulation of the sole HT growth time are investigated by complementary structural, microscopic, and spectroscopic techniques. Electrochemical tests demonstrate good durability and very attractive EOR performances, mainly influenced by the morphology and the NiOOH surface content of the target systems. Overall, the present work advances an attractive route to transition-metal-based electrocatalysts for efficient alcohol-oxidation-assisted water electrolysis. Full article

Electrocatalytic H₂O₂ production via the two-electron oxygen reduction reaction (ORR) is a highly sustainable alternative to industrial methods. To further optimize non-noble catalysts, we report an interfacial engineering strategy to stabilize the metastable P6₃/mmc-La₂O₃ phase on SrTiO₃. This symmetry evolution from the low-symmetry $\mathrm{P}\stackrel{\mathrm{-}}{3}\mathrm{m}1$ (trigonal) to the high-symmetry P6₃/mmc (hexagonal) space group yields a composite with >95% H₂O₂ selectivity. Mechanistic studies demonstrate that the symmetry-regulated interface optimizes *OOH conversion and suppresses O–O bond cleavage. This work offers a robust design principle for high-performance, noble-metal-free H₂O₂ electrosynthesis. Full article

The PGM-free Fe–Ni–Co trimetallic catalysts developed in this study demonstrated outstanding performance for the oxygen evolution reaction (OER), achieving overpotentials as low as 300 mV at 10 mA cm⁻² in rotating disk electrode (RDE) measurements, a value competitive with the most efficient non-noble electrocatalysts reported in the literature. This study validates the strong catalytic performance of the baseline trimetallic configuration and provides important insights into the relationships among synthesis, structure, and morphology that govern catalyst activity. In particular, the findings highlight that although organic additives can be promising modifiers, the interaction between precursors and transition metals must be carefully controlled to avoid active-site isolation when designing efficient catalysts for sustainable hydrogen production. Actually, to further enhance catalytic activity, the nitrogen-rich precursor melamine was introduced into the supported trimetallic catalyst and then carbonized. However, no improvement in OER performance was observed. During carbonization, melamine promotes the formation of tip-growth carbon nanotubes, which mechanically disrupt the catalyst structure and degrade the supported active phase. Full article

The oxygen evolution reaction (OER), a key half-reaction in electrochemical water splitting, is limited by sluggish multi-electron transfer kinetics, starting extensive research into efficient, low-cost nanoscale electrocatalysts, particularly those based on nickel, cobalt, and iron, as well as mixed-metal, hybrid, and heteroatom-doped carbon-based metal-free systems, as presented here. Ni- and Co-based electrocatalysts show high efficiency for alkaline OER due to optimized nanostructures, surface modifications, heterostructure design, and multi-metal doping, which enhance activity, stability, and electronic properties. Their performance relies on precise atomic-level control of structure and synergistic interactions, enabling them to approach or rival noble-metal catalysts. Iron-based electrocatalysts are also promising due to their abundance, low cost, and flexible redox chemistry, forming active iron oxyhydroxide species during operation; however, their low conductivity requires structural and electronic optimization. Beyond Fe, Ni, and Co, copper-based compounds, zeolitic imidazolate framework-derived structures, and manganese phosphide–cerium oxide composites offer enhanced oxygen vacancies, tunable structures, and strong interfacial synergy. Furthermore, heteroatom-doped carbon materials incorporating nitrogen, phosphorus, or sulfur improve catalytic activity by modifying electronic structure, creating active sites, and enhancing charge transfer. Overall, careful control of composition, structure, and electronic properties enables the development of efficient, durable, and scalable noble-metal-free catalysts for OER. Full article