Modulating Electronic Structure and Atomic Insights into the Novel Hierarchically Porous PdCuFe Trimetallic Alloy Aerogel for Efficient Oxygen Reduction.

The high cost of noble Pd/Pt required for the oxygen reduction reaction (ORR) in the cathode restricts the wide applications of fuel cells. In this study, the synthesis of a novel Pd 3 CuFe 0.5 aerogel electrocatalyst is successfully demonstrated using self-assembly and lyophilization techniques, employing a mild reducing agent. The resulting aerogel electrocatalyst exhibits a distinctive 3D network structure, possessing a substantial BET-specific surface area of 75.19 m 2  g -1 . It is worth noting that the optimized Pd 3 CuFe 0.5 aerogel demonstrates exceptional ORR performance with a high half-wave potential of 0.92 V versus RHE, a significant limiting current density of 7.6 mA cm -2 , and the excellent electrocatalytic stability, superior to the reported noble metal electrocatalysts, with the ORR activity decays only 4.9% after 16 000 s. In addition, the Pd 3 CuFe 0.5 aerogel electrocatalyst shows superior cycling stability for ≈120 h at a charge/discharge current density of 10 mA cm -2 , indicating its promising application in fuel cells. Furthermore, the resulting composite aerogel possesses excellent hydrogen evolution reaction and ethanol oxidation reaction activity. The density functional theory calculations show that the partial oxidation of Pd 3 CuFe 0.5 aerogel leads to a negative shift of the d-band center, which energetically optimizes the binding strength of *O intermediates, therefore accelerating the ORR activity.