Co-based antiperovskite nitrides (CuNCo3/NF and CoN0.73Co3/NF) for overall water splitting are designed. An alkaline electrolyzer composed of CuNCo3/NF and CoN0.73Co3/NF has low cell voltage of 1.53 V at 10 mA cm−2 and maintains remarkable stability.

Adjustable antiperovskite cobalt-based nitrides as efficient electrocatalysts for overall water splitting

Urea oxidation reaction (UOR) assisted water‐splitting is a promising approach for effective treatment of urea‐rich waste‐water at the anode and parallelly generate green‐hydrogen (H2) energy at the cathode via hydrogen evolution reaction (HER). However, facile designing and fabricating robust and cheap electrodes derived from earth‐abundant materials is a great challenge. This work reports the synthesis of vanadium sulfide (VS2) micro‐flowered structure via solvent‐assisted hydrothermal method using ethylene glycol as an additive in the aqueous‐based reaction medium, which has imparted a significant effect on the morphology and the crystallinity of the VS2. In addition, in contrast to the VS2 electrode fabricated in a pure aqueous medium, the ethylene glycol mediated VS2 electrode upon coupling as a cathode and anode in an HER||UOR vs reversible hydrogen electrode (RHE)‐based three‐electrode configuration demonstrates a significantly reduced overall urea decomposition potential of 1.38 V at a current density of 10 mA cm−2 as compared to the conventional water‐splitting of 1.75 V vs RHE. The obtained high‐performance electrocatalytic activity on UOR and HER can be ascribed to the influence of ethylene glycol solvent, particularly on VS2 growth, morphology, and crystallinity, favoring the formation of abundant catalytic sites with facile electrolyte diffusion and electrolysis.

Solvent modulated self‐assembled VS2 layered microstructure for electrocatalytic water and urea decomposition

The high overpotential required for the oxygen evolution reaction (OER)-due to the transfer of four protons and four electrons-has greatly hindered the commercial viability of water electrolysis. People have been committed to the development of alternative precious metal-free OER electrocatalysts, especially electrocatalysts for alkaline media. In this study, we report the application of Sr6(Co0.8Fe0.2)5O15 (SCF-H) perovskite oxide with a hexagonal phase structure in the field of OER electrocatalysis. Synthesized by a simple and universal sol-gel method, the SCF-H perovskite oxide shows prominent OER activity with an overpotential of 318 mV at a current density of 10 mA cm-2 and a Tafel slope of only 54 mV dec-1, which is significantly better than the cubic phase structure SrCo0.8Fe0.2O3-δ (SCF-C), benchmark noble-metal oxide RuO2 and Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF). Compared with cubic SCF-C, the hexagonal SCF-H perovskite oxide has abundant surface oxygen species (O22-/O-), a faster charge transfer rate, and a higher electrochemical surface area. In addition, the DFT calculation results show that the center of the O p-band of SCF-H is closer to the Fermi level than that of SCF-C, which leads to the better OER activity of SCF-H. This work finds that the new hexagonal structure perovskite may become a promising OER electrocatalyst.

Hexagonal perovskite Sr6(Co0.8Fe0.2)5O15 as an efficient electrocatalyst towards the oxygen evolution reaction.

A large variety of nickel-based catalysts has been investigated for the oxygen evolution reaction (OER) in alkaline media. However, their reported activity, as well as Tafel slope values, vary greatly. To understand this variation, we studied electrodeposited Ni80 Fe20 OOH catalysts with different loadings at varying rotation rates, hydroxide concentrations, with or without sonication. We show that, at low current density (<5 mA cm-2 ), the Tafel slope value is ≈30 mV dec-1 for Ni80 Fe20 OOH. At higher polarization, the Tafel slope continuously increases and is dependent on rotation rate, loading, hydroxide concentration and sonication. These Tafel slope values are convoluted by non-kinetic effects, such as bubbles, potential-dependent changes in ohmic resistance and (internal) OH- gradients. As best practise, we suggest that Tafel slopes should be plotted vs. current or potential. In such a plot, it can be appreciated if there is a kinetic Tafel slope or if the observed Tafel slope is influenced by non-kinetic effects. 

Non‐Kinetic Effects Convolute Activity and Tafel Analysis for the Alkaline Oxygen Evolution Reaction on NiFeOOH Electrocatalysts

Coupling of ruthenium with hybrid metal nitrides heterostructure as bifunctional electrocatalyst for water electrolysis.

The development of a low-cost and high-efficiency oxygen evolution reaction (OER) catalyst is essential to meet the future industrial demand for hydrogen production by electrochemical water splitting. Given the limited reserves of noble metals and many competitive applications in environmental protection, new energy, and chemical industries, many studies have focused on exploring new and efficient non-noble metal catalytic systems, improving the understanding of the OER mechanism of non-noble metal surfaces, and designing electrocatalysts with higher activity than traditional noble metals. This Review summarizes the research progress of anode OER catalysts for hydrogen production by electrochemical water splitting in recent years, for noble metal and non-noble metal catalysts, where non-noble metal catalysts are highlighted. The categories are as follows: (1) Transition metal-based compounds, including transition metal-based oxides, transition metal-based layered hydroxides, and transition metal-based sulfides, phosphides, selenides, borides, carbides, and nitrides. Transition metal-based oxides can also be divided into perovskite, spinel, amorphous, rock-salt-type, and lithium oxides according to their different structures. (2) Carbonaceous materials and their composite materials with transition metals. (3) Transition metal-based metal-organic frameworks and their derivatives. Finally, the challenges and future development of the OER process of water splitting are discussed.

Guangli He

Papers

Research Progress of Oxygen Evolution Reaction Catalysts for Electrochemical Water Splitting.