Understanding the Role of Cracks in Active Oxygen Species Formation during Oxygen Evolution Reaction

Abstract

Understanding the formation and location of catalytic intermediates is crucial for unraveling the mechanism of oxygen evolution reaction (OER), a key process in electrochemical water splitting. Despite the availability of various in-situ and ex-situ characterization methods, the formation and location of intermediates remain elusive, hindering the development of more efficient electrocatalysts. In this work, we discovered a stable static active oxygen species formed during the chemical oxidation of cobalt hydroxide flakes, providing a unique opportunity to probe the intermediates involved in OER. We are able to monitor the equilibrium conversion between stable peroxo structure and superoxo radical via EPR and Raman test, shedding light on the nature of the active oxygen species. In addition, CoOOH flakes with cracks were synthesized via controlled chemical oxidation, enabling the investigation of the role of crack/edge structures in the electrocatalytic activity. Statistical regression analysis combining morphological features, electrochemical performance, and Raman spectroscopy confirmed a strong correlation between morphology evolution, OER activity, and active oxygen species, highlighting the importance of controlling the morphology of electrocatalysts for enhancing their performance. Therefore, we propose that the source of active oxygen intermediates can be attributed to the presence of crack/edge structures. The crack-rich CoOOH exhibit significantly higher current density at a lower overpotential, providing a new direction for the design of efficient water oxidation electrocatalysts. Overall, this work offers important insights into the mechanism of OER and provides a basis for the development of more efficient and sustainable electrocatalysts for energy conversion and storage.