Water-splitting Devices Research Articles

Synthesis and Tuning of Electronic, Optical, and Photoelectrochemical Properties of Copper Metavanadate Alloys via Alkaline Earth Metal Substitution

Unlike the well-studied and technologically advanced Group III-V and Group II-VI compound semiconductor alloys, alloys of ternary metal oxide semiconductors have only recently begun to receive widespread attention. Here, we describe the effect of alkaline earth metal substitution on the optical, electronic, and photoelectrochemical (PEC) properties of copper metavanadate (CuV2O6). As a host, the Cu-V-O compound family presents a versatile framework to develop such composition-property correlations. Alloy compositions of A0.1Cu0.9V2O6 (A = Mg, Ca) photoanodes were synthesized via a time and energy-efficient solution combustion synthesis (SCS) method. The effect of introducing alkaline earth metals (Mg, Ca) on the crystal structure, microstructure, electronic, and optical properties of copper metavanadates was investigated by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), and Raman spectroscopy. The PXRD, TEM, and Raman spectroscopy data demonstrated the polycrystalline powder samples to be mutually soluble, solid solutions of copper and alkaline earth metal metavanadates and not simple mixtures of these compounds. The DRS data showed a systematic decrease in the optical bandgap with Cu incorporation. These trends were corroborated by electronic band structure calculations. Finally, the PEC properties exhibited a strong dependence on the alloy composition, pointing to possible applicability in solar water splitting, heterogeneous photocatalysis, phosphor lighting/displays, and photovoltaic devices.

Unveiling the marine Sargassum horneri material for energy and active sensor devices: Towards multitasking approaches

The quest for a future with greater environmental sustainability has led to a rising focus on investigating innovative methods for energy production and storage. However, marine invasions have steadily increased over the past two centuries, necessitating innovative approaches for the remediation and preservation of oceanic environments. Especially, Sargassum horneri (S. horneri) is a brown algae that causes massive floating macroalgal blooms along the coasts of East Asia. Given these facts, this paper develops high-performance triboelectric nanogenerator (TENG), and electrode material for both supercapacitor and water-splitting devices based on S. horneri. The TENG device, constructed using S. horneri coastal bio-waste collected from Jeju Island, yields impressive results. The output current, voltage and power generated by the S. horneri-based triboelectric nanogenerator (SH-TENG) is around 47 µA, 775 V, and 2880 µW, respectively. The electrochemical analysis of carbon derived from S. horneri reveals an excellent electrode capacitance of 225 F/g at 2.5 mA. Constructing the symmetric supercapacitor device using S. horneri-derived carbon, which shows excellent energy and power densities around 14.85 Wh/kg and 972.22 W/kg, with remarkable cyclic stability of 81.3 % for 5000 GCD cycles at 7 mA. On the other hand, the developed S. horneri electrode demonstrated much-improved activity towards water splitting application, exhibiting overpotentials of 0.101 V and 0.198 V for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at an applied current density of 20 mA/cm2, respectively. The fabricated sample also demonstrated the lowest Tafel values towards HER (119 mv/dec) and for OER (109 mv/dec). Finally, the time series analysis (TSA) technique was employed for modeling and prediction of capacity retention of the SH//SH supercapacitor and electrochemical potential (E) of SH/NF║SH/NF cell. In both cases, the mean squared error between experimental and predicted data was very small, suggesting the TSA is a powerful statistical technique to model and predict the vial features of the electrochemical devices. Overall, these results suggest that S. horneri-derived carbon presents a viable alternative in the realm of energy storage and harvesting, promising sustainable technological advancements.

Highly Porous Ni Electrode Decorated with Fe<sub>3</sub>O<sub>4 </sub>for Oxygen Evolution Reaction(OER)

