Hierarchical Cu/Cu2O structure derived from hexagonal Cu9S5 nanocrystal with enhanced electrocatalytic ability for hydrogen evolution reaction

Abstract

A hierarchical structure of Cu nanosheets grown on pyramidal Cu2O was obtained via in-situ electrochemical reduction of hexagonal Cu9S5 nanocrystal. The detailed morphology evolution and corresponding catalytic performances for hydrogen evolution reaction (HER) were discussed. Greatly enhanced HER activities were achieved in the hierarchical Cu/Cu2O. Compared with the pristine Cu9S5 which required an overpotential of −360 mV to attain a current density of 10 mA cm−2, the overpotential was greatly reduced to −120 mV for hierarchically structured Cu/Cu2O. Moreover, the hierarchically structured Cu/Cu2O possessed a much lower value of tafel slope and achieved a high current density of 100 mA cm−2 at −260 mV. The drastically improved HER performances were due to the following two aspects: 1) the huge amount of newly exposed active surfaces (including grain boundries, defects, point vacancies) derived from the in-situ evolution from hexagonal Cu9S5 nanocrystals to hierarchical Cu/Cu2O, proved by the electrochemical surface area (ECSA) analysis; 2) the enhanced charge transfer ability in hierarchical Cu/Cu2O, as proved by the electrochemical impedance spectroscopy (EIS).