Synthesis and Characterisation of Pd-Ni-Sn Electrocatalyst for Use in Direct Ethanol Fuel Cells

Abstract

One critical challenge to commercialise direct ethanol fuel cells (DEFCs) is catalyst poisoningassociated with the strongly adsorbed CO intermediate on catalyst’s surface at low temperature. The present worktherefore aimed to develop a highly electrochemically active catalyst which is durable to the presence of COcontaminant. Different Pd-Ni-Sn compositions impregnated on carbon black were synthesised by sodium borohydridereduction method which can be classified as mono-, binary- and ternary-catalyst systems at which 20%w Pd/C wasutilised as a base catalyst. The addition of 5-20%w Ni and/or 5-20%w Sn metals was found to increase catalyticactivity and catalyst stability for ethanol oxidation reaction (EOR). Several diagnostic techniques were employed toassess their suitability for use in DEFCs including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS),transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive spectrometry (SEM-EDX)and electrochemical techniques. The XRD and XPS spectra verified that the existence of Pd, Ni and Sn in the aspreparedcatalysts was in the oxidation state of Pd0 and Pd2+, Ni2+ (in form of Ni(OH)2) and Sn4+ (in form of SnO2),respectively, which were known to promote the EOR and CO oxidation. The average particle size was in the range of5.46-10.56 nm for all samples. By using SEM-EDX, it was found that the actual ratios of metal loadings were relativelysimilar to the desired compositions and their surface morphology was uniformly distributed. Moreover, electrocatalyticactivity towards EOR was evaluated using cyclic voltammetry in 1M ethanol (in 1M KOH). Among various catalyticcompositions, 20%w Pd/C containing 10%w Ni and 10%w Sn exhibited excellent catalytic activity and CO tolerance asthe maximum current density of 146 mA cm-2 for EOR and the highest electrochemical surface area were obtainedwhile lowering the CO-stripping peak potential to -0.525 V (vs Ag/AgCl).