Hydrogen Evolution Reaction Rate Research Articles

Dual-Vacancy-Engineered ZnIn2S4 Nanosheets for Harnessing Low-Frequency Vibration Induced Piezoelectric Polarization Coupled with Static Dipole Field to Enhance Photocatalytic H2 Evolution.

This study investigates the impact of In- and S-vacancy concentrations on the photocatalytic activity of non-centrosymmetric zinc indium sulfide (ZIS) nanosheets for the hydrogen evolution reaction (HER). A positive correlation between the concentrations of dual In and S vacancies and the photocatalytic HER rate over ZIS nanosheets is observed. The piezoelectric polarization, stimulated by low-frequency vortex vibration to ensure the well-dispersion of ZIS nanosheets in solution, plays a crucial role in enhancing photocatalytic HER over the dual-vacancy engineered ZIS nanosheets. The piezoelectric characteristic of the defective ZIS nanosheets is confirmed through the piezopotential response measured using piezoelectric force microscopy. Piezophotocatalytic H2 evolution over the ZIS nanosheets is boosted under accelerated vortex vibrations. The research explores how vacancies alter ZIS's dipole moment and piezoelectric properties, thereby increasing electric potential gradient and improving charge-separation efficiency, through multi-scale simulations, including Density Functional Theory and Finite Element Analysis, and a machine-learning interatomic potential for defect identification. Increased In and S vacancies lead to higher electric potential gradients in ZIS along [100] and [010] directions, attributing to dipole moment and the piezoelectric effect. This research provides a comprehensive exploration of vacancy engineering in ZIS nanosheets, leveraging the piezopotential and dipole field to enhance photocatalytic performances.

Pb/(Ni@RC) composite derived from rice for lead carbon batteries: excellent conductivity, mass transfer, and reactivity

Enhancing electron/ion transfer and suppressing the hydrogen evolution reaction (HER) represent key objectives in the quest for carbonaceous additives in lead carbon batteries. In this study, we synthesize a porous cellular carbon structure comprising cross-linked nano carbon sheets through a straightforward process involving the expansion and carbonization of rice. Furthermore, by leveraging the distinct reactions of metal oxides and carbon at elevated temperatures, we achieve the simultaneous uniform in-situ loading and embedding of Pb/Ni bimetallic nanoparticles in Pb/(Ni@RC). The etching and embedding of Ni nanoparticles result in remarkable conductivity and the development of an open pore structure. Meanwhile, the incorporation of Pb nanoparticles ensures a low HER rate and a favorable affinity for the anode active material. This positive synergistic mechanism endows Pb/(Ni@RC) with abundant redox-active sites, and mitigates the performance degradation caused by water loss and the disruption of the lead carbon binary phase. Notably, the designed anode demonstrates a high reversible capacity (170 mAh g−1), an exceptionally long cycle life (16830 cycles) under high rate partial state of charge conditions, and an enhanced capacity retention rate (85%) during partial state of charge operation.

Construction of 2D/2D ZnIn2S4/Nb2CTx (MXene) hybrid with hole transport highway and active facet exposure boost photocatalytic hydrogen evolution

In this study, leveraging the tunable surface groups of MXene, the two-dimensional (2D) Nb2CTx with OH terminal (NC) was synthesized. 2D ZnIn2S4 (ZIS) nanosheets were prepared with the aid of sodium citrate, enhancing the exposure ratio of active (110) facet. On this basis, 2D/2D ZnIn2S4/Nb2CTx heterojunctions were fabricated to improve photocatalytic hydrogen evolution reaction (HER) performance. The optimized 6 wt%Nb2CTx/ZnIn2S4-450 (6NC/ZIS-450) photocatalyt exhibits a remarkable HER rate of 3603 μmol g−1h−1, which is 10 times superior to that of the original ZnIn2S4. Its apparent quantum efficiency (AQE) at 380 nm reaches 14.9 %. Meanwhile, even after 5 rounds of HER, the activity of 2D/2D ZnIn2S4/Nb2CTx heterojunction remained at 90 %, far superior to that of pure ZnIn2S4 (34 % and 31 %). Energy band structure analysis and density functional theory (DFT) calculation indicate that Nb2CTx adsorbed with OH exhibit a low work function. By serving as a hole cocatalyst, it effectively boosts the photocatalytic HER rate of ZnIn2S4/Nb2CTx heterojunction and inhibits the photocorrosion of ZnIn2S4. This unique insight, via hole transport highways and increased exposure of active facets, effectively enhances the activity and stability of sulfides photocatalysts.

