Porous PdWM (M = Nb, Mo and Ta) Trimetallene for High C1 Selectivity in Alkaline Ethanol Oxidation Reaction

Abstract

Direct ethanol fuel cells are among the most efficient and environmentally friendly energy-conversion devices and have been widely focused. The ethanol oxidation reaction (EOR) is a multielectron process with slow kinetics. The large amount of by-product generated by incomplete oxidation greatly reduces the efficiency of energy conversion through the EOR. In this study, a novel type of trimetallene called porous PdWM (M = Nb, Mo and Ta) is synthesized by a facile method. The mass activity (15.6 A mgPd-1) and C1 selectivity (55.5%) of Pd50W27Nb23/C trimetallene, obtained after optimizing the compositions and proportions of porous PdWM, outperform those of commercial Pt/C (1.3 A mgPt-1, 5.9%), Pd/C (5.0 A mgPd-1, 7.2%), and Pd97W3/C bimetallene (9.5 A mgPd-1, 14.1%). The mechanism by which Pd50W27Nb23/C enhances the EOR performance is evaluated by in situ Fourier transform infrared spectroscopy and density functional theory calculations. It is found that W and Nb enhance the adsorption of CH3CH2OH and oxophilic high-valence Nb accelerates the subsequent oxidation of CO and -CHx species. Moreover, Nb promotes the cleavage of C-C bonds and increases the C1 selectivity. Pd60W28Mo12/C and Pd64W27Ta9/C trimetallene synthesized by the same method also exhibit excellent EOR performance.