A Central Role of Nitrogen Atoms in a Highly Efficient Catalyst for Cathodic Hydrogen Evolution.

Abstract

Platinum (Pt) usually offers the most effective active centre for hydrogen evolution reaction (HER), because of the optimal trade-off between the adsorption and desorption of hydrogen atoms (H*) on Pt atoms. Herein, we report an unusual result regarding the active centre of a HER catalyst, which was synthesized by electrodepositing traces of Pt nanoparticles (NPs) into a porous nitrogen-rich dodecahedron matrix derived from zeolitic imidazolate framework-8. With an ultra-low Pt loading of 2.76 μg cm -2 , the N-Pt bonded catalyst can produce a current density of 117 mA cm -2 for the HER in 1.0 M H 2 SO 4 at an overpotential of 50 mV, while the commercial Pt/C (300 μg Pt cm -2 ) can only reach 50 mA cm -2 under the same conditions. Cyclic voltammetry demonstrates that both the H* adsorption and the Pt oxidation are not allowed to occur on this catalyst, due to a full surface coverage of the trace Pt NPs by imidazole. The results from the specially designed experiments indicate that the imidazole N atoms may act as proton anchor-sites for the HER due to their electron donor nature. Density functional theory calculations also support a catalytic HER mechanism centred at the Pt-supported N active centre, which needs a Gibbs free energy of H* absorption (∆ G H* ) significantly smaller than the absolute value of ∆ G H* on the Pt (111) surface. We hope that the results of this study will encourage the research on novel N-centred catalysts for the HER.