Hydrogen is an environmentally friendly energy source that can be extracted from water through electrolysis. However, the slow oxygen evolution reaction (OER) at the anode side is the main obstacle to the widespread use of water-splitting devices. This study used self-developed highly porous nickel structures (SMNF) and commercial nickel foam (CNF) as working electrodes in the electrolysis process. Iron (II, III) Oxide (Fe3O4) as a catalyst is coated with a dip coating technique on the Ni porous structure and then calcined using a laser process to produce a Ni-Fe3O4-based electrode. Electrochemical test results show that the presence of Fe3O4 significantly impacts high reaction kinetics. The SMNF-Fe3O4 demonstrated an overpotential of 217,3 mV at 1 M KOH electrolyte, at a current density of 10 mA, lower to SMNF electrode without Fe3O4 with an overpotential of 361,4 mV under the same conditions. In addition, the difference in porosity less significantly affects the electrode's effectiveness due to the slight difference in mass loading, which is only < 5 mg. However, electro-impedance spectroscopy (EIS) testing shows better performance on SMNF-Fe3O4 with a smaller electrical series resistance (ESR), around 0.638 Ω, compared to CNF-Fe3O4, which is 0.767 Ω. Overall, observations by chronoamperometry test at an overpotential of 155 mV at 5 hrs show stable performance of SMNF-Fe3O4 electrodes.

The photocatalytic degradation performance of Dion-Jacobson-type layered perovskites AMCa2Ta3O10 (AM=Rb, Cs): A DFT study

The structural, electronic, redox potential, mechanical, photocatalytic, and optical properties of the Dion-Jacobson-type triple-layered perovskites AMCa2Ta3O10 (AM = Rb, Cs) are investigated via density functional theory (DFT) study. The electronic properties are calculated through HSE-06 functional technique which confirmed the semiconducting behavior with the energy band gap values of 1.67 eV and 1.71 eV for RbCa2Ta3O10 and CsCa2Ta3O10, respectively. The calculated results of redox potential indicate that both materials are favorable for water splitting and as an agent for pollutant degradation. Both studied compounds exhibit a reduced effective mass of electrons, which suggests the high capacity to transfer the charge to the surface, indicative of superior electrical conductivity. Poisson's and Pugh's ratios suggest that both the materials are brittle. Optical parameters are calculated within the energy range of 0–6 eV, which strongly correlates with the energy band gap's high absorption and low reflection in the visible region. Our findings indicate high photocatalytic efficiency in organic pollutant degradation, suggesting the potential for developing advanced photocatalytic devices for water splitting and environmental pollutant decomposition.

A dual spin-controlled chiral two-/three-dimensional perovskite artificial leaf for efficient overall photoelectrochemical water splitting

The oxygen evolution reaction, which involves high overpotential and slow charge-transport kinetics, plays a critical role in determining the efficiency of solar-driven water splitting. The chiral-induced spin selectivity phenomenon has been utilized to reduce by-product production and hinder charge recombination. To fully exploit the spin polarization effect, we herein propose a dual spin-controlled perovskite photoelectrode. The three-dimensional (3D) perovskite serves as a light absorber while the two-dimensional (2D) chiral perovskite functions as a spin polarizer to align the spin states of charge carriers. Compared to other investigated chiral organic cations, R-/S-naphthyl ethylamine enable strong spin-orbital coupling due to strengthened π–π stacking interactions. The resulting naphthyl ethylamine-based chiral 2D/3D perovskite photoelectrodes achieved a high spin polarizability of 75%. Moreover, spin relaxation was prevented by employing a chiral spin-selective L-NiFeOOH catalyst, which enables the secondary spin alignment to promote the generation of triplet oxygen. This dual spin-controlled 2D/3D perovskite photoanode achieves a 13.17% of applied-bias photon-to-current efficiency. Here, after connecting the perovskite photocathode with L-NiFeOOH/S-naphthyl ethylamine 2D/3D photoanode in series, the resulting co-planar water-splitting device exhibited a solar-to-hydrogen efficiency of 12.55%.

Insights into the role of Co3O4/Ti3C2 MXene hybrid material in photoelectrochemical water oxidation over BiVO4 photoanode

