Exploring the origin of the high electro-catalytic activity for nitrate-to-ammonia conversion on electrodeposited Ni/Ru hydroxide hybrids

Abstract

Nitrate electro-reduction reaction (NITRR) offers a promising alternative approach for ammonia synthesis under mild conditions. Our previous studies have shown that electrodeposited Ni/Ru hydroxide hybrid exhibits highly catalytic NITRR activity. Therefore, this study focuses on investigating the origin of the high activity on Ni/Ru hydroxide hybrid by comparing it with drop-cast Ru nanoparticles on nickel foam, which show much lower activity for NITRR. This was attributed to the interaction between Ru and the nickel substrate formed during electrodeposition. To host electrodeposited Ni/Ru hydroxide hybrid nanoparticles, we used a series of nickel foams with varying amounts of surface-oxidized nickel layers prepared by heat treatments. The introduction of moderate oxidized nickel layers in Ni/Ru hydroxide hybrid electrodes increased the interactions between Ru and the Ni species, and the synergistic effect further promotes nitrate-to-ammonia conversion. However, excessive increases in oxidized nickel layers lead to a deterioration in catalytic performance.