Simple vapor-solid-reaction route for porous Cu₂O nanorods with good HER catalytic activity

In this work, a simple vapor-solid reaction route was designed for the preparation of porous Cu2O nanorods with good HER catalytic performance, employing Cu(OH)2 nanorods as the precursor and ethylene glycol as the reductant. The reaction was carried out under an Ar atmosphere in the temperature range of 200-280 °C for 2 h. The final product was characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), (high-resolution) transmission electron microscopy (TEM/HRTEM), X-ray photoelectron spectroscopy (XPS), HAADF-STEM-EDS mapping and nitrogen adsorption-desorption isotherms. It was found that pure Cu2O was always obtained in the temperature range of 200-280 °C and well retained the outline of the precursor. Nevertheless, electrochemical experiments showed that porous Cu2O nanorods prepared at 200 °C (labeled as Cu2O-200) exhibited much stronger HER catalytic activity than those obtained at higher temperatures, which were labeled as Cu2O-220, Cu2O-240, Cu2O-260 and Cu2O-280, respectively. In an alkaline solution of 1.0 M KOH, Cu2O-200 presented a low overpotential of ∼184 mV, a small Tafel slope of 106 mV dec-1, and a high durability over 20 h at a current density of 10 mA cm-2. The above good performances were attributed to the high surface area and high-speed electronic transmission networks of Cu2O-200, which provided fast transportation and short diffusion path for the electrolyte and evolved H2 bubbles.