Self-template activated carbons for aqueous supercapacitors

Activated carbons have been employed widely in aqueous supercapacitors due to their merits of large specific surface area (SSA), good electrical conductivity and chemical stability. However, toxic, corrosive and complicated activation processes hinder the further development of their industrialization. Here, we report a green and facile self-template activation strategy to synthesize hierarchical porous carbons as the electrode material for aqueous supercapacitors. Without pre-mixing procedures and additional activation processes, the hierarchical porous carbons can be obtained by one-step pyrolysis of sodium carboxymethylcellulose (CMCNa). This work reveals the dependence of aqueous capacitive performance on the pyrolysis temperature (PT), molecular weight (MW) and degree of substitution (DS, the number of hydroxyl groups substituted by sodium carboxymethyl groups on the monomeric anhydroglucose unit) of CMCNa. The results indicate that the DS is a more important factor because the obtained porosity is determined by the addition of the activating agent (Na2CO3) decomposed from sodium carboxymethyl groups. The optimized porous carbon pyrolyzed from CMC-Na with DS of 1.2 exhibits a large SSA of 1,274 m(2) g(-1) with a specific capacitance of 197 F g(-1) at the current density of 0.5 A g(-1) and 77% retaining capacitance even at 50 A g(-1) in a three-electrode cell. The assembled aqueous coin cell shows no capacitance fading after 10,000 cycles at 5 A g(-1) and possesses a higher energy density compared to commercial activated carbon. Hence, self-template activated carbons are promising candidates in the fabrication of high-performance aqueous supercapacitors.

Automated summary

This study presents a green and facile self-template activation strategy for synthesizing hierarchical porous carbons as electrode materials for aqueous supercapacitors. The hierarchical porous carbons can be obtained by one-step pyrolysis of sodium carboxymethylcellulose (CMCNa) without pre-mixing procedures and additional activation processes. The dependence of aqueous capacitive performance on the pyrolysis temperature, molecular weight, and degree of substitution of CMCNa is revealed.