Developing efficient hole transport layers and water oxidation electrocatalysts is vital for improving the performance of photoelectrochemical (PEC) devices for water-splitting. In this work, we synthesized Co3O4 nanoparticles/Ti3C2-MXene hybrid material and utilized it as a dual-function material to transport the photogenerated holes and catalyze the water oxidation reaction. It was found that the modification of BiVO4 with Co3O4/Ti3C2-MXene prolonged the lifetime of the photogenerated holes by 13.7-fold (i.e. from 0.26 s for BiVO4 to 3.56 s for Co3O4/Ti3C2/BiVO4) and significantly reduced the charge transfer resistance. The modification of BiVO4 with only Ti3C2-MXene resulted in significant surface recombination more likely due to the high concentration of the accumulated holes in the Mxene layer because of its low electrocatalytic activity toward water oxidation reaction. Employing the Co3O4/Ti3C2-MXene hybrid material significantly reduced the rate constant of surface recombination and dramatically enhanced the charge transfer efficiency (i.e. from 0.17% for BiVO4 to 14.0% for Co3O4/Ti3C2/BiVO4 at 0.65 VRHE). Under optimized conditions, the Co3O4/Ti3C2/BiVO4 photoanode was able to deliver 5.05 mA cm−2 at 1.23 VRHE and outperforms Ti3C2/BiVO4 and Co3O4/BiVO4 photoanodes. Moreover, it showed high stability for over 50 hours and reached a Faradaic efficiency of 90%. An applied bias photo-to-current efficiency (ABPE) value of 1.71% at 0.62 VPt was obtained for the overall water splitting. This work provides a facile method to reduce surface recombination and enhance the stability and PEC efficiency of BiVO4 photoanodes via the modification with dual-function oxygen evolution catalyst/hole transport layer hybrid material.

Superhydrophilic and heterostructured NiCu/polyaniline nanocomposites as highly efficient electrocatalyst and photothermal conversion layer integrated thermoelectric device for overall water splitting

The large-scale production of green hydrogen from water electrolysis has recently gained extensive attention. However, the high overpotential leads to the excessive costs of electricity consumption. Herein, a novel research scheme was proposed to design photothermal electrocatalyst with photothermal effect and highly efficient hydrogen evolution reaction (HER) performance, which can be integrated with thermoelectric (TE) device to effectively lower the cell voltage in the overall water splitting. Experimental and DFT calculations results demonstrated that NiCu/PANI/NF catalyst displayed superior HER performance (28 mV@10 mA cm−2, 89 mV@50 mA cm−2), exceptional durability (110 h@10, 50 mA cm−2), as well as good infrared photoresponsivity (93.4 ℃@200 mW cm−2 @10 min). It can be mainly attributed to the synergy of polyaniline and the introduction of Cu, which can effectively modulate the d-band center of Ni active site, and attenuate H adsorption energy, then promote H2 generation. Additionally, superhydrophilicity of NiCu/PANI/NF can facilitate mass transfer and accelerate H2 evolution. Notably, in a self-designed electrolyzer-TE integrated device, the cell voltage was significantly lowered for the overall water splitting (0.29 V @50 mA cm−2). This work presented an efficient photothermal electrocatalyst and provided novel insights for investigations into water electrolysis with cost-effective hydrogen production in the future.

RuSe2 and CoSe2 Nanoparticles Incorporated Nitrogen-Doped Carbon as Efficient Trifunctional Electrocatalyst for Zinc-Air Batteries and Water Splitting.

The development of affordable, highly active, and stable trifunctional electrocatalysts is imperative for sustainable energy applications such as overall water splitting and rechargeable Zn-air battery. Herein, we report a composite electrocatalyst with RuSe2 and CoSe2 hybrid nanoparticles embedded in nitrogen-doped carbon (RuSe2CoSe2/NC) synthesized through a carbonization-adsorption-selenylation strategy. This electrocatalyst is a trifunctional electrocatalyst with excellent hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) activities. An in-depth study of the effect of Se on the electrocatalytic process was conducted. Notably, the incorporation of Se moderately adjusted electronic structure of Ru and Co, enhancing all three types of catalytic performance (HER, η10 = 31 mV; OER, η10 = 248 mV; ORR, E1/2 = 0.834 V) under alkaline condition with accelerated kinetics and improved stability. Density functional theory (DFT) calculation reveals that the (210) crystal facet of RuSe2 is the dominant HER active site as it exhibited the lowest ΔGH* value. The in situ Raman spectra unravel the evolution process of the local electronic environment of Co-Se and Ru-Se bonds, which synergistically promotes the formation of CoOOH as the active intermediate during the OER. The superior catalytic efficiency and remarkable durability of RuSe2CoSe2/NC as an electrode for water splitting and zinc-air battery devices demonstrate its great potential for energy storage and conversion devices.

