H2 Evolution Reaction Research Articles

(Corrosion Division H. H. Uhlig Award) A Journey From Ice-Breakers to Biomedical Implants: Multifacets of Corrosion

Understanding of corrosion mechanisms enables safe, durable and sustainable application of metallic materials in various fields. The presentation will shortly summarize a personal selection of most important lessons learned in the last 30 years of corrosion research, and then highlights some recent developments for methodologies to study atmospheric and immersion corrosion by respirometry. The approach is based on monitoring the rate of cathodic reactions with help of different types of sensors; this enables a real-time, simultaneous quantification of the rate of the O2 reduction reaction (OER) and the H2 evolution reaction (HER). The respirometric setups can be coupled with electrochemistry, enlarging the corrosion cases to be studied from open-circuit conditions to potential-controlled systems. Examples will be presented, to illustrate the potential of these techniques to reveal insights on corrosion mechanisms of active (e.g. Mg and Zn) and passive metals and alloys (e.g. stainless steels). For passive metals and alloys, special focus in this presentation will be on transpassive dissolution. In essence, three processes can take place in this potential regime: metal dissolution, oxide film formation, and oxygen evolution from water oxidation. In this case, respirometric determination of the oxygen evolution reaction (ORR) helps to distinguish the current (charge) consumed for metal oxidation reactions vs. water oxidation. Most recent developments to enable high-resolution respirometric measurements – and hence to study corrosion in the passive state and its localized breakdown – will be presented.

Electrochemical Gaseous Carbon Monoxide Reduction Using Cu Nanoparticles in Acidic Electrolytes

The electrochemical CO2 reduction reaction (CO2RR) into value-added multi-carbon products (C2+), using renewable electricity is an attractive strategy for closing the carbon cycle. Electrolysis of gaseous CO2 using a gas diffusion electrodes (GDEs) enables electrolysis at high current density1, and various studies are being conducted for its practical application2. Multi-carbon compounds (ethylene, ethanol, acetic acid and n-propanol) can be obtained electrochemically from CO2 using only Cu-based electrocatalysts. CO2RR measurements using Cu-based catalysts have generally been performed in neutral-alkaline electrolytes because the competing H2 evolution reaction (HER) can be suppressed. However, CO2 is easily converted to inert (bi)carbonate, which migrates to an anode compartment or is discharged at the outlet of a cathode compartment, and thus, there is a drawback in neutral and alkaline electrolytes from the point of view of substrate utilization efficiency3. Therefore, efficient CO2RR using acidic solutions has been required. In recent years, although several studies on CO2 reduction under acidic conditions have been reported4, the requirements for C2+ formation in acidic electrolytes are still uncovered. Direct CO electrolysis is more desirable than CO2 electrolysis for studying CO dimerization to C2+ in acidic electrolytes because a constant amount of CO can be supplied to the catalytic surfaces, and local pH variations due to CO2 dissolution can be eliminated. However, compared to CO2RR in acidic solutions, the CO reduction reaction to C2+ in acidic electrolytes has been little studied. In this work, we quantitatively study the CO reduction reaction (CORR) to C2+ products in an acidic solution through experimental gaseous CO electrolysis and multiphysics simulation of the local pH. We used Cu nanoparticles (CuNPs) as catalysts, which are commonly used in CO2RR. CuNPs were synthesized using a chemical reduction method using NaBH4 as the reductant. The oxidation state of copper nanoparticles is Cu(II), confirmed by XPS and XRD. A catalyst ink was prepared by dispersing 1.7 mg CuNPs in 2.2 μL 5 wt% Nafion solution and 600 μL iso-propanol. 80 μL ink was added dropwise onto the GDE. For CORR measurements, a home-made three-compartment electrochemical cell was employed. A solution of pH 2.0 (0.5 M H3PO4 0.5 M KH2PO4 1.5 M KCl) and pH 1.0 (1.0 M H3PO4 2.0 M KCl) were used for the catholyte. Gas and liquids products were quantified by gas chromatography and 1H-NMR, respectively. A reaction-diffusion model based on Nernst-Planck equation was used to simulate the local pH using COMSOL Multiphysics software. A one-dimensional model was used with a diffusion layer of 100 μm. For simplicity, only proton-consuming reactions were considered. Phosphate equilibrium reactions were introduced. Electrochemical CO reduction was performed in acidic solutions. Hydrogen evolution was dominant at low current densities (below 50 mA/cm2) in both pH 1.0 and 2.0 solutions. The C2+ production became dominant at 200 mA/cm2, and its faradaic efficiency was almost equivalent to that of neutral and alkaline solutions. We assumed that the suppression of hydrogen evolution was due to the increase in pH at the electrode surface with increasing current density. Therefore, we calculated the local pH by multiphysics simulation. The surface pH suddenly increased to about 13 at 200 mA/cm2 at pH 2.0. Taking into account these results, the selectivity of C2+ increased with increasing pH on the electrode surface. At the conference, we will also present the effect of surface cations on CORR.

