NiO@CoxSy nanostructures electrocatalysts designed for efficient alkaline water electrolysis

Abstract

Rational design of composite-structured electrocatalysts presents a promising strategy for enhancing water electrolysis efficiency. In this work, two NiO-based heterostructured electrocatalysts were rationally constructed by coupling NiO with cobalt sulfides possessing different crystalline phases, synthesized via two distinct methods. Despite sharing the same NiO substrate, the two resulting heterostructures exhibit significantly different electrocatalytic performances: NiO@Co₉S₈ material demonstrates superior hydrogen evolution reaction (HER) activity, while the other(NiO@CoS₂) exhibits enhanced oxygen evolution reaction (OER) activity. This finding reveals that the electrocatalytic behavior can be finely tuned by modulating the crystalline structure of the cobalt sulfide component, while keeping the NiO support constant. Notably, the NiO@Co₉S₈ catalyst exhibits excellent HER performance, requiring an overpotential of only 158.8 mV at a current density of 50 mA/cm², the corresponding Tafel slope is 142.72 mV/dec. Conversely, the NiO@CoS₂ electrocatalyst exhibits even stronger OER activity, achieving an overpotential of 340.2 mV at 50 mA/cm² with a Tafel slope of 178.81 mV/dec. Extended stability tests under high current density conditions over 50 h confirmed the exceptional durability of both electrocatalysts in overall water splitting applications. These results underscore NiO@CoS₂ and NiO@Co₉S₈ potential as novel high-efficiency bifunctional catalysts for advanced water electrolysis systems.