The electrochemical surface treatments to improve the stability and activity of a nickel phosphide catalyst for hydrogen evolution reaction in acid media

Abstract

In this work, electrochemical surface treatment methods are reported to improve the activity and durability of electroplated nickel phosphide catalyst for hydrogen evolution reaction (HER) in acid media. The nickel phosphide is receiving a lot of attention because of low cost and remarkable activity, however, the nickel phosphide has a problem on a stability due to its high corrosive in acid media. Therefore, this work investigates a predeposition of Ni-Cu layer and a dealloying of Ni-P catalyst at before and after electroplating of nickel phosphide catalyst, respectively. Because the predeposition of rough Ni-Cu layer is acted as a substitute of catalyst, Ni-P/Ni-Cu/CP catalyst shows 129% larger surface area than Ni-P/CP catalyst. Furthermore, the rough morphology forms the removal pathway of hydrogen bubbles during both of electroplating and HER. Therefore, predeposition of Ni-Cu layer improves the activity and stability of nickel phosphide catalyst, however, it is difficult to prevent the galvanic corrosion of nickel phosphide. Therefore, a dealloying treatment of Ni-P/CP catalyst, conducted by the CV process, is designed to remove ‘isolated Ni’ which arouse the galvani corrosion of Ni-P. As a result, an atomic ratio of phosphorus increases about 186% higher after 20 cycles of dealloying treatment (Ni-P/CPx20) than the Ni-P/CP which does not conduct surface treatment, and kept 77.2% retention of catalytic activity after 6 h of stability test. Furthermore, the Ni-P/CPx20 catalyst showed a lower overpotential (124 mV at -10 mA cm-2) than the Ni-P/CP catalyst (179 mV at -10 mA cm-2) in acidic HER test.