Hydroxylated MXene ‐Assisted In Situ Synthesis of Ultrafine CoHCC Nanoparticles for High‐Performance Potassium‐Ion Battery Anodes

Cobalt‐based Prussian blue analogs (CoHCC) have emerged as highly promising anode materials for potassium‐ion batteries due to their open framework structure, suitable potassium‐ion insertion potential, and high theoretical capacity. However, the intrinsically low electronic conductivity of CoHCC, its tendency for particle agglomeration during traditional synthesis, and the uncontrollable particle size have severely restricted its potassium‐ion storage performance. This study reports a hydroxylated MXene‐assisted in situ synthesis strategy for constructing ultrafine CoHCC nanoparticles anchored on a Ti 3 C 2 T x MXene substrate (CoHCC@MX) as a high‐performance potassium‐ion battery anode. The –OH groups on the MXene surface serve as effective anchoring sites, enabling uniform nucleation and growth of CoHCC nanocrystals while preventing particle aggregation. The MXene substrate forms a continuous metallic conductive network, significantly enhancing electron transport and alleviating the poor conductivity of pristine CoHCC. Density functional theory calculations indicate strong interfacial electronic coupling between the –OH‐functionalized MXene and CoHCC, which not only stabilizes the composite structure but also inhibits the dissolution of active materials. The optimized CoHCC@MX‐1.0 composite anode delivers a high reversible capacity of 289.3 mAh g −1 after 1000 cycles at 500 mA g −1 , and exhibits excellent rate performance. When paired with a K 1.92 Fe[Fe(CN) 6 ] 0.94 ·0.5H 2 O cathode to assemble a full cell, it achieves a high energy density of 228.1 Wh kg −1 and retains 80.8% of its energy after 600 cycles. This work underlines the crucial role of functionalized MXene in interface engineering, providing a promising design strategy for advanced potassium‐ion storage materials.