Lead as an effective facilitator for ethanol electrooxidation on Rh catalyst in alkaline media: RhPb/C vs RhRu/C

Abstract

Rh-based catalysts have attracted much attention due to their ability to efficiently break CC bonds in ethanol oxidation reaction(EOR), while pure Rh catalyst have low EOR activity. It is important to improve the EOR activity of Rh-based catalyst. Herein, we have been successfully synthesized carbon supported Rh, Rh-Pb, and Rh-Ru alloy catalysts. The catalytic activity of RhPb/C for ethanol oxidation is 0.96 mA/cm2, which is 8 times than that of Rh/C. The steady-state current density of RhPb/C at 0.5 V is 17 and 20 times higher than that of RhRu/C and Rh/C, respectively. The results show that adding a small portion of lead significantly enhanced the Rh-based catalyst activity, stability, and anti-poisoning ability during EOR in alkaline media. Moreover, the Tafel slope of RhPb/C catalyst for EOR is 118 mVdec−1, which is similar with that of Pt/C(116 mVdec−1), while the Tafel slope of RhRu/C is 77 mVdec−1, similar to that of Rh/C(87 mVdec−1). The CO-stripping potential of RhRu/C, Rh/C and RhPb/C is 0.535 V, 0.573 V and 0.601 V, respectively. Combined with the cyclic voltammetry, chronoamperometry, CO-stripping and Tafel analysis, it is concluded that for RhRu/C catalyst, the improvement of EOR is mainly attributed to the bifunctional mechanism, while for RhPb/C catalyst, the ensemble effect and the electronic effect of Pb is essential to the improvement of EOR.