Promotion of PdCu/C Catalysts for Ethanol Oxidation in Alkaline Solution by SnO₂ Modifier

The development of high performance PdCu/C catalysts through manipulation of reduction temperatures and addition of SnO₂ promoter has been elucidated systematically in order to enhance ethanol oxidation reaction (EOR) performance. The structure, morphology, surface species, and electroactivity of the PdCu/C and SnO₂-modified PdCu/C catalysts are characterized by use of X-ray diffraction, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry. For the PdCu/C catalysts, the ratio of the forward anodic peak current density to that of the reverse, that is, the I_f/I_b ratio, the degree of alloying (D_alloy), grain size, and EOR performance increases as the reduction temperature increases to 570K. However, severe sintering at 670K deteriorates EOR performance. Therefore, 570K is a suitable reduction temperature for the preparation of PdCu/C catalysts with fine alloy structure, small crystal size, good D_alloy, good anti-poisoning ability, and excellent EOR performance. For the SnO₂ modified PdCu/C catalysts, addition of 20wt% Sn may cause a large amount of SnO₂ to form on the surface and block the active site of the catalysts, thus decreasing EOR performance. However, addition of 10wt% Sn promotes stability in EOR performance, attributable to the significant amount of PdSn phase in the bulk and SnO₂ species on the surface, which enhance the CO oxidation ability and electrochemical surface area. Consequently, based on the chronoamperometric measurements after 1hr, the EOR activity of PdCu/C catalysts with 10wt% SnO₂ modification is enhanced by approximately 230% compared with the as-reduced sample.