Carbon nanotubes embedded with PtRu nanoparticles as methanol fuel cell electrocatalysts

In this study, we investigate the influence of Pt:Ru atomic ratio on the electrochemical activity of PtRu/carbon nanotube (CNT) catalysts in the electrooxidation of methanol. Bimetallic PtRu alloy nanoparticles were embedded onto the CNTs by chemical impregnation, followed by the refluxing of ethylene glycol. Four types of catalysts, namely Pt100Ru0, Pt75Ru25, Pt50Ru50, and Pt25Ru75, were synthesized for the investigation of the compositional effect. The crystalline size of PtRu nanocatalysts generally decreased with the Ru atomic ratio, i.e., from 4.34 to 2.77 nm. The measurement of electrooxidation of methanol was carried out in 1 M H2SO4 electrolyte containing 0.5 M CH3OH with PtRu/CNT, catalysts using cyclic voltammetry (CV) and AC electrochemical impedance spectroscopy (EIS). CV analysis revealed that the Pt50Ru50/CNT electrode had the highest electrochemical activity, owing to its lower onset potential and higher ratio of the forward to reverse anodic peak current. EIS combined with equivalent circuit reflected that after cycling, Pt50Ru50/CNT electrode has not only a much lower charge-transfer resistance, but also higher capacitance than Pt100Ru0/CNT. This enhancement of electrochemical activity can be ascribed to the presence of Pt–Ru atomic pair sites in the bimetallic alloys, which play an important role in regenerating the inactive Pt–COads sites, according to the bifunctional theory.