Utilizing Direct Membrane Deposition to Improve the Performance of Forward-Bias Bipolar Membrane CO2 Electrolysers

The electrochemical conversion of CO2 to multi-carbon products (C2+), such as ethylene and ethanol, is an attractive technology towards achieving net zero carbon emission goals. Among the available configurations of CO2 electrolysers, those employing a bipolar membrane (BPM) in forward-bias mode (f-BPM) reduce CO2 loss to the anode – a problem commonly faced in traditional anion exchange membrane (AEM) electrolysers. Therefore, carbon efficiency (the percent of input CO2 that is converted to C2+ products) and system operational costs can be improved.In f-BPM electrolysers, (bi)carbonate ions move through the AEM then combine with protons moving through the cation exchange membrane (CEM) to regenerate CO2 and H2O at the AEM|CEM interface. Recent reports have implemented a porous AEM structure or an added AEM|CEM interface channel to aid the movement of CO2 from the AEM|CEM interface to the cathode and, thus, avoid blistering. Despite the advantage of f-BPM CO2 electrolysers, their performance is limited by the parasitic H2 evolution reaction (>20% Faradaic efficiency, or FE) and the low C2+ FE (<40%) at industrially relevant reaction rates (≥200 mA cm-2). We attribute this performance limitation to the unintended gaps between the used AEM and CEM. Inadequate contact between the AEM and CEM is anticipated to reduce the extent of local CO2 regeneration and promote unwanted proton crossover to the cathode; both phenomena could be contributing to the commonly observed FEs.In this report, we enhanced the contact between the AEM and CEM through the use of direct membrane deposition (DMD) over a Cu-based cathode. The DMD approach enabled modular control over the AEM and CEM thicknesses and structures, which improved ion and gas transport. Through electrochemical impedance spectroscopy, the DMD system was observed to improve the mass transport by >58% compared to a system that is similar to current f-BPM electrolysers (i.e., control system). The facilitated mass transport resulted in a reduction of the operating cell potential (by 0.84 V) and an enhancement of the C2+ FE to 65% (from 29% in the control system) at 300 mA cm-2. The flexibility of the DMD approach also enabled the fabrication of asymmetric BPMs, resulting in a record low H2 FE of 12% at 300 mA cm-2. We also demonstrated a 79% single-pass CO2 conversion (SPC) with 67% C2+ FE, resembling the highest simultaneous SPC and C2+ FE achievement at high current density (300 mA cm-2)among current f-BPM electrolysers. The DMD benefit was also applicable to other types of CO2 electrolysers, such as CO2-to-CO silver catalyst electrolysers, in which the CO FE was boosted to 90% (from 65% in the control system) at 90 mA cm-2. Figure 1

Effective Photocatalytic Ethanol Reforming into High-Value-Added Multicarbon Compound Coupled with H2 Production Over Pt-S3 Sites at PtSA-ZnIn2S4 Interface.

