Pure Reduced Polyoxometalates Materials as Electroactive Materials Toward Proton Energy Storage Device

Abstract

The integration of efficient proton transport and reversible redox activity in a single material is highly desirable for advanced electrochemical devices, yet remains challenging. Herein, two novel crystalline pyridine-decorated polyoxometalates, namely H10{CuII0.5[MoV6O12(OH)3(HPO4)4]2}2·8HPy·24H2O (1) and H8CdII[MoV6O12(OH)3(HPO4)4]2·2Cl·2HPy·2Me2NH (2), are designed and synthesized via a hydrothermal route. The pyridine molecules endow the materials with remarkable proton conductivity reaching 9.63 × 10-3 S cm-1 (1) and 2.21× 10-3 S cm-1 (2) at 85 ℃ and 95% RH, the excellent proton conduction stems from the ordered hydrogen-bonding networks facilitated by both the pyridine N sites and the terminal/surface oxygen atoms of the {P4MoV6O31} anions. Furthermore, the title complexes as electrochemically active materials are loaded onto the surface of carbon paper to assemble solid-state proton energy storage devices, the 1-CP@PANI-SC devices can achieve an outstanding specific capacitance of 330.12 F g-1 and cyclic stability of 94.2% after 1000 cycles. Crucially, electrochemical analysis coupled with proton conduction studies indicates that the pre-established proton-conducting pathways significantly facilitate the transport of charge-compensating protons (H+) during the rapid redox reactions of molybdenum centers, thereby enhancing the pseudo-capacitive kinetics and overall electrochemical efficiency. This work not only presents high-performance multifunctional electroactive materials but also establishes a material design principle that links proton conduction with charge storage dynamics for next-generation energy storage systems.