THE HYDROGEN EVOLUTION REACTION ON AMORPHOUS NICKEL AND COBALT ALLOYS

The mechanism of the hydrogen evolution reaction (HER) on Ni70P30, Co7 2P28, Ni40Co23P37 and Ni72Fe1P27 was studied by impedance spectroscopy and steady-state polarization measurements. Only the Ni-Fe-P presents a good electrocatalytic activity with an overpotential approximate to 200 mV lower than that for mild steel or Ni (the traditional material s used as cathodes in water electrolysers). Impedance studies of the H ER were carried out on these amorphous alloys and it was concluded tha t 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 a nd Ni-Co-P the mechanism is Volmer-Tafel with the Volmer step being th e r.d.s. From the rate constants the following catalytic sequence was determined: Ni-Fe-P > Co-P > Ni-Co-P > Ni-P.