Electrocatalytic Water Splitting Research Articles

Breaking barriers in electrocatalysis: unleashing the power of highly efficient Mn/CoS@S-g-C3N4 nanocomposite for electrocatalytic water splitting and superior H2 production

Breaking barriers in electrocatalysis: unleashing the power of highly efficient Mn/CoS@S-g-C3N4 nanocomposite for electrocatalytic water splitting and superior H2 production

Synthesis Framework for Designing PtPdCoNiMn High-Entropy Alloy: A Stable Electrocatalyst for Enhanced Alkaline Hydrogen Evolution Reaction.

High entropy alloys (HEAs) are an emerging class of advanced materials characterized by their multifunctionality and potential to replace commercial catalysts in electrocatalytic water splitting. The synergy among the various alloyed elements in HEAs makes them particularly promising for applications in electrocatalysis. However, preparation of HEA via bottom-up approaches by avoiding the formation of mono, di, and tri metallic alloys in the nanoscale is challenging. This aspect is addressed, in this study by exploring the logical selection of solvents, reducing agents, and capping agents, along with their relative fractions, in the solvothermal synthesis of the HEA comprising platinum-palladium-cobalt-nickel-manganese (PtPdCoNiMn). It is established that the reducing capabilities of both the solvent and reducing agent are crucial for the reduction of each metal to form a single-phase HEA. The synthesized HEA (20 wt.%)/functionalized carbon (FC) demonstrates excellent performance as an HER catalyst, exhibiting a low overpotential of 48.7mV at -10 mA cm-2 in an alkaline electrolyte. This performance is characterized by high reaction kinetics and stability at elevated current densities. Furthermore, the catalyst shows impressive performance in both simulated and actual seawater. This development reduces the reliance on platinum while enhancing the long-term durability and catalytic efficiency of the electrocatalyst.

Surface Sulfurization of Cubic Cu2O to Form Cu2S Nanostructure-Decorated Catalysts for Light-enhanced Electrocatalytic H2 Evolution and Photocatalytic CO2 Reduction.

Developing highly efficient bifunctional catalysts for electrocatalysis and photocatalysis suffers from sluggish charge transfer and poor photo-to-electric conversion rate. Herein, micro-sized Cu2O cubes were initially prepared for subsequent transformation into Cu2O@Cu2S core-shell structures by a slight surface sulfurization. The formation of nanostructured Cu2S thin layer at Cu2O surface can endow an immediate charge separation and migration under light irradiation, leading to high surface photovoltages (SPV, 18-30 mV). As a result, the as-prepared Cu2O@Cu2S catalysts exhibited reduced overpotentials (η, only 86 mV is required for the optimized sample to achieve a current density of 10 mA cm-2) for H2 evolution with good cycling stability in electrocatalytic water splitting. Meanwhile, a high methane (CH4) production rate of 30.3 μmol h-1 g-1 can be delivered from the optimized Cu2O@Cu2S sample when used for photocatalytic CO2 reduction. This work has provided a strategy to prepare bifunctional catalysts with improved photoelectric properties for photo/electrocatalytic applications.

Low-Spin Fe3+ Evoked by Multiple Defects with Optimal Intermediate Adsorption Attaining Unparalleled Performance in Water Oxidation.

Electrocatalytic water splitting is long constrained by the sluggish kinetics of anodic oxygen evolution reaction (OER), and rational spin-state manipulation holds great promise to break through this bottleneck. Low-spin Fe3+ (LS, t2g 5eg 0) species are identified as highly active sites for OER in theory, whereas it is still a formidable challenge to construct experimentally. Herein, a new strategy is demonstrated for the effective construction of LS Fe3+ in NiFe-layered double hydroxide (NiFe-LDH) by introducing multiple defects, which induce coordination unsaturation over Fe sites and thus enlarge their d orbital splitting energy. The as-obtained catalyst exhibits extraordinary OER performance with an ultra-low overpotential of 244 mV at the industrially required current density of 500 mA cm-2, which is 110 mV lower than that of the conventional NiFe-LDH with high-spin Fe3+ (HS, t2g 3eg 2) and superior to most previously reported NiFe-based catalysts. Comprehensive experimental and theoretical studies reveal that LS Fe3+ configuration effectively reduces the adsorption strength of the O* intermediate compared with that of the HS case, thereby altering the rate-determining step from (O* → OOH*) to (OH* → O*) of OER and lowering its reaction energy barrier. This work paves a new avenue for developing efficient spin-dependent electrocatalysts for OER and beyond.

