Catalysts For Hydrogen Evolution Research Articles

Colloid synthesis of Ni12P5/N, S-doped graphene as efficient bifunctional catalyst for alkaline hydrogen evolution and triiodide reduction reaction

Designing high-efficient bifunction catalysts with excellent catalytic activity and enhanced charge-transfer capability in both alkaline hydrogen evolution reaction (HER) and triiodide reduction reaction (IRR) is of utmost significance to advance the development of green hydrogen production and photovoltaics, respectively, yet remains a crucial challenge. Here, highly dispersed and small-sized Ni12P5 nanocrystals with narrow size distribution was well attached on the surface of N, S co-doped graphene (Ni12P5/NSG) by the facile hot-injection method. As expected, the optimized Ni12P5/NSG requires a relatively low overpotential of 132.94 ± 0.08 mV to deliver a current density of 10 mA cm−2 in alkaline condition, accompanied with remarkable long-time durability with negligible attenuation over 50 h. Density functional theory (DFT) calculations revealed that the positively synergic effect between Ni12P5 and NSG are in favor of modulating the rate determining step of the dissociation of H2O to *(OH-H), thereby upgrading its HER activity. When used as the counter electrode catalyst for IRR in DSSCs, the resultant Ni12P5/NSG exhibits extraordinary Pt-like catalytic activity and well electrochemical stability in iodide-based electrolyte, delivering a high photoelectric conversion performance (PCE) comparable to Pt. The improved PCE can be attributed to the accelerated interfacial charge-transfer capability around active sites for facilitating the reaction kinetics of IRR, as demonstrated by DFT calculations. This work provides an effective strategy for synthesizing cost-effective composites with multi-active sites and offering valuable insight into the structure-performance relationship, which is conducive to guide the synthesis of promising catalysts in the energy conversion field.

Electrolytic Hydrogen Evolution Study of Porous Tungsten Carbide‐Loaded Pt Derived from ZIFs

AbstractThe development of an electrochemical hydrogen evolution catalyst with high activity and low Pt loading and excellent stability is of high significance for the extensive promotion and practical application of hydrogen energy. Hence, we introduced ZIFs and their derivatives with tunable pore size and large specific surface area, which were carbonized at high temperatures and supported with Pt as catalysts for hydrogen evolution reaction. We used ZIF‐8 as the seed to obtain the precursor Co@ZIFs, W element was introduced into Co@ZIFs by impregnation method to synthesize WC. A series of Pt/WC catalysts were prepared with WC as support. The best sample Pt/WC‐3 in 0.5 M H2SO4 with a Pt content of 8.3 wt % has a low overpotential (η10=28 mV), which is much less than the 34 mV of 20% commercial Pt/C and had a Tafel slope of only 18.9 mV dec−1. It is noteworthy that at 8.3% Pt/WC after 40,000 s of continuous operation at 10 mA cm−2, the overpotential of Pt/WC‐3 barely rises by 5%, which indicates its excellent durability.

Integration of Alloy Segregation and Surface CoO Hybridization in Carbon‐Encapsulated CoNiPt Alloy Catalyst for Superior Alkaline Hydrogen Evolution

AbstractConstructing an efficient alkaline hydrogen evolution reaction (HER) catalyst with low platinum (Pt) consumption is crucial for the cost reduction of energy devices, such as electrolyzers. Herein, nanoflower‐like carbon‐encapsulated CoNiPt alloy catalysts with composition segregation are designed by pyrolyzing morphology‐controlled and Pt‐proportion‐tuned metal–organic frameworks (MOFs). The optimized catalyst containing 15% CoNiPt NFs (15%: Pt mass percentage, NFs: nanoflowers) exhibits outstanding alkaline HER performance with a low overpotential of 25 mV at a current density of 10 mA cm−2, far outperforming those of commercial Pt/C (47 mV) and the most advanced catalysts. Such superior activity originates from an integration of segregation alloy and Co‐O hybridization. The nanoflower‐like hierarchical structure guarantees the full exposure of segregation alloy sites. Density functional theory calculations suggest that the segregation alloy components not only promote water dissociation but also facilitate the hydrogen adsorption process, synergistically accelerating the kinetics of alkaline HER. In addition, the activity of alkaline HER is volcanically distributed with the surface oxygen content, mainly in the form of Co3dO2p hybridization, which is another reason for enhanced activity. This work provides feasible insights into the design of cost‐effective alkaline HER catalysts by coordinating kinetic reaction sites at segregation alloy and adjusting the appropriate oxygen content.

