S-doped AuPd aerogels as high efficiency catalysts for the oxygen reduction reaction by balancing the ratio between bridging S22− and apical S2− ligands

Abstract

In this work, AuPd–S_B67A33 aerogels with an optimal ratio of bridging S₂²⁻ and apical S²⁻ ligands (abbreviated as S_B and S_A, respectively) are synthesized by conformal growth of Pd onto S-doped AuPb aerogels. It is found that the content of S species (PbS and PbS₂) in the S-doped AuPb aerogels has to be optimized by the amount of NaBH₄ during the reduction of networks of Au nanoclusters (Au NCs) connected by Pb²⁺ ions, which can guarantee the presence of an appropriate ratio of Pd_2.8S and PdS₂ in the resulting AuPd–S_B67A33 aerogels, and thus in turn can downshift the d-band center of Pd to an optimal level. Moreover, the formation of alloys AuPd, Pd_2.8S and PdS₂ on their surface can not only achieve high dispersion of Pd active sites, but also improve their anti-oxidation resistance, which in turn can greatly improve their catalytic activity towards the ORR. Furthermore, the as-prepared AuPd–S_B67A33 aerogels indeed exhibit excellent electrocatalytic activity towards the ORR (e.g., E_onset = 1.067 V and E_1/2 = 0.970 V) and better durability in alkaline media, which are 35 mV and 85 mV higher than those (1.032 V and 0.885 V) of commercial Pt/C catalysts. In addition, their j_k (41.67 mA cm⁻²), mass activity (2.60 A mg_Pd⁻¹) and specific activity (2.67 mA cm⁻²) at 0.9 V vs. RHE are 12.5, 20 and 12 times higher than those (3.34 mA cm⁻², 0.13 A mg_Pt⁻¹ and 0.22 mA cm⁻²) of commercial Pt/C catalysts.