Partial Selenization Strategy for Fabrication of Ni0.85Se@NiCr-LDH Heterostructure as an Efficient Bifunctional Electrocatalyst for Overall Water Splitting.

NiCr-LDH and its partial selenization as Ni0.85Se@NiCr-LDH heterostructure is established here as an alkaline water electrolyzer for achieving enhanced overall water splitting efficiency. The hydrothermally synthesized optimized batch of Ni0.85Se@NiCr-LDH is thoroughly characterized to elucidate its structure, morphology, and composition. Compared to pristine NiCr-LDH, the batch of Ni0.85Se@NiCr-LDH exhibits exceptional alkaline OER and HER activity with low overpotentials of 258 and 85 mV at 10 mA cm-2, respectively. Besides, Ni0.85Se@NiCr-LDH also exhibits excellent acidic HER with an overpotential of only 61 mV at 10 mA cm-2, indicating that Ni0.85Se@NiCr-LDH can operate effectively across a wide pH range. The excellent electrochemical stability of Ni0.85Se@NiCr-LDH for 24 h operation is attributed to the formation of a thin layer of SeOx during OER operation. The role of selenization and the effect of Cr in the LDH lattice toward enhanced electrocatalytic water splitting is discussed. The outstanding OER and HER performances of Ni0.85Se@NiCr-LDH are attributed to the higher electrochemical active surface area, favorable conditions for adsorption of HER/OER intermediates, low charge transfer resistance, and improved conductivity. The practical application ofNi0.85Se@NiCr-LDHas a bifunctionalelectrocatalyst for overall water splitting is reflected from the low cell voltage of 1.548 V at 10 mA cm-2.

Enhanced oxygen evolution reaction in flexoelectric thin-film heterostructures

Recently, the flexoelectric effect has triggered considerable interest in energy-related applications, such as flexo-actuation, flexo-photovoltaic, and flexo-catalysis, because of its ubiquitous feature allowing the creation of electric polarity, i.e., the flexoelectric polarization (Pflexo), in non-polar materials by strain gradient. Here, we show a flexoelectric strategy in electrocatalytic water splitting. Remarkably enhanced oxygen evolution reaction (OER) properties are achieved in strain-gradient LaFeO3 (LFO) thin-film heterostructures owing to the promotion of kinetic processes by Pflexo. The improved OER is demonstrated by increased current density of ∼300% in linear sweep voltammetry and lowered charge transfer resistance by two orders of magnitude in electrochemical impedance spectroscopy. These are ascribed to the flexoelectric-induced downward bending of the LFO band, as revealed by density functional theory calculations and band structure measurements. With Pflexo in the thin-film heterostructure catalysts, the adsorption of hydroxyl ions is strengthened on the polar LFO surface, and the transfer of electrons is accelerated from the reactants/key intermediates to the catalyst across the band-tilted LFO layer. These findings indicate the significance of flexoelectric effect in OER kinetics and open a new perspective for exploiting catalytic mechanisms and performances in water splitting.

Reinforcement of electrocatalytic overall water splitting by constructing Mo-doped NiFe LDH/NiS heterostructure

Electrochemical water splitting is considered to be an environmentally friendly and efficient method of hydrogen production. NiFe LDH is a well-known electrocatalyst for oxygen evolution, yet its effectiveness in HER has been suboptimal. In this research, we created a Mo-NiFe LDH@NiS catalyst on carbon cloth via cation doping and heterointerface construction of NiFe LDH. The resulting Mo-NiFe LDH@NiS/CC showed remarkable HER activity. Furthermore, when used as a bifunctional electrode for overall water splitting, Mo-NiFe LDH@NiS/CC operated at a cell voltage of 1.58V at a current density of 10mA/cm² and exhibited outstanding durability. This study emphasizes the significant enhancement in HER and overall water-splitting efficiency of NiFe LDH achieved through Mo doping and heterostructure engineering, advancing its potential for effective water splitting applications.