Integration of Multijunction Absorbers and Catalysts for Efficient Solar‐Driven Artificial Leaf Structures: A Physical and Materials Science Perspective

Artificial leaves could be the breakthrough technology to overcome the limitations of storage and mobility through the synthesis of chemical fuels from sunlight, which will be an essential component of a sustainable future energy system. However, the realization of efficient solar‐driven artificial leaf structures requires integrated specialized materials such as semiconductor absorbers, catalysts, interfacial passivation, and contact layers. To date, no competitive system has emerged due to a lack of scientific understanding, knowledge‐based design rules, and scalable engineering strategies. Herein, competitive artificial leaf devices for water splitting, focusing on multiabsorber structures to achieve solar‐to‐hydrogen conversion efficiencies exceeding 15%, are discussed. A key challenge is integrating photovoltaic and electrochemical functionalities in a single device. Additionally, optimal electrocatalysts for intermittent operation at photocurrent densities of 10–20 mA cm−2 must be immobilized on the absorbers with specifically designed interfacial passivation and contact layers, so‐called buried junctions. This minimizes voltage and current losses and prevents corrosive side reactions. Key challenges include understanding elementary steps, identifying suitable materials, and developing synthesis and processing techniques for all integrated components. This is crucial for efficient, robust, and scalable devices. Herein, corresponding research efforts to produce green hydrogen with unassisted solar‐driven (photo‐)electrochemical devices are discussed and reported.

Solution Processing Silicon Heterojunction Photocathode for Efficient and Stable Hydrogen Production.

Efficient and stable photocathodes are crucial for the development of photoelectrochemical (PEC) water-splitting devices. Silicon heterojunction (SHJ) solar cell is one of the most advanced photovoltaic cells. However, due to the instability of its outermost indium tin oxide (ITO) layers in the electrolyte, a protective layer needs to be introduced on its surface. Previously reported high-quality protective layers almost all involved the use of expensive thin film manufacturing techniques such as atomic layer deposition (ALD). In this work, for the first time, a new strategy is proposed of modifying SHJ-based photocathode with yttrium hydroxide (Y(OH)3) through two-step solution methods to simultaneously improve the stability and activity. The optimized SHJ photocathode exhibits a high applied bias photon-to-current efficiency (ABPE) of 8.4% under simulated 100mWcm-2 (1 Sun) with an AM 1.5G filter in 0.5m KOH. Furthermore, the obtained SHJ photocathode demonstrates excellent stability of at least 110h at 0.3V versus RHE. In this work, combining facile direct current magnetron sputtering with a solution treatment technique provides a novel design strategy, which lowers the threshold for preparing high-quality protective layer, and paves the way for developing economic, efficient, and stable SHJ-based PEC devices.

Self-assembled monolayer mediated fast charge transport of Sb2(S,Se)3 photocathode enabling high-performance unbiased water splitting

The photoelectrochemical (PEC) water splitting system, capable of generating green hydrogen fuel, is crucial for achieving carbon net zero. However, the performance of the photocathode, responsible for the hydrogen evolution reaction, remains suboptimal. We propose bottom interface engineering using a self-assembled monolayer (SAM) to enhance the quality of the Sb2(S,Se)3 absorber layer. The SAM, composed of (3-aminopropyl)triethoxysilane (APTES), is introduced on the Au substrate to enhance adhesion between the substrate and the Sb2(S,Se)3 absorber. Notably, the APTES treatment facilitates the formation of strong electrophile functional groups on the substrate, which predominantly attract tartrate-Sb-Se ionic clusters in the precursor ink. This interaction between the precursor and the substrate induces preferential nucleation of Sb2Se3 near the substrate, followed by Sb2S3 formation at a later stage near the top surface. The APTES-treated Sb2(S,Se)3 photocathodes exhibit a steep band energy gradient, resulting in a photocurrent density of 16 mA cm–2, an onset potential of 0.24 V versus the standard hydrogen electrode, and stability of 24 h in neutral electrolyte (0.5 M K-Pi, pH 6.13). By combining the APTES-treated Sb2(S,Se)3 photocathode with a perovskite photoanode, the co-planar PEC–PEC water splitting device achieves a remarkable solar-to-hydrogen efficiency of 6.5 % under unbiased conditions, along with operating stability for over 120 min. This study suggests that SAM treatment-based interface engineering could be a potential breakthrough in improving the performance of chalcogenide photocathodes in solar-driven water splitting systems.