A Review on Hydrogen Generation by Photo-, Electro-, and Photoelectro-Catalysts Based on Chitosan, Chitin, Cellulose, and Carbon Materials Obtained from These Biopolymers

Biopolymer-based catalysts like chitosan, chitin, and cellulose offer sustainability and high efficiency both as the catalyst or catalyst support in a broad range of applications, especially in hydrogen evolution reactions. This review focused on hydrogen evolution catalysts of chitosan, chitin, cellulose, and carbon materials obtained from these biopolymers to highlight the opportunities of these sustainable catalysts in this field. All the reports in this area could be classified as one of the photocatalysts, electrocatalysts, and photoelectrocatalysts, and their mechanisms were clarified in the beginning. Then, the results of catalysts obtained from each of these biopolymers were discussed separately to reveal the roles of the biopolymers. It was concluded that all of the biopolymers enjoy some common benefits like hydrogen bonding, chelating with transition metals, easy chemical modification, high performance, and potential to be used as the precursors of carbon or porous materials. Among them, chitosan showed outstanding merit due to the better performance in metal grafting, amendment, and ability of hydrogen bonding. Moreover, it provides highly active nitrogen-doped carbon as the support of transition metals in the hydrogen generation, enhancing the reaction rate by retarding the charges recombination.

Computational Insights into the Influence of Ligands on Hydrogen Generation with [Cp*Rh] Hydrides.

This work reports a computational investigation of the effect of ancillary ligands on the activity of an Rh catalyst for hydrogen evolution based on the [Cp*Rh] motif (Cp* = η5-pentamethylcyclopentadienyl). Specifically, we investigate why a bipyridyl (bpy) ligand leads to H2 generation but diphenylphosphino-based (dpp) ligands do not. We compare the full ligands to simplified models and systematically vary structural features to ascertain their effect on the reaction energy of each catalytic step. The calculations based on density functional theory show that the main effect on reactivity is the choice of linker atom, followed by its coordination. In particular, P stabilizes the intermediate Rh-hydride species by donating electron density to the Rh, thus inhibiting the reaction toward H2 generation. Conversely, N, a more electron-withdrawing center, favors H2 generation at the price of destabilizing the hydride intermediate, which cannot be isolated experimentally and makes determining the mechanism of this reaction more difficult. We also find that the steric effects of bulky substituents on the main ligand scaffold can lead to large effects on the reactivity, which may be challenging to fine-tune. On the other hand, structural features like the bite angle of the bidentate ligand have a much smaller impact on reactivity. Therefore, we propose that the choice of linker atom is key for the catalytic activity of this species, which can be further fine-tuned by a proper choice of electron-directing groups on the ligand scaffold.

Synergy of Torsion Strained and Ligand Effect for Relay Acceleration of Industrial High‐pH Hydrogen Evolution

AbstractNoble metal Pt‐based catalysts have slow water dissociation kinetics at high pH conditions, making it difficult for water molecules to be electrochemically activated. Utilizing ligand effect and strain effect to tailor catalytic active sites is a common method, while the understanding of mechanism of their interaction remains obscure due to the complexity of the process. This study proposes a pulse‐induced torsional strained PtRu mesocrystals (PtRu MCs) with 20 times higher mass activity than commercial Pt/C. The combination of experimental results and theoretical calculations reveals that the ligand effect induced by Ru doping accelerates the kinetics of the water dissociation reaction, while the pulse‐induced torsion strained dominates the thermodynamic optimization of the hydrogen adsorption reaction. The structure‐activity relationship defined by the synergistic effect under the complementary advantages of the strain and doping provides guidance for the design of future basic hydrogen evolution catalysts. The catalyst can run stably at 1 A cm−2 for 500 h, showing potential for industrial application.