Engineering the Coordination Environment in the Silver(I)- and Ruthenium(II)-N-Heterocyclic Carbene Complexes in Instigating the Electrocatalytic Hydrogen Evolution Reaction.

The quest for cost-efficient and high-performance electrocatalysts towards electrocatalytic water splitting is a key and an interdisciplinary area of study. Considerable progress is being driven by developments in the field of energy research. In a fundamental study, we have synthesized NHC precursors (6 and 7) and corresponding metal-NHC complexes of silver(I)- (8 and 9) and ruthenium(II)- (10 and 11) of a N-heterocyclic carbene-based ligand type incorporating coumarins. These NHC precursors and metal-NHC complexes were characterized through various analytical and spectral techniques. The silver(I)-NHC complexes 8 and 9 displayed a linear coordination geometry with a center of inversion, which is evidenced by the single-crystal X-ray diffraction technique. Both the series of complexes were assessed for their efficacies in the hydrogen evolution reaction (HER). The results demonstrated that attributed to its peculiar coordination geometry, high electrical conductivity the silver(I)- and ruthenium(II)-NHC complexes exhibited exemplary electrocatalytic activity. Activities of the hydrogen evolution reaction on two differently modified electrode substrates with metal-NHC complexes have been studied. To attain the benchmark HER current density of 10 mA cm-2, in 1.0 M KOH, an overpotential of -375 to -527 mV vs RHE was required for the metal-NHC complexes. Based on the analysis of the Tafel slope values, the rate-determining step was the adsorption of hydrogen as investigated in the potential window. The molecular electrocatalyst 10 presented a superior stability and maintained the electrocatalytic activity for a duration of 18 h with complex 8 and 24 h with respect to complex 10 in 1.0 M KOH. Apace with these studies, hydrogen oxidation studies were examined in 0.5 M H2SO4 by a substantial current density at the platinum ring electrode. This research offers feasible guidance for developing organometallic-based molecular electrocatalysts with good electrocatalytic performance.

Research Progress on Clay‐Based Materials for Electrocatalytic Water Splitting

AbstractClay‐based materials are an emerging family of earth‐abundant and low‐cost inorganic functional materials with an modifiable layered‐structure mode similar to hydroxides. They are considered as competitive electrocatalysts for water splitting due to their variable intra‐layer ions, exchangeable interlayer molecules/ions, and large reaction surfaces, which demonstrate fascinating engineering opportunities at the microscale, mesoscale, and macroscale levels. We systematically summarized the research progress of clay‐based materials by classifying clay‐like compounds, clay‐based composites, and clay‐based derivatives, from the viewpoint of structural geometries towards optimizing functionalities. The design strategies for regulating and optimizing clay‐based materials to meet the requirements of electrocatalysts with excellent activity and stability were outlined through representative examples. In addition, the hydrogen production applications of these clay‐based materials were discussed reasonably including recent advances. Finally, the future perspectives of clay‐based materials for electrocatalytic water splitting were demonstrated.

Metal Imidazole-Modified Covalent Organic Frameworks as Electrocatalysts for Alkaline Oxygen Evolution Reaction.

Since the product contains no carbon-based substances and can be driven by non-carbon-based electricity, electrocatalytic water splitting is considered to be among the most effective strategies for alleviating the energy crisis and environmental pollution. This process helps lower greenhouse gas emissions while also supporting the shift toward renewable energy sources. The anodic oxygen evolution reaction (OER) involves a more complex multi-electron transfer process, which is the principal limiting factor in overall water splitting. Extensive research has demonstrated that the controlled design of effective electrocatalysts can address this limitation. In this study, a previously unreported covalent organic framework material (COF-IM) was synthesized via a post-synthetic modification strategy. Notably, COF-IM contains imidazole nitrogen metal active sites. Transition metal-coordinated COF-IM@Co can function as a highly effective electrocatalyst, exhibiting a lower overpotential (403.8 mV@10 mA cm-2) in alkaline electrolytes, thereby highlighting its potential for practical applications in energy conversion technologies. This study offers new perspectives on the design and synthesis of COFs, while also making substantial contributions to the advancement and application of OER electrocatalysts.

