Water Splitting For Hydrogen Production Research Articles

Soluble Gd6Cu24 clusters: effective molecular electrocatalysts for water oxidation.

The water oxidation half reaction in water splitting for hydrogen production is extremely rate-limiting. This study reports the synthesis of two heterometallic clusters (Gd6Cu24-IM and Gd6Cu24-AC) for application as efficient water oxidation catalysts. Interestingly, the maximum turnover frequency of Gd6Cu24-IM in an NaAc solution of a weak acid (pH 6) was 319 s-1. The trimetallic catalytic site, H2O-GdIIICuII2-H2O, underwent two consecutive two-electron two-proton coupled transfer processes to form high-valent GdIII-O-O-CuIII2 intermediates. Furthermore, the O-O bond was formed via intramolecular interactions between the CuIII and GdIII centers. The results of this study revealed that synergistic catalytic water oxidation between polymetallic sites can be an effective strategy for regulating O-O bond formation.

Defective Biphenylene as High-Efficiency Hydrogen Evolution Catalysts.

Electrocatalysts play a pivotal role in advancing the application of water splitting for hydrogen production. This research unveils the potential of defective biphenylenes as high-efficiency catalysts for the hydrogen evolution reaction. Using first-principles simulations, we systematically investigated the structure, stability, and catalytic performance of defective biphenylenes. Our findings unveil that defect engineering significantly enhances the electrocatalytic activity for hydrogen evolution. Specifically, biphenylene with a double-vacancy defect exhibits an outstanding Gibbs free energy of -0.08 eV, surpassing that of Pt, accompanied by a remarkable exchange current density of -3.08 A cm-2, also surpassing that of Pt. Furthermore, we find the preference for the Volmer-Heyrovsky mechanism in the hydrogen evolution reaction, with a low energy barrier of 0.80 eV. This research provides a promising avenue for developing novel metal-free electrocatalysts for water splitting with earth-abundant carbon elements, making a significant step toward sustainable hydrogen production.

Analysis of Photocatalytic Properties of Titanium Dioxide Electrode Supported By Hydroxyapatite Co-Catalyst in a Marine Solar Cell

Titanium dioxide (TiO2), as an n-type semiconductor photocatalyst, has been widely studied and used in many environmental and energy applications such as solar cells, wastewater treatment, air purification, water splitting for hydrogen production and CO2 conversion due to its superior electrical and optical properties, stability, and biocompatibility. Using its photocatalytic and other properties, we have been studying a floating photoelectrochemical cell that can be applicable to the marine environments. This cell is designed to utilize titanium dioxide as its photoanode and copper oxides photocathode, and seawater is used as an electrolyte between electrodes. The drawbacks of using titanium dioxide as photocatalysts are its high electron-holes recombination rates and lower absorption efficiency in visible light regions. To improve against these drawbacks, we studied hydroxyapatite (HAp, Ca10(PO4)6(OH)2) as co-catalyst for titanium dioxide electrode. Since HAp possesses biocompatibility, it is suitable to be used with TiO2 electrode in marine environments. In previous studies, it was found that HAp improved and boosted the current density produced by the titanium dioxide electrode. However, removal of HAp occurred from the surface of titanium dioxide during the photoelectrochemical measurements. Therefore, in this study, we have optimized the content of HAp paste that would be applied to the surface of titanium dioxide electrode by screen printing method.For preparation of titanium dioxide electrode, type 329J4L stainless steel was selected as the base substrate. Firstly, surface of the substrate was grinded to form the grid pattern and cleaned with ethanol in ultrasonic cleaner and then with distilled water. After that, the substrate was passivated with 10 % HNO3 at 60 ºC for 30 minutes. The passivated substrate was then printed and heat treated with TiO2 paste twice at 150 ºC for 1 hour and 550 ºC for 30 minutes respectively. Double layered titanium dioxide electrode was then printed with HAp paste and heat treated at 150 ºC for 1 hour. To check the characteristics of photocatalytic effect of electrode, photopotential and potentiodynamic polarization measurements were performed to the electrode. For illumination test, xenon light with an intensity of 10.5 mW/cm2 and a calibrated wavelength of 250-800 nm was used as the light source. The measurement was conducted in artificial seawater as the controlled electrolyte. Standard calomel electrode (SCE) was used as a reference electrode and platinum electrode as a counter electrode. The measurement was performed both with and without irradiated conditions. The microstructures and surface morphology of electrode before and after electrochemical measurements were analyzed and examined by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD).The results show optimized HAp also improve the photocatalytic activities of n-type semiconductor titanium dioxide. In previous study, removal of HAp was considered due to the addition of carboxymethyl cellulose (CMC) as a viscosity modifier to HAp paste. CMC possess higher hydration rate which may cause rapid agglomeration when it is introduced to water. Although it has satisfactory quality to control the viscosity of the paste, rapid hydration cause removal of HAp after the electrode was heat treated and measurement was performed in artificial seawater. In this study, polyethylene glycol (PEG) was used as the viscosity modifier for HAp paste and Triton-X-100 was used as the surfactant to control the surface tension of the paste. As a result, HAp paste was produced to be screen-printable onto the surface of TiO2 electrode and removal of HAp was minimized compared to the previous study. Moreover, HAp became a good sorbent and co-catalyst for titanium dioxide electrode in its photocatalytic activities.

