The quest for green and effective synthetic routes towards energy grade materials is of utmost relevance in the transition to a fossil-free energy model. In a previous work we have shown the promising role of harmless MgSO4 in the synthesis of S-doped carbon anodes for fast sodium storage. Herein, we show that the same simple procedure can be used for the production of high surface, supercapacitor-type materials, by merely changing the temperature of the thermal treatment. We also found that the addition of an inert salt such as KCl -in small amounts- greatly boosts the porogenic activity of MgSO4, leading to carbons with SBET above 2000 m2 g−1. As a proof of concept, and using biomass-based substances as carbon precursors, we have built a hybrid sodium-ion capacitor out of a S-doped carbon and a highly porous carbon, both of them prepared using similar MgSO4-assisted synthetic schemes. The full cell built with similar positive and negative electrode masses exhibited a good energy/power performance (38Wh kg−1 at 22 kW kg−1), as well as a very robust cycling stability, with a capacity fade of only 0.00078 % cycle−1.

This research work was supported by project IDI/2018/000148 (FICYT/FEDER) and PID2021-123648OB-I00 (MCIN/AEI/10.13039/501100011033/and ERDF A way of making Europe). S. Payá also thanks the Principality of Asturias for her Yo Investigo contract.

Peer reviewed