Nickel Hydroxysulfide Electrocatalyst Promotes Urea Oxidation for Energy‐Saving Hydrogen Production

AbstractThe occurrence of oxygen evolution reaction (OER) almost consumes most of the electric energy of hydrogen production by electrocatalytic water splitting. The energy required in the process of electrochemical hydrogen production can be reduced by choosing urea oxidation reaction (UOR) instead of OER. In this work, nickel hydroxysulfide is synthesized on nickel foam (NiSOH/NF) and its electrocatalytic performance was tested in UOR. Experimental results show that the vulcanization catalyst requires a low potential of 1.38 V (vs RHE) to achieve a current density of 100 mA cm−2 in an electrolyte containing 0.5 M urea, which is 270 mV lower than the conventional OER process. This innovative approach has yielded a substantial reduction in the cell voltage necessary for overall water splitting under two electrode system, thereby enhancing its efficiency and feasibility.

Band Engineering of Mn-P Alloy Enables HER-suppressed Aqueous Manganese Ion Batteries.

Aqueous manganese ion batteries hold potential for stationary storage applications owing to their merits in cost, energy density, and environmental sustainability. However, the formidable challenge is the instability of metallic manganese (Mn) anodes in aqueous electrolytes due to severe hydrogen evolution reaction (HER), which is more serious than the commonly studied Zn metal anodes. Moreover, the mechanism of HER side reactions has remained unclear. Herein, we design a series of Mn-P alloying anodes by precisely regulating their energy band structures to mitigate the HER issue. It is found that the serious HER primarily originates from the spontaneous Mn-H2O reaction driven by the excessively high HOMO energy level of Mn, rather than electrocatalytic water splitting. Owing to a reduced HOMO energy level and enhanced electron escape work function, the MnP anode achieves an evidently enhanced cycle durability (over 1000 hours at a high current density of 5 mA cm-2). The MnP||AgVO full cell with an N/P ratio of 4 exhibits better rate capability and extended cycle life (7000 cycles) with minimal capacity degradation than the cell using metallic Mn anode (less than 100 cycles). This study provides a practical approach for developing highly durable aqueous Mn ion batteries.

Band Engineering of Mn‐P Alloy Enables HER‐suppressed Aqueous Manganese Ion Batteries

Aqueous manganese ion batteries hold potential for stationary storage applications owing to their merits in cost, energy density, and environmental sustainability. However, the formidable challenge is the instability of metallic manganese (Mn) anodes in aqueous electrolytes due to severe hydrogen evolution reaction (HER), which is more serious than the commonly studied Zn metal anodes. Moreover, the mechanism of HER side reactions has remained unclear. Herein, we design a series of Mn‐P alloying anodes by precisely regulating their energy band structures to mitigate the HER issue. It is found that the serious HER primarily originates from the spontaneous Mn‐H2O reaction driven by the excessively high HOMO energy level of Mn, rather than electrocatalytic water splitting. Owing to a reduced HOMO energy level and enhanced electron escape work function, the MnP anode achieves an evidently enhanced cycle durability (over 1000 hours at a high current density of 5 mA cm‐2). The MnP||AgVO full cell with an N/P ratio of 4 exhibits better rate capability and extended cycle life (7000 cycles) with minimal capacity degradation than the cell using metallic Mn anode (less than 100 cycles). This study provides a practical approach for developing highly durable aqueous Mn ion batteries

ZnS-zeolitic imidazolate framework nanostructure anchored on Ni nanowires as a bifunctional electrocatalyst for high-efficiency overall water splitting

The design and construction of stable and inexpensive bifunctional catalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) present a challenge in electrocatalytic water splitting. In this study, we utilized zeolitic imidazolate frameworks-8 (ZIF-8) as the precursor to fabricate ZnS-ZIF-8 via facile sulfidation processes. The ZnS-ZIF-8 nanostructures were anchored on the surface of the nickel nanowire (denoted as Ni NWs@ ZnS-ZIF-8 nanocomposite) and their catalytic activity for HER, OER, and overall water splitting were studied. The prepared Ni NWs@ ZnS-ZIF-8 revealed a low overpotentials value of 90 and 260 mV at 10 mA cm−2 for HER and OER in 1.0 M KOH solution, respectively. The alkaline electrolyzer assembled by Ni NWs@ ZnS-ZIF-8 provides a low cell voltage of 1.61 V at 10 mA cm−2 current density to boost the overall water splitting and robust stability for 15 h. The superior electrocatalytic activity of Ni NWs@ ZnS-ZIF-8 is owing to the facile and effective electron transport of Ni NWs, accessible active sites of ZnS-ZIF-8, and as well as the synergistic effect of the nanocomposite structures. This finding presents a viable methodology for synthesizing a proficient noble-metal-free catalyst for energy conversion and storage.

