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–SB67A33 aerogels with an optimal ratio of bridging S22− and apical S2− ligands (abbreviated as SB and SA, 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 Pd2.8S and PdS2 in the resulting AuPd–SB67A33 aerogels, and thus in turn can downshift the d-band center of Pd to an optimal level. Moreover, the formation of alloys AuPd, Pd2.8S 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–SB67A33 aerogels indeed exhibit excellent electrocatalytic activity towards the ORR (e.g., Eonset = 1.067 V and E1/2 = 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 jk (41.67 mA cm−2), mass activity (2.60 A mgPd−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 mgPt−1 and 0.22 mA cm−2) of commercial Pt/C catalysts.