Selective photocatalytic production of high-value acetaldehyde concurrently with H2 from bioethanol is an appealing approach to meet the urgent environment and energy issues. However, the difficult ethanol dehydrogenation and insufficient active sites for proton reduction within the catalysts, and the long spatial distance between these two sites always restrict their catalytic activity. Here, guided by the strong metal-substrate interaction effect, an atomic-level catalyst design strategy to construct Pt-S3 single atom on ZnIn2S4 nanosheets (PtSA-ZIS) is demonstrated. As active center with optimized H adsorption energy to facilitate H2 evolution reaction, the unique Pt single atom also donates electrons to its neighboring S atoms with electron-enriched sites formed to activate the O─H bond in *CH3CHOH and promote the desorption of *CH3CHO. Thus, the synergy between Pt single atom and ZIS together will reduce the energy barrier for the ethanol oxidization to acetaldehyde, and also narrow the spatial distance for proton mass transfer. These features enable PtSA-ZIS photocatalyst to produce acetaldehyde with a selectivity of ≈100%, which will spontaneously transform into 1,1-diethoxyethane via acetalization to avoid volatilization. Meanwhile, a remarkable H2 evolution rate (184.4µmolh-1) is achieved with a high apparent quantum efficiency of 10.50% at 400nm.

Highly intra- and inter-plane crystalline ReSx/g-C3N4: Facile synthesis and boosted photocatalytic H2 evolution

Improving the crystallinity of g-C3N4 is regarded as a desirable pathway to boost its photocatalytic activity. However, the current highly crystalline g-C3N4 photocatalysts are mainly emphasized on increasing their inter-plane crystallinity through ordered stacking layers while their intra-plane crystallinity has been seldomly concerned, causing the finitely enhanced photocatalytic performance. In this work, the high intra- and inter-plane crystallinity of g-C3N4 accompanied by the deposition of amorphous ReSx cocatalyst are simultaneously realized through a facile strategy, causing the successful formation of highly intra- and inter-plane crystalline ReSx/g-C3N4 (ReSx/c-CN) photocatalysts. In this case, the mixture of melamine and NaCl is initially calcined to prepare highly intra-plane crystalline g-C3N4 (i-CN). Subsequently, the i-CN is further treated by HCl to improve its inter-plane crystallinity, which can simultaneously realize the deposition of amorphous ReSx cocatalyst on g-C3N4 surface to finally produce ReSx/c-CN photocatalysts. Consequently, the high intra- and inter-plane crystallinity of g-C3N4 can effectively boost the separation and migration of photogenerated carriers, while the amorphous ReSx cocatalyst can supply abundant active sites for interfacial H2-evolution reaction. Thus, the optimized ReSx/c-CN(3.0 wt%) photocatalyst exhibit remarkably improved H2-generation activity (23.4 μmol h−1), which is about 8.4-fold of the ReSx/bulk g-C3N4(3.0 wt%) photocatalyst. This work may supply new ideas for exploring other highly efficient photocatalysts in various applications.

CeNCl‐CeO2 Heterojunction‐Modified Ni Catalysts for Efficient Electroreduction of CO2 to CO

AbstractRenewable‐electricity‐powered electrochemical CO2 reduction (CO2RR) is considered one of the most promising ways to convert exhaust CO2 into value‐added chemicals and fuels. Among various CO2RR products, CO is of great significance since it can be directly used as feedstock to produce chemical products through the Fischer–Tropsch process. However, the CO2‐to‐CO electrocatalytic process is often accompanied by a kinetically competing side reaction: H2 evolution reaction (HER). Designing electrocatalysts with tunable electronic structures is an attractive strategy to enhance CO selectivity. In this work, a CeNCl‐CeO2 heterojunction‐modified Ni catalyst is successfully synthesized with high CO2RR catalytic performance by the impregnation‐calcination method. Benefiting from the strong electron interaction between the CeNCl‐CeO2 heterojunction and Ni nanoparticles (NPs), the catalytic performance is greatly improved. Maximal CO Faradaic efficiency (FE) is up to 90% at −0.8 V (vs RHE), plus good stability close to 12 h. Detailed electrochemical tests and density functional theory (DFT) calculation results reveal that the introduction of the CeNCl‐CeO2 heterojunction tunes the electronic structure of Ni NPs. The positively charged Ni center leads to an enhanced local electronic structure, thus promoting the activation of CO2 and the adsorption of *COOH.

