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

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. We have revealed that solution plasma assisted Mn-doping is a powerful strategy for enhancing the durability and activity of Co-based OER catalysts, where the OER activity is enhanced by a factor of 11 for Ca3Co4O9.