Metal organic framework-derived CoPS/N-doped carbon for efficient electrocatalytic hydrogen evolution

CoPS/Co4S3 Heterojunction with Highly Exposed Active Sites and Dual-site Synergy for Effective Hydrogen Evolution Reactions

Cobalt phosphosulphide (CoPS) has recently been recognized as a potentially effective electrocatalyst for the hydrogen evolution reaction (HER). However, there have been no research on the design of CoPS-based heterojunctions to boost their HER performance. Herein, CoPS/Co4S3 heterojunction was prepared by phosphating treatment based on defect-rich flower-like Co1-xS precursors. The high specific surface area of nanopetals, together with the heterojunction structure with inhomogeneous strain, exposes more active sites in the catalyst. The electronic structure of the catalyst is reconfigured as a result of the interfacial interactions, which promote the catalyst's ability to adsorb hydrogen and conduct electricity. The synergistic effect of the Co and S dual-site further enhance the catalytic activity. The catalyst has overpotentials of 61 and 70 mV to attain a current density of 10 mA cm-2 in acidic and alkaline media, respectively, which renders it competitive with previously reported analogous catalysts. This work proposes an effective technique for constructing transition metal phosphosulfide heterojunctions, as well as the development of an efficient HER electrocatalyst.

Highly Efficient ZIF-67-Derived PtCo Alloy-CN Interface for Low-Temperature Aqueous-Phase Fischer-Tropsch Synthesis

Designing new materials for selective Fischer-Tropsch synthesis (FTS) is an elegant way to enhance local feedstock utilization like biomass and waste. In this approach, we have designed a thermally and chemically stable bimetallic PtCo/NC hybrid nanocomposite catalyst derived from a zeolitic imidazolate framework (ZIF-67, which contains cobalt as a metal center) through carbonization for low-temperature (413-473 K) aqueous-phase Fischer-Tropsch synthesis (AFTS). The selectivity of the desired range of hydrocarbons is adjusted using a highly dispersed PtCo bimetallic alloy, which facilitates extraordinary reduction of a metal oxide to active species by the synergic effect under the AFTS reaction conditions. The ZIF-derived catalyst tested in this study exhibited the highest activity to date for very low temperatures (433 K) in aqueous-phase Fischer-Tropsch synthesis with CO conversion rates between 0.61 and 1.20 mol_CO·mol_Co^-1·h^-1. Insights of the remarkable catalyst activity were examined by in situ X-ray photoelectron spectroscopy (XPS) studies corroborated by density functional theory (DFT) calculation. The bimetallic Co₃Pt (111) surface was found to be highly active for the C-C coupling reaction between surface-adsorbed C and CO, forming a CCO intermediate with a very low activation barrier (E_a = 0.37 eV), in comparison to the C-C coupling activation barrier obtained over the Co (111) surface (E_a = 0.87 eV). This unique approach and observations create a new path for developing next-generation advanced catalyst systems and processes for selective low-temperature FTS.

Nanostructured Metal Phosphide Based Catalysts for Electrochemical Water Splitting: A Review

Amongst various futuristic renewable energy sources, hydrogen fuel is deemed to be clean and sustainable. Electrochemical water splitting (EWS) is an advanced technology to produce pure hydrogen in a cost-efficient manner. The electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are the vital steps of EWS and have been at the forefront of research over the past decades. The low-cost nanostructured metal phosphide (MP)-based electrocatalysts exhibit unconventional physicochemical properties and offer very high turnover frequency (TOF), low over potential, high mass activity with improved efficiency, and long-term stability. Therefore, they are deemed to be potential electrocatalysts to meet practical challenges for supporting the future hydrogen economy. This review discusses the recent research progress in nanostructured MP-based catalysts with an emphasis given on in-depth understanding of catalytic activity and innovative synthetic strategies for MP-based catalysts through combined experimental (in situ/operando techniques) and theoretical investigations. Finally, the challenges, critical issues, and future outlook in the field of MP-based catalysts for water electrolysis are addressed.