Highly efficient CoTiO3/MOF-derived In2S3 photo-electrocatalysts: Degradation kinetics, pathways, and mechanism

MOF-derived catalysts with well-defined morphology have garnered significant interest and research in their potential applications in the fields of photocatalysis and electrocatalysis. In the article, a neoteric and promising photocatalytic system of CoTiO3/MOF-derived In2S3 type-Ⅱ heterogeneous catalyst with different weight percentages was prepared by a simple hydrothermal method. The system displayed remarkable photocatalytic and electrocatalytic properties. Under optimal conditions, the CoTiO3/MOF-derived In2S3 catalyst achieved a high photocatalytic degradation efficiency within 30 min for terramycin, tetracycline hydrochloride (TCH), Rhodamine B (RhB), methylene blue (MB), bright blue (BB) and methyl orange (MO). The respective degradation efficiencies were 91.07%, 87.77%, 99.85%, 99.78%, 97.85%, and 93.94%. In addition, when subjected to H2 evolution reaction (HER) at a current density of 10 mA/cm2, CoTiO3/MOF-derived In2S3 (65 mV) demonstrated superior electrocatalytic performance compared to pure CoTiO3 (429 mV) and MOF-derived In2S3 (109 mV). Surprisingly, cyclic voltammetry yielded an electrochemical active area of 62 cm2, further confirming the enhanced electrochemical performance of CoTiO3/MOF-derived In2S3. The results of the characterization indicate that design of type-Ⅱ heterostructure significantly enhances the specific surface area and interfacial charge transfer. In addition, the results of liquid chromatography-mass spectrometry (LC-MS) revealed the degradation intermediates of RhB and suggested its possible degradation pathways. This lays a solid foundation for the development of catalysts which are viable for use in both photocatalysis and electrocatalysis.

Two in one is really better: NiAl-LDH/[CoNi(μ3-tp)2(μ2-py)2] nanocomposite for enhanced antibiotic norfloxacin degradation and H2 evolution reaction

As an astonishing way of dealing with both environmental pollution and the energy crisis, we report the synthesis of a remarkable nanocomposite comprising Co-Ni-based metal–organic framework [CoNi(μ3-tp)2(μ2-py)2 or CNTP-MOF] allied with Ni-Al-based layered double hydroxide (NiAl-LDH) via a facile thermal impregnation technique. It showed outstanding degradation of norfloxacin and renewable H2 evolution under simulated solar light irradiation. Notably, the photocatalytic performance of NiAl-LDH/CNTP-MOF nanocomposite was significantly improved compared to its two individual components, reaching a high norfloxacin degradation level of 96 % in 60 min and H2 evolution of around 1914 µmol g−1 within 5 h of irradiation time. In addition, four successive photocatalytic cycles using the NiAl-LDH/CNTP-MOF nanocomposite revealed that our synthesized material has extremely excellent stability without affecting the morphological structure. Potential reaction routes for norfloxacin degradation and H2 evolution over the most active NiAl-LDH/CNTP-MOF nanocomposite are also discussed in detail, wherein the heterojunction plays a key role in the enhancement of electron-hole pair separation, consequently substantial efficiency. Eventually, this work provides excellent insights for designing and constructing MOF-based nanocomposite with notable photocatalytic performance toward wide-ranging environmental remediation.

Enhanced Visible Light-Driven Photocatalytic Water-Splitting Reaction of Titanate Nanotubes Sensitised with Ru(II) Bipyridyl Complex.