An intermediary route to CdS/Bi2S3 architectures with high-activity and stability in photocatalytic water splitting and dye degradation

The binary CdS/Bi2S3 heterostructures were fabricated by employing ZnO/Bi2S3 as active intermediates for the first time, which consisted of 0D CdS nanoparticles with sizes of 10–20 nm decorated on 3D Bi2S3 mircoflowers assembled by 1D nanorods. The whole formation mechanism of CdS/Bi2S3 heterostructure was systematically investigated. Specifically, the optimal CdS/Bi2S3 sample (CB-3) achieved the highest photocatalytic hydrogen evolution reaction rate of 3.85 mmol·g−1·h−1, about 16.74 and 25.67 times greater than that of single Bi2S3 and CdS. Besides, the apparent reaction rate constant of CB-3 for photodegradation of Congo red reached up to 0.0412 min−1, being 41.2 and 4.08 folds higher than that of solo Bi2S3 and CdS. The recycled tests over CB-3 were ready to take on the superb photostability. Furthermore, the S-scheme mechanism of photoinduced charges was rationally proposed. This work provides a new insight for the construction of composite photocatalysts for boosted solar-light-driven photocatalytic performance.

Hydrophilic Photocrosslinkers as a Universal Solution to Endow Water Affinity to a Polymer Photocatalyst for an Enhanced Hydrogen Evolution Rate.

A universal approach for enhancing water affinity in polymer photocatalysts by covalently attaching hydrophilic photocrosslinkers to polymer chains is presented. A series of bisdiazirine photocrosslinkers, each comprising bisdiazirine photophores linked by various aliphatic (CL-R) or ethylene glycol-based bridge chains (CL-TEG), is designed to prevent crosslinked polymer photocatalysts from degradation through a safe and efficient photocrosslinking reaction at a wavelength of 365nm. When employing the hydrophilic CL-TEG as a photocrosslinker with polymer photocatalysts (F8BT), the hydrogen evolution reaction (HER) rate is considerably enhanced by 2.5-fold compared to that obtained using non-crosslinked F8BT photocatalysts, whereas CL-R-based photocatalysts yield HER rates comparable to those of non-crosslinked counterparts. Photophysical analyses including time-resolved photoluminescence and transient absorption measurements reveal that adding CL-TEG accelerates exciton separation, forming long-lived charge carriers. Additionally, the in-depth study using molecular dynamics simulations elucidates the dual role of CL-TEG: it enhances water penetration into the polymer matrix and stabilizes charge carriers after exciton generation against undesirable recombination. Therefore, the strategy highlights endowing a high-permittivity environment within polymer photocatalyst in a controlled manner is crucial for enhancing photocatalytic redox reactivity. Furthermore, this study shows that this hydrophilic crosslinker approach has a broad applicability in general polymer semiconductors and their nanoparticulate photocatalysts.

