Core–shell Ru/NiOx@graphene composite aerogels as efficient bifunctional electrocatalysts for overall water splitting

Abstract

The development of bifunctional catalysts with excellent catalytic properties is an important focus in alkaline electrolytic water splitting, and accordingly, the construction of novel crystalline/amorphous heterojunction catalysts has been proven to be an effective strategy to realize bifunctional electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this study, uniformly dispersed and highly active Ru/NiO_x heterojunctions anchored onto GA composites (Ru/NiO_x@GA) were successfully synthesized by freeze-drying and calcination processes. The results of XRD, TEM, and XPS analyses indicated strong interactions in the Ru/NiO_x heterojunction, where the NiO_x in the outer layer exerted a squeezing effect on the Ru in the inner layer, generating charge transfer from Ni to Ru. As an excellent bifunctional electrocatalyst, Ru/NiO_x@GA required overpotentials of only 32 mV (HER) and 237 mV (OER) to achieve a current density of 10 mA cm⁻² in a 1 M KOH electrolyte while exhibiting robust cycling stability for over 200 h. A low decomposition voltage of 1.53 V and high faradaic efficiency of 100% were obtained for the assembled overall water splitting (OWS) device. All these properties were attributed to the Ru/NiO_x interaction, resulting in charge-enriched Ru sites and oxidation state-corrected Ni sites. This study highlights the unique advantages of the synergistic effect of both crystalline/amorphous heterojunctions and GA, which provides a new approach to prepare GA-based materials for advanced multifunctional electrocatalytic applications.