Characterization of electrochemically deposited films from aqueous and ionic liquid cobalt precursors toward hydrogen evolution reactions

By Dushatinski, Thomas; Huff, Clay; Abdel-Fattah, Tarek M.
Published in Applied Surface Science NULL 2016

Abstract

Abstract Electrodepositions of cobalt films were achieved using an aqueous or an ethylene glycol based non-aqueous solution containing choline chloride (vitamin B4) with cobalt chloride hexahydrate precursor toward hydrogen evolution reactions from sodium borohydride (NaBH4) as solid hydrogen feedstock (SHF). The resulting cobalt films had reflectivity at 550 nm of 2.2% for aqueously deposited films (ACoF) and 1.3% for non-aqueously deposited films (NCoF). Surface morphology studied by scanning electron microscopy showed a positive correlation between particle size and thickness. The film thicknesses were tunable between 100 ?m and <300 ?m for each film. The roughness (Ra) value measurements by Dektak surface profiling showed that the {NCoF} (Ra = 165 nm) was smoother than the {ACoF} (Ra = 418 nm). The {NCoFs} and {ACoFs} contained only ? phase (FCC) crystallites. The {NCoFs} were crystalline while the {ACoFs} were largely amorphous from X-ray diffraction analysis. The {NCoF} had an average Vickers hardness value of 84 {MPa} as compared to 176 {MPa} for ACoF. The aqueous precursor has a single absorption maximum at 510 nm and the non-aqueous precursor had three absorption maxima at 630, 670, and 695 nm. The hydrogen evolution reactions over a 1 cm2 catalytic surface with aqueous NaBH4 solutions generated rate constants (K) = equal to 4.9

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