Zr dopant acting shallow donor and active site in CdS lattice for co-catalyst free photocatalytic H2 evolution

Hydrogen evolution by photocatalysis shows great potential in solar energy conversion process and thus has become an active field of research. Separation efficiency of photogenerated carriers, light absorption and surface reaction are the dominant aspects that affect the photocatalytic hydrogen evolution. Creating traps to prolong the lifetime of photogenerated charge carriers has been widely used but may be considered detrimental if they lead to recombination process of the photogenerated charge carriers. Herein, we design a kind of efficient atomic substitution strategy to create shallow donor for highly efficient hydrogen evolution reaction. The photocatalytic hydrogen evolution reaction rate reaches 3766.9 μmol h−1 g−1, which is about 2.98 times higher of pure CdS. The injected foreign atoms (Zr) not only reduce bandgap to extend light absorption but also generate shallow trap level to reduce recombination of photogenerated carriers. Moreover, the introduced atoms could downshift Fermi level to supply more carriers and act the role as active center to reduce Gibbs free energy, leading to the enhanced hydrogen generation rate and superior stability. This report offers new enlightenment into designing noble-metal free photocatalysts with extraordinary catalytic performance and excellent stability.

Effect of nitro-substituted ending group on the photovoltaic and photocatalytic performance of non-fullerene acceptors

The Y-series non-fullerene acceptors (NFAs) significantly enhance organic photovoltaic device efficiency, approaching 20%. Recent studies demonstrate their commendable photocatalytic performance in bulk heterojunction photocatalysis. Chemical modification of end groups emerges as a pivotal way to modulate molecular electrical and optical characteristics, thereby improving the organic solar cells (OSCs) performance. Among Y-series NFAs, 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene)propanedinitrile (INCN) and its derivatives stand out as the most successful end groups. However, a restricted range of modifying groups, such as the fluorine atom (–F) and the hydroxyl group (–OH), are currently employed to explore both the photovoltaic and photocatalytic properties of Y-series NFAs, research on other substituents for INCN remains largely unexplored to date. In this study, nitro-substituted end groups were incorporated into the Y6 skeleton, resulting in a new NFA, named Y6-NO. Simultaneously, INCN is incorporated into the Y6 skeleton to create Y6-IN as a reference molecule for simultaneously investigating the photovoltaic and photocatalytic properties of the two NFAs. In organic photovoltaics, Y6-NO, featuring nitro groups, exhibits a red-shifted absorption, lower molecular energy levels, and enhanced electron transport, leading to a superior power conversion efficiency (PCE) of 17.03 % for OSCs, as opposed to 10.45 % for Y6-IN. Conversely, in the photocatalytic hydrogen evolution reaction (HER) for water splitting, the nitro groups in Y6-NO lowers the energy level of the lowest unoccupied molecular orbital (LUMO), resulting in a reduced overpotential when combined with the co-catalyst Pt. Consequently, the HER rate of PM6:Y6-NO nanoparticles (72.2 mmol h−1 g−1) is lower than that of PM6:Y6-IN nanoparticles (108.5 mmol h−1 g−1). This study highlights that through judicious end-group chemical modification, the photovoltaic and photocatalytic properties of the acceptors can be effectively modulated.

A bifunctional cobalt bis(terpyridine) complex for efficient water splitting to green hydrogen generation

Photocatalytic hydrogen evolution is considered to be the holy grail of artificial photosynthesis. Here, we report a novel bifunctional Cobalt bis-(terpyridine) complex on dual role in photocatalytic and electrocatalytic hydrogen generations. The integrated Co-complex as photosensitizer attached to TiO2 shows an impressive hydrogen evolution reaction rate of 715 µmol g−1 h−1 with a high turnover number of 5718 and apparent quantum yield of 5.34%. The co-functionalized electrode shows significantly enhanced electrocatalytic activity through proton-coupled electron transfer path in CH3CN/trifluoroacetic acid at 0.63 V with a turn-over frequency of 18.64 s−1 at an optimal acid to catalyst ratio of 8:1. The electron-rich 4′-(5-(4-diphenylamino)phenylthiophen-2-yl)-2,2′:6′,2″-terpyridine π-conjugation synergistically enhances the catalytic performances and effectively transmits electronic charge to the terpyridine core via the thienyl spacer and supports mechanistic insight of the Co-center in the catalytic cycle. The simple design strategy of molecular catalysts with structural integrity is expected to offer an economically viable approach for practical energy conversion applications.