Hierarchical Bifunctional NiO Electrocatalyst: Highly Porous Structure Boosting the Water Splitting Activity.

The development of an efficient, low-cost and earth-abundant electrocatalyst for water splitting is crucial for the production of sustainable hydrogen energy. However their practical applications are largely restricted by their limited synthesis methods, large overpotential and low surface area. Hierarchical materials with a highly porous three-dimensional nanostructure have garnered significant attention due to their exceptional electrocatalytic properties. These hierarchical porous frameworks enable the fast electron transfer, rapid mass transport, and high density of unsaturated metal sites and maximize product selectivity. Here the process involved obtaining monodispersed microrod-shaped Ni(OH)2 through a hydrothermal reaction, followed by a heat treatment to convert it into hierarchical microrod-shaped NiO materials. N2 sorption analysis revealed that the BET surface area increased from 9 to 89 m2/g as a result of the heat treatment. The hierarchical microrod-shaped NiO materials demonstrated outstanding bifunctional electrocatalytic water splitting capabilities, excelling in both HER and OER in basic solution. Overpotential of 347 mV is achieved at 10 mA/cm2 for OER activity, with a Tafel slope of 77 mV/dec. Similarly, overpotential of 488 mV is achieved at 10 mA/cm2 for HER activity, with a Tafel slope of 62 mV/dec.

The tunable double-layer self-supporting Sb-Ni(OH)2 catalyst for boosting electrocatalytic water splitting

Green hydrogen preparation by electrolysis of water is key to driving the energy transition revolution. The development of low-cost, highly active and highly selective catalysts is a top priority for the commercial application from electrolytic water. This paper presents the synthesis of Sb-doped Ni(OH)2 nanosheets growing in situ on Ni foam, which serves as a self-supporting electrode. A straightforward one-step hydrothermal technique was employed to craft a dual-layer catalyst with a tunable morphology. Under the 1 M KOH conditions, Sb-Ni(OH)2-2.5/NF emerged as a bifunctional electrocatalyst, demonstrating an impressive HER performance of 159 mV (η10) and an OER performance of 430.8 mV (η50). The Sb-Ni(OH)2-2.5/NF also demonstrated remarkable stability by 3000 CV cycling tests. The Sb-Ni(OH)2-2.5/NF catalytic material prepared in this paper under laboratory conditions has a simple and inexpensive synthesis method, which helps to move electrolytic water catalysts from the laboratory to industry.

Chemically driven BaTiO3–CoFe2O4 nanocomposite with strong dielectric and low leakagecharacteristics for electrocatalytic water splitting reaction

The switchable electronic properties at the surface of ferroelectric nanomaterials offer possibilities for electrocatalytic hydrogen and oxygen evolution reactions, HER and OER respectively. Here, 0.5(BaTiO3)-0.5(CoFe2O4) (abbreviated as BTCF0.5) are prepared chemically. The material shows a high dielectric constant in the order of 107. Nyquist plot is consistent with non-Debye-type and negative temperature coefficient of resistance (NTCR) characteristics with low leakage current. BTCF0.5 shows superior electrocatalytic HER and OER with a low overpotential of ∼156 and ∼284 mV at current density10 mA/cm2 along with Tafel slopes of 43.37 mV/dec and 41.52 mV/dec respectively. The stability of the electrocatalyst is checked through a chronoamperometry test and up to 1000 cycles of CV both for HER and OER operations. The non-traditional behavior of the nanocomposite may make it highly desirable for usage in numerous renewable and sustainable energy-related applications in the present-day scenario.

