Different chain length hydrophilic ionic liquids on the surface properties of activated carbon

Based on issues such as poor interfacial wettability when using activated carbon (AC) as a supercapacitor electrode material, this study employs two hydrophilic ionic liquids with different chain lengths, 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium tetrafluoroborate ([Emim][BF₄] and [Bmim][BF₄]); commercial activated carbon with larger pore size (1.73 nm) and higher mesopore fraction (11.63%) was modified by the impregnation method to prepare ILs-AC composite materials. The study found that the ionic liquids were successfully loaded onto the surface of activated carbon through physical adsorption. Although some micropores were blocked, resulting in a decrease in specific surface area, the hydrophilicity of the material was significantly enhanced, effectively reducing charge transfer resistance and markedly lowering the contact angle of AC, thus improving the interfacial wettability between the electrode and the electrolyte. Electrochemical tests demonstrated that AC modified with the shorