Understanding the pH-Dependent Catalytic Activity for the Layered LixCoO2 Oxygen Evolution Catalysts

Many highly active catalysts for the oxygen evolution reaction (OER) demonstrate strong pH-dependent catalytic activities. However, the exact mechanism behind this phenomenon is still a subject of debate. In this study, delithiated Li0.5CoO2 is utilized as a model catalyst due to its tunable chemical states and layered structure that can facilitate reversible intercalation and deintercalation of cations. By increasing the pH to 14 using a 1.0 M CsOH solution, rapid intercalation of Cs+ cations and water molecules induce notable lattice expansion up to 9.9 Å, resulting in an order of magnitude higher OER intrinsic activity comparing to that in 0.1 M CsOH. It is hypothesized that lattice water in layered structure facilitates the dynamic intercalation and deintercalation of Cs+ cations, promoting the so-called "electrochemical-chemical" reaction mechanism. These findings provide valuable insights into the intricate nature of surface dynamics and the redox chemistry on the catalyst/electrolyte interface during the OER.