A computational study photophysical properties of a series phenothiazine-linked-BODIPY as D-D-π-a photosensitizer unit for photo-induced hydrogen production from water

Phenothiazine-derivatives are designed as sensitizers which covalently-linked with BODIPY for application in a system of dye-sensitized photoelectrochemical cells (DSPECs). A series of phenothiazine-linked-BODIPY as D-D-π-A chromophore have been investigated by a computational approach for studying the capability of the photosensitizers for application in photoinduced water splitting hydrogen production in DSPECs. The geometries of sensitizers at the ground state and excited state were optimized by the CAM-B3LYP/6-31G (d,p) level method. The theoretical study has been done in order to investigate the photophysical properties such as absorption profile, HOMO-LUMO energy and surface plots of the photosensitizer. The result of calculation for HOMO-LUMO energy level of each dyes showed that the LUMO energy are ranging more than -2.8 - (-2.86) eV which is higher than -4.0 eV of conduction band of TiO2 as semiconductor in DSPEC, meaning that all these dyes could be used as photosensitizers in DSPECs. In addition, the oscillator strength data of each dyes showed the dyes have absorption profile in visible region, meaning the dyes could harvest higher intensity of sunlight to induce water splitting reaction to produce hydrogen.

Direct seawater splitting by photo-piezoelectric coupling based on surface protonated perovskite

Photocatalytic water splitting for hydrogen evolution has become one of the most important and effective ways to produce green and renewable hydrogen energy, the centre of which is the efficient, stable and inexpensive photocatalyst. The part of perovskite oxides have a wide range of properties such as ferroelectricity, piezoelectricity and pyroelectricity, as well as good photoresponsivity and chemical stability, which are promising for catalytic conversion applications. In this study, the Ruddlesden-Popper (RP) phase perovskite La2NiO4 is investigated from enhanced charge separation as well as accelerated surface redox reaction rates. In the case of the existence of piezoelectric response of La2NiO4, the photo-piezoelectric coupling strategy not only realize the catalytic pure water splitting, but also greatly improve the efficiency. The lattice structure is twisted when the catalyst is subjected to external stress and the electric dipole moment is no longer zero. The resulting piezoelectric potential not only enables the free charge in the bulk phase to migrate directionally, but also inhibits the recombination of photogenerated carriers, which ultimately achieves highly efficient photo-piezoelectric coupling for water splitting for hydrogen production. In addition, the protonation of the catalyst surface is used to further enhance the interfacial reaction of the catalysts, which improves the solution-catalysts contact efficiency and generates vacancy defects to strengthen the spontaneous polarization of the lattices, contributing to the enhancement of the redox reaction rate. This optimization strategy of surface protonation treatment combined with photo-piezoelectric coupling is not only applicable to nanocatalyst powders but also has a significant enhancement effect in perovskite ceramic membranes. When La2NiO4 powders are sintered into the porous ceramic membrane and the surface is protonated with 0.006 mol L−1 hydrochloric acid, the hydrogen production rate of seawater splitting under the photo-piezoelectric coupling condition can reach 7750.41 μmol m−2 h−1. This study contributes to further understanding of photo-piezoelectric coupling catalysis, leading to a new solutions for expanding the application of coupled multifield water splitting for hydrogen evolution.