Synthesis of Copper Nanoparticles Supported over Graphene-like Material Composite as a Catalyst for Hydrogen Evolution

The need for an alternative energy source that is both clean and abundant has led to research into a hydrogen economy. Hydrogen gas can be produced slowly via the hydrolysis of sodium borohydride (NaBH4). A catalyst can be used to speed up the rate at which hydrogen is produced, however many catalysts involve relatively expensive materials like precious metals. This study explores a novel copper nanoparticle supported on a graphene-like material composite as a catalyst for the hydrolysis of NaBH4. The material was characterized via powdered X-ray diffraction (P-XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), and Energy Dispersive spectroscopy (EDS). The P-XRD confirmed the crystallinity structures of graphene-like material (GLM) and copper nanoparticles supported over graphene-like material (CuGLM). The P-XRD spectra indicated the (110), (111), and (200) lattice planes of copper nanoparticles. In FTIR analysis, the shifted and sharpening functional group peaks were observed when copper nanoparticles were supported by the GLM template. The TEM result indicated that the copper nanoparticle had a size of approximately 10 nm. The catalyst (CuGLM) was tested under different doses of NaBH4, solution pH, and reaction temperatures. Temperature data were used to determine the activation energy of the reaction to be 46.8 kJ mol−1, which is competitive when compared to similar catalysts. The catalyzed reaction generated the highest volume of hydrogen at pH 8 (51 mL), 303 K (32 mL), and 1225 μmol of NaBH4 (37 mL). The catalyst was found to be able to be used multiple times in succession without any significant loss in hydrogen generated. This catalyst is an exciting option for the sustainable generation of hydrogen gas as a fuel source.

Molybdenum oxysulfide MoOS2 as a hydrogen evolution catalyst: On the possible role of coordinated oxygen

Amorphous molybdenum oxysulfide MoOS2 obtained by acidification of aqueous MoO2S22− solutions was structurally characterized and tested as a catalyst for hydrogen evolution reaction (HER). Raman, XPS and XAS characterizations show that the solid contains oligomers based on the Mo(V) core Mo2O2S4 units, exposing dangling MoO bonds and connected via Mo-S-Mo bridges. MoOS2 demonstrated higher HER activity than reference catalysts including nanocrystalline MoS2, amorphous MoS3 and MoS2/MoO2 composite obtained by thermal decomposition of MoOS2. DFT calculations suggest that introduction of oxygen adjacent to the disulfide bridges in the molybdenum coordination does not change significantly the free energy of hydrogen desorption, as compared with fully sulfided MoxSy clusters. Higher HER catalytic activity of the MoOS2 material was explained by abundance of disulfide S22− moieties able to dissociate hydrogen and by fine dispersion of the material.

Unveiling Interfacial Effects for Efficient and Stable Hydrogen Evolution Reaction on Ruthenium Nanoparticles-Embedded Pentlandite Composites.

Heterogenous catalysis is important for future clean and sustainable energy systems. However, an urgent need to promote the development of efficient and stable hydrogen evolution catalysts still exists. In this study, ruthenium nanoparticles (Ru NPs) are in situ grown on Fe5 Ni4 S8 support (Ru/FNS) by replacement growth strategy. An efficient Ru/FNS electrocatalyst with enhanced interfacial effect is then developed and successfully applied for pH-universal hydrogen evolution reaction (HER). The Fe vacancies formed by FNS during the electrochemical process are found to be conducive to the introduction and firm anchoring of Ru atoms. Compared to Pt atoms, Ru atoms get easily aggregated and then grow rapidly to form NPs. This induces more bonding between Ru NPs and FNS, preventing the fall-off of Ru NPs and maintaining the structural stability of FNS. Moreover, the interaction between FNS and Ru NPs can adjust the d-band center of Ru NPs, as well as balance the hydrolytic dissociation energy and hydrogen binding energy. Consequently, the as-prepared Ru/FNS electrocatalyst exhibits excellent HER activity and improved cycle stability under pH-universal conditions. The developed pentlandite-based electrocatalysts with low cost, high activity, and good stability are promising candidates for future applications in water electrolysis.