Metal-organic framework derived bimetal oxide CuCoO2 as efficient electrocatalyst for the oxygen evolution reaction

Metal-organic framework (MOF) materials with tunable porous morphology, controlled crystalline structure, various compositions, and high specific surface area are widely used as precursors to synthesize electrocatalysts for water splitting, which is beneficial for improving their oxygen evolution reaction (OER) performance. Using ZIF-67 as a Co source and Cu-BTC as a Cu source, hexagonal MOF-derived CuCoO₂ (MOF-CCO) nanocrystals with the size of ∼288 nm were prepared through a one-step solvothermal method. The influence of the content of the precursor solvents (absolute ethanol and deionized water), reaction temperature, mass ratio of reactants, NaOH addition, and reactant concentration of precursors on the structure and morphology of the products was investigated. The optimal CuCoO₂ nanocrystals (MOF-CCO1) around 288 nm present the highest OER activity, such as a low overpotential of 364.7 mV at 10 mA cm^-2, a small Tafel slope of 64.1 mV dec^-1, and attractive durability in 1.0 M KOH solution. The XPS results showed that the higher catalytic efficiency of MOF-CCO1 nanocrystals could be due to the oxygen vacancies caused by lattice oxygen loss, the increase of OH^- content on the surface, and the synergistic effect of Cu²⁺/Cu⁺ and Co²⁺/Co³⁺ redox pairs. Finally, a possible OER mechanism for MOF-CCO nanocrystals of water splitting was proposed. This study provides a new approach for the preparation of delafossite nanomaterials and for the improvement of their OER performances.

Critical Review, Recent Updates on Zeolitic Imidazolate Framework-67 (ZIF-67) and Its Derivatives for Electrochemical Water Splitting

Design and construction of low-cost electrocatalysts with high catalytic activity and long-term stability is a challenging task in the field of catalysis. Metal-organic frameworks (MOF) are promising candidates as precursor materials in the development of highly efficient electrocatalysts for energy conversion and storage applications. This review starts with a summary of basic concepts and key evaluation parameters involved in the electrochemical water-splitting reaction. Then, different synthesis approaches reported for the cobalt-based Zeolitic imidazolate framework (ZIF-67) and its derivatives are critically reviewed. Additionally, several strategies employed to enhance the electrocatalytic activity and stability of ZIF-67-based electrocatalysts are discussed in detail. The present review provides a succinct insight into the ZIF-67 and its derivatives (oxides, hydroxides, sulfides, selenides, phosphide, nitrides, telluride, heteroatom/metal-doped carbon, noble metal-supported ZIF-67 derivatives) reported for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting applications. Finally, this review concludes with the associated challenges and the perspectives on developing the best economic, durable electrocatalytic materials.

Nickel supported on Nitrogen-doped biomass carbon fiber fabricated via in-situ template technology for pH-universal electrocatalytic hydrogen evolution

Developing alternatives to noble metal electrocatalysts for hydrogen production via water splitting is a challenging task. Herein, a novel electrocatalyst with Ni nanoparticles disperesed on N-doped biomass carbon fibers (NBCFs) was prepared through a simple in-situ growth process using Ni-ethanediamine complex (NiC) as the structure-directing agent. The in-situ template effect of the NiC facilitated the formation of Ni-N bonds between the Ni nanoparticles and NBCFs, which not only prevented the aggregation and corrosion of the Ni nanoparticles, but also accelerated the electron transfer in the electrochemical reaction, thus improving the hydrogen evolution reaction (HER) activity of the electrocatalyst. As expected, the optimal Ni/NBCF-1-H₂ electrocatalyst exhibited better HER activity over the entire pH range than the control Ni/NBCF-1-N₂ and Ni/NBCF-1-NaBH₄ samples. The HER overpotentials of the Ni/NBCF-1-H₂ electrocatalyst were as low as 47, 56, and 100 mV in alkaline (pH = 13.8), acidic (pH = 0.3), and neutral (pH = 7.3) electrolytes, respectively at the current density of 10 mA cm^-2. Meanwhile, the Ni/NBCF-1-H₂ sample could run continuously for 100 h, exhibiting outstanding stability. This work provides a feasible method for developing efficient and cheap electrocatalysts derived from biomass carbon materials using the in-situ template technology.

