Electrocatalytic properties of electrodeposited Ni-15Mo cathodes for the HER in acid solutions: Synergistic electronic effect

The electrocatalytic evolution of H-2 in acid solution on well-adhering layers of Ni and Ni-Mo alloy (15 at.% Mo) electrodeposited from a citrate bath onto a glassy carbon disc has been investigated. The kinetic parameters and the rate constants of the forward and backward reactions of Volmer, Heyrovsky and Tafel steps for the hydrogen evolution reaction (HER) were deduced from the linear polarization and electrochemical impedance spectroscopy (EIS) measurements. The high apparent catalytic activity was interpreted with a porous structure of the Ni-15Mo deposits having an enlarged number of active sites. The main factor influencing outstandingly high electrocatalytic activity of the Ni-15Mo electrodes as a cathode material in terms of HER in acid media has been explained by the synergistic electronic effects. The synergy was interpreted with theoretical predictions based on the complex band structure calculations and magnetic properties of Ni-Mo which suggest a pronounced density of states in d orbitals at the Fermi level obtained by alloying Ni with the threshold content of paramagnetic Mo. The enhanced catalytic activity of the Ni-15Mo catalyst in comparison with the Ni catalyst in an acid solution was discussed within the framework of a bifunctional Volmer-Heyrovsky mechanism in which the simple cooperative functioning of the alloy components is mediated via a rapid intra-(inter) H-adatoms diffusion. Ni-sites act as an H-source for Mo-sites where the ion-atom recombination (and H-2 desorption) takes place. As a results, the ion-atom recombination reaction rate increases in comparison to pure Ni. (c) 2005 Elsevier B.V. All rights reserved.