Direct Observation of Z-Scheme Route in Cu31 S16 /Znx Cd1-x S Heteronanoplates for Highly Efficient Photocatalytic Hydrogen Evolution.

Although photocatalytic hydrogen production from water holds great potential as a renewable and sustainable energy alternative, the practical application of the technology demands cost-effective, simple photocatalytic systems with high efficiency in hydrogen evolution reaction (HER). Herein, the synthesis and characterization of Cu31 S16 /Znx Cd1-x S heterostructured nanoplates (Cu31 S16 /ZnCdS HNPs) as a high photocatalytic system are reported. The cost-effective, hierarchical structures are easily prepared using the Cu31 S16 NPs as the seed by the epitaxial growth of the ZnCdS nanocrystals (NCs). The Cu31 S16 /ZnCdS without the noble metal cocatalyst exhibits a high HER rate of 61.7mmolg-1 h-1 , which is 8,014 and 17 times higher than that of Cu31 S16 and ZnCdS, respectively, under visible light irradiation. The apparent quantum yield (AQY) of Cu31 S16 /ZnCdS reaches 67.9% at 400nm with the highest value so far in the reported ZnCdS-based photocatalysts. The excellent activity and stability of the Cu31 S16 /ZnCdS are attributed to the formation of a strong internal electric field (IEF) and the Z-scheme pathway. The comprehensive experiments and theoretical calculations provide the direct evidences of the Z-scheme route. This work may offer a way for the design and development of efficient photocatalysts to achieve solar-to-chemical energy conversion at a practically useful level.

Accelerating photoelectrochemical CO2RR selectively of C2+ products by integrating Ag/Pd cocatalysts on Cu/Cu2O/CuO heterojunction nanorods

The Cu-based photoelectrochemical CO2 reduction reaction (PEC–CO2RR) represents a convenient approach for producing value-added C2+ products, aiming to achieve carbon neutrality by reducing greenhouse gas emissions. However, these reactions typically suffer from limited selectivity. In this work, we fabricate Cu/Cu2O/CuO nanorod (CuR)-based heterojunction architectures integrated with Ag and Pd cocatalysts to boost the selectivity of C2+ products. The proposed Cu/Cu2O/CuO/Ag-Pd (CuR/Ag-Pd) photoelectrodes are used as photocathodes to generate a maximum Faradaic efficiency (FE) of C2+ products exceeding 53% by suppressing the hydrogen evolution reaction (HER). The FE improvement is approximately 22-fold (n-propanol), 12-fold (ethanol), 13-fold (acetaldehyde), and 6-fold (acetate) compared with CuR photoelectrodes operating at a negative applied potential of −1.8 V (vs. reversible hydrogen electrode, RHE). Conversely, the CuR photoelectrodes exhibit a maximum HER rate of ∼86% at −1.8 V (vs. RHE), higher than those of the CuR/Ag (54%) and CuR/Ag-Pd (35%) photoelectrodes. The superior PEC–CO2RR performance of CuR/Ag-Pd photoelectrodes is attributable to the higher electrochemical active surface area (6.7 mF/cm2) and faster charge transfer rate at the electrode/electrolyte interface owing to the presence of cocatalysts. In addition, the CuR/Ag-Pd photoelectrodes exhibit remarkable long-term stability retaining 70% of the initial performance even after a relatively more negative applied potential at −1.2 V. A comprehensive investigation into the changes in surface morphology, crystal structure, and elemental composition after PEC–CO2RR confirms the higher stability of CuR/Ag-Pd photoelectrodes. Thus, this work provides novel perceptions into the development of Cu-based heterojunction photoelectrodes integrated with Ag/Pd cocatalysts for improving the selectivity of C2+ products.

Cooperative Effect of Cations and Catalyst Structure in Tuning Alkaline Hydrogen Evolution on Pt Electrodes.

The kinetics of hydrogen evolution reaction (HER) in alkaline media, a reaction central to alkaline water electrolyzers, is not accurately captured by traditional adsorption-based activity descriptors. As a result, the exact mechanism and the main driving force for the water reduction or HER rate remain hotly debated. Here, we perform extensive kinetic measurements on the pH- and cation-dependent HER rate on Pt single-crystal electrodes in alkaline conditions. We find that cations interacting with Pt step sites control the HER activity, while they interact only weakly with Pt(111) and Pt(100) terraces and, therefore, cations do not affect HER kinetics on terrace sites. This is reflected by divergent activity trends as a function of pH as well as cation concentration on stepped Pt surfaces vs Pt surfaces that do not feature steps, such as Pt(111). We show that HER activity can be optimized by rationally tuning these step-cation interactions via selective adatom deposition at the steps and by choosing an optimal electrolyte composition. Our work shows that the catalyst and the electrolyte must be tailored in conjunction to achieve the highest possible HER activity.

In-situ decorated cobalt phosphide cocatalyst on Hittorf's phosphorus triggering efficient photocatalytic hydrogen production

Hittorf's phosphorus (HP) is a promising visible-light-driven photocatalyst, yet the slow charge migration and sluggish surface reaction kinetics have limited its photocatalytic hydrogen evolution reaction (HER) efficiency. In this work, cobalt phosphide (CoP2) modified rod-like HP (HP/CoP2) composite was designed and synthesized by a template-assisted chemical vapor deposition strategy. The optimal HP/CoP2 composite yields a HER rate reaching 13.1 μmol·h-1 through pure water splitting under visible light irradiation, which is approximately 4 times higher than that of HP using Pt as cocatalyst (3.3 μmol·h-1). It was experimentally indicated that the accelerated photogenerated charge transfer and promoted surface HER kinetics in the composite gave rise to the superior photocatalytic HER performance.

THE IMPACT OF CHAOTIC FLUX REFLECTION FIELD ON HYDROGEN EVOLUTION REACTION OF WATER ELECTROLYSIS

Water electrolysis promises the capability to produce green hydrogen in the future. The efficiency and hydrogen evolution reaction rate (HER) of water electrolysis can be improved through magnetic field assisted electrolysis. External magnetic field exposure improves hydrogen production without requiring complex catalyst synthesis technique. The purpose of this study is to introduce chaos into a magnetic field assisted electrolysis system which disturbs the water molecules stability. The chaos effect was triggered by irregular flux reflection technique. The flux reflection was generated using diamagnetic tourmaline stones which sticked all over the electrolyzer wall. Consequently, the rotational speed of DMF does not reduce the effectiveness of chaotic flux. As a result, the hydrogen bond of the water molecules is destabilized irregularly. In conjuction with that, the bonds are unable to be reformed which make the water molecules continuously in movement. The critical effect of chaotic flux is the shear force that experienced by water molecules. The paramagnetic OH- ion movement is also slowed down so that H+ ion and electrons interaction were occurred in less restrictive manner. Hence, the chaotic magnetic field able to improve HER. The chaotic flux reflection improves hydrogen production in magnetic field assisted water electrolysis through water properties and ion transfer mechanism modification.

Unravelling co-catalyst integration methods in Ti-based metal-organic gels for photocatalytic H2 production.

