Electrochemical Characterization of Pd and PdCo nanostructures

AGUIRRE MARIA DEL CARMEN, URRETA SILVIA

Buenos Aires

Workshop; 1st Argentine-German Workshop (A-G nanobio 2017) on Nanotechnology and Nanobiosensors; 2017

INTI_Buenos Aires

Pd and Pd-Co nanostructures are synthesized by a soft-template chemical route, with distinctive morphologies: nanowires (NW), nanocubes (NC), and nanospheres (NS). Pd and Pd-Co nanostructures both crystallize in an fcc structure. Nanowires 33 nm in diameter and nanocubes 64 nm in side are obtained in the case of pure Pd while for Pd-Co nanospheres 60 nm in average diameter result. Two Pd:Co feed mol ratios (2:1) and (5:1) were used and the composition of the nanospheres was corroborated by energy-dispersive X-ray analysis (EDX). A glassy carbon (GC) electrode was then modified with these colloidal dispersions, and the systems were further characterized by electrochemical methods. The modified PdNW/GC, PdNC/GC, and PdCoNS/GC electrodes are electrochemically characterized with the oxygen reduction (ORR) and oxygen evolution (OER) reactions, in a 0.1 M NaOH and phosphate buffer pH 7 solution. Measurements in 0.1 M NaOH solution, demonstrated a mechanism of 4-electron reduction from O2 to H2O, controlled by diffusion, and an irreversible chemical reduction in all the Pd and PdCo nanoelectrodes. The electrochemical surface area (ESA) is evaluated and it is used to obtain the turnover frequency in ORR and OER [1, 2]. Kinetic parameters as Tafel slope, turnover frequency TOF(s-1) allowed us to classify the effectiveness in ORR as PdCo(5:1)NS/GC> PdCo(2:1)NS/GC> PdNC/GC  PdNW/GC>GC. For the OER, Tafel slopes of 47-44 mV/dec in the low section and of 125-239 mV/dec in the upper one are measured for nanosized electrodes. Turnover frequencies (TOF) (s-1) for the OER demonstrate that combined nanstructured PdCoNS/GC electrodes exhibit better activity than Pd/GC ones.- [1] C-H. Lee, C-C lieng,H-P Chiou, C-R Liu, C-H Huang, Electrochim Acta 59 (2012) 587-591.-[2] B.S.Yeo and A.T.Bell, J.Am.Chem.Soc. 133(2011)5587-5593.