Shining Light on Anion-Mixed Nanocatalysts for Efficient Water Electrolysis: Fundamentals, Progress, and Perspectives

This review introduces recent advances of various anion-mixed transition metal compounds (e.g., nitrides, halides, phosphides, chalcogenides, (oxy)hydroxides, and borides) for efficient water electrolysis applications in detail. The challenges and future perspectives are proposed and analyzed for the anion-mixed water dissociation catalysts, including polyanion-mixed and metal-free catalyst, progressive synthesis strategies, advanced in situ characterizations, and atomic level structure-activity relationship. Hydrogen with high energy density and zero carbon emission is widely acknowledged as the most promising candidate toward world's carbon neutrality and future sustainable eco-society. Water-splitting is a constructive technology for unpolluted and high-purity H₂ production, and a series of non-precious electrocatalysts have been developed over the past decade. To further improve the catalytic activities, metal doping is always adopted to modulate the 3d-electronic configuration and electron-donating/accepting (e-DA) properties, while for anion doping, the electronegativity variations among different non-metal elements would also bring some potential in the modulations of e-DA and metal valence for tuning the performances. In this review, we summarize the recent developments of the many different anion-mixed transition metal compounds (e.g., nitrides, halides, phosphides, chalcogenides, oxyhydroxides, and borides/borates) for efficient water electrolysis applications. First, we have introduced the general information of water-splitting and the description of anion-mixed electrocatalysts and highlighted their complementary functions of mixed anions. Furthermore, some latest advances of anion-mixed compounds are also categorized for hydrogen and oxygen evolution electrocatalysis. The rationales behind their enhanced electrochemical performances are discussed. Last but not least, the challenges and future perspectives are briefly proposed for the anion-mixed water dissociation catalysts.

Fe, B, and N Codoped Carbon Nanoribbons Derived from Heteroatom Polymers as High-Performance Oxygen Reduction Reaction Electrocatalysts for Zinc-Air Batteries

For zinc-air batteries, it is of great importance to heighten the oxygen reduction reaction (ORR) activity of cathode electrocatalysts. Herein, we synthesized carbon nanoribbons doped with Fe, B, and N as high-activity ORR electrocatalysts by a templating method. Benefiting from the melamine fiber (MF) and B doping, the as-prepared carbon nanoribbon has a high specific surface area, and the improved turnover frequency of Fe sites increases the ORR activity. The as-synthesized Fe-B-N-C electrocatalyst shows an improved half-wave potential and limited current density compared to Fe-N-C, B-N-C, and N-C. Moreover, zinc-air batteries with the Fe-B-N-C electrocatalyst exhibit a higher specific capacity and better long-term durability compared to those with commercial Pt/C. This work provides an effective strategy to synthesize noble-metal-free electrocatalysts for wide applications of zinc-air batteries.

A Co-MOF-derived flower-like CoS@S,N-doped carbon matrix for highly efficient overall water splitting

In this study, we constructed a highly effective, low-cost, non-noble-metal-based electrocatalyst to replace Pt catalysts, with a CoS@SNC catalyst being successfully synthesized. The obtained nanocatalyst was characterized via scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, powder X-ray diffraction studies, and X-ray photoelectron spectroscopy. Herein, an initially prepared N-containing Co MOF formed flower-like particles, which were obtained via a solvothermal method; further it was used for a sulfuration process as a template to achieve an S,N (heteroatom)-doped carbon electrocatalyst with embedded CoS (CoS@SNC). The synthesized flower-like CoS@SNC electrocatalyst derived from a novel MOF showed a uniform distribution of Co, S, N, and C at the molecular level in the MOF and it was rich in active sites, facilitating enhanced electrocatalytic performance. During the HER and OER in 0.1 M KOH solution, to reach a current density of 10 mA cm⁻², lower overpotentials of −65 mV and 265 mV, respectively, were required and Tafel slopes of 47 mV dec⁻¹ and 59.8 mV dec⁻¹, respectively, were seen. In addition, due to a synergistic effect between CoS and the S,N-doped carbon matrix, long-term durability and stability were obtained. This facile synthetic strategy, which is also environmentally favorable, produces a promising bifunctional electrocatalyst.