N,S-codoped carbon encapsulated Co3S4@NiS/Cu2S hierarchical yolk-shell nanopolyhedron as bifunctional catalyst for efficient photovoltaics and alkaline hydrogen evolution

The yolk-shell structure electrocatalysts formed by polymetallic sulfides hold great promise in a variety of energy conversion/storage fields. Herein, the nitrogen/sulfur codoped porous carbon encapsulated Co3S4@NiS/Cu2S nanopolyhedrons (NSC-Co3S4@NiS/Cu2S) with hierarchical yolk-shell structures were successfully designed and synthesized by a facile one-step high-temperature degradation of zeolite imidazolate framework-67 (ZIF-67) wrapped with metal-doped trithiocyanuric acid (TCA-M). Trithiocyanuric acid played a dual role, not only providing nitrogen, sulfur, and carbon sources, but also playing a role in the sulfurization of metal elements. It is worth noting that, due to the higher specific surface area, unique morphology, multi-element synergies, and more favorable chemical composition, the synthesized samples possessed outstanding bifunctional electrocatalytic performance for dye-sensitized solar cells (DSSCs) and hydrogen evolution reactions (HERs). Experimental results showed that NSC-Co3S4@NiS/Cu2S electrode has a high photoelectric conversion efficiency (9.57%) in DSSCs. In addition, NSC-Co3S4@NiS/Cu2S electrode also showed a lower initial overpotential (65.1 mV) and Tafel slope (49.7 mV dec-1) in the alkaline HERs test. The present approach has proposed a new synthetic idea of hierarchical yolk-shell metal sulfide in different new energy catalysis fields.

First-Principles Study of MoS2, WS2, and NbS2 Quantum Dots: Electronic Properties and Hydrogen Evolution Reaction

The electronic and catalytic properties of two-dimensional MoS2, WS2, and NbS2 quantum dots are investigated using density functional theory investigations. The stability of the considered structures is confirmed by the positive binding energies and the real vibrational frequencies in the infrared spectra. The ab initio molecular dynamics simulations show that these nanodots are thermally stable at 300 K with negligible changes in the potential energy and metal–S bonds. The pristine nanodots are semiconductors with energy gaps ranging from 2.6 to 3 eV. Edge sulfuration significantly decreases the energy gap of MoS2 and WS2 to 1.85 and 0.75 eV, respectively. The decrease is a result of the evolution of low-energy molecular orbitals by the passivating S-atoms. The energy gap of NbS2 is not affected, which could be due to the spin doublet state. Molecular electrostatic potentials reveal that the edge sulfur/transition metal atoms are electrophilic/nucleophilic sites, while the surface atoms are almost neutral sites. MoS2 quantum dots show an interestingly low change in the hydrogen adsorption free energy ~0.007 eV, which makes them competitive for hydrogen evolution catalysts.

Nanoscale heterogeneous FeB metallic glass as highly active and stable catalyst for hydrogen evolution

Metallic glasses (MGs, also known as amorphous alloys) have shown excellent hydrogen evolution performances due to the unique long-distance disorder atomic structures. Here, we demonstrate that the hydrogen evolution performances of MG can be greatly improved by introducing nanoscale heterogeneous structures. A nanoscale homogeneous Fe75B25 MG (Homo-MG) is prepared by melt-spinning, and then it is processed by severe plastic deformation to form a nanoscale heterogenous Fe75B25 MG (Hetero-MG). The hetero-MG shows superior activity and stability of hydrogen evolution compared with those of the homo-MG. The overpotential at 10 mA cm−2 of the hetero-MG is only 116 mV in 1 M KOH, which is much smaller than that of the homo-MG of 402 mV. Moreover, the hetero-MG shows very high and stable catalytic performances even at industrial level current densities (e.g., 300 mA cm−2) which could not be obtained in the homo-MG. This study clearly shows that fabrication of nanoscale heterogeneous structures is an effective strategy to improve the catalytic performances of MGs, and it also has a very positive guiding significance for further promoting the application of MG in energy conversion and storage, sewage degradation, catalysis, and other fields.

