▎ 摘　　要

NOVELTY - Preparing cobalt catalyst comprises (i) preparing a reduced graphene oxide in which cobalt oxide is dispersed by spray pyrolysis of cobalt precursor solution and graphene oxide, (ii) carrying out primary oxidation or reduction reaction by heat-treating the cobalt oxide-dispersed reduced graphene oxide at 300-600 degrees C, and (iii) carrying out secondary oxidation at 250-350 degrees C to form cobalt hollow nanoparticles supported by reduced graphene oxide. USE - The cobalt catalyst is useful in electrodes and membrane electrode assembly for water electrolysis, useful in water cell and for oxygen evolution reaction (claimed). ADVANTAGE - The cobalt catalyst has electrochemical reaction activity suitable for electrolysis, and has improved catalyst stability under acidic high potential condition. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for cobalt catalyst for oxygen evolution reaction, comprising cobalt trioxide hollow nanoparticles dispersed on a reduced graphene oxide support, and at least one cobalt oxide including cobalt(III) oxide and cobalt oxide.