Embedding biocatalysts in a redox polymer enhances the performance of dye-sensitized photocathodes in bias-free photoelectrochemical water splitting

Dye-sensitized photoelectrodes consisting of photosensitizers and molecular catalysts with tunable structures and adjustable energy levels are attractive for low-cost and eco-friendly solar-assisted synthesis of energy rich products. Despite these advantages, dye-sensitized NiO photocathodes suffer from severe electron-hole recombination and facile molecule detachment, limiting photocurrent and stability in photoelectrochemical water-splitting devices. In this work, we develop an efficient and robust biohybrid dye-sensitized NiO photocathode, in which the intermolecular charge transfer is enhanced by a redox polymer. Owing to efficient assisted electron transfer from the dye to the catalyst, the biohybrid NiO photocathode showed a satisfactory photocurrent of 141±17 μA·cm−2 at neutral pH at 0 V versus reversible hydrogen electrode and a stable continuous output within 5 h. This photocathode is capable of driving overall water splitting in combination with a bismuth vanadate photoanode, showing distinguished solar-to-hydrogen efficiency among all reported water-splitting devices based on dye-sensitized photocathodes. These findings demonstrate the opportunity of building green biohybrid systems for artificial synthesis of solar fuels.

Low-temperature plasma-assisted synthesis of iron and nitrogen co-doped CoFeP-N nanowires for high-efficiency electrocatalytic water splitting

Designing efficient, stable, and low-cost non-precious metal electrocatalysts is critical for gainful utilization of renewable resources and effective water splitting. The catalytic efficiency is determined by interactions between the multiple main constituent elements and dopants. However, achieving performance-boosting synergistic interactions between different species in the catalyst is challenging. This work demonstrates such effect using low-temperature plasma-enhanced hydrothermal-phosphorization synthesis of Fe, N co-doped CoFeP-N nanowires. Nickel foam was utilized as the substrate to prepare CoFe-LDH precursor by hydrothermal method and CoFeP nanoparticles were obtained by phosphorization in a tube furnace. The N element was further doped into CoFeP using a low-temperature plasma discharge. The produced CoFeP-N nanowires exhibit far superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities in an alkaline medium compared to the original CoP due to the incorporation of Fe and N elements, with overpotentials of 64 mV and 219 mV at 10 mA cm−2 respectively, and excellent cycling stability. When CoFeP-N is used as both the cathode and anode of a two-electrode water splitting device, low voltages of only 1.516 V and 1.636 V were needed to achieve current density of 10 mA cm−2 and100 mA cm−2 respectively, which are better than that of Pt/C||RuO2 and most non-precious metal-based electrocatalysts reported to date. These experimental results provide new insights and strategies for developing efficient, stable, and low-cost bifunctional water splitting electrocatalysts.

3D hierarchical porous N-doped carbon nanoarchitecture coated bimetallic phosphides as a highly efficient bifunctional electrocatalyst for overall water splitting

As the energy and ecological crises are increasingly grim, it is challengeable but extremely attractive to fabricate highly efficient and low-cost bifunctional electrocatalysts for overall water splitting (OWS). Herein, a bimetallic phosphide embedded in N-doped hierarchical porous carbon (CoP/Ni2P@NHPC) framework was successfully constructed by calcination and phosphorization of cobalt–nickel coordination polymer nanoflowers (Co/Ni CPNFs), which were obtained by a facile hydrothermal process. Benefitting from their fascinating architecture and composition, the as-prepared CoP/Ni2P@NHPC exhibits outstanding electrochemical properties for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with small Tafel slopes (103.9 mV dec-1, 62.58 mV dec-1) and ultralow overpotentials (275 mV, 159 mV at 10 mA cm−2) in alkaline medium. Additionally, the CoP/Ni2P@NHPC can be used as a bifunctional catalyst in a two-electrode water splitting device, and it only requires a low cell voltage of 1.55 V to attain the current density of 10 mA cm−2. Meanwhile, the CoP/Ni2P@NHPC also present admirable durability (at least 20 h) under long-term electrolysis. This work gives inspiration for the preparation of highly active bifunctional electrocatalysts for OWS.

