Boosted charge transfer in oxygen vacancy-rich K+ birnessite MnO2 for water oxidation and zinc-ion batteries

Abstract Manganese Dioxide (MnO2) as an efficient cathode material for zinc-ions battery (ZIBs) and water oxidation has always been a research emphasis because of its rich crystal phases, tunnel and layered structure, which is conducive to the deintercalation / intercalation of zinc ions. However, the key bottleneck of MnO2 electrode materials are their poor rate capability and electrochemical stability. Herein, we successfully obtained oxygen vacancy-rich K-birnessite MnO2 (KxMnO2) by plasma etching strategy. K+ intercalation in MnO2 can adjust the interlayer distances, which improves the structural stability of material, and constructs a tunable Zn2+ channel. Meanwhile, the oxygen vacancy is not only contribute to the fast adsorption and diffusion of electrolytic ions, but also to the rapid transfer of charges. In addition, the nano-structure could provide abundant reaction sites and short diffusion pathways. Remarkably, the KxMnO2 is used cathode material of ZIBs after plasma optimization treatment presents reversible specific capacity of 272 mAh g−1 at 1 mA cm−2, and then it could reach an admirable capacity of 310 mAh g−1 after 100 cycles. As the oxygen evolution reaction (OER) electrocatalysts, the overpotential to reach 10 mA cm−2 of KxMnO2 is 1.47 V of versus RHE. The Tafel slope is 36 mV dec−1, which is lower than that of the KxMnO2 without plasma treatment (244 mV dec−1). This study provides a new opportunity to design low-cost and high-performance electrode materials for rechargeable zinc-ion batteries and OER catalyst by using plasma processing technology.