Consecutive layers of Ni(OH)2 and Co(OH)2 were electrodeposited on stainless steel current collectors for preparing charge storage electrodes of high specific capacity with potential application in hybrid supercapacitors. Different electrodes were prepared consisting on films of Ni(OH)2, Co(OH)2, Ni1/2Co1/2(OH)2 and layered films of Ni(OH)2 on Co(OH)2 and Co(OH)2 on Ni(OH)2 to highlight the advantages of the new architecture. The microscopy studies revealed the formation of nanosheets in the Co(OH)2 films and of particles agglomerates in the Ni(OH)2 films. Important morphological changes were observed in the double hydroxides films and layered films. Film growth by electrodeposition was governed by instantaneous nucleation mechanism. The new architecture composed of Ni(OH)2 on Co(OH)2 displayed a redox response characterized by the presence of two peaks in the cyclic voltammograms, arising from redox reactions of the metallic species present in the layered film. These electrodes revealed a specific capacity of 762 C g−1 at the specific current of 1 A g−1. The hybrid cell using Ni(OH)2 on Co(OH)2 as positive electrode and carbon nanofoam paper as negative electrode display specific energies of 101.3 W h g−1 and 37.8 W h g−1 at specific powers of 0.2 W g−1 and 2.45 W g−1, respectively.
Estudaram-se as propriedades semicondutoras de filmes passivos formados em aço inoxidável AISI 304 e em ligas de base Ni (Alloy 600) em soluções tampão de borato. Os filmes foram estudados por medidas de capacidade (Mott-Schottky ) e de fotocorrente. Estudaram-se também filmes formados em aço inoxidável AISI 304 por oxidação ao ar, à temperatura de 350ºC. Os resultados mostram que a estrutura electrónica dos filmes é comparável à de uma heterojunção do tipo p-n, onde as cargas de espaço desenvolvidas nas interfaces filme -metal e filme -electrólito devem ser consideradas. O estudo electroquímico está de acordo com os resultados analíticos que demonstram que os filmes de óxido são, em todos os casos, compostos por uma região interna rica em óxido de crómio e por uma região externa rica em óxido de ferro.The semiconducting properties of passive films formed on AISI 304 stainless steel and Alloy 600 in borate buffer solution were studied by capacitance (Mott-Schottky approach) and photocurrent measurements. Oxide films formed on 304 stainless steel in air at 350 ºC have also been studied. The results obtained show that, in all cases the electronic structure of the films is comparable to that of a pn heterojunction in which the space charges developed at the metal-film and film-electrolyte interfaces have also to be considered. This is in accordance with analytical results showing that the oxide films are in all cases composed of an inner region rich in chromium oxide and an outer region rich in iron oxide.
Controlling the surface morphology of mixed nickel manganese oxides prepared by electrodeposition and thermal annealing for use as charge storage electrodes.
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