Electrocatalysts for bifunctional oxygen/air electrodes

Oxygen reduction and evolution have been studied with respect to the development of bifunctional air/oxygen electrode (BFE). Three groups of catalysts have been prepared: (i) CuxCo3-xO4 by thermal decomposition of mixed nitrate and carbonate precursors; (ii) thin films of Co-Ni-Te-O and Co-Te-O were deposited by vacuum co-evaporation of Co, Ni and TeO2 and (iii) CoxOv/ZrO2 films were obtained by electrochemical deposition. The electrochemical behavior of the chemically synthesized catalysts was studied on classical bilayered gas diffusion electrodes (GDEs), where the catalyst is in form of powder. The GDE catalyzed with vacuum deposited catalysts was prepared by direct deposition of the catalyst on gas-supplying layer, thus creating a ready-to-use gas diffusion electrode. Catalysts prepared electrochemically were first deposited on Ni foam and than pressed onto the gas-supplying layer. Different catalysts deposited on classical and originally designed GDEs were compared by their electrochemical performances. Cu0.3Co2.7O4 deposited on a classical bilayered GDE with loading of 50 mg cm(-2) exhibits stable current-voltage characteristics after 200 charge-discharge cycles in a real metal hydride-air battery. The electrochemically and vacuum deposited CoxOv/ZrO2, Co-Ni-Te-O and Co-Te-O films exhibit much higher mass activity compared to Cu0.2Co2.8O4 for both oxygen reduction and evolution reactions. The difference is that the loading of electrochemically and vacuum deposited films is 0.06 mg cm(-2) only, which is a substantial advantage from a practical viewpoint. (C) 2008 Elsevier B.V. All rights reserved.