Time-Dependent Surface Structure Evolution of NiMo\nFilms Electrodeposited Under Super Gravity Field as Electrocatalyst\nfor Hydrogen Evolution Reaction

The\nsurface structures of the electrodeposited NiMo films from\ncompact to porous structure are adjusted by the combination of gravity\nacceleration and electrodeposition time. The evolution mechanism of\nsurface structure is discussed based on the protrusion growth theory.\nThe dependence of catalytic activity of the NiMo films for hydrogen\nevolution reaction (HER) on surface structure evolution is studied.\nThe results indicate that compact NiMo layer is first electrodeposited,\nand then protrusions are formed. Finally, the protrusions rapidly\ngrow and form a porous structure. It is found that only the compact\nNiMo films are electrodeposited under normal gravity condition due\nto a long induced time for the protrusions formation. Under super\ngravity field, the induced time for the protrusions formation is only\nless than 5 min owing to the enhanced mass transfer by the gravity-induced\nconvection and hydrogen bubble agitation convection. So, a porous\nstructure is easily formed under high gravity acceleration and long\nelectrodeposition time. The HER activities of NiMo films are improved\nwith the surface structure evolution from compact to porous structure\ndue to the increase of active area. All NiMo films exhibit a good\nlong-term durability, and the cell voltage of water electrolysis on\nporous NiMo films is lower.