Single-crystalline NiO octahedrons with (111) facets as a bifunctional electrocatalyst for overall water splitting

Abstract

The production of hydrogen energy through electrocatalysis has garnered significant attention due to its minimal environmental pollution. To achieve cost parity for electrolysis technology, there is a pressing need for a non-precious, stable, and earth-abundant transition metal-based bifunctional catalyst that can efficiently facilitate water splitting. Developing cost-effective and efficient electrocatalysts for overall water splitting remains a significant challenge. Faceted crystals with highly reactive planes have garnered considerable attention for this purpose. In this study, we present the synthesis of octahedron-shaped NiO crystals, in which 100% of the surface is dominated by exposed {111} reactive facets. The octahedron-shaped NiO is demonstrated as a potential bifunctional electrocatalyst for both HER and OER in an alkaline medium. For hydrogen evolution, an overpotential of 371.0 mV is required to achieve a current density of 10 mA cm⁻², whereas for oxygen evolution, an overpotential of 389.6 mV is sufficient to produce a current density of 10 mA cm⁻². Notably, the {111} reactive facets of NiO crystals exhibit a cell potential of 1.99 V for overall water splitting and show excellent stability with negligible current density change over 12 h.