Solution plasma assisted Mn-doping: a novel strategy for developing highly durable and active oxygen evolution catalysts

Abstract

Oxygen evolution and oxygen reduction catalysts play a crucial role in energy conversion technologies for achieving a decarbonized society. In the present study, we introduce the Mn-doping as a tool for the dual enhancement of activity and durability in a Co-based oxygen evolution catalyst, Ca₃Co₄O₉. We have discovered that Mn-doping in combination with solution plasma treatment remarkably enhances the OER durability, and also the OER activity is enhanced by a factor of 11. Crystallographically, it is known that Co exists at two atomic sites (Co1 and Co2) for Ca₃Co₄O₉ in which the Co1 atomic site exists at the Ca₂CoO₃ layer, and the Co2 atomic site exists at the CoO₂ layer. Based on a series of electrochemical studies, we suggest that the poor durability of Ca₃Co₄O₉ comes from the Co dissolution and that such Co dissolution can be prevented by the Mn-doping at the Co2 atomic site within the CoO₂ layer. At the same time, the Mn³⁺-rich surface of Mn-doped Ca₃Co₄O₉ with the OER active Mn³⁺ may have contributed to the OER activity enhancement. Furthermore, the solution plasma treatment combined with Mn-doing has an effect of improving the atomic order of the Mn³⁺-rich surface, which could act as a durable surface for the OER. Therefore, our study has revealed that solution plasma assisted Mn-doping is a powerful strategy for enhancing the durability and activity of Co-based oxygen evolution catalysts, contributing to the better understanding of oxygen evolution and oxygen reduction catalysis.