High-entropy conductive manganese-based Prussian blue analogue cathode for high-performance ammonium ion storage

Abstract

Manganese-based Prussian blue analogues (MnPBA) are promising cathode materials for aqueous ammonium ion storage due to their high theoretical capacity and attractive redox potential, but they present issues of structural instability, manganese dissolution, and intrinsically low electronic conductivity, which cause inferior practical capacity and rate performance. Herein, a strategy based on a high-entropy structure and carbon nanotube (CNT) connectors is proposed to synthesize a high-entropy conductive MnPBA cathode (HEPBA/CNT) that realizes impressive ammonium ion storage performance. In the HEPBA/CNT composite cathode, the high-entropy structure introduces heterogeneous metal species into the MnPBA framework to optimize the coordination environment of the Mn atoms, effectively alleviating lattice distortion and suppressing manganese dissolution, and simultaneously, the conductive CNT channels guarantee fast electron transport to improve the utilization of electrochemically active sites. Accordingly, the HEPBA/CNT cathode delivers a high capacity of 88 mAh g⁻¹, an impressive rate performance (48 mAh g⁻¹ at 1 A g⁻¹), and outstanding cycling stability (45 mAh g⁻¹ after 1000 cycles at 1 A g⁻¹), making it notably superior to the pristine MnPBA cathode, whose capacity is only 36 and 1 mAh g⁻¹ at 0.1 and 1 A g⁻¹, respectively. On this basis, high-performance ammonium ion hybrid capacitors using the HEPBA/CNT cathode are constructed. This study provides new insights into designing high-performance cathodes for aqueous ammonium ion storage.