Capacitive deionization using biomass-based microporous salt-templated heteroatom-doped carbons

Microporous carbons are an interesting material for electrochemical applications. In this study, we evaluate several such carbons without/with N or S doping with regard to capacitive deionization. For this purpose, we extent the salt-templating synthesis towards biomass precursors and S-doped microporous carbons. The sample with the largest specific surface area (2830 m²g^-1) showed 1.0 wt% N and exhibited a high salt-sorption capacity of 15.0 mgg^-1 at 1.2 V in 5 mM aqueous NaCl. While being a promising material from an equilibrium performance point of view, our study also gives first insights to practical limitations of heteroatom-doped carbon materials. We show that high heteroatom content may be associated with a low charge efficiency. The latter is a key parameter for capacitive deionization and is defined as the ratio between the amounts of removed salt molecules and electrical charge.