The synthesis, characterization and photocatalytic hydrogen evolution reaction (HER) performance of a series of metal-organic gels (MOGs) constructed from titanium(IV)-oxo clusters and dicarboxylato linkers (benzene-1,4-dicarboxylato and 2-aminobenzene-1,4-dicarboxylato) are described. All the MOGs exhibit a microstructure comprised of metal-organic nanoparticles intertwined into a highly meso-/macroporous structure, as demonstrated by cryogenic transmission electron microscopy and gas adsorption isotherms. Comprehensive chemical characterization enabled the estimation of the complex formula for these defective materials, which exhibit low crystallinity and linker vacancies. To gain deeper insights into the local structure, X-ray absorption fine structure (XAFS) spectroscopy experiments were performed and compared to that of the analogous crystalline metal-organic framework. Additionally, the ultraviolet-visible absorption properties and optical band gaps were determined from diffuse reflectance spectroscopy data. The MOGs were studied as light absorbers for the sacrificial photocatalytic HER under simulated solar light irradiation using a platinum co-catalyst by either (1) in situ photodeposition or (2) ex situ doping process, through a post-synthetic metalation of the MOG structure. The chemical analysis of the metalation, along with high-angle annular dark-field scanning transmission electron microscopy, revealed that although the in situ addition of the co-catalyst led to greater HER rates (227 vs. 110 μmolH2 gMOG-1 h-1 for in situ and ex situ, respectively), the ex situ modification provided a finer distribution of platinum nanoparticles along the porous microstructure and, as a result, it led to a more efficient utilization of the co-catalyst (45 vs. 110 mmolH2 gPt-1 h-1).

What Controls Activity Trends of Electrocatalytic Water Splitting? - Activation Energy Vs. Frequency Factor

Electrocatalytic water splitting is a topic of investigation of numerous research groups for decades. Oxygen evolution reaction (OER), as a more complex and more demanding reaction, is more frequently studied, despite of the fact that the simpler hydrogen evolution reaction (HER), is generally not well understood. Nowadays, recurrent approach to electrocatalysis is conquest for more active and more stable electrode materials, very often lacking significant input to better understanding of reaction mechanisms or understanding of what are the drivers of electrocatalytic activity [1].Importantly, if one asks the key question from the conceptual point of view, and that is: what are the origins of electrocatalytic activity? - the answer will be, in the predominant majority of cases, like 70 years ago. Namely, paradigm of electrocatalysis is Sabatier principle, that suggests optimal (“not too strong, not too weak”) binding of intermediates as main precondition of high reaction rate [2]. Conventional wisdom suggests that confirmation of this should be relatively simple. Namely, Brönsted-Evans-Polanyi (BEP) relations suggest linear relationship between adsorption energy of key intermediates and activation energy. In other words, if we have reliable values of adsorption energies relevant for the electrochemical environment [3], they should form linear dependence with experimentally obtained activation energies.However, high-temperature hydrodynamic experiments on HER indicate that reducing of activation energy by tuning of adsorption energy of intermediates is not necessarily beneficial for enhancement of HER rate. Namely, HER rate is strongly influenced by preexponential frequency factor. Therefore, we propose discussion that will analyse several key aspects of HER electrocatalysis: 1) interplay of activation energy and preexponential factor as a driver of electrocatalytic activity 2) are BEP relations relevant for electrocatalysis 3) can we assess adsorption energies experimentally 4) what are relevant descriptors that shed light on HER activation process, 5) what else is important beyond Sabatier principle for rate of HER [1-7]. Figure 1. Graphical illustration of four interfacial descriptors relevant for HER. Adapted from Ref. [4] with permission from the PCCP Owner Societies, under the terms and conditions of the Creative Commons Attribution 3.0 Unported License.

Deconvoluting the Role of Electrolyte pH, Structural Sensitivity, and Electric Field Effects on the Electrochemical Hydrogenation of Phenol

