Uniform distribution of Ni3V2O8 nanoparticles over N-doped RGO in a hybrid nanostructure demonstrates efficient and durable electrocatalytic alkaline hydrogen evolution activity with a low overpotential (η10) of 43 mV.

Tuning of morphology and the electronic structure through substitution in the crystal lattice can enhance the performance of electrocatalysts. In view of this, the present work is focused on one-step hydrothermal fabrication of graphite paper (GP)supported cobalt carbonate hydroxide (Co 2 (CO 3 )(OH) 2 /GP) nanostructures and its nickel-and manganese-substituted products, Co 1.9 Ni 0.1 (CO 3 )(OH) 2 /GP and Co 0.95 Mn 0.05 CO 3 /GP, respectively. This is followed by the investigation of their crystal structure, morphology, and electrocatalytic oxygen evolution activity. Our findings showed modification of the electronic structure in substituted cobalt carbonate hydroxides. In addition, specific and electrochemically active surface areas were also enhanced in Co 1.9 Ni 0.1 (CO 3 )(OH) 2 /GP and Co 0.95 Mn 0.05 CO 3 /GP compared to pure Co 2 (CO 3 )(OH) 2 /GP. It was noted that Ni-and Mn-substituted Co 2 (CO 3 )(OH) 2 exhibited dramatically enhanced oxygen evolution reaction (OER) performance in 1.0 M KOH. In addition, the mechanism of the OER was explored experimentally to reveal the origin of their enhanced electrocatalytic activity. Our findings also established the relatively superior performance of Co 1.9 Ni 0.1 (CO 3 )(OH) 2 /GP and Co 0.95 Mn 0.05 CO 3 /GP compared to the commercial RuO 2 electrocatalyst for oxygen evolution in alkaline media. It was also inferred that Co 1.9 Ni 0.1 (CO 3 )(OH) 2 /GP exhibited the best performance as indicated by the lowest overpotential (∼ 266 mV) in achieving 10 mA cm −2 current density, a small Tafel slope (∼ 44.8 mV dec −1 ), quite low chargetransfer resistance (∼ 0.72 Ω), and excellent durability. Thus, Ni-substituted Co 2 (CO 3 )(OH) 2 nanostructures could be employed as promising, efficient, and durable electrocatalysts for the OER in alkaline media.

The present work is focused on the protective-agent-free synthesis of interconnected copper cobaltite (CuCoO) nanochains by temperature-controlled solvothermal method followed by post-thermal treatment of the precursors. Furthermore, CuCoO interconnected nanochains are employed as electrocatalyst for water oxidation in alkaline medium for the first time. Extensive studies of physiochemical properties showed the formation of interconnected 1D nanochains of CuCoO exhibiting a larger specific surface area (139.5 m g) and enhanced electrochemical water oxidation ability. It delivered excellent mass activity (∼50.0 A g), high anodic current density (∼124.9 mA cm at 1.75 V versus reversible hydrogen electrode), and turnover frequency (∼4.26 × 10 s) in 1.0 M KOH. These CuCoO nanochains also demonstrated low overpotential (∼351 mV) and good cycling stability (1000 cycles) in strong alkaline media. The fabricated CuCoO nanochains could be a good alternative to the commercial OER electrocatalysts (RuO and IrO) and also advantageous to the development of efficient, cost-effective, and durable electrocatalysts for electrochemical water splitting.

To date, conventional fossil fuels have been considered the main energy source for modern civilization. [1] The nonrenewable nature and continuous depletion of fossil fuels and the increasing CO 2 emission levels necessitate the development of cost-effective renewable energy conversion/storage systems. [2][3][4][5] In this context, hydrogen, as a fuel, is considered an important alternative to many conventional energy resources owing to its several advantages, such as facile energy storage/carrier, high energy density, and zero-emission upon combustion. [6][7][8] Hydrogen has applications in heat generation, [9] refining processes in industry, [10] and provides electricity in stationary and transport/ vehicle. [11] Hydrogen can be manufactured using a variety of methods, such as hightemperature steam reforming, water electrolysis, solar water splitting-thermolysis, and biomass conversion. [12] Among these methods, steam reforming is the preferred method; it fulfills %96% of global hydrogen demand. [13,14] However, this process requires high temperatures (700-1100 °C) and fossil fuels/natural hydrocarbons, and it is accompanied by greenhouse gas (CO 2 ) emissions. [15][16][17] Among various hydrogen production technologies, water electrolysis can be considered a major contributor to the production of ultrapure hydrogen (>99.9%); moreover, water electrolysis is environmentally benign. In addition, the electrolysis of water in alkaline media is a highly cost-effective, sustainable, and industrially viable method for hydrogen production. [18] However, efficient hydrogen production through water electrolysis is limited by the high overpotential and sluggish kinetics of the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER). [11] The OER involves four-electron transfer pathways under acidic and alkaline conditions. Further, OER is associated with many other energy conversion and storage processes/devices, such as solar fuel production [2] and metal-air batteries. [19] The OER is a four-electron transfer process and has a relatively higher overpotential than the HER and a complex reaction mechanism; hence, OER can be considered the rate-determining step (RDS) for hydrogen production through water electrolysis. [20] Furthermore, the OER has unusually low rate constants and high

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