Synthesis of Hureaulite Mn5(H2O)4(PO3OH)2(PO4)2 with an Open 3D Network Structure as Electrode Material for Electrochemical Capacitors

Abstract

Mn5(H2O)4(PO3OH)2(PO4)2 with an open 3D network was prepared and studied as electrode material for electrochemical capacitors. The material exhibits a tunnel structure along the c axis, characterized by a hydrogen bond network formed by water molecules bonded to MnO6 octahedra and PO3-OH tetrahedra units, the latter containing an acidic proton. Electrochemical studies were conducted on both alkaline and neutral electrolytes, revealing a profile indicative of a rapid faradaic process coupled with pseudocapacitance and electrochemical double-layer capacitance. This study proposes a mechanism that involves the interaction between the acidic proton in the tunnel structure and OH− ions from the electrolyte, which diffuse through the hydrogen bond network. The material achieved a maximum specific capacitance of 184 Fg−1 at a scan rate of 5 mVs−1, with an areal capacitance of 4600 µFcm−2 in 3M KOH. This demonstrates its potential as a high-performance electrode for energy storage applications.