In Situ Synthesis of MoO 3 by Surface Oxidation of Mo 2 C (MXene) for Stable Near‐Surface Reactions in Aqueous Aluminum‐Ion Battery

Abstract Molybdenum trioxide (MoO 3 ) is a promising positive electrode material for aqueous aluminum‐ion batteries (AAIBs) due to its high theoretical capacity. However, MoO 3 faces several challenges in an aqueous electrolyte, such as easy dissolution of reaction products, volume expansion, and low conductivity, which severely limit its application in aqueous batteries. In this work, we effectively increased the overall conductivity of the electrode by in situ growing MoO 3 on the Mo 2 C MXene layer. MXene can effectively inhibit the dissolution and structural loss of MoO 3 reaction products. Additionally, the coordination effect of Mo 2 C and MoO 3 achieves a stable near‐surface reaction on the MXene laminates, resulting in the Mo 2 C/MoO 3 composite exhibiting excellent aluminum storage properties (123.5 mAh/g after 200 cycles at 0.4 A/g). The energy storage mechanism of H + /Al 3+ co‐insertion/extraction was elucidated through ex situ characterization, and the promotion effect of Mo 2 C on MoO 3 reaction kinetics was verified by density functional theory (DFT) calculations. This work provides new insights into improving the stability of AAIBs cathodes and extends the application of Mo‐based MXene in aqueous batteries.