Microporous structure flowing integrated with electrolytic water splitting based on stacked mesh electrode for hydrogen production

In order to promote gas bubble transport during water splitting for hydrogen production, stacked mesh electrodes integrated microporous structure flowing and electrolytic water splitting have been fabricated by electrodepositing CoFe alloy. The average size of the bubble on the mesh electrode surface is 40 μm and the release time of trapped bubbles in the pores of the electrode is 2.11 s during the process of water splitting at 50 mA cm−2 and 1 M KOH. The electrodes show excellent performance in both hydrogen evolution reaction (HER, 247 mV at 1000 mA cm−2) and oxygen evolution reaction (OER, 350 mV at 1000 mA cm−2). The required cell voltage at 1000 mA cm−2 for flow-through electrolyzer assembled with the stacked mesh electrodes is only 2 V under the condition of 6 M KOH, and 343 K. The voltage caused by the bubble in the flow-through electrolyzer assembled with stacked mesh electrodes is just about 50 mV at the current density of 1000 mA cm−2. The energy required for hydrogen production is only 4.04 kWh Nm−3 and 4.78 kWh Nm−3 under the current density of 200 mA cm−2 and 1000 mA cm−2, respectively. Besides, the flow-through electrolyzer assembled with the stacked mesh electrodes shows excellent stability with only a 60 mV increase in cell voltage after continuing electrolytic water splitting for 100 h at 1000 mA cm−2.

S-scheme heterojunction constructed by ZnCdS and CoWO4 nano-ions promotes photocatalytic hydrogen production

Low-cost and efficient photocatalyst is an important aspect of photocatalytic hydrogen production. In this study, a highly efficient and stable composite photocatalyst was synthesized by assembling ZnCdS nanoparticles and CoWO4 nanoparticles. Under the 5 W LED lamp, the hydrogen production of the composite catalyst ZCS/CW-10 is as high as 839.85 μmol in five hours, which is 5.2 times that of the pure ZnCdS photocatalyst, respectively. After four cycles, the hydrogen production still reaches 640.37 μmol, which is 76.3% of the initial activity. This is because the introduction of CoWO4 increases the absorption of visible light by ZnCdS, and effective interface contact with each other between nanoparticles can effectively accelerate the transfer of photo generated charges between semiconductors, increase the active sites of surface hydrogen production, and achieve efficient H2 production. The staggered band structure makes ZnCdS and CoWO4 follow the electron flow scheme of S-scheme heterojunction, which is proved by in-situ XPS. The S-scheme heterostructure of ZCS/CW retains high redox potential and prolongate the lifetime of electron-generated carriers, making it more conducive to proton reduction to produce H2. This work provides a novel and convenient way to construct an efficient S-scheme heterojunction scheme, which is helpful for the rapid and effective production of metal sulfide-based photocatalysts and the rapid construction of photocatalytic water splitting hydrogen production systems. It has important research value in the utilization of new energy hydrogen energy and environmental protection.