Traditional thermochemical hydrogenation (TCH) methods that are used in the U.S. chemical and petroleum industries to produce value-added fuels are highly energy intensive. To achieve hydrogenation, they require high temperature and pressure, along with an external source of hydrogen that usually comes from steam methane reformation. Electrochemical hydrogenation (ECH) is an attractive alternative that replaces the thermal driving force with an applied electrical potential, allowing ECH to operate near ambient conditions. The participating protons come from the aqueous electrolyte solution rather than externally produced hydrogen. These features of ECH lower its energy demand compared to TCH and result in less greenhouse gas emissions. ECH is also promising for the processing of biomass feedstocks and could be powered directly by renewable energy, further minimizing the environmental impact.The addition of an aqueous electrolyte and electric field means that insights from TCH should not be directly translated to ECH systems, however, this is often the case in the literature. Fundamental studies on ECH of aromatic hydrocarbons (AHs) are necessary to address current limitations including: competition with the hydrogen evolution reaction (HER) resulting in lower faradaic efficiency, low rates compared to TCH, and little control over selectivity and degree of hydrogenation. For instance, the role of electrolyte pH on phenol ECH remains poorly understood. While some groups have reported negligible phenol turnover rates in electrolytes of pH 10 and above on Pt/C and Pd/C catalysts [1], Song et al. have shown that turnover rates and efficiency are highest on Rh/C at pH 10 [2]. Yet, the idea that low pH (3-5) is best has persisted and the source of the pH dependence remains unknown.In this work we use phenol as a simple representative AH for lignocellulosic bio-oil. We have shown with rotating disk electrode voltammetry that the presence of phenol in electrolytes of pH ~10 enhances HER rates on Pt, Pd, and Au catalysts. Considering that the pKa of phenol is also 10.0, we propose that interfacial phenol molecules channel protons to the catalyst surface by way of facile proton dissociation/reassociation, lowering the barrier for adsorbed H formation in alkaline electrolytes. While this may explain, in part, the low phenol turnover rates observed at higher pH, we further investigate why the opposite is observed on Rh/C catalysts. The role of atomic surface structure is also critical to the adsorption geometry and coverage of AHs. We use well-defined, low-index Pt single crystals to identify the true structural sensitivity for the ECH of AHs. We show with select stepped single crystal surfaces that there is a synergetic role between terrace width/step density that defines activity, balancing coverage of AH molecules, formation of surface adsorbed H, and transfer of that H to AH reactants. We use a low-volume, membrane-separated flow cell for chrono-amperometry followed by product analysis to correlate pH, structural sensitivity, and applied potential to phenol ECH rates and faradaic efficiency. With an understanding of the role of atomic surface structure and the true source of pH dependence, we propose strategies for enhancing phenol turnover rates at lower overpotentials, improving faradaic efficiency, and controlling selectivity.

Synthesize magnetic ZnFe2O4@C/Cd0.9Zn0.1S catalysts with S-scheme heterojunction to achieve extraordinary hydrogen production efficiency

Suppressing the electron-hole recombination rate of catalyst legitimately is one of the effective strategies to improve photocatalytic hydrogen evolution. Herein, carbon-coated metal oxide, ZnFe2O4@C (ZFO@C), nanoparticles were synthesized and employed to couple with quadrupedal Cd0.9Zn0.1S (CZS) via an ordinary ultrasonic self-assembly method combined with calcination to form a novel ZFO@C/CZS catalyst with step-scheme (S-scheme) heterojunction. The photocatalytic hydrogen evolution reaction (HER) was conducted to verify the enhanced photoactivity of ZFO@C/CZS. The optimal ZFO@C/CZS exhibits an extraordinary photocatalytic HER rate of 111.3 ± 0.9 mmol g-1 h−1 under visible-light irradiation, corresponding to an apparent quantum efficiency as high as (76.2 ± 0.9)% at 450 nm. Additionally, the as-synthesized ZFO@C/CZS composite exhibits high stability and recyclability. The excellent photocatalytic hydrogen evolution performance should arise from the formed S-scheme heterojunction and the unique ZFO@C core–shell structure, which inhibit electron hole recombination as well as provide more reactive sites. The pathway of S-scheme charge transfer was validated through density functional theory calculations and electrochemical measurements. This work provides a rational strategy for the synthesis of unique magnetic S-scheme heterojunction photocatalysts for water splitting under visible light irradiation.

