Bifunctional NiCo2Se4 and CoNi2Se4 nanostructures: Efficient electrodes for battery-type supercapacitors and electrocatalysts for the oxygen evolution reaction

Abstract We report the fabrication of bimetallic NiCo 2 Se 4 and CoNi 2 Se 4 nanostructures on nickel-foam (Ni-foam) substrates via a potentiostatic-deposition method by adjusting the molar ratio of Ni and Co metals. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses show that burl-like clusters with characteristic fluffy NiCo 2 Se 4 and flake-like CoNi 2 Se 4 hierarchical structures were deposited on the Ni-foam substrates. When used as battery-type electrodes in supercapacitors, both NiCo 2 Se 4 and CoNi 2 Se 4 electrodes exhibited outstanding capacity and good electrochemical properties. The CoNi 2 Se 4 electrode delivered excellent capacity and cycling stability (602 C g –1 at 1 A g –1 and 98.30% retention after 5000 cycles at 40 A g –1 ) when compared to the NiCo 2 Se 4 electrode (353 C g –1 at 1 A g –1 and 96.83% retention after 5000 cycles at 40 A g –1 ). Furthermore, as-deposited NiCo 2 Se 4 and CoNi 2 Se 4 hierarchical structures were employed as efficient electrocatalysts for water oxidation in alkaline solutions. NiCo 2 Se 4 and CoNi 2 Se 4 electrocatalysts showed low overpotentials of 257 and 244 mV in a 1.0 M KOH aqueous solution, respectively. The electrocatalysts also exhibited prolonged stability (NiCo 2 Se 4 and CoNi 2 Se 4 maintained currents of 95.6% and 97.5%, respectively, over 10 h), which makes them comparable to well-known Ni and Co-based catalysts. Collectively, the as-deposited NiCo 2 Se 4 and CoNi 2 Se 4 are the most efficient bifunctional electrodes and electrocatalysts for application in battery-type supercapacitors and the oxygen evolution reaction, respectively, and can potentially be applied for energy conversion and storage processes.