Indoor water splitting for hydrogen production through electrocatalysis using composite metal oxide catalysts

This study explores an optimistic approach for large-scale hydrogen production by employing electrocatalysts based on nickel, cobalt, iron, and aluminum oxides as alternatives to costlier metals. This approach offers a cost-effective solution to electrolysis in water media for hydrogen production. This investigation is focused on the electrolysis process, engaging NiO–Al2O3–CoO–Fe2O3 in 1M solution of NaOH and KOH. The environmental and economic analyses are conducted to evaluate the overall effect and cost-effectiveness of the electrolysis process. These findings provide valuable insights into the performance, feasibility, and challenges of using oxides of aluminum, nickel, iron, and cobalt in electrolysis for hydrogen production. The structural and morphological analyses of metal oxides are conducted using XRD and SEM tools, which showed reduced crystallinity and open pore structure of the samples. Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), and Linear Sweep Voltammetry (LSV) revealed a higher electrocatalytic activity, a larger electrochemical active surface area, a higher current density, and a high density of active sites of NiO–Al2O3–CoO–Fe2O3 composite. Electrode 1 of the composite catalyst produced 500 ml of hydrogen after 30 min of the process, while electrodes 2 and 3 produced 263 and 249 ml of hydrogen, respectively. This study also elucidated the electrocatalytic mechanism involved in water splitting using these composite materials.

1D/3D Heterogeneous Assembling Body of Cobalt Nitrides for Highly Efficient Overall Hydrazine Splitting and Supercapacitors.

Herein, the construction of a heterostructured 1D/3D CoN-Co2 N@NF (nickel foam) electrode used for thermodynamically favorable hydrazine oxidation reaction (HzOR), as an alternative to sluggish anodic oxygen evolution reaction (OER) in water splitting for hydrogen production, is reported. The electrode exhibits remarkable catalytic activities, with an onset potential of -0.11V in HzOR and -71mV for a current density of 10mA cm-2 in hydrogen evolution reaction (HER). Consequently, an extraordinary low cell voltage of 53mV is required to achieve 10mA cm-2 for overall hydrazine splitting in a two-electrode system, demonstrating significant energy-saving advantages over conventional water splitting. The HzOR proceeds through the 4e- reaction pathway to release N2 while the 1e- pathway to emit NH3 is uncompetitive, as evidenced by differential electrochemical mass spectrometric measurements. The X-ray absorption spectroscopy, in situ Raman spectroscopy, and theoretical calculations identify cobalt nitrides rather than corresponding oxides/(oxy)hydroxides as catalytic species for HzOR and illustrate advantages of heterostructured CoN-Co2 N in optimizing adsorption energies of intermediates/reagents and promoting catalytic activities toward both HzOR and HER. The CoN-Co2 N@NF is also an excellent supercapacitive material, exhibiting an increased specific capacity (938 F g-1 at 1 A g-1 ) with excellent cycling stability (95.8%, 5000 cycles).

In-situ reconstruction of self-supported amorphous Ni-Mo electrode for stable hydrogen evolution at large and intermittent current density

Solar power drived water splitting for hydrogen production is pivotal for sustainable energy conversion. Yet, it is challenging to develop earth abundant, high active, and durable electrodes to catalyzing hydrogen evolution reaction (HER) under fluctuating solar electricity. Herein we report self-supprted NiMo phosphate (NiMo-Pi) electrodes, where amorphous NiMo-Pi with nanosheets-like structure grow directly on conductive Ni foam by a facile one-step hydrothermal treatment. The electronic structures of Ni and Mo are tuned by O and P in NiMo-Pi electrodes, resulting the down-shift of their d-band centers. NiMo-Pi electrodes offer high activity and stability for HER, delivering -100 and -500 mA cm−2 mgcat−1 with overpotentials of 343 and 461 mV, repectively. They also sustain long-term electrolysis at a constant industrial-level current density of 500 mA cm−2 and at dynamic current densities ranging from -10 to -1 000 mA cm−2. Their HER activity become higher after stability tests, benefitting from in-situ surface reconstruction. This reconstruction makes the surface rich in active higher-lying d-band centers. This work suggests that tuning the electronic structure of electrodes is an efficient way to design efficient and stable electrodes for HER under harsh conditions.