Three-dimensional cage based on porous Ni–Co–Cu phosphide as efficient and stable bifunctional electrocatalysts for overall water splitting

The development of cheap and high-performance dual electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an electrolyte is of great importance. Tuning the electronic structure through heteroatom doping and increasing the catalytic sites through designing the morphology of nanostructures are the most popular approaches to enhance electrocatalytic performance. In recent years, with the development of nanotechnology and interface engineering, significant progress has been made in this field, but it is still challenging. Here three-dimensional porous NiCoCu–P cage were synthesized using a quick and easy method with the help of 26-face Cu2O as a sacrificial template, then it was phosphidated by a facile phosphidation heat treatment in N2 atmosphere and then for the electrochemical evaluations, the glassy carbon electrode surface (GCE) surface was modified with it. Taking advantage of these strategies, NiCoCu–P cage offer large surface area, fast electron/mass transfer and open channels for efficient gas release, which show improved electrochemical performance in alkaline environment and achieved an overpotential of −210 mV at 10 mA cm−2 for HER and 240 mV at 50 mA cm−2 for OER. Also, an overall water splitting device is assembled by two symmetric NiCoCu–P cage/carbon cloth as cathode and anode, that can provide a current density of 100 mA cm−2 at a cell voltage of less than 1.6 V.

Study of double perovskite materials RbX2Y3O10 (X[dbnd]Mg, Ca, Y[dbnd]Ti, Zr) for photocatalytic applications: A DFT insights

The double perovskites have excellent photocatalytic capabilities and could be used for water splitting purposes. Herein, we used density functional theory (DFT) computations to inspect the compound's characteristics. Generalized gradient approximation (GGA)-Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional with compounds space group 123 (p4/mmm) are used for investigations. According to the findings, The structural characteristics show that these compounds have a tetragonal nature (a = b≠c) with 16 atoms. The electronic band structures indicate that all compounds have a semiconductor nature with an indirect energy bandgap Eg of 2.25 eV, 2.92 eV, and 2.31 eV for RbCa2Ti3O10, RbMg2Zr3O10, and RbMg2Ti3O10, respectively. According to analyses of the Mulliken atomic (MA) populations, every chemical has complex bonding with both covalent and ionic characteristics. The elastic characteristics of the perovskite revealed that it is elastically anisotropic and mechanically stable. The calculated values of Pugh's (1.48, 1.91, 4.42) and Poisson's (0.22, 0.28, 0.39) ratios indicate that the substances RbCa2Ti3O10 and RbMg2(Zr/Ti)3O10 under study are brittle and ductile by nature. As a result, we anticipate that these compounds are valuable in the growth of high-performance photocatalytic devices for water splitting for various applications like producing hydrogen and oxygen.

Bifunctional low-Pt content nanocatalysts supported on carbons functionalized with a Cu-organometallic compound: Tailoring of d-band center with high catalytic activity for electrochemical oxygen reactions

In this study, Vulcan XC-72 (C) and sewage sludge-derived biocarbon (SSB) are functionalized with mesitylcopper (Cu-mes) and implemented to produce the low-Pt content and thus low-cost (5 wt %) Pt/CCu-mes10, Pt/CCu-mes20, Pt/SSBCu-mes10, and Pt/SSBCu-mes20 nanocatalysts. This approach facilitates the generation of various functional groups along with the CuO and Cu2O phases. The nanocatalysts show the formation of the PtCu3 alloy, with the two first having an atomic fraction of Cu alloyed (XCu) of 55 and 67%, respectively. Pt/CCu-mes10 shows a comparable catalytic activity for the oxygen reduction reaction (ORR) before and after an accelerated degradation test (ADT) to 20 wt % Pt/C and 5 wt % Pt/C. It also shows the highest performance for the oxygen evolution reaction (OER), with remarkable electrochemical stability. The outstanding performance of Pt/CCu-mes10 is attributed to the presence of Cu-phases, its high degree of alloying and its d-band center which favorably promotes the adsorption of O-species and their further reaction. Specifically, the PtCu3 alloy promotes the kinetics of the reactions by modulating the electronic properties of Pt and creating dual active sites. Meanwhile, Pt/SSB demonstrates an encouraging performance for the reactions before ADT, with electrochemical parameters similar to those of 20 wt % Pt/C. However, its stability is poor, with low catalytic activity after ADT. Therefore, it is found that there is a significant effect of the electrochemical behavior of the carbon support on the performance and stability of the nanocatalysts. The potential application of Pt/CCu-mes10 in water splitting devices is identified.

