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

Molybdenum trioxide (MoO3) is a promising positive electrode material for aqueous aluminum‐ion batteries due to its high theoretical capacity. However, MoO3 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 MoO3 on the Mo2C MXene layer. MXene can effectively inhibit the dissolution and structural loss of MoO3 reaction products. Additionally, the coordination effect of Mo2C and MoO3 achieves a stable near‐surface reaction on the MXene laminates, resulting in the Mo2C/MoO3 composite exhibiting excellent aluminum storage properties (123.5 mAh/g after 200 cycles at 0.4 A/g). The energy storage mechanism of H+/Al3+ co‐insertion/extraction was elucidated through non‐in‐situ characterization, and the promotion effect of Mo2C on MoO3 reaction kinetics was verified by density functional theory calculations. This work provides new insights into improving the stability of AAIB cathodes and extends the application of Mo‐based MXene in aqueous batteries.