The ion exchange of Na+ cations was used to photosensitise titanates nanotubes (Ti-NTs) with tris(2,2'-bipyridine)ruthenium(II) cations (Ru(bpy)32+); this yielded a light-sensitised Ti-NTs composite denoted as (Ru(bpy)3)Ti-NTs, exhibiting the characteristic absorption of Ru(bpy)32+ in visible light. Incident photon-to-current efficiency (IPCE) measurements and the photocatalytic reduction of methyl viologen reaction confirmed that in the photosensitisation of the (Ru(bpy)3)Ti-NTs composite, charge transfer and charge separation occur upon excitation by ultraviolet and visible light irradiation. The photocatalytic potential of titanate nanotubes was tested in the water-splitting reaction and the H2 evolution reaction using a sacrificial agent and showed photocatalytic activity under various light sources, including xenon-mercury lamp, simulated sunlight, and visible light. Notably, in the conditions of the H2 evolution reaction when (Ru(bpy)3)Ti-NTs were submitted to simulated sunlight, they exceeded the photocatalytic activity of pristine Ti-NTs and TiO2 by a factor of 3 and 3.5 times, respectively. Also, (Ru(bpy)3)Ti-NTs achieved the photocatalytic water-splitting reaction under simulated sunlight and visible light, producing, after 4 h, 199 and 282 μmol×H2×gcat-1. These results confirm the effective electron transfer of Ru(bpy)3 to titanate nanotubes. The stability of the photocatalyst was evaluated by a reuse test of four cycles of 24 h reactions without considerable loss of catalytic activity and crystallinity.

Synthesis of Poly (3‑bromo thiophene) supported cobalt molybdate bifunctional catalyst: Manifestation of overall water splitting and hydrazine assisted water splitting

The article reports a one-step hydrothermal synthesis of hydrated cobalt molybdate, grown in-situ on the conducting polymer poly (3-bromothiophene) (PTBr) surface, which can act as a superior bifunctional electrocatalyst to exploit O2 evolution reaction (OER), Hydrazine oxidation reaction (HzOR) and H2 evolution reaction (HER) as compared to pristine cobalt molybdate (CoMoO4.xH2O) and PTBr. The material architecture was evaluated critically using PXRD, TGA, FTIR, HRTEM, XPS and BET surface area measurement to understand the structural and compositional status of the catalyst. The performance of the CoMoO4@30% PTBr composite catalyst appears to be significantly high demanding low overpotentials of 308 mV in case of OER and 198 mV regarding HER compared to polymer unsupported catalyst for affording 10 mA cm−2 current density. The upliftment of catalytic action of composite is an outcome of synergistic effect between CoMoO4 and optimal concentration of PTBr which assists to achieve large electrochemically active surface area (ECSA) (89.50 m2 g−1) and thereby faster charge transport efficiency compared to its pristine counterpart. In summary, the introduction of polymer with CoMoO4 categorically reduces the cell potential for overall water splitting by 0.108 V (vs RHE) in presence and 0.178 V in absence of hydrazine proving composite as a beneficial energy-saving electrocatalyst.

Rhombohedral boron monosulfide as a metal-free photocatalyst

Most of previous photocatalysts contain metal species, thus exploring a metal-free photocatalyst is still challenging. A metal-free photocatalyst has an advantage for the development of economical and non-toxic artificial photosynthesis system and/or environmental purification applications. In this study, rhombohedral boron monosulfide (r-BS) was synthesized by a high-pressure solid-state reaction, and its photocatalytic properties were investigated. r-BS absorbed visible light, and its photocurrent action spectrum also exhibited visible light responsivity. The r-BS evolved hydrogen (H2) from water under ultraviolet (UV) as well as under visible light irradiation, and its internal quantum efficiency reached 1.8% under UV light irradiation. In addition to the H2 evolution reaction, the r-BS photocatalyst drove carbon dioxide (CO2) reduction and dye oxidation reactions under UV irradiation. Although bare r-BS was not so stable under strong light irradiation in water, cocatalyst modification improved its stability. These results indicate that r-BS is a new class of non-metal photocatalyst applicable for H2 production, CO2 reduction, and environmental purification reactions.