Stable and wide spectrum response Zn3As2/Al2O3 photocatalyst for photocatalytic overall water splitting

Constructing highly efficient and durable non-noble-metal photocatalysts with a broad spectral response for promoting sluggish photocatalyticover water splitting reaction is very desirable but still challenging. To realize scalable hydrogen production, an energy conversion efficiency of 10 % and stable photocatalysts with broad light-absorption are required. To this end, a wide spectrum response Zn3As2/Al2O3 has been successfully synthesized by a layer-by-layer coating method as a photocatalyst utilized in the hydrogen evolution reaction (HER) for the first time, which gave the HER rate of 92.5 μmol·g−1·h−1. The HER activity did not decline obviously after three runs. Characterization results and photocatalytic performance confirmed that the Al2O3 layer could protect Zn3As2 from photocorrosion, which exhibited preeminent stability and outstanding photocatalytic performance. In addition, Zn3As2/Al2O3 showed light response extending to ∼1300 nm, and more efficient separation capability of photogenerated charges benefited from the built-in electric field between Al2O3 and Zn3As2, which were verified by UV–Vis–NIR DRS and electrochemical measurements. Our research results may provide a new route of design and construction of stable and efficacious photocatalysts to realize solar energy conversion to hydrogen.

S vacancies engineering ZnIn2S4 nanosheets for boosted photocatalytic hydrogen evolution

2D-layered ZnIn2S4 nanosheets (ZIS NSs) have been considered as a promising photocatalysts to produce H2. Nevertheless, the carrier recombination of 2D ZnIn2S4 is still severe, which limits its photocatalytic efficiency and practical applications. Herein, the defective ZnIn2S4 nanosheets with S vacancies (DZIS NSs) is fabricated via an easy one-step solvothermal process only by changing the used solvent without a complex physical or/and chemical secondary treatment, which can realize efficient photocatalytic H2 generation. The resultant DZIS NSs show enhanced photocatalytic hydrogen evolution reaction (HER) activity and well stability after 5 cycles. And the photocatalytic HER rate of DZIS NSs is up to 5437 μmol−1 h−1 g−1, nearly 2.6 times of pristine ZIS NSs (2090 μmol−1 h−1 g−1). The experimental data suggest that the excellent photocatalytic HER performance of DZIS NSs is attributable to the existence of S vacancies, which can form a S defect energy level under the lower conduction band (CB), offering abundant active sites for hydrogen activation, extending the visible light absorption range and narrowing the bandgap of DZIS NSs. Such defect engineering strategy opens new avenues for other sulfide photocatalysts to further boost photocatalytic activity.

Nickel and/or platinum modified crystalline silicon–carbon composites and their electrochemical behaviour towards the hydrogen evolution reaction

Generation of hydrogen is very important, as it is one of the most desired alternatives to fossil fuels. Moreover, designing of cheap and stable electrocatalysts is the task for the efficient generation of hydrogen with reasonable activity. Materials hybridization can be considered a tool for engineering different material properties. Composites of modified silicon such as C–Si, Ni/(C–Si), Pt/(C–Si), and Pt–Ni/(C–Si) were prepared (in weight percent) and studied as electrocatalysts for the hydrogen evolution reaction (HER) in 0.5 M H2SO4 solution. The surface morphologies and chemical compositions of the composites were confirmed using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray fluorescence analysis (XRF), elemental mapping, and BET surface analysis. The electrochemical measurements of linear sweep voltammetry (LSV), Tafel plots, chronoamperometry, and electrochemical impedance spectroscopy (EIS) were used to study the behaviour of the prepared electrodes toward the hydrogen evolution process. Among the various prepared composites, [7%Pt–3%Ni]/[C–Si (1:1)] composite shows the best catalytic activity with the highest HER rate (940.95 µA cm−2 s−1), the lowest overpotential [0.358 V vs. (Ag/AgCl) ≈ 0.161 V vs. (RHE)] at 10 mA cm−2, and the lowest charge transfer resistance (2.657 Ω) compared to other prepared electrodes. In addition, it gives the highest values of 4.219 × 10−3 s−1 turn over frequency (TOF) and 642 mA g−1 mass activity. It shows good stability towards the hydrogen evolution reaction as the current density reaches about 34.28 mA cm−2 after 5 h.Graphical abstract