Study On Cobalt Complex Oxides As Al-H₂O₂ Semi-fuel Cell Cathode Catalyst

The fuel cells using H₂O₂ as oxidant have high energy density, simple structure, easy operation and are independent on the environments with air. Therefore, they are good candidates of underwater and space power. Current catalysts for hydrogen peroxide electro-reduction are noble metals, which are efficient for catalyzing hydrogen peroxide reduction, but cause significant decomposition of hydrogen peroxide. Besides, they are expensive. Therefore, research on the catalysts having high activity, high selectivity, good stability and low-cost is of great significance.In this paper, Co₃O₄ and NiCo₂O₄ were synthesized using a precipitation method and a sol-gel method, respectively, and characterized by X-diffraction spectroscopy (XRD) and transmission electron microscopy (TEM). Results indicated that Co₃O₄ and NiCo₂O₄ are all spinel structure, and have an average diameter of around 17nm and 5nm, respectively. Co₃O₄/C/Ni and NiCo₂O₄/C/Ni electrodes were prepared using Co₃O₄ and NiCo₂O₄ powder as catalyst.Their performance for hydrogen peroxide electro-reduction in KOH solution were investigated. Results demonstrated that the optimum ratio of carbon to catalyst was 3:7 and the optimum KOH electrolyte concentration was 3 mol·L^-1.Stability test shown that Co₃O₄/C/Ni and NiCo₂O₄/C/Ni electrodes exhibited excellent stability for reduction of hydrogen peroxide in alkaline electrolyte. When the concentration of hydrogen peroxide was no more than 0.4 mol·L^-1,the decomposition reaction of hydrogen peroxide is neglectable, and the main reaction was direct electro-reduction of hydrogen peroxide on the surface of electrode.Al-H₂O₂ semi-fuel cells were fabricated using Co₃O₄ and NiCo₂O₄ as cathode catalyst,respectively.Results shown that employing LF6 Al alloy as anode can obtain better cell performance than LF21 Al alloy as anode. Using Co₃O₄ cathode can obtain better cell performance than using NiCo₂O₄ cathode. An Al-H₂O₂ semi-fuel cell constructed using Co₃O₄ as cathode catalyst, Al alloy (LF6) as anode,3 mol·L^-1 KOH +1.5 mol·L^-1 H₂O₂ as catholyte and 3mol·L^-1 KOH as anolyte displayed an open circuit voltage of 1.45V and a peak power density of 190 mW·cm^-2 at 255 mA·cm^-2 running on 1.5 mol·L^-1 hydrogen peroxide at room temperature.