A novel ternary nano-photocatalyst (Ni/Ni3C/CdS) for HER and water purification with enhanced photocatalytic activity

CdS-based nanomaterials received much attention since it was synthesized and used as photocatalysts in HER reaction and degradations of organic pollutants. However, it is still an urgent issue to improve the stability and catalytic performance of these kinds of materials before they meet the requirements of the practical applications. Therefore, A novel nano-photocatalyst named as NC-15 was prepared in this paper by loading Ni3C nanosheets (NSs) and Ni nanoparticles (NPs) to the surface of CdS nanowires (NWs). Using a 300 W Xe-lamp (≥400 nm) as the illumination source, NC-15 could accelerate the H2-evolution reaction (HER) in aqueous solution of lacticacid (10 vol%) with the rates of 15247 μmol·g-1h−1 which is ca. 381-time higher than that of CdS NWs, and OTC (LEF) could be ca. 91 % (89 %) degenerated as its aqueous solution (40 ppm) were irradiated 60 mins. The electrochemical analysis indicates that NC-15 should be an n-type semiconductor with the overpotential of −1.08 V vs. Ag/AgCl, which is much lower than those of CdS NWs (-1.20 V), Ni3C/CdS (-1.18 V) and Ni/CdS (-1.13 V) and indicates a faster-photogenerated electrons transfer rate of NC-15. The theoretical simulations confirm that the Ni NPs should supply the active sites during the photocatalytic procedure and the internal electric field at the interfaces of CdS/Ni3C and Ni3C/Ni could accelerate the photogenerated carriers’ separation and migration. In a word, CdS-based ternary nano-photocatalysts possess great potential in the practical application of HER and photodegradation reactions.

Initial Quenching Efficiency Determines Light-Driven H2 Evolution of [Mo3 S13 ]2- in Lipid Bilayers.

Nature uses reactive components embedded in biological membranes to perform light-driven photosynthesis. Here, a model artificial photosynthetic system for light-driven hydrogen (H2 ) evolution is reported. The system is based on liposomes where amphiphilic ruthenium trisbipyridine based photosensitizer (RuC9 ) and the H2 evolution reaction (HER) catalyst [Mo3 S13 ]2- are embedded in biomimetic phospholipid membranes. When DMPC was used as the main lipid of these light-active liposomes, increased catalytic activity (TONCAT ~200) was observed compared to purely aqueous conditions. Although all tested lipid matrixes, including DMPC, DOPG, DPPC and DOPG liposomes provided similar liposomal structures according to TEM analysis, only DMPC yielded high H2 amounts. In situ scanning electrochemical microscopy (SECM) measurements using Pd microsensors revealed an induction period of around 26 minutes prior to H2 evolution, indicating an activation mechanism which might be induced by the fluid-gel phase transition of DMPC at room temperature. Stern-Volmer-type quenching studies revealed that electron transfer dynamics from the excited state photosensitizer are most efficient in the DMPC lipid environment giving insight for design of artificial photosynthetic systems using lipid bilayer membranes.

General Formation of Interfacial Assembled Hierarchical Micro‐Nano Arrays for Biomass Upgrading‐Coupled Hydrogen Production

AbstractConstruction of efficient catalysts to couple biomass upgrading with hydrogen production is significant for improving energy efficiency, which remains a challenge. Herein, a general method for manufacturing 3D hierarchical micro‐nano arrays consisting of template framework and nanoparticle‐decorated nanosheets is reported. This strategy provides an opportunity to controllably tailor the interfacial assembly of nanosheets on precursor template materials. The obtained Co@NiMoO‐Ni/NF exhibits enhanced electrocatalytic performance for biomass oxidation and hydrogen production. It only needs 1.21 V to achieve 10 mA cm−2 for 5‐hydroxymethylfurfural electrooxidation reaction (HMFOR) assisted H2 evolution reaction (HER). The good catalytic performance is ascribed to the intense interaction between template (Co) and nanoparticle‐decorated nanosheets (NiMoO‐Ni), which tunes the electron structure of the catalyst to optimize the adsorption behavior of HMFOR/HER intermediates and promote the bonds breakage of key intermediates in the HMFOR/HER process. This work thus provides a strategy for designing ideal catalysts for biomass upgrading‐coupled H2 production.

