Effects of cyclic current modulation on cathode materials for the hydrogen evolution reaction

Commercial industrial water electrolysers often operate discontinuously. The efficiency of the hydrogen evolution reaction (HER) requires cathode materials to have a high intrinsic electrocatalytic activity. Under intermittent operation, it is desirable that both the activity and the structure of the material remain stable.; In this study, intermittent industrial water electrolysis conditions were simulated in the laboratory with a cyclic current modulation test. A conventional material, commercially pure nickel sheet, and a novel material, amorphous {dollar}rm Nisb{lcub}50{rcub}Cosb{lcub}25{rcub}Psb{lcub}15{rcub}Bsb{lcub}10{rcub}{dollar} melt-spun ribbon were evaluated in 8 M KOH electrolyte at 70{dollar}spcirc{dollar}C. The electrochemical activity of the material was determined with Tafel (overpotential vs. current density) plots and surface structure was assessed with scanning electron microscopy, energy dispersive x-ray analysis and x-ray photoelectron spectroscopy.; Nickel initially deactivated at constant current due to hydrogen absorption and remained deactivated during cyclic modulation. In a lower-purity electrolyte, nickel partially recovered activity during cycling due to surface growth from electrodeposition of iron impurities.; {dollar}rm Nisb{lcub}50{rcub}Cosb{lcub}25{rcub}Psb{lcub}15{rcub}Bsb{lcub}10{rcub}{dollar} deactivated in a similar manner to nickel but partially recovered activity with cyclic modulation. This is attributed to Ni enrichment at the surface via in-situ electrochemical dealloying; elements with lower HER activities were depleted. The amorphous alloy was embrittled under HER conditions.; For as-polished and cyclically modulated nickel and as-polished {dollar}rm Nisb{lcub}50{rcub}Cosb{lcub}25{rcub}Psb{lcub}15{rcub}Bsb{lcub}10{rcub},{dollar} the rate-determining step for the HER at low overpotentials is H adsorption and at high overpotentials is H absorption. For cyclically modulated {dollar}rm Nisb{lcub}50{rcub}Cosb{lcub}25{rcub}Psb{lcub}15{rcub}Bsb{lcub}10{rcub},{dollar} the rate determining step of HER at low overpotentials is H absorption.; With cathodic polarization and cyclic modulation, the surfaces were micro-roughened. After cathodic polarization, surface films on Ni metal and {dollar}rm Nisb{lcub}50{rcub}Cosb{lcub}25{rcub}Psb{lcub}15{rcub}Bsb{lcub}10{rcub}{dollar} were thickened and had a hydroxide character and {dollar}rm Nisb{lcub}50{rcub}Cosb{lcub}25{rcub}Psb{lcub}15{rcub}Bsb{lcub}10{rcub}{dollar} had an increased ratio of Ni:Co.