Synergistic effect of multiferroicity in GdFeO3 nanoparticles for significant hydrogen production through photo/electrocatalysis

Due to chemical stability and visible-light driven features, perovskite-based photocatalysts and electrocatalysts are potential candidates for implementation of water-splitting hydrogen production to help tackle the present fuel crisis. In this study, it is shown that multiferroic GdFeO3 nanoparticles can help meet this need. GdFeO3 nanoparticles were solvothermally produced in pristine form, and the chemical purity of these particles was evaluated by powder X-ray diffraction, while the morphology and average particle size of 71 nm were determined by scanning and transmission electron microscopy techniques. Oxygen vacancies and grain-mediated two-dimensional planar defects in GdFeO3 nanoparticles were identified with high-resolution transmission electron microscopy along with Raman and X-ray photoelectron spectroscopies. Magnetization and electric polarization studies confirmed the multiferroic nature of the nanoparticles. Without the use of a co-catalyst, GdFeO3 nanoparticles exhibited a hydrogen evolution rate of 685 μmol h−1g−1 and an apparent quantum yield of 14% which was attributed to electric-polarization-induced band bending. The effect of sacrificial agents in H2 production was also evaluated to find the true hydrogen evolution. Moreover, in contrast to other cutting-edge oxygen evolution reaction electrocatalysts as Ba0.5Sr0.5Co0.8Fe0.2O3−δ, GdFeO3 nanoparticles showed a very low overpotential of 320 mV in an alkaline media with favorable chemical stability.

Cyanogel-Based Preparation of Amorphous NiFe Nanoaggregates with Enhanced Activity and Stability for OER

The development of cost-efficient electrocatalysts for oxygen evolution reaction (OER) with high efficiency is crucial to widespread applications of water splitting for hydrogen production. In this work, porous three-dimensional (3D) amorphous NiFe nanoaggregates composed of interconnected nanograins were synthesized by a cyanogel-based wet chemical reduction method using the NiCl2/Na4Fe(CN)6 cyanogel as the precursor and NaBH4 as the reducing agent. The influence of the incorporated Fe amount was carefully studied by slightly changing the feeding molar ratios of the Ni/Fe atoms in the precursors. The intrinsic 3D backbone structure of the cyanogel resulted in crystal nuclei tending to generate along with the backbones, which is key to the formation of NiFe nanoaggregates with a porous 3D interconnected structure. The synthesized NiFe nanoaggregates with a 3D interconnected structure and high porosity, as well as the incorporation of Fe, are in favor of high surface area, more active sites, and abundant oxygen vacancies, leading to superior activity and stability of OER in alkaline electrolytes with a low overpotential of 0.35 V at 10 mA cm−2, a high current density of 24.8 mA cm−2 at 1.65 V, a small Tafel slope of 76.9 mV dec−1, and attractive durability in 1 M KOH solution.

ZnCoNiS nanoflowers electrodes with rich heterointerface as efficient bifunctional electrocatalyst for overall water splitting

Constructing heterojunction nanocomposites is promising for overall water splitting. Herein, the metal-organic frameworks (MOFs) derived multiphasic transition metal sulfide nanoflowers heterostructure electrode (ZnCoNiS) was synthesized by the hydrothermal and sulfuration methods. The nanoflowers structure can provide a large electrochemical active surface area and the abundant heterogeneous interfaces are beneficial to increase the synergy between different components to improve the kinetic energy of the reaction. The obtained ZnCoNiS shows outstanding electrocatalytic performance with low overpotentials of 134 mV for the oxygen evolution reaction (OER) and 146 mV for hydrogen evolution reaction (HER) at 10 mA cm−2. Impressively, the ZnCoNiS catalyst exhibits remarkable overall water-splitting performances with a cell voltage of 1.52 V at 10 mA cm−2 and excellent stability in catalysis for over 100 h. This study demonstrates an approach for the design of rich heterogeneous junctions with high activity and stability, which can be used in the fields of solar energy to drive water splitting for hydrogen production.