Exploring the Multifarious Role of the Ligand in Electrocatalytic Hydrogen Evolution Reaction Pathways.

In recent years, researchers have shifted their focus towards investigating the redox properties of ancillary ligand backbones for small-molecule activation. Several metal complexes have been reported for the electrocatalytic H2 evolution reaction (HER), providing valuable mechanistic insights. This process involves efficient coupling of electrons and protons. Redox-active ligands stipulate internal electron transfer and promote effective orbital overlap between metal and ligand, thereby, enabling efficient proton-coupled electron transfer reactions. Understanding such catalytic mechanisms requires thorough spectroscopic and computational analyses. Herein, we summarize recent examples of molecular electrocatalysts based on 3d transition metals that have significantly influenced mechanistic pathways, thus, emphasizing the multifaceted role of metal-ligand cooperativity.

Enhanced Z-scheme water splitting at atmospheric pressure with suppression of reverse reactions using Zr-doped BaTaO2N as hydrogen evolution photocatalyst

The present work demonstrates a Z-scheme overall water splitting (ZOWS) system for the photocatalytic production of H2 capable of operating under Ar at near-atmospheric pressure using a narrow-bandgap Zr-doped BaTaO2N photocatalyst. Reverse reactions are suppressed in this system as a consequence of a surface modification of the Pt-loaded, Zr-doped BaTaO2N (Pt/BaTaO2N:Zr) photocatalyst with Cr2O3. The introduction of a Cr2O3 shell was found to effectively inhibit the reduction of [Fe(CN)6]3- that otherwise competes with the H2 evolution reaction, resulting in an improved apparent quantum yield of 1.1 % at 420 nm. By combining this H2 evolution photocatalyst with an O2 evolution photocatalyst based on BiVO4, ZOWS was achieved at near-atmospheric pressure with a solar-to-hydrogen energy conversion efficiency of 0.08 %. This work demonstrates the importance of suppressing reverse reactions during ZOWS at atmospheric pressure and provides valuable guidance for the design and construction of practical green H2 production systems.

Influence of Pt Oxidation State on the Activity and Selectivity of g-C3N4-Based Photocatalysts in H2 Evolution Reaction

Graphitic carbon nitride g-C3N4 has been modified using platinum and platinum oxide (0.5–5 wt.%) and studied in photocatalytic H2 evolution reactions with ethanol aqueous solution under visible light irradiation (λ = 409 nm). An analysis of the by-products of the reaction (CO2, CH4, C2H6 etc.) was also carried out. The morphology, particle size distribution, and optical properties of the photocatalysts, and the chemical states of platinum cations were examined using various methods. The photocatalysts were investigated using a wide range of methods to clarify the morphology, particle size distribution, optical properties, and the chemical states of platinum cations. Factors affecting not only the activity, but also the selectivity of the photocatalyst in the target process of hydrogen production, have been established. The highest rate of H2 evolution achieved over 0.5 wt.% Pt/g-C3N4 photocatalyst is 0.6 mmol h−1 g−1 (selectivity 98.9%), which exceeds the activity of pristine g-C3N4 by 250 times. Increasing the Pt or PtO content up to 5 wt.% leads to an increase in the rate of formation of by-products (CH4, C2H6, and CO2) and a decrease in the selectivity of H2 evolution. The study also delves into the role of platinum and the mechanism of charge transfer in PtO/g-C3N4 and Pt/g-C3N4 photocatalysts due to light irradiation.

