Nanostructured CuCo2S4, a mixed metal thiospinel, is found to be a benchmark electrocatalyst for oxygen evolution reaction (OER) in this study with a low overpotential, a low Tafel slope, a high durability, and a high turnover frequency (TOF) at lower mass loadings. Nanosheets of CuCo2S4 are realized from a hydrothermal synthesis method in which the average thickness of the sheets is found to be in the range of 8–15 nm. Aggregated nanosheets form a highly open hierarchical structure. When used as an electrocatalyst, CuCo2S4 nanosheets offer an overpotential value of 310 mV at a 10 mA cm–2 current density, which remains consistent for 10000 measured cycles in a 1 M KOH electrolyte. A chronoamperometric study reveals constant oxygen evolution for 12 h at a 10 mV s–1 scan rate without any degradation of the activity. Furthermore, the calculated mass activity of the CuCo2S4 electrocatalyst is found to be 14.29 A/g and to afford a TOF value of 0.1431 s–1 at 310 mV at a mass loading of 0.7 mg cm–2. For comparison, nanostructures of Co3S4 and Cu0.5Co2.5S4 have been synthesized using a similar method followed for CuCo2S4. When compared to the OER activities among these three thiospinels and standard IrO2, CuCo2S4 nanosheets offered the highest OER activities at the same mass loading (0.7 mg/cm2). Extensive X-ray photoelectron spectroscopy and electron paramagnetic resonance analyses for a mechanistic study reveal that introduction of Cu into the Co3S4 lattice enhances the oxygen evolution and kinetics by offering Cu2+ sites for utilitarian adsorption of OH, O, and OOH reactive species and also by offering a highly active high-spin state of octahedral Co3+ for OER catalysis.

Short peptides have attracted much attention due to their easy synthesis, diverse functionalisation possibilities, low cost, possibility to make a large range of hierarchical nanostructures and most importantly their high biocompatibility and biodegradability.

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Multifunctional materials are quite fascinating and conveniently serve the purpose where two or more efficient materials are required. Herein, we report such a bifunctional material which is new by its morphology and enables the provision of a reliable power output as a supercapacitor electrode as well as oxygen evolution in water splitting as an efficient electrocatalyst material. A coral-shaped NiCo2O4 nanostructure was developed by the oriented attachment pathway of nanocrystal building blocks, which can provide efficient energy storage and energy conversion bifunctional properties which are not realized earlier. Here, the less stable and highly reactive (111) planes of NiCo2O4 small single crystals grow at the expense of the (100) planes in the ⟨111⟩ direction to decrease the total interfacial free energy and get attached with each other to form the coral-shaped nanostructure. The outstanding battery-like capacitive features (e.g., maximum specific capacitance of 1297 F·g–1 or specific capacity of 180 mA·h·g–1, energy density of 45 W·h·kg–1 at high charge–discharge rates, and a minimum stability of 10,000 cycles) with a high Coulombic efficiency (>96%) are attributed to faster ion intercalation between an electrode and an electrolyte and redox pseudocapacitance, high conductivity, and highly porous coral morphology that decreases diffusion distances and exposure of mixed metal valence at the surface. In addition to these features, a higher Ni2+ content enhances the adsorption of OH– species on the material surface and a high electrochemically active surface area of the material attributed to a lower overpotential (0.29 V) and longer stability at a higher current density during precious metal-free electrocatalytic oxygen evolution reaction.