Preparation of porous carbon nanowires for hydrogen evolution reaction

Hydrogen for clean energy resources has attracted more and more attention, and water splitting for hydrogen production also has been widely studied. Electrocatalysis water splitting is considered the most efficient method for hydrogen production. In this work, we prepared a metal-free porous carbon nanowires catalyst with an electrostatic spinning method using granular poly styrol as the precursor and zinc chloride as the activating agent for forming a porous structure. The obtained catalysts exhibited a plentiful porous structure and an SSA value, which is beneficial for catalyzing hydrogen evolution reactions. The SSA is up to 329 m2 g−1, and the OP value at 10 mA·cm−2 is 386 mV. The materials presented good stability for hydrogen evolution reaction.

Synthesis of Multiple Emission Carbon Dots from Dihydroxybenzoic Acid via Decarboxylation Process.

Carbon dots (CDs), as a new zero-dimensional carbon-based nanomaterial with desirable optical properties, exhibit great potential for many application fields. However, the preparation technique of multiple emission CDs with high yield is difficult and complex. Therefore, exploring the large-scale and straightforward synthesis of multicolor CDs from a simple carbon source is necessary. In this work, the solvent-free method prepares a series of multicolor emission CDs from dihydroxybenzoic acid (DHBA). The maximum emission wavelengths are 408, 445, 553, 580, and 610 nm, respectively, covering the visible light region. The 2,4- and 2,6-CDs possess the longer emission wavelength caused by the 2,4-, and 2,6-DHBA easily undergo decarboxylation to form the larger sp2 domain graphitized structure. These CDs incorporated with g-C3N4 can significantly improve the photocatalytic water-splitting hydrogen production rate by extending the visible light absorption and enhancing the charge separation efficiency. The long-wavelength emission CDs can further enhance photocatalytic activity primarily by improving visible light absorption efficiency.

Enabling high-efficiency ethanol oxidation on NiFe-LDH via deprotonation promotion and absorption inhibition

Nucleophile oxidation reaction (NOR), represented by ethanol oxidation reaction (EOR), is a promising pathway to replace oxygen evolution reaction (OER). EOR can effectively reduce the driving voltage of hydrogen production in direct water splitting. In this work, large current and high efficiency of EOR on a Ni, Fe layered double hydroxide (NiFe-LDH) catalyst were simultaneously achieved by a facile fluorination strategy. F in NiFe-LDH can reduce the activation energy of the dehydrogenation reaction, thus promoting the deprotonation process of NiFe-LDH to achieve a lower EOR onset potential. It also weakens the absorption of OH− and nucleophile electrooxidation products on the surface of NiFe-LDH at a higher potential, achieving a high current density and EOR selectivity, according to density functional theory calculations. Based on our experiment results, the optimized fluorinated NiFe-LDH catalyst achieves a low potential of 1.386 V to deliver a 10 mA cm−2 EOR. Moreover, the Faraday efficiency is greater than 95%, with a current density ranging from 10 to 250 mA cm−2. This work provides a promising pathway for an efficient and cost-effective NOR catalyst design for economic hydrogen production.

One-pot synthesis of crystalline structure: Nickel-iron phosphide and selenide for hydrogen production in alkaline water splitting

Electrocatalytically active nanocomposites play a vital role in energy generation, conversion, and storage technologies. Transition metal-based catalysts such as nickel and iron and their pnictide (phosphide), and chalcogenide (selenide) compounds exhibit good activity for hydrogen evolution reaction (HER) in the alkaline environment. In this study, transition metals-based catalysts (Ni-P-Se, Fe-P-Se, and Ni-Fe-P-Se) solutions were prepared using a simple one-pot method. Prepared solutions were deposited on Ni foam, and different characterization techniques were used to determine the composition, structure, and morphology of as-prepared catalysts. Furthermore, it was found that Ni-Fe-P-Se as a cathode material showed better HER performance compared to other investigated materials with the overpotential value of 316 mV at 10 mA cm-2 current density and 89 mV dec-1 Tafel slope value. The stability tests of the as-prepared catalyst confirmed that the synergistic effect between various elements enhances the electrocatalytic performance for up to 24 hours, providing a fair, stable nature of Ni-Fe-P-Se based sample.

