Potential-driven restructuring of lithium cobalt oxide yields an enhanced active phase for the oxygen evolution reaction

Abstract

Electrocatalysts often undergo significant restructuring depending on the applied potential under operating conditions. Although such restructured surfaces govern the catalytic performance, rationally controlling catalyst restructuring via an electrochemical protocol remains elusive. In addition, the depth and spatial distribution of these restructured phases are often heterogeneous, complicating the identification of the new active phase. Here, we demonstrate an electrochemical activation protocol that substantially increases the catalytic performance of the less-active LiCoO₂ (LCO) by cycling at 1.8 V_RHE for the oxygen evolution reaction. Multifaceted analysis enables the identification of the transformation of LCO into the catalytically more active β-CoOOH phase and elucidates how the activation protocol induces this restructuring process. Specifically, Raman mapping reveals that the higher oxidative potential triggers the delithiation of LCO particles, leading to the phase transformation into the β-CoOOH phase as the cycle number increases at 1.8 V_RHE. LCO particles with increasing contents of β-CoOOH species exhibited enhanced catalytic activity. However, lower potentials (i.e. 1.6–1.7 V_RHE) were not effective in extracting lithium, and consequently, resulting in minimal phase evolution of LCO. We demonstrate how electrochemical methods can derive a highly active catalyst from a less active material and correlate the restructured phases with catalytic activity. Spatial phase distribution obtained from Raman spectroscopy sheds light on the mechanisms of the potential-controlled restructuring protocol.