Cascade Anchoring Strategy for Fabricating High-Loading Pt Single Atoms as Bifunctional Catalysts for Electrocatalytic Hydrogen Evolution and Oxygen Reduction Reactions.

Carbon supports containing single-atomically dispersed metal-Nx (denoted as MSAC-NxCy, x, y: coordination number) have attracted increasing attention due to their superb performance in heterogeneous catalysis. However, large-scale controllable preparation of single-atom catalysts (SACs) with high concentration of supported metal-Nx is still a big challenge because of the metal atom agglomeration during synthesis at high density and temperatures. Herein, we report a stepwise anchoring strategy from a 1,10-o-phenanthroline Pt chelate to an Nx-doped carbon (NxCy) with isolated Pt single-atom catalysts (PtSAC-NxCy) containing Pt loadings up to 5.31 wt % measured via energy-dispersive X-ray spectroscopy (EDS). The results show that 1,10-o-phenanthroline Pt chelate predominantly contributes to the formation of chelate single metal sites that bind tightly to platinum ions to prevent metal atoms from aggregating, resulting in high metal loading. The high-loading PtSAC-NxCy exhibits a low hydrogen evolution (HER) overpotential of 24 mV at 0.010 A cm-2 current density with a relatively small Tafel gradient of 60.25 mV dec-1 and excellent stable performance. In addition, the PtSAC-NxCy catalyst shows excellent oxygen reduction reaction (ORR) catalytic activity with good stability, represented by the fast ORR kinetics under high-potential conditions. Theoretical calculations show that PtSAC-NC3 (x = 1, y = 3) offers a lower H2O activation energy barrier than Pt nanoparticles. The adsorption free energy of a H atom on a Pt single-atom site is lower than that on a Pt cluster, which is easier for H2 desorption. This study provides a potentially powerful cascade anchoring strategy in the design of other stable MSAC-NxCy catalysts with high-density metal-Nx sites for the HER and ORR.

Effect of Pd crystal facet on the reaction of oxygen-promoted hydrogen evolution from formaldehyde driven by visible light

For heterogeneous catalysis reaction, the facet effect plays an important role in affecting the activity of the catalyst. In this paper, we prepared Pd catalysts exposed to (111) and (100) crystal planes by controlling the type of end capping agent and the structure of the catalysts were characterized using techniques such as TEM, XRD, XPS. The eosin Y (EY) sensitized Pd catalysts were used to catalytic hydrogen production from formaldehyde driven by visible light under alkaline conditions. The experimental results show that the Pd(100)/RGO catalyst exhibits highest catalytic performance, the hydrogen evolution rate was 86.85μmol/h. This can be attributed to the strong interaction between the Pd(100) facet and graphite oxide, which is conducive to improving the transfer rate on the catalyst surface. In addition, the dissociation energy barrier of oxygen molecules on the surface of the Pd(100) catalyst is an important reason for the high activity of the catalyst. Our results give a new viewpoint to the development of high efficiency catalysts for hydrogen evolution from formaldehyde.