In this study, we constructed a highly effective, low-cost, non-noble-metal-based electrocatalyst to replace Pt catalysts, with a CoS@SNC catalyst being successfully synthesized.

Designing MOF Nanoarchitectures for Electrochemical Water Splitting

Electrochemical water splitting has attracted significant attention as a key pathway for the development of renewable energy systems. Fabricating efficient electrocatalysts for these processes is intensely desired to reduce their overpotentials and facilitate practical applications. Recently, metal-organic framework (MOF) nanoarchitectures featuring ultrahigh surface areas, tunable nanostructures, and excellent porosities have emerged as promising materials for the development of highly active catalysts for electrochemical water splitting. Herein, the most pivotal advances in recent research on engineering MOF nanoarchitectures for efficient electrochemical water splitting are presented. First, the design of catalytic centers for MOF-based/derived electrocatalysts is summarized and compared from the aspects of chemical composition optimization and structural functionalization at the atomic and molecular levels. Subsequently, the fast-growing breakthroughs in catalytic activities, identification of highly active sites, and fundamental mechanisms are thoroughly discussed. Finally, a comprehensive commentary on the current primary challenges and future perspectives in water splitting and its commercialization for hydrogen production is provided. Hereby, new insights into the synthetic principles and electrocatalysis for designing MOF nanoarchitectures for the practical utilization of water splitting are offered, thus further promoting their future prosperity for a wide range of applications.

Enhancing the efficiency of the hydrogen evolution reaction utilising Fe3P bulk modified screen-printed electrodes via the application of a magnetic field

We report the fabrication and optimisation of Fe3P bulk modified screen-printed electrochemical platforms (SPEs) for the hydrogen evolution reaction (HER) within acidic media. We optimise the achievable current density towards the HER of the Fe3P SPEs by utilising ball-milled Fe3P variants and increasing the mass percentage of Fe3P incorporated into the SPEs. Additionally, the synergy of the application of a variable weak (constant) external magnetic field (330 mT to 40 mT) beneficially augments the current density output by 56%. This paper not only highlights the benefits of physical catalyst optimisation but also demonstrates a methodology to further enhance the cathodic efficiency of the HER with the facile application of a weak (constant) magnetic field.

Enhancing electrocatalytic water splitting by surface defect engineering in two-dimensional electrocatalysts

Overall electrocatalytic water splitting can efficiently and sustainably produce clean hydrogen energy to alleviate the global energy crisis and environmental pollution. Two-dimensional (2D) materials with a unique band structure and surface conformation have emerged as promising electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). However, the intrinsic activities of primitive 2D materials in the catalytic process are still inferior to those of noble metal-based electrocatalysts. Surface defect engineering can modulate the electronic structure of 2D materials and induce new physicochemical properties, promoting their electrocatalytic performance. Herein, this minireview focuses on some recent developments in surface defect engineering, including the contribution of active sites, the derivation of the heterogeneous interface, and the anchoring of active substances, which provides an effective way to further optimize 2D electrocatalysts for water splitting. Furthermore, the typical morphological characteristics, catalytic activity, stability and catalytic mechanism of these 2D electrocatalysts are introduced. We believe that this minireview will help design more efficient and economical electrocatalysts for overall water splitting.

Novel Aggregation-Induced Emission Materials/Cadmium Sulfide Composite Photocatalyst for Efficient Hydrogen Evolution in Absence of Sacrificial Reagent

This work focuses on the development of a novel organic–inorganic photoactive material composited by aggregation-induced emission luminogens (AIE) and CdS. Tetraphenylethene-based AIE (TPE-Ca) is synthesized on CdS to form CdS/TPE-Ca electrode, due to its suitable band structure and potential capability of renewable energy production. The CdS/TPE-Ca electrode presents over three-fold improved photocurrent density and dramatically reduced interfacial resistance, compared with the pure CdS electrode. In addition, the engineering of the band alignment allows the holes to accumulate on the valance band of TPE-Ca, which would partially prevent the CdS from photo-corrosion, thus improving the stability of the sacrificial-free electrolyte photoelectrochemical cell.

