Effect of Hierarchical Porosity on PMo12Adsorption and Capacitance in Hybrid Carbon-PMo12Electrodes for Supercapacitors

Abstract

Here, we report an industrially scalable synthetic strategy to develop efficient hybrid supercapacitor electrodes with practical mass loading (∼10 mg·cm-2), combining hierarchical mesoporous carbons (HMC) and phosphomolybdic acid, H3PMo12O40(PMo12). A thoughtful analysis on the relationship between the carbon structure and PMo12incorporation over a family of HMC-PMo12hybrid materials prepared from carbons with different textures revealed a preferential absorption of PMo12on small mesopores (∼5 nm). These findings challenge the widespread idea that micropores are the optimal choice for PMo12incorporation; as we have proved, small mesopores maximized PMo12adsorption, and this later ensured the proper electrolyte diffusion due to bigger interconnected mesopores (∼25 nm). Thus, on account of PMo12incorporation and improved electrolyte diffusion, the hybrid electrode capacitance exhibited a significant increase (up to 119%), observing an enhanced electron transport and improved rate capability performance. In terms of specific capacitance, our material outperforms all of the previously published carbon-polyoxometalate (POMs) systems with practical mass loading, reaching a value up to 326 F·g-1. Therefore, in this paper, we proposed the use of small carbon mesopores for optimal PMo12adsorption as a novel conceptual approach to develop a hierarchical mesoporous carbon-POM hybrid material, which proved to be an excellent candidate for electrodes in supercapacitors.