▎ 摘　　要

Ru- or Ir-based precious metal oxides are typically applied as oxygen evolution reaction (OER) catalysts, owing to their high activity in acidic media and at high operating potentials. However, their expense and unsatisfactory durability prevent their application as anode catalysts in proton exchange membrane water electrolyzer stacks. This study presents the synthesis of various noble metal-free cobalt oxides supported on reduced graphene oxide catalysts using ultrasonic spray pyrolysis following different heat treatment processes. The catalyst prepared through additional thermal reduction and subsequent oxidation exhibits highly dispersed and Co3+ ion-rich hollow Co3O4 spheres on crumpled reduced graphene oxide sheets, thereby providing additional catalytically active sites for the OER. Under severe potential cycling, this catalyst exhibits acid-stability and a robust nanostructure, thereby demonstrating an extraordinarily superior stability in comparison to that of a commercially available Ir black catalyst. (C) 2021 Elsevier Ltd. All rights reserved.