V-Doped CoP Nanosheet Arrays as Highly Efficient Electrocatalysts for Hydrogen Evolution Reaction in Both Acidic and Alkaline Solutions

It is of significant necessity to explore inexpensive and high-active electrocatalysts toward hydrogen evolution reaction (HER) in both acidic and basic media. In this work, V-doped CoP nanosheet arrays supported on the carbon cloth (V-CoP/CC) are fabricated though a facile water-bath/phosphorization method. The nanoarray structure on the three-dimensional self-supporting electrode can provide a large electrochemical active surface area with more exposed active sites to accelerate the reaction kinetics. Furthermore, V doping is able to tune the electronic properties and thus enhance the intrinsic catalytic activity of CoP. Consequently, the V-CoP/CC electrode exhibits excellent electrocatalytic activities toward HER in both 0.5 M H₂SO₄ and 1 M KOH solutions with small overpotentials of 88 and 98 mV at a current density of 10 mA cm⁻², respectively. The present work will offer a feasible way to tailor the catalytic activity by hetero-atoms doping toward HER.

In Situ Growth of Amorphous Fe(OH)3 on Nickel Nitrate Hydroxide Nanoarrays for Enhanced Electrocatalytic Oxygen Evolution

Development of highly efficient electrocatalyst for the oxygen evolution reaction (OER) is urgently demanded by the clean hydrogen energy. Herein, in order to further boost the OER activity of metal nitrate hydroxide materials, amorphous Fe(OH)₃ layer is in situ grown on nickel nitrate hydroxide (NiNH) nanoarrays supported on nickel foam (NF) through an interfacial hydrolysis approach, where the loading amount of the Fe(OH)₃ can be simply manipulated by the hydrolysis time. Taking advantage of the synergy of Fe(OH)₃ and NiNH, the optimized Fe(OH)₃@NiNH/NF sample shows a very promising electrocatalytic OER activity in 1 M KOH solution, requiring a very low overpotential of 212 mV vs. reversible hydrogen electrode (RHE) to deliver a geometrical catalytic current density of 100 mA cm^-2 and a low Tafel slope of 49 mV dec^-1. This work provides a new strategy for boosting the electrocatalytic activity of metal hydroxide nitrates through the interface engineering.

Acid-directed morphology control of molybdenum carbide embedded in a nitrogen doped carbon matrix for enhanced electrocatalytic hydrogen evolution

By an acid-directed strategy, β-Mo₂C nanomaterials embedded in a nitrogen doped carbon matrix (β-Mo₂C/NC) with controlled morphology are synthesized and exhibit outstanding HER activities in both acidic and alkaline solutions.

Template-Directed Bifunctional Dodecahedral CoP/CN@MoS2 Electrocatalyst for High Efficient Water Splitting

Designing high efficient and noble metal-free bifunctional electrocatalysts for both hydrogen and oxygen generation is still critical and challenged. In this study, hierarchical dodecahedral-structured CoP/CN@MoS₂ is prepared through a two-step calcination treatment and a solvothermal approach. The metal-organic framework of ZIF-67 is chosen to serve as the template and for providing Co sources, in which ZIF-67 is first transformed to Co nanoparticles embedded in nitrogen-doped carbon polyhedrons and then transformed to CoP/CN. MoS₂ nanosheets are further grown on the surface of dodecahedral-structured CoP/CN with a solvothermal method. Benefiting from the synergistic coupling effect of CoP and MoS₂ and the nitrogen-doped carbon matrix, advanced hydrogen evolution reaction (HER) both in acid and alkaline solution as well as splendid oxygen evolution reaction (OER) performance in alkaline aqueous were achieved. Moreover, the coupling effect of CoP/CN and MoS₂ is disclosed theoretically by density functional theory calculations to validate the increased HER activity. The as-prepared hybrid CoP/CN@MoS₂ not only exhibits decent HER activity in acidic (η₁₀ = 144 mV) and alkaline solutions (η₁₀ = 149 mV), but also exhibits splendid OER activity (η₁₀ = 289 mV) in 1.0 M KOH. This work represents a solid step toward boosting the electrocatalytic kinetics of nonprecious catalysts.

