Influence of the composition and crystalline phase of electrodeposited CoNi films in the preparation of CoNi oxidized surfaces as electrodes for urea electro-oxidation

Abstract

Oxidized species of CoNi have been obtained by means of electrodeposition of CoNi films and posterior electro-oxidation, to obtain electrodes able to be catalysts of oxidative reactions in alkaline medium. The products of electro-oxidation formed, which depend on the composition and the crystal phase of CoNi deposits, have been identified; for this, Co-fcc, Co-hcp, Co7Ni3-fcc, Co7Ni3-hcp, Co5Ni5-fcc and Ni-fcc films have been electrodeposited and oxidized. The influence of the crystalline phase of the films in the nature of the superficial oxides formed has been demonstrated: the electrodes prepared from CoNi-fcc films contained _-CoxNi(1−x)(OH)2, while those prepared from Co7Ni3-hcp films contained Co2NiO4and _- CoxNi(1−x)(OH)2. The catalytic behaviour of the electro-oxidized electrodes for urea electrooxidation was evaluated. Separate tests were performed to differentiate the influence of the composition and the crystalline structure of the initial films and, therefore, of the different oxidized species formed. The electrodes prepared by electro-oxidation of the Co7Ni3-hcp films show better electro-catalytic performance for urea's oxidation than those obtained by oxidation of the Co7Ni3-fcc, because they induce higher intensity, lower onset potential and lesser simultaneous oxygen evolution, becoming a good anode for ureelectro-oxidation in urea electrolysis for hydrogen production or waste water treatment