Enhanced performance of nano-electrocatalysts of Pd and PdCo in neutral and alkaline media

Abstract

Pd and PdCo nanostructures are synthesized by a soft-template route to be applied as electrocatalysts. Distinctive morphologies are obtained: nanowire-like structures, with mean diameter d = 33 nm (PdNW), forming an entangled network; nanocubes (PdNC) 64 nm in side, and PdCo(NS) nanospheres 60 nm in diameter. Pd:Co feed mol ratios (2:1) and (5:1) are used. Pd and Pd–Co nanostructures both crystallize in an fcc structure. A glassy carbon (GC) electrode is then modified with these colloidal dispersions, and further characterized by electrochemical methods. The modified PdNW/GC, PdNC/GC, and PdCoNS/GC electrodes are applied in the oxygen reduction (ORR) and oxygen evolution (OER) reactions, in a phosphate buffer pH 7 and 0.1 M NaOH solution. Voltammetric measurements are consistent with a diffusion-controlled mechanism, with a four-electron reduction process in each Pd and PdCo nanoelectrode. Resulting values of kinetic parameters indicate that the relative effectiveness of these solutions in ORR may be ordered as PdCo (5:1)NS/GC ≥ PdCo (2:1)NS/GC > PdNC/GC ≥ PdNW/GC > GC. For the OER, Tafel slopes are measured for the nanosized electrodes in both types of supporting electrolytes. Turnover frequencies estimated in alkaline solution for the OER indicate that nanostructured bimetallic PdCoNS/GC electrodes exhibit better activity than Pd/GC ones.