Liquid electrolyte determines the voltage window and extreme working temperature of supercapacitors. However, the effect of weak interaction between electrolyte species on voltage window and low-temperature capacitive performance is unclear. Herein, an electrolyte model system with increasing Hbond interaction was constructed to clarify this concern. The results indicated that strong H-bond interaction was positively correlated with the number of hydroxyls, which was beneficial to expand voltage window, but deteriorated rate performance; weak H-bond improved low-temperature performance. Supercapacitors with an optimized electrolyte presented high voltage and good low-temperature performance; even at À 40 °C, the maximum energy density could be maintained at 7.0 Wh kg À 1 (> 80 % retention relative to at À 20 °C). This study revealed the mechanism of the influence of the H-bonds on electrolyte voltage window and anti-freezing capability and provided a new insight for the design of electrolytes with both high working voltage and low-temperature performance.

Ionic liquid analogues (ILAs) are promising electrolytes for supercapacitors due to their low cost and considerable voltage (>2.0 V). However, the voltage is <1.1 V for water-adsorbed ILAs. Herein for the first time, an amphoteric imidazole (IMZ) additive is reported to address this concern by reconfiguring the solvent shell of ILAs. Addition of only 2 wt % IMZ increases the voltage from 1.1 to 2.2 V, with an increase in capacitance from 178 to 211 F g–1 and an increase in energy density from 6.8 to 32.6 Wh kg–1. In situ Raman reveals that the strong H-bonds formed by IMZ with completive ligands 1,3-propanediol and water induce a reversal of the polarity of the solvent shells, suppressing absorbed water electrochemical activity and thus increasing the voltage. This study solves the problem of low voltage for water-adsorbed ILAs and reduces the equipment cost of ILA-based supercapacitor assembly (e.g., assembly in air without a glovebox).

Deep eutectic solvents (DES) are known as low-cost and environmentally friendly electrolytes for supercapacitors. However, because DES is particularly vulnerable to moisture adsorption in the air, the voltage window (<...

Template carbon (TC) is one of the most promising electrode materials for clean-energy devices (e.g., supercapacitors), but its application is hampered by the high cost of templates and carbon sources. Here, we report a green MgO template recycling technology that converts CO2 to high specific-surface-area TC by establishing a zero-emission chemical cycle at one-third the cost of nonrecycling methods. Up to 10 cycles of recycling demonstrate that the template’s dissolution and regeneration, as well as TC’s pore structure and physical properties, are extremely repeatable. Supercapacitors using symmetric TC electrodes deliver high-capacitance and -rate performances either in aqueous (KOH/H2O, >154 F g–1) or organic (Et4NBF4/AN, >140 F g–1) and ionic liquid (EMIMBF4, >178 F g–1) electrolytes, and ≈100% Coulomb efficiency, outperforming traditional commercial supercapacitors. This progress greatly reduces the cost of large-scale use of TC in supercapacitors and creates a sustainable link between CO2 reduction and clean-energy development.

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