Hierarchy and delithiation regulations on mesoporous LiCoO₂ nanosheets for boosted water oxidation electrocatalysis

Layered lithium cobaltite (LiCoO₂) is currently an emerging low-cost and active electrocatalyst in oxygen evolution reaction (OER) with good stability. However, most of its OER catalytic studies are mainly based on aggregated LiCoO₂ powder, and thus construction of distinct LiCoO₂ nanostructures would be the primary quest for OER performance optimization. In this work, mesoporous LiCoO₂ hierarchical nanosheets were hydrothermally synthesized on carbon cloth and then chemically delithiated for OER electrocatalysis. Two types of LiCoO₂ hierarchical nanostructures, including sheet-on-rod and sheet-on-sheet features, have been prepared and compared for OER activity. The LiCoO₂ sheet-on-sheet structure with higher OER performance was further chemically delithiated towards Li_1-xCoO₂ to activate the Co⁴⁺/Co³⁺pair and boost the OER process. As a result, the delithiated LiCo_0.72O₂ catalyst delivers an outstanding and durable catalytic performance toward OER in alkaline solution, including an overpotential of 289 mV at 10 mA cm⁻², small Tafel slope, and low charge transfer resistance. First-principle calculations indicate that the delithiation can change the electronic state of the LiCoO₂ system, and the water oxidation can be promoted by optimizing the adsorption Gibbs free energy of OER intermediates. The present investigation paves an interesting avenue for the rational design of highly efficient LiCoO₂ water oxidation catalysts.