Cathodic activation of titanium-supported gold nanoparticles: An efficient and stable electrocatalyst for the hydrogen evolution reaction

Abstract

As-polished titanium (Ti) substrates decorated with dispersed gold nanoparticles (Au NPs/Ti) of various sizes and densities were prepared here to effectively catalyze hydrogen evolution reaction (HER) in 0.5 M H2SO4. These materials were synthesized adopting a facile one-step wet chemical method without using reducing agents, stabilizers, or any chemical pre-treatment, where Ti acts as both the reducing agent and support. This was achieved via soaking the Ti substrates for 30 min in a gold precursor bath as a function of temperature (5-65°C). Morphological characterizations of the synthesized Au NPs/Ti catalysts indicated a size decrease and density increase of loaded Au NPs with the rise of temperature. Cathodic polarization measurements revealed that the catalyst loaded with the highest density of Au NPs exhibited the best HER activity with onset potential (EHER), exchange current density (jo), and Tafel slope (βc) of -44 mV (RHE), 6.0 × 10-3 mA cm-2, and 40 mV decade-1, respectively. This activity has markedly increased upon cathodic activation (cathodic pre-polarization treatment at -2 V (SCE) for 12 h) that yielded a Ti substrate with a porous-like network structure decorated with highly dispersed Au NPs. In addition, a catalytically active TiH2 phase was formed (as evidenced from XRD and XPS) on such a porous substrate. Such cathodically pre-treated catalyst recorded HER electrochemical parameters of -18 mV (RHE), 0.117 mA cm-2, and 38 mV decade-1, thus approaching the commercial Pt/C catalyst (EHER: 0.0 mV, jo: 0.78 mA cm-2, and βc: 31 mV dec-1). The stability of the best catalyst was assessed employing cyclic polarization and chronoamperometry measurements. It exhibited a good stability with improved activity during stability testing.