Nickel selenide as a high-efficiency catalyst for oxygen evolution reaction

Abstract

A metal-rich form of Ni-selenide, nickel subselenide, Ni₃Se₂ has been investigated as a potential oxygen evolution electrocatalyst under alkaline conditions for the first time. The Ni₃Se₂ phase has a structure similar to the sulfur mineral heazlewoodite, which contains metal–metal bonding. The electrocatalytic activities of Ni₃Se₂ towards OER were seen to be at par with or even superior to the transition metal oxide based electrocatalyst in terms of onset overpotential for O₂ evolution as well as overpotential to reach a current density of 10 mA cm⁻² (observed at 290 mV). The electrocatalytic Ni₃Se₂ films were grown by electrodeposition on conducting substrates and the deposition parameters including the pH of the electrolytic bath, deposition potential, and substrate composition were seen to have some influence on the catalytic activity. So far, Ni₃Se₂ films deposited on the Au-coated Si substrate was seen to have the lowest overpotential. Annealing of the as-deposited electrocatalytic films in an inert atmosphere, enhanced their catalytic efficiencies by decreasing the overpotential (@10 mA cm⁻²) as well as increasing the current density. The structure and morphology of these films has been characterized by powder X-ray diffraction, scanning and transmission electron microscopy, Raman, and X-ray photoelectron spectroscopy. Catalytic activities were investigated through detailed electrochemical studies under alkaline conditions, including linear sweep voltammetry, chronoamperometric studies at constant potential, electrochemical surface area determination and calculation of the Tafel slope. The Faradaic efficiency of this catalyst has been estimated by reducing the evolved O₂ in a RRDE set-up which also confirmed that the evolved gas was indeed O₂. In addition to low overpotentials, these Ni₃Se₂ electrodeposited films were seen to be exceptionally stable under conditions of continuous O₂ evolution for an extended period (42 h).