Novel templated mesoporous carbons as electrode for electrochemical capacitors with aqueous neutral electrolytes

Abstract

In search for new electrodes for electrochemical capacitors, two template mesoporous carbons (TMC) are prepared with the replica method by using Plugged Hexagonal Templated Silica (PHTS) and Mesostructured Cellular Foam (MCF) as hard templates. No subsequent activation after synthesis is carried out in order to correlate textural and electrochemical properties in neutral sulfate electrolytes. TMC show interesting textural and conductive properties for capacitor electrode purposes: specific surface areas higher than 1000 m2 g−1, and low D/G bands ratio in the Raman spectra. Mesopore presence accounts for the fast formation of the double layer and the decrease of resistive properties which implies increased power properties referred to activated carbons. Symmetric carbon/carbon devices can provide energy densities 7–9 Wh kg−1and maximal powers higher than 50 kW kg−1. These values compare well with 9 Wh kg−1and 26 Wh kg−1furnished by activated carbons. Nevertheless, such TMCs show two major issues for performing better than activated carbons in aqueous electrolyte capacitors. Firstly, they show surface carbon functionalities, narrowing the electrochemical window of the capacitor and decreasing the capacitor cycling life. Secondly, pore saturation is evidenced in these systems, unlike activated carbon, showing higher specific surface area and micropores content. Under prolonged cycling, our TMC electrode performance is poorer than that of activated carbon. However, mesoporosity positively affects the electrode response against increasing power. Beyond a power of 1.4 kW kg−1, only TMCs provide stable energy densities (>6.5 Wh kg−1), comparable or higher than those observed for activated carbons in corrosive electrolytes.