The enhancement in the performance of ultra-small core-shell Au@AuPt nanoparticles toward HER and ORR by surface engineering.

In this work, ultra-small core-shell (USCS) Au 38.4 @Au 4.1 Pt 57.5 nanoparticles (NPs) with an optimal Pt-to-Au ratio were successfully prepared by the optimal etching treatment of USCS Au@AuPt NPs by Fe(III) ions to remove some exposed Au atoms on their outermost surfaces. The as-prepared USCS Au 38.4 @Au 4.1 Pt 57.5 NPs with Fe(III)-etching treatment for 2 h loaded on carbon black as catalysts (USCS 2h Au 38.4 @Au 4.1 Pt 57.5 -NP/C catalysts) exhibit superior electrocatalytic activity and durability for both the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in acidic media. For instance, the overpotential of USCS 2h Au 38.4 @Au 4.1 Pt 57.5 -NP/C catalysts toward the HER is 13 mV at a current density of -10 mA cm -2 ( η 10 = 13 mV), which is much better than that of commercial Pt/C catalysts ( η 10 = 31 mV). Moreover, their mass activity (63.8 A mg Pt -1 ) is about 16.4 times larger than that of commercial Pt/C catalysts (3.9 A mg Pt -1 ). In addition, they also present better long-term stability. Furthermore, they also show an improved activity toward the ORR in terms of the half-wave potential ( E 1/2 ) (0.89 V vs. RHE), which is more positive by about 38 mV than commercial Pt/C catalysts (0.852 V). In addition, they also show a higher kinetic current density (14.22 mA cm -2 at 0.85 V) and better long-term durability. This etching-treatment strategy can be extended to further improve the catalytic performance of ultra-small Au-based bimetallic or multi-metallic NPs by surface engineering.