Al-etching-induced defect engineering in NiAl LDHs for promoting multifunctional electrocatalytic oxidations: Water oxidation and urea oxidation

Electrocatalytic water splitting is a promising avenue to produce green hydrogen for future sustainable development. Developing multifunctional catalysts with high-performance toward urea oxidation reaction (UOR) and oxygen evolution reaction (OER) offers a unique approach for simultaneously achieving the degradation of urea-containing wastewater and energy-saving hydrogen production. Ni-based materials are a kind of promising materials for electrocatalysis, since its abundant reserve and tolerance. However, low intrinsic activity and catalytic efficiency hinder its wide application. Here, a defect engineering strategy is developed to create vacancies on NiAl layer double hydroxides (LDHs) catalysts by selectively etching Al ions in strong alkaline solution. The obtained NiAl LDHs with rich defects (D-NiAl LDHs) exhibit good OER performance with overpotential of 264 mV to achieve a current density of 10 mA cm−2 and a Tafel slope of 39.8 mV dec−1. In addition, the D-NiAl LDHs catalysts also show excellent UOR activity using a potential of 1.328 V vs. RHE @ 10 mA cm−2 in alkaline solution. In comparation to NiAl LDHs, the enhanced performance of D-NiAl LDHs toward oxidation of small-molecule OH− and urea could be attributed to electronic regulation of defects and a larger electrochemical surface area. Partially replacing the OER with the UOR, the driving voltage of overall water splitting reduces effectively from 1.856 V to 1.688 V at a current of 100 mA cm−2.

NiFe LDH/Fe2O3/Ni3S2 Heterostructure with a Superhydrophilic/Superaerophobic Surface for Solar-Driven Electrolytic Water Splitting.

The development of a bifunctional electrocatalyst with high efficiency, high stability, and low cost is of great significance in practical applications of electrocatalytic water splitting. Herein, a self-supporting bifunctional electrocatalyst with a NiFe layered double hydroxide/Fe2O3/Ni3S2 heterostructure (NiFe LDH/Fe2O3/Ni3S2/IF) for hydrogen evolution and oxygen evolution reactions (HER/OER) is synthesized by the self-corrosion of iron foam (IF) and hydrothermal strategies. The constructed NiFe LDH/Fe2O3/Ni3S2/IF hierarchical heterostructure was not only beneficial to expose active sites and promote charge/mass transfer but also generate a superhydrophilic/superaerophobic surface, thereby accelerating the reaction kinetics to improve the HER/OER activity. Therefore, NiFe LDH/Fe2O3/Ni3S2/IF exhibited superior overpotentials of 226.2 and 162.8 mV for the OER and HER at 100 mA cm-2, respectively. NiFe LDH/Fe2O3/Ni3S2/IF was employed as both the cathode and the anode to assemble a device for overall water splitting and displayed a voltage of 1.55 V at 10 mA cm-2. The overall water splitting device was coupled with a solar cell to simulate a solar-powered water splitting system, resulting in a superior solar-to-hydrogen conversion efficiency of 15.16%. This work can promote the development of clean energy sources such as solar hydrogen production.

Transition Metal Dichalcogenides in Electrocatalytic Water Splitting

Two-dimensional transition metal dichalcogenides (TMDs), also known as MX2, have attracted considerable attention due to their structure analogous to graphene and unique properties. With superior electronic characteristics, tunable bandgaps, and an ultra-thin two-dimensional structure, they are positioned as significant contenders in advancing electrocatalytic technologies. This article provides a comprehensive review of the research progress of two-dimensional TMDs in the field of electrocatalytic water splitting. Based on their fundamental properties and the principles of electrocatalysis, strategies to enhance their electrocatalytic performance through layer control, doping, and interface engineering are discussed in detail. Specifically, this review delves into the basic structure, properties, reaction mechanisms, and measures to improve the catalytic performance of TMDs in electrocatalytic water splitting, including the creation of more active sites, doping, phase engineering, and the construction of heterojunctions. Research in these areas can provide a deeper understanding and guidance for the application of TMDs in the field of electrocatalytic water splitting, thereby promoting the development of related technologies and contributing to the solution of energy and environmental problems. TMDs hold great potential in electrocatalytic water splitting, and future research needs to further explore their catalytic mechanisms, develop new TMD materials, and optimize the performance of catalysts to achieve more efficient and sustainable energy conversion. Additionally, it is crucial to investigate the stability and durability of TMD catalysts during long-term reactions and to develop strategies to improve their longevity. Interdisciplinary cooperation will also bring new opportunities for TMD research, integrating the advantages of different fields to achieve the transition from basic research to practical application.