A Roadmap to Low-Cost Hydrogen with Hydroxide Exchange Membrane Electrolyzers

Hydrogen is an ideal alternative energy carrier to generate power for all of society's energy demands including grid, industrial, and transportation sectors. Among the hydrogen production methods, water electrolysis is a promising method because of its zero greenhouse gas emission and its compatibility with all types of electricity sources. Alkaline electrolyzers (AELs) and proton exchange membrane electrolyzers (PEMELs) are currently used to produce hydrogen. AELs are commercially mature and are used in a variety of industrial applications, while PEMELs are still being developed and find limited application. In comparison with AELs, PEMELs have more compact structure and can achieve higher current densities. Recently, however, an alternative technology to PEMELs, hydroxide exchange membrane electrolyzers (HEMELs), has gained considerable attention due to the possibility to use platinum group metal (PGM)-free electrocatalysts and cheaper membranes, ionomers, and construction materials and its potential to achieve performance parity with PEMELs. Here, the state-of-the-art AELs and PEMELs along with the current status of HEMELs are discussed in terms of their positive and negative aspects. Additionally discussed are electrocatalyst, membrane, and ionomer development needs for HEMELs and benchmark electrocatalysts in terms of the cost-performance tradeoff.

Enhanced electrochemical properties of cellular CoPS@C nanocomposites for HER, OER and Li-ion batteries

Cellular CoPS@C nanocomposites were successfully synthesized via a facile two-steps route. The performances of the CoPS@C electrode as a non-noble metal electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) show good activity. On the other hand, the electrochemical investigation of CoPS systems for lithium ion batteries (LIBs) is reported for the first time. The CoPS@C nanocomposite as a novel anode can maintain a capacity of about 713 mA h g-1 after 50 cycles at a current density of 0.2 A g-1, indicating its potential applications in lithium storage. Test results also demonstrate that the CoPS@C nanocomposite exhibit more excellent HER, OER and Li storage performances compared to the bulk CoPS sample.

Fabrication of uniform Ru-doped NiFe2O4 nanosheets as an efficient hydrogen evolution electrocatalyst

Ru-doped NiFe₂O₄ nanosheets exhibit outstanding electrocatalytic hydrogen evolution activity and stability.

Synthesis, structure, fluorescence and electrochemical properties of a new Zn(ii)–organic framework constructed by a tricarboxylic acid ligand

A new efficient fluorescent sensor [Zn₃(L)(HL)(OH)(H₂O)₃]·H₂O (1) for detecting Cr₂O₇²⁻ anions has been synthesized. Moreover, compound 1 has been calcined to prepare a new electrocatalyst R-C@800 for HER.

Homogeneous Metal Nitrate Hydroxide Nanoarrays Grown on Nickel Foam for Efficient Electrocatalytic Oxygen Evolution

Developing facile routes for fabricating highly efficient oxygen evolution reaction (OER) electrocatalysts is in great demand but remains a great challenge. Herein, a novel molten salt decomposition method to prepare 3D metal nitrate hydroxide (MNH, M = Ni, Co, and Cu) nanoarrays homogenously grown on different conductive substrates, especially on nickel foam (NF) for OER applications, is reported. Compared with the as-prepared CoNH/NF and CuNH/NF, NiNH/NF presents a superior electrocatalytic OER activity and stability in an alkaline solution, with a very low overpotential of only 231 mV versus a reversible hydrogen electrode to deliver a geometrical catalytic current density of 50 mA cm^-2 and a low Tafel slope of 81 mV dec^-1 , outperforming most reported transition metal compound catalysts. Structural investigation after the OER process reveals the morphology integrity of the nanoarrays but the formation of metal oxyhydroxide (for NiNH and CoNH) or oxide (for CuNH) as the likely real active species. These metal nitrate hydroxide non-noble metal electrocatalysts can be prepared by an economical and simple method, with enhanced intrinsic activity and long-term stability and durability, which might be new candidates for energy conversion and storage applications.

