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Water electrolysis is a highly efficient route to produce ideally clean H2 fuel with excellent energy conversion efficiency and high gravimetric energy density, without producing carbon traces, unlike steam methane reforming, and it resolves the issues of environmental contamination via replacing the conventional fossil fuel. Particular importance lies in the advancement of highly effective non-precious catalysts for the oxygen evolution reaction (OER). The electrocatalytic activity of an active catalyst mainly depends on the material conductivity, accessible catalytically active sites, and intrinsic OER reaction kinetics, which can be tuned via introducing N heteroatoms in the catalyst structure. Herein, the efficacious nitrogenation of CuS was accomplished, synthesized using a hydrothermal procedure, and characterized for its electrocatalytic activity towards OER. The nitrogen-doped CuO@CuS (N,CuO@CuS) electrocatalyst exhibited superior OER activity compared to pristine CuS (268 and 602 mV), achieving a low overpotential of 240 and 392 mV at a current density of 10 and 100 mA/cm2, respectively, ascribed to the favorable electronic structural modification triggered by nitrogen incorporation. The N,CuO@CuS also exhibits excellent endurance under varied current rates and a static potential response over 25 h with stability measured at 10 and 100 mA/cm2. [ABSTRACT FROM AUTHOR]

Summary: Replacing oxygen in an oxide‐based material with sulfur can produce improved flexibility and more efficient electron transport in its structure leading to enhanced electrical performance. Herein, facile template‐free growth of free‐standing cobalt (II, III) oxide (Co3O4) on Ni foam via a mild hydrothermal technique followed by its transformation to cobalt (II, III) sulfide (Co3S4) via an ion‐exchange is reported. The microstructural morphology, phase, and porosity of the prepared Co3O4 and Co3S4 are characterized by FESEM, XRD, Raman, XPS, TEM, and BET analyses. The electrochemical performance of the Co3S4 film with a microporous morphology is considerably superior to that of Co3O4, exhibiting a high specific capacitance of 1604 F g−1 (905 F g−1 for Co3O4), the excellent restorative ability of ~99% at 1 A g−1 (~96% for Co3O4), and good retention of 98% at 10 A g−1 (~70% for Co3O4). The Co3S4 electrode shows excellent capacitance endurance even after 10 000 charge/discharge cycles and a high energy density of 128.32 Wh kg−1 at 0.72 kW kg−1. A fabricated symmetric Co3S4 supercapacitor device also reveals superior charge/discharge, restorative, and retention performances compared to a Co3O4 one. The excellent supercapacitive performance of phase‐transformed Co3S4 electrode is due its large electrochemically active surface area along with synergetic effect of small charge transfer resistance and high relative diffusion coefficient. [ABSTRACT FROM AUTHOR]

• An anti-corrosive FeO-coated CuCo 2 S 4 catalyst is fabricated for HER catalysis. • Low overpotential of 107 mV at 10 mAcm─2 and small Tafel slope of 136 mVdec─1 are obtained. • Excellent electrocatalytic HER activity and long–term sustainability are observed. • The excellent catalytic performance is attributed to the synergy between FeO and CuCo 2 S 4. An anti-corrosive FeO@CuCo 2 S 4 electrocatalyst, with highly-active catalytic sites, is fabricated using a mild hydrothermal and magnetron sputtering growth technique. FeO@CuCo 2 S 4 shows excellent hydrogen evolution reaction (HER) in an alkaline KOH electrolyte with a low overpotential of 107 mV at 10 mA/cm2 and a small Tafel slope of 136 mV/dec. Moreover, long-term stability tests at various current densities, up to 100 mA/cm2, demonstrate its excellent sustainability. The excellent HER catalytic performance and stability are attributed to the synergy between FeO and CCS elucidated by density functional theory, which is aroused from electrocatalytically activated surface, anti-corrosive surface, and the improved electronic conductivity. [ABSTRACT FROM AUTHOR]

The enhancement in intrinsic catalytic activity and material conductivity of an electrocatalyst can leads to promoting HER activity. Herein, a successful nitrogenation of CoS 2 (N–CoS 2) catalyst has been investigated through the facile hydrothermal process followed by N 2 annealing treatment. An optimized N–CoS 2 catalyst reveals an outstanding hydrogen evolution reaction (HER) performance in alkaline as well as acidic electrolyte media, exhibiting an infinitesimal overpotential of −0.137 and −0.097 V at a current density of −10 mA/cm2 (−0.309 and −0.275 V at −300 mA/cm2), corresponding respectively, with a modest Tafel slope of 117 and 101 mV/dec. Moreover, a static voltage response was observed at low and high current rates (−10 to −100 mA/cm2) along with an excellent endurance up to 50 h even at −100 mA/cm2. The excellent catalytic HER performance is ascribed to improved electronic conductivity and enhanced electrochemically active sites, which is aroused from the synergy and mutual interaction between heteroatoms that might have varied the surface chemistry of an active catalyst. • N–CoS 2 catalyst was fabricated on the microporous Ni foam architecture via a hydrothermal procedure pursued by N 2 treatment. • Small overpotentials in alkaline (−0.137 V) and acidic (−0.97 mV) electrolyte media and associated low Tafel slope. • Excellent long–term sustainability at low and high current rate in alkaline and acidic electrolyte media. • The incorporation of heteroatoms leads to the varied electrocatalytically active sites and improved conductivity. [ABSTRACT FROM AUTHOR]