Active Site Implantation for Ni(OH)2 Nanowire Network Achieves Superior Hybrid Seawater Electrolysis at 1 A cm−2 with Record‐Low Cell Voltage

AbstractDirect seawater electrolysis provides a grand blueprint for green hydrogen (H2) technology, while the high energy consumption has severely hindered its industrialization. Herein, a promising active site implantation strategy is reported for Ni(OH)2 nanowire network electrode on nickel foam substrate by Ru doping (denoted as RuNi(OH)2 NW2/NF), which can act as a dual‐function catalyst for hydrazine oxidation and hydrogen evolution, achieving an ultralow working potential of 114.6 mV to reach 1000 mA cm−2 and a small overpotential of 30 mV at 10 mA cm−2, respectively. Importantly, using the two‐electrode hydrazine oxidation assisted seawater electrolysis, it can drive a large current density of 500 mA cm−2 at 0.736 V with over 200 h stability. To demonstrate the practicability, a home‐made flow electrolyzer is constructed, which can realize the industry‐level rate of 1 A cm−2 with a record‐low voltage of 1.051 V. Theoretical calculations reveal that the Ru doping activates Ni(OH)2 by upgrading d‐band centers, which raises anti‐bonding energy states and thus strengthens the interaction between adsorbates and catalysts. This study not only provides a novel rationale for catalyst design, but also proposes a feasible strategy for direct alkaline seawater splitting toward sustainable, yet energy‐saving H2 production.

Copper Phosphide Nanowires as High-Performance Catalysts for Urea-Assisted Hydrogen Evolution in Alkaline Medium.

Water electrolysis represented a promising avenue for the large-scale production of high-purity hydrogen. However, the high overpotential and sluggish reaction rates associated with the anodic oxygen evolution reaction (OER) posed significant obstacles to efficient water splitting. To tackle these challenges, the urea oxidation reaction (UOR) emerged as a more favorable thermodynamic alternative to OER, offering both the energy-efficient hydrogen evolution reaction (HER) and the potential for the treating of urea-rich wastewater. In this work, a two-step methodology comprising nanowire growth and phosphating treatment was employed to fabricate Cu3P nanowires on Cu foam (Cu3P-NW/CF) catalysts. These novel catalytic architectures exhibited notable efficiencies in facilitating both the UOR and HER in alkaline solutions. Specifically, within urea-containing electrolytes, the UOR manifested desirable operational potentials of 1.43 V and 1.65 V versus the reversible hydrogen electrode (vs. RHE) to reach the current densities of 10 and 100 mA cm-2, respectively. Concurrently, the catalyst displayed a meager overpotential of 60 mV for the HER at a current density of 10 mA cm-2. Remarkably, the two-electrode urea electrolysis system, exploiting the designed catalyst as both the cathode and anode, demonstrated an outstanding performance, attaining a low cell voltage of 1.79 V to achieve a current density of 100 mA cm-2. Importantly, this voltage is preferable to the conventional water electrolysis threshold in the absence of urea molecules. Moreover, our study shed light on the potential of innovative Cu-based materials for the scalable fabrication of electrocatalysts, energy-efficient hydrogen generation, and the treatment of urea-rich wastewater.

Amorphous co-modified catalyst based on interfacial coupling effect for efficient hydrogen production by water electrolysis

Development of synthesis procedures of efficient amorphous heteroatom coupling interfaces is important for the improvement of electrocatalyst performance. Herein, the Co/Ni NWs/NF composite electrode was prepared using magnetic effect, where Ni nanowires were initially grown on Ni foam to increase its specific surface area, followed by the electrodeposition of amorphous cobalt nanosheets to form multiple active sites for the hydrogen evolution reaction (HER). The electrochemical results show that the prepared Co/Ni NWs/NF can deliver a current density of 10 mA cm−2 at an overpotential of 49 mV in 1 M KOH electrolyte. The physical test results demonstrate that the introduction of cobalt species onto Ni nanowire result in the interface coupling effect, which can efficiently increase the HER active surface sites and modify the interface charge distribution. The study provides new approach for design and preparation of highly active hydrogen evolution catalysts for water electrolysis.