Construct Ni–SnO2 core coated amorphous Ni(BO2)2 shell boosts water splitting for hydrogen production

Through a simple redox reaction, the precursor of Ni (OH)2 mixed with SnO2 was in situ transformed into a core-shell structure with elemental Ni blend SnO2 as the core and nickel metaborate as the shell. The metaborate shell is an excellent adsorption site for water molecules, which paves the way for subsequent hydride adsorption. When a small amount of SnO2 is mixed with elemental Ni, the electronic structure is optimized, and the electron enrichment of Ni is realized, making the hydrogen adsorption performance better. This core-shell synergy promotes the Vomer step in HER, thereby enhancing HER performance. In addition, Ni–Sn@NiBO/NF possesses larger electrochemical surface area and smaller charge transfer resistance. Only an overpotential of 22 mV is needed to drive a current density of 10 mA cm−2, indicating the excellent HER performance of the Ni–Sn@NiBO/NF catalyst. At high current density of 50 mA cm−2, the overpotential is only 79 mV. When Ni–Sn@NiBO/NF is used as the bifunctional catalyst for coupling HER and OER, the voltage is only 1.595 V at 10 mA cm−2. It shows that the catalyst has great application potential in electrocatalytic water decomposition to produce hydrogen.

Cu@S-Co(OH)2 hybrid electrocatalysts with high performance for alkaline hydrogen evolution reaction

Transition metal hydroxides have superior oxygen evolution reaction (OER) activity but poor hydrogen evolution reaction (HER) performance, which greatly limits the water splitting for hydrogen production. Herein, copper modification of sulfur doped Co(OH)2 hybrid catalyst (Cu@S-Co(OH)2) was prepared by one-step of electrodeposition method which can serve as efficient hydrogen evolution reaction catalyst. In the presence of sulfur and copper, Cu@S-Co(OH)2 hybrid catalyst exhibits the best catalytic activity, showing ultralow overpotential of 42 mV at a current density of 10 mA cm−2. Compared with Co(OH)2, the overpotential is improved by nearly 100 mV as well as enhanced stability. In addition, the active site poison experiments proved that the active center is cobalt metal. Combined with the adsorption strength of the catalyst for OH and H species, it is considered that both S and Cu can enhance the adsorption of OH for Co(OH)2, while S is contributed to the adsorption of H, and Cu can promote the desorption of H. This work provides a facile method and new insight to enhance the HER activity for transitional metal hydroxides via metal and non-metallic elements co-modulation.

Interface-Engineered Ni-Coated CdTe Heterojunction Photocathode for Enhanced Photoelectrochemical Hydrogen Evolution

Photoelectrochemical (PEC) water splitting for hydrogen production using the CdTe photocathode has attracted much interest due to its excellent sunlight absorption property and energy band structure. This work presents a study of engineered interfacial energetics of CdTe photocathodes by deposition of CdS, TiO2, and Ni layers. A heterostructure CdTe/CdS/TiO2/Ni photocathode was fabricated by depositing a 100-nm n-type CdS layer on a p-type CdTe surface, with 50 nm TiO2 as a protective layer and a 10 nm Ni layer as a co-catalyst. The CdTe/CdS/TiO2/Ni photocathode exhibits a high photocurrent density (Jph) of 8.16 mA/cm2 at 0 V versus reversible hydrogen electrode (VRHE) and a positive-shifted onset potential (Eonset) of 0.70 VRHE for PEC hydrogen evolution under 100 mW/cm2 AM1.5G illumination. We further demonstrate that the CdTe/CdS p-n junction promotes the separation of photogenerated carriers, the TiO2 layer protects the electrode from corrosion, and the Ni catalyst improves the charge transfer across the electrode/electrolyte interface. This work provides new insights for designing noble metal-free photocathodes toward solar hydrogen development.