Probing the Crystal Plane Effect of CoO for Enhanced Electrocatalytic Performance toward Efficient Overall Water Splitting.

Identifying effective methods to enhance the properties of catalysts is urgent to broaden the scanty technologies, so far. Herein, we synthesized four CoO crystals with different crystal planes and explored the crystal planes' effects on electrochemical water splitting through theoretical and experimental studies for the first time. The results illustrate that the correlation of catalytic activity is established as {111} > {112} > {110} > {001}. CoO crystals exposed with {111} facets show the highest OER (oxygen evolution reaction) and HER (hydrogen evolution reaction) activities. Upon fabrication in an alkaline electrolyzer, the bifunctional {111}∥{111} couple manifests the highest catalytic activity and satisfying durability for overall water splitting. Density functional theory (DFT) explains that the {111} facet possesses the biggest dangling bond density, highest surface energy, and smallest absolute value of ΔG, leading to the enhanced electrocatalytic performance. This work will broaden our vision to improve the activity of various electrocatalysts by selectively exposing the specific crystal planes.