Organic-inorganic p-type PEDOT:PSS/CuO/MoS2 photocathode with in-built antipodal photogenerated holes and electrons transfer pathways for efficient solar-driven photoelectrochemical water splitting

Organic PEDOT:PSS thin film and n-type MoS2 flakes were incorporated on CuO photocathode as the underlying layer and surface co-catalysts, respectively, establishing a rationally-designed novel integrated structure of PEDOT:PSS/CuO/MoS2. The organic-inorganic interface of PEDOT:PSS/CuO effectively shuttles photogenerated holes towards the FTO/PEDOT:PSS junction. Furthermore, the surface MoS2 co-catalysts form a p-n junction with CuO, which accelerates the transport of photogenerated electrons towards the photocathode/electrolyte junction, in addition to providing more reactive sites for the H2 evolution reaction. These synergistically formed antipodal charge transfer pathways have led to improved charge separation, rapid interfacial charge transfer kinetics and impeded electron-hole recombination in the PEDOT:PSS/CuO/MoS2 photocathode, which can achieve a photocurrent density of – 2.26 mA/cm2 at −0.6 V vs Ag/AgCl (2.1 times higher than that of the bare CuO photocathode). Analytical characterisations, electrochemical impedance spectroscopy (EIS) and intensity-modulated photocurrent spectroscopy (IMPS), also provide supporting evidence for its dramatically enhanced PEC water splitting performance.

Hybridization of covalent organic frameworks and photosensitive metal‐organic rings: A new strategy for constructing supramolecular Z‐scheme heterostructures for ultrahigh photocatalytic hydrogen evolution

AbstractThe rational design of Z‐scheme heterojunction photosystems based on covalent organic frameworks (COFs) is a promising strategy for harnessing solar energy for hydrogen conversion. Herein, a direct Z‐scheme single‐atom photocatalyst based on COF and metal‐organic ring has been constructed through the supramolecular interactions of coral‐like COF (S‐COF) and photosensitized Pd2L2 type metal‐organic ring (MAC‐FA1). The MAC‐FA1/S‐COF heterojunction exhibits good light absorption, efficient charge separation and transfer, slow electron‐hole recombination, and highly dispersed Pd active sites, enabling an efficient and stable H2 evolution reaction. The optimized 4% MAC‐FA1/S‐COF achieves an H2 evolution rate of 100 mmol g−1 h−1 within 5 h and obtains a total accumulated turn‐over number relative to Pd (TONPd) of 437,685 within 20 h, far superior to S‐COF, MAC‐FA1, M‐5/S‐COF, Pd/S‐COF, and M‐5/Pd/S‐COF, which is one of the highest records among COF‐based photocatalysts for solar‐driven H2 evolution. This is the first work to incorporate photosensitized metal‐organic rings/cages into porous crystalline COFs to form a supramolecular Z‐scheme heterojunction, which has significant potential as a high‐performance photocatalyst for solar‐driven H2 production.

Effects of Anionic Polymer Modification of Dye‐Sensitized Niobate Photocatalysts on Solar‐Driven Z‐Scheme Overall Water Splitting

Pt‐intercalated calcium niobate nanosheets (Pt/HCa2Nb3O10) sensitized by a Ru(II) complex dye are good photocatalysts for producing H2 from aqueous solutions containing I− as a reversible electron donor. These materials are applicable to Z‐scheme overall water splitting in combination with a WO3‐based O2‐evolving photocatalyst under simulated sunlight. In this work, the effects of anionic polymer modification of the dye‐sensitized nanosheets are examined by adsorbing sodium poly(styrenesulfonate) (PSS), sodium polyacrylate, sodium polymethacrylate (PMA), or sodium poly(4‐styrenesulfonic‐co‐maleic acid) onto the dye‐sensitized nanosheet surface. For half‐cell H2‐evolution reaction in the presence of NaI, all of the polymers have a positive impact on the activity under visible light at lower light intensity, whereas only PMA is effective under high light‐intensity condition. For Z‐scheme overall water splitting with PtOx/H‐Cs‐WO3, PSS and PMA give almost the same solar‐to‐hydrogen energy conversion efficiencies (0.12% ± 0.01%) under optimized conditions. However, PMA operates better than PSS at relatively low and high NaI concentrations, which are in general disadvantageous for the H2‐ and O2‐evolving components of the Z‐scheme, respectively.