Restructuring A Gold Nanocatalyst By Electrochemical Treatment To Recover Its H-2 Evolution Catalytic Activity

Gold nanoparticles have been demonstrated to be an attractive alternative to Pt catalyst for the hydrogen evolution reaction in water. Herein, we report a detailed investigation on the impacts of surface chemistry and particle shape on the apparent catalytic activity of gold nanoparticles. To make a fair comparison, the apparent catalytic current densities of gold nanoparticles are normalized by their relative electrochemical surface area, which is determined using either the [Fe(CN)(6)](3-)/[Fe(CN)(6)](4-) redox couple or the underpotential deposition of Pb. Cetyltrimethylammonium bromide-stabilized gold nanoparticles having spherical (Au-SP), rod (Au-NR) or bipyramidal shape (Au-BP) show negligible catalytic activity in a 0.5 M H2SO4 solution. Elimination of the surfactant by dynamic potential cycling between -0.25 to 0 V vs. RHE resulted in a significant enhancement of catalytic activity. The activity slightly depends on the particle shape, e.g. the Au-NR showed higher intrinsic activity as compared with the Au-BP or Au-SP counterparts. A drastic enhancement of activity was achieved when conditioning these gold nanoparticles in a larger potential range, e.g. -0.25 to 1.5 V vs. RHE. Under these conditions, Au-NR and Au-BP were corroded, generating tiny spherical nanoparticles, whereas the Au-SP were corroded, generating a coral-like morphology. The restructured Au-BP, Au-NR and Au-SP showed similar catalytic activities that are among the best performances ever reported for Pt-free catalysts. The best gold catalyst operates with a moderate onset overpotential of 50 mV, high catalytic turnover frequency of 0.56 s(-1) at 200 mV overpotential.