Impact of Co:Fe cations composition in amorphous and mesoporous cobalt iron phosphate electrocatalysts synthesized by SILAR method on durable electrochemical water splitting

Efficient and durable electrocatalysts are crucial for energy conversion devices that perform the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The structural and morphological characteristics of the electrocatalyst can significantly impact the HER/OER performance. Therefore, it is essential to develop a high-performing electrocatalyst with desired properties using a simple and cost-effective chemical process. So, herein, successive ionic layer adsorption and reaction (SILAR) deposited amorphous, hydrous cobalt iron phosphate (CFP) thin film electrocatalysts are implemented toward electrochemical water splitting. Moreover, in the present work, the molar proportions of cobalt and iron were streamlined to study their synergistic effect on electrochemical HER and OER performance. The electrode of best-performing (CFP–S2) requires the lowest overpotentials of 242 mV for OER and 67.9 mV for HER at a current density of 10 mA/cm2, which maintains its activity after 24 h. The alkaline water splitting into a similar electrolytic bath using two electrode systems was demonstrated for 100 h with the lowest overpotential of 1.72 V. The remarkable electrochemical performance and postmortem analysis unambiguously demonstrate that CFP electrodes are a highly promising and robust option for long-duration water-splitting devices, and the facile SILAR method for scalable CFP electrode synthesis indicates enormous potential for commercial applications.

Flexible Bifunctional Electrode for Alkaline Water Splitting with Long-Term Stability.

Progress in electrochemical water-splitting devices as future renewable and clean energy systems requires the development of electrodes composed of efficient and earth-abundant bifunctional electrocatalysts. This study reveals a novel flexible and bifunctional electrode (NiO@CNTR) by hybridizing macroscopically assembled carbon nanotube ribbons (CNTRs) and atmospheric plasma-synthesized NiO quantum dots (QDs) with varied loadings to demonstrate bifunctional electrocatalytic activity for stable and efficient overall water-splitting (OWS) applications. Comparative studies on the effect of different electrolytes, e.g., acid and alkaline, reveal a strong preference for alkaline electrolytes for the developed NiO@CNTR electrode, suggesting its bifunctionality for both HER and OER activities. Our proposed NiO@CNTR electrode demonstrates significantly enhanced overall catalytic performance in a two-electrode alkaline electrolyzer cell configuration by assembling the same electrode materials as both the anode and the cathode, with a remarkable long-standing stability retaining ∼100% of the initial current after a 100 h long OWS run, which is attributed to the "synergistic coupling" between NiO QD catalysts and the CNTR matrix. Interestingly, the developed electrode exhibits a cell potential (E10) of only 1.81 V with significantly low NiO QD loading (83 μg/cm2) compared to other catalyst loading values reported in the literature. This study demonstrates a potential class of carbon-based electrodes with single-metal-based bifunctional catalysts that opens up a cost-effective and large-scale pathway for further development of catalysts and their loading engineering suitable for alkaline-based OWS applications and green hydrogen generation.

Hematite Hollow-Sphere-Array Photoanodes for Efficient Photoelectrochemical Water Splitting.

Constructing 3D nanophotonic structures is regarded as an effective method to realize efficient solar-to-hydrogen conversion. These photonic structures can enhance the absorbance of photoelectrodes by the light trapping effect, promote the charge separation by designable charge transport pathway and provide a high specific surface area for catalytic reaction. However, most 3D structures reported so far mainly focused on the influence of light absorption and lacked a systematic investigation of the overall water splitting process. Herein, hematite hollow-sphere-array photoanodes are fabricated through a facile hydrothermal method with polystyrene templates. Validating by simulations and experiments, the hollow sphere array is proved to enhance the efficiency of light harvesting, charge separation and surface reaction at the same time. With an additional annealing treatment in oxygen, a photocurrent density of 2.26mA cm-2 at 1.23V versus reversible hydrogen electrode can be obtained, which is 3.70 times larger than that with a planar structure in otherwise the same system. This work gains an insight into the photoelectrochemical water splitting process, which is valuable for the further design of advancing solar driven water splitting devices.