Electrocatalytic activity of porous Ni–Fe–Mo–C–LaNi5 sintered electrodes for hydrogen evolution reaction in alkaline solution

Abstract

The hydrogen evolution reaction (HER) was studied in 6 M KOH solution at temperatures ranging between 303 K and 353 K on a porous Ni–Fe–Mo–C–LaNi₅ electrode. By using steady-state polarization curves and electrochemical impedance spectroscopy (EIS), the surface roughness factor and the intrinsic activities of the porous Ni–Fe–Mo–C–LaNi₅ electrode have been determined. The Tafel slope of the best-performing porous Ni–Fe–Mo–C–LaNi₅ cathode materials is 140 mV dec⁻¹, and the exchange current density is 9.9 × 10⁻⁴ A cm⁻² at elevated temperature. The roughness factor is 8600, which was obtained for the HER on studied electrodes in 6 M KOH solution at 323 K temperature using the EIS data and complex nonlinear least square (CNLS) approximation method. These techniques also permitted us to determine the mechanism and kinetics of the HER on the investigated electrode. The overall experimental data indicates that the porous Ni–Fe–Mo–C–LaNi₅ electrode yields electrocatalytic activity in the HER. Nevertheless, when the effect of the surface roughness is taken into consideration, it is demonstrated that alloying Ni with Fe, Mo, C and LaNi₅ results in an increased electrocatalytic activity in the HER when comparing to pure Ni. This is due to an improved intrinsic activity of the material, which is explained on the basis of the synergism among the catalytic properties of Ni and of Fe, Mo, and induced by C embedded into Ni–Fe matrix and Ni–Fe–Mo matrix. LaNi₅ enhances the H adsorption on the electrode surface and mainly plays a role of hydrogen storage for HER.