Recent Advances of Cobalt-Based Electrocatalysts for Oxygen Electrode Reactions and Hydrogen Evolution Reaction

This review summarizes recent progress in the development of cobalt-based catalytic centers as the most potentially useful alternatives to noble metal-based electrocatalysts (Pt-, Ir-, and Ru-based) towards the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) in acid and alkaline media. A series of cobalt-based high-performance electrocatalysts have been designed and synthesized including cobalt oxides/chalcogenides, Co–Nx/C, Co-layered double hydroxides (LDH), and Co–metal-organic frameworks (MOFs). The strategies of controllable synthesis, the structural properties, ligand effect, defects, oxygen vacancies, and support materials are thoroughly discussed as a function of the electrocatalytic performance of cobalt-based electrocatalysts. Finally, prospects for the design of novel, efficient cobalt-based materials, for large-scale application and opportunities, are encouraged.

MOF derived carbon based nanocomposite materials as efficient electrocatalysts for oxygen reduction and oxygen and hydrogen evolution reactions

The escalating global energy demands and the formidable risks posed by fossil fuels coupled with their rapid depletion have inspired researchers to embark on a quest for sustainable clean energy. Electrochemistry based technologies, e.g., fuel cells, Zn-air batteries or water splitting, are some of the frontrunners of this green energy revolution. The primary concern of such sustainable energy technologies is the efficient conversion and storage of clean energy. Most of these technologies are based on half-cell reactions like oxygen reduction, oxygen and hydrogen evolution reactions, which in turn depend on noble metal based catalysts for their efficient functioning. In order to make such green energy technologies economically viable, the need of the hour is to develop new noble metal free catalysts. Porous carbon, with some assistance from heteroatoms like N or S or earth abundant transition metal or metal oxide nanoparticles, has shown excellent potential in the catalysis of such electrochemical reactions. Metal-organic frameworks (MOFs) containing metal nodes and organic linkers in an ordered morphology with inherent porosity are ideal self-sacrificial templates for such carbon materials. There has been a recent spurt in reports on such MOF-derived carbon based materials as electrocatalysts. In this review, we have presented some of this research work and also discussed the practical reasons behind choosing MOFs for this purpose. Different approaches for synthesizing such carbonaceous materials with unique morphologies and doping, targeted towards superior electrochemical activity, have been documented in this review.

Microporous 2D NiCoFe phosphate nanosheets supported on Ni foam for efficient overall water splitting in alkaline media

The development of high-performance non-precious electrocatalysts for both H2 and O2 evolution reactions (HER and OER activities) and overall water splitting is highly desirable but remains a grand challenge. Herein, we report a facile method to synthesize ultrathin, amorphous, porous, oxygen and defect enriched NiCoFe phosphate nanosheets (NSs). Owing to their microporous confinement in a 2D orientation, which can reduce the ion transport resistance during electrochemical processes, and defect enriched structure with higher electrochemically active surface area, these NiCoFe phosphate porous nanosheets supported on nickel foam (NiCoFe phosphate NSs/NF) facilitate the diffusion of gaseous products (H2 and O2) and exhibit remarkable catalytic performance and outstanding stability for both HER, OER and overall water splitting in an alkaline electrolyte (1.0 M KOH). For the OER electrocatalyst, 2D NiCoFe phosphate NSs/NF was oxidized to NiCoFe oxides/hydroxides on the catalyst surface and exhibited remarkable OER activity with a low overpotential of only 240 mV needed to reach a current density of 10 mA cm-2. For HER, 2D NiCoFe phosphate NSs/NF afforded a current density of 10 mA cm-2 at a low overpotential of only -231 mV. Furthermore, employing 2D NiCoFe phosphate NSs/NF as the electrocatalyst for both the anode and the cathode, a water splitting electrolyzer was able to reach 10 mA cm-2 at a cell voltage of 1.52 V with robust durability. Various characterization techniques indicated that the long term stability and the activity for overall water splitting are due to the porosity, the electrochemically active constituents, and synergistic effects. This work could be inspiring in the design of Earth abundant and highly efficient electrocatalysts for overall water splitting, especially for OER.

Hydrothermal synthesis of ternary MoS2xSe2(1−x) nanosheets for electrocatalytic hydrogen evolution

MoS_2xSe_2(1−x) nanosheets exhibit promising electrocatalytic hydrogen evolution activity in acidic media.