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

Cubic Co 3 O 4 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/cm 2 were achieved at overpotentials of 328, 363, and 382 mV for anodes loaded with 1 mg/cm 2 of small, medium, and large sized Co 3 O 4 nanoparticles, respectively. The activity correlates with the BET surface area of the isolated particles. A plot of the electrochemical overpotential at 10 mA/cm 2 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.