CO2 outperforms KOH as an activator for high-rate supercapacitors in aqueous electrolyte.

Although high-surface area activated carbons used as supercapacitor (SC) electrodes are frequently produced by KOH activation, this study shows that, when aqueous electrolytes are used, CO 2 activation is a better choice from the point of view of SC performance, environment and economy. Ordered mesoporous carbons (OMCs) produced by a mechanochemical synthesis method from mimosa tannin are activated with KOH to use these materials as electrodes for SCs. A comparative analysis of the same OMCs but activated with CO 2 is presented to examine the effect of the activation process on materials performance. KOH-activated materials exhibit good electrochemical performance at low charging rates, reaching specific cell capacitance values of 49 F g−1 at 0.5 Ag−1, however, restricted access to microporosity and low water affinity water reduces their performance at high charging rates. In contrast, the best performing CO 2 -activated material can retain 81% of capacitance at 20 A g−1, compared to 25% for a KOH-activated OMC with similar properties and tested under the same conditions. A thorough review of the open literature suggests that CO 2 activation would produce materials with a suitable combination of pore network connectivity and water affinity, resulting in SCs with high rate capability in an aqueous electrolyte. These conclusions were drawn by judiciously integrating the analysis of: (i) the hysteresis loop scanning of N 2 adsorption-desorption isotherms; and (ii) water adsorption isotherms as tools to more accurately assess the pore network connectivity and water affinity of the materials, which are not generally considered when studying SC performance. • Pore connectivity and water affinity control the performance of SCs. • Scanning the N 2 hysteresis loop allows the assessment of pore connectivity. • Poor connectivity and hydrophobicity of KOH-activated OMCs hinder SC performance. • Good connectivity and hydrophilicity of CO 2 -activated OMCs enhance SC performance. • CO 2 activation is better in terms of SC performance and sustainability. [ABSTRACT FROM AUTHOR]