Electrocatalytic Activities of Oxygen Reduction Reaction on Pd/C and Pd–B/C Catalysts

Abstract

The investigation of electrocatalysis of oxygen reduction reaction (ORR) on non-Pt electrodes is of great interest to address the current technical bottleneck of using costly and rare metal Pt in the cathodes of low-temperature fuel cells. The present work presents a comparative study of ORR on carbon supported Pd and B-doped Pd (with ca. 7 at. % B doping) nanocatalysts with well-controlled particle sizes, dispersions, and loadings (both with 20 wt % Pd). It is found that the Pd–B/C exhibits a modestly higher electrocatalytic activity toward ORR: the specific activity is enhanced by factors of ca. 2.0 and 2.7 on Pd–B/C as compared to that on Pd/C in acidic media at 0.85 and 0.90 V, respectively. In contrast, the corresponding enhancement factors are ca. 1.3 and 1.6, respectively, in alkaline media. To understand the promoted ORR activity by B-doping, density functional theory (DFT) calculations are applied, revealing weakened adsorption of the O-containing species on B-doped Pd surfaces, consistent with the XPS and CO stripping results. Despite the modest improvement at this moment, it raises the hope of further developing Pd-based ORR catalysts as well as the concern of reasonable comparison of two sets of non-Pt catalysts.