A strategy to promote the ORR electrocatalytic activity by the novel engineering bunched three-dimensional Pd-Cu alloy aerogel

Pd has been considered as a potential substitution of the Pt-based electrocatalyst for oxygen reduction reaction (ORR) in the fields of fuel cells, however, the binding strength between the bare surface and the intermediates is much stronger than that on Pt, leading to its inferior ORR activity. Alloying noble metals with nonprecious metals provides a cost-effective strategy for electrocatalyst design. In this work, we have demonstrated a novel Pd₃Cu aerogel electrocatalyst derived from a mild reduction agent via the self-assembly and freeze-drying technique. The resulting catalyst shows a typical three-dimensional and “pearl-like” aerogel structure. Combining the structural features and optimized chemical compositions, the Pd₃Cu aerogel exhibits remarkable pH-independent performance over the commercial Pt/C electrocatalyst. Notably, the optimized Pd₃Cu aerogel displays excellent ORR activity with a half-wave potential of 0.90 V vs RHE, with a limiting current density of 5.8 mA/cm² under the alkaline conditions, which is among the best of the reported noble metal-based ORR electrocatalysts. In addition, the resulting Pd₃Cu aerogel delivers excellent hydrogen evolution reaction (HER) and ethanol oxidation reaction (EOR) performance. Furthermore, the density functional theory (DFT) calculations reveal that the unique partially oxidized Pd₃Cu aerogel has led to a shift-down of the d-band center of the active sites, which energetically optimizes the binding strength of the adsorbed O intermediate during the ORR process, therefore accelerating the ORR activity. These findings provide a new pathway for the integrated engineering of geometric and electronic structures of metal alloys to improve their electrocatalytic property.