Effect of Hierarchical Porosity on PMo12 Adsorption and Capacitance in Hybrid Carbon–PMo12 Electrodes for Supercapacitors

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 PMo12 incorporation over a family of HMC–PMo12 hybrid materials prepared from carbons with different textures revealed a preferential absorption of PMo12 on small mesopores (∼ 5 nm). These findings challenge the widespread idea that micropores are the optimal choice for PMo12 incorporation; as we have proved, small mesopores maximized PMo12 adsorption, and this later ensured the proper electrolyte diffusion due to bigger interconnected mesopores (∼ 25 nm). Thus, on account of PMo12 incorporation 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 PMo12 adsorption 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.