Novel carbon nanotube supported Co@Ag@Pd formic acid electrooxidation catalysts prepared via sodium borohydride sequential reduction method

Abstract

At present, monometallic Pd/CNT, bimetallic Pd50Ag50/CNT, Pd50Co50/CNT, Ag50Pd50/CNT catalysts are prepared by NaBH4 co-reduction method. Ag@Pd/CNT catalysts at varying Ag:Pd ratios and Co@Ag@Pd/CNT catalysts at varying Co:Ag:Pd atomic ratios are prepared via NaBH4 sequential reduction method. These catalysts are characterized with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The characterization results show that all catalysts are successfully synthesized at desired molar composition. Furthermore, Ag and Co addition change electronic state of catalyst. Formic acid electrooxidation measurements of these catalysts are performed by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) to investigate the effect of Ag and Co addition through the formic acid electrooxidation activity. Considering the bimetallic catalysts, Ag20@Pd80/CNT exhibits better catalytic activity than the one of other bimetallic catalysts. It is clear that the addition of Ag to Pd improves electrocatalytic activity due to synergetic effects. Furthermore, Co0.072@Ag19.98@Pd79.98/CNT has the best activity, lowest charge transfer resistance (Rct), and a long term stability. EIS and CA results are in a good agreement with CV results. Co0.072@Ag19.98@Pd79.98/CNT is a promising catalyst for Direct formic acid fuel cells.