Phosphonium-based protic ionic liquid as electrolyte for carbon-based supercapacitors

This study describes the use of a solution of a phosphonium protic ionic liquid [Bu3HP][BF4] (3.4 mol L−1) in acetonitrile as an electrolyte for carbon-based supercapacitors, with an operating voltage of 1.5 V and capacities comparable to conventional aqueous electrolytes. The combination of good cycling abilities and an operating temperature ranging from − 40 °C to 80 °C rendered possible the realization of supercapacitors having an extended specific energy in a large temperature range.

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► The conductivity of mixture PIL + acetonitrile increased when increasing the temperature (from σ = 29 mS cm−1 at 25 °C to σ = 46.8 mS cm−1 80 °C).
► The PIL exhibited in a mixture with acetonitrile on glassy carbon working electrode a large electrochemical window at around 6 V.
► At 20 °C, the PIL electrolyte for carbon-based supercapacitors could operate up to 1.5 V.
► Stability tests performed at 3.5 A.g−1 shows that the capacitance evolved from 130 F.g−1 to 120 F.g−1 after 1000 cycles.
► The combination of remarkable cycling stability and large temperature operating (from 80 °C to −40 °C).