Size-Dependent Activity of Co₃O₄ Nanoparticle Anodes for Alkaline Water Electrolysis

Cubic Co3O4 nanoparticles with average diameters of 5.9, 21.1, and 46.9 nm (hereafter small, medium, and large) have been synthesized and characterized by pXRD, TEM, and BET. The nanoparticles were loaded onto Ni foam supports for evaluation as anodes for water electrolysis in 1.0 M KOH. Current densities of 10 mA/cm2 were achieved at overpotentials of 328, 363, and 382 mV for anodes loaded with 1 mg/cm2 of small, medium, and large sized Co3O4 nanoparticles, respectively. The activity correlates with the BET surface area of the isolated particles. A plot of the electrochemical overpotential at 10 mA/cm2 against the log of the BET surface area gives a linear relation with a slope of −47 ± 7 mV/dec, showing unequivocally that the activity increase is a function of accessible catalyst surface area.