The hydrogen evolution reaction on amorphous nickel and cobalt alloys

Abstract

The mechanism of the hydrogen evolution reaction (HER) on Ni 70P 30, Co 72P 28, Ni 40Co 23P 37 and Ni 72Fe 1P 27 was studied by impedance spectroscopy and steady-state polarization measurements. Only the Ni-Fe-P presents a good electrocatalytic activity with an overpotential ≈200 mV lower than that for mild steel or Ni (the traditional materials used as cathodes in water electrolysers). Impedance studies of the HER were carried out on these amorphous alloys and it was concluded that Ni-Fe-P is the only material to present a Volmer-Heyrovsky mechanism with the Heyrovsky step being the r.d.s. In contrast, on Co-P, Ni-P and Ni-Co-P the mechanism is Volmer-Tafel with the Volmer step being the r.d.s. From the rate constants the following catalytic sequence was determined: Ni-Fe-P > Co-P > Ni-Co-P > Ni-P.