Tailor-designed nanowire-structured iron and nickel oxides on platinum catalyst for formic acid electro-oxidation.

This investigation is concerned with designing efficient catalysts for direct formic acid fuel cells. A ternary catalyst containing iron (nano-FeO) and nickel (nano-NiO) nanowire oxides assembled sequentially onto a bare platinum (bare-Pt) substrate was recommended for the formic acid electro-oxidation reaction (FAOR). While nano-NiO appeared as fibrillar nanowire bundles ( 82 nm and 4.2 μm average diameter and length, respectively), nano-FeO was deposited as intersecting nanowires ( 74 nm and 400 nm average diameter and length, respectively). The electrocatalytic activity of the catalyst toward the FAOR depended on its composition and loading sequence. The FeO/NiO/Pt catalyst exhibited 4.8 and 1.6 times increases in the catalytic activity and tolerance against CO poisoning, respectively, during the FAOR, relative to the bare-Pt catalyst. Interestingly, with a simple activation of the FeO/NiO/Pt catalyst at -0.5 V Ag/AgCl/KCl (sat.) in 0.2 mol L NaOH, a favorable Fe/Fe transformation succeeded in mitigating the permanent CO poisoning of the Pt-based catalysts. Interestingly, this activated a-FeO/NiO/Pt catalyst had an activity 7 times higher than that of bare-Pt with an -122 mV shift in the onset potential of the FAOR. The presence of nano-FeO and nano-NiO enriched the catalyst surface with extra oxygen moieties that counteracted the CO poisoning of the Pt substrate and electronically facilitated the kinetics of the FAOR, as revealed from CO stripping and impedance spectra.