Molecular Insights into Photochemical Hydrogen Evolution Dual Catalysis within the Shell of Polymer Micelle-Based Nanoreactors

Polymer micelles are promising candidates for facilitating efficient catalysis within their distinguished nanospaces. However, the design of polymer micelle-based nanoreactors for dual photocatalysis, where a photocatalyst and another catalyst are involved in a single catalysis, remains limited in scope due to the lack of molecular insight into the bimolecular process within polymer micelles. Here, we investigated the cooperativity of a photocatalyst and a hydrogen evolution catalyst immobilized within the shell of polymer micelle-based nanoreactors. The results of several photochemical experiments suggested the existence of two types of catalyst pairs, the fluctuated and contacted pairs of the photocatalyst and hydrogen evolution catalyst within the nanoreactors. Moreover, the reaction rates of the photochemical hydrogen evolution were strongly affected by molecular crowding within the shell. Our study paves the way for developing polymer micelle-based nanoreactors for efficient dual photocatalysis.

Defect-engineered carbon-confined silver for enhanced CO2 electrocatalytic reduction to CO in acidic media

Electrocatalytic CO2 reduction (CO2RR) to carbon monoxide (CO) holds great promise for carbon capture and utilization. Despite the proposal of electrocatalytic CO2RR in acidic media for high-efficiency CO2 conversion, the challenges of low CO selectivity caused by the highly competitive hydrogen evolution reaction and catalyst corrosion have not been adequately addressed. Here, we present a strategy that restricts proton migration and stabilizes key intermediates over a defective carbon layers confined Ag catalyst (Ag@C-d) to enhance the catalytic selectivity and stability for CO2RR in acidic media. Density functional theory simulations first discovered that electron polarization from Ag to vacancy-defective carbon creates the desired electric field at the interface between Ag and defective carbon layers, enabling efficient acidic CO2RR to CO. We synthesized Ag@C-d catalyst and that exhibits exceptional CO Faraday efficiency (FE, >98 %) and activity across a wide range of current densities (50–500 mA cm−2) in an acidic flow cell. At a current density of 500 mA cm−2, the single-pass conversion efficiency of CO2RR to CO can reached 71.5 %, surpassing that of alkaline systems. An excellent operational stability, operating continuously for over 100 h at industrial-scale current density, was also achieved. In a membrane electrode assembly electrolyzer incorporating the Ag@C-d catalyst at the cathode, a 91.6 % CO FE at 200 mA cm−2 can be achieved, accompanied by an energy conversion efficiency of nearly 40 %. These findings highlight the promising performance and potential applications of the developed catalyst for acidic CO2RR.

Investigation of Electron Extraction and Protection Layers on Cu2O Photocathodes

Many semiconductor photoelectrodes used for solar fuel production require the addition of buffer and protection layers to enhance their solar-to-fuel conversion efficiency and long-term stability. For example, Cu2O, which is the most efficient oxide-based photocathode but suffers from photocorrosion, has been assembled with various buffer and protection layers to suppress photocorrosion and use more photoexcited electrons for useful reactions such as water reduction to H2. However, the abilities of various buffer and protection layers to extract electrons from Cu2O have never been directly evaluated. Instead, their abilities were estimated based on the photocurrent for water reduction after adding a hydrogen evolution catalyst on top of them. In these evaluations, as the photocurrent is affected not only by the buffer or protection layer but also by the catalyst, the ability of the buffer or protection layer to extract electrons from Cu2O could not be accurately determined or compared. In this study, we demonstrate that 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL), whose reduction rate is faster than the photocorrosion rate of Cu2O, can be used as an effective electron scavenger to directly evaluate any change caused by a buffer or protection layer in electron–hole separation in Cu2O. In particular, we compared the performances of ZnO and TiO2 layers on Cu2O for extracting electrons and suppressing photocorrosion. We also compared the performances of TiO2 layers prepared by electrodeposition and atomic layer deposition (ALD) to show that the deposition method can make a striking impact on the performance of the same TiO2 because it can affect the critical characteristics of the layer (e.g., defect levels, conductivity, interfacial atomic arrangements) that govern interfacial charge transfer in multilayer photoelectrodes.