Superior performance and stability of anion exchange membrane water electrolysis: pH-controlled copper-cobalt oxide nanoparticle for oxygen evolution reaction
The application of electrocatalysts having a high activity to a practical water electrolysis cell is a crucial challenge for the production of pure hydrogen and commercialization of the water electrolyzer. Herein, nanosized Cu0.5Co2.5O4 catalyst synthesized by co-precipitation with adjusting pH is applied to the anion exchange membrane water electrolysis (AEMWE) cell as an anode, which is demonstrated to have higher efficiency and stability than noble metal. The Cu0.5Co2.5O4 is changed in the composition of Cu/Co and morphology as pH increases and forms into nanoparticles at pH 11, where oxygen vacancy is formed by etching of Cu. In density functional theory study, the electronic structure of Co modified by Cu in Co3O4 lattice leads to optimal adsorption strength, showing a free energy diagram in which thermodynamically favorable potential of Cu0.5Co2.5O4 (1.756 V vs. reversible hydrogen electrode, RHE) than of Co3O4 (1.951 V vs. RHE). The Cu0.5Co2.5O4 catalyst is recorded overpotential of 285 mV at 10 mA cm-2 in 1 M KOH. Furthermore, the AEMWE cell using Cu0.5Co2.5O4 as an anode is exhibited a current density of 1.3 A cm-2 at 1.8 V, which is the highest performance among the reported papers and maintains around 80% energy conversion efficiency for 100 hours.