ИСТИНА

The development of non-platinum catalysts for hydrogen evolution reaction (HER) is important for the optimization of the process of ultra pure hydrogen production. Such hydrogen is necessary for hydrogen energetics. The cathode materials including iron group metals and refractory metals (Mo, W, Re) attract the interest of investigators for a long time [1]. It had been shown that very high currents of HER can be achieved at these cathodes. It was believed, in the basis of classical ideas that the dependence of HER velocity on the enthalpy of metal-hydrogen bond has a «volcano» form [2,3]. The optimum value of MH bond energy should be close to that of platinum metals. Consequently, the cathode materials containing metals from the ascending and descending branches of volcano plot should be effective catalysts for HER since their electronic properties are similar to platinum. It has been shown that CoMo and NiMo cathodes [4] and even the modification of CoNi alloys surface by molybdenum compounds [5,6] are very perspective for HER catalysis. However, both theoretical and experimental investigations carried out in the early 2000s revealed [7] that the nature of processes occurring at the surface of such cathodes in the course of HER is much more complicated. The oxide layers are present at the surface of such metals as molybdenum and tungsten even under condition of cathode polarization. As the surface is covered by oxides, the true position of Mo and W on volcano curve is debatable. Therefore, the investigations of HER kinetics at cathodes containing refractory metals are not complete, and the future studies are really needed. The voltammetric characteristics of HER at CoMo, CoW and NiRe alloys prepared by the electrolysis were obtained in the present study. The stability of cathode materials under the conditions of hydrogen evolution was evaluated. A phenomenological modeling of HER at these cathodes was performed. It has been shown that the insertion of Mo, W and Re in the composition of cathode materials causes the increase of the part of electrode surface occupied by hydrogen adatoms under the equilibrium conditions up to 1. The catalytic effect of these metals towards HER is associated with the considerable increase of Volmer reaction rate. The impedance studies at the cathodes materials under study were carried out under the conditions of hydrogen evolution. The experimental data can be explained by the equivalent circuit for two-step electrode reaction with the adsorption of intermediate (in our case the intermediate is Hads). It should be mentioned that the double layer capacities calculated from Nyquist plots were unusually high. It allows us to suppose the existence of oxide layer at the surface of cathode, which retains even under conditions of HER. Research was carried out with support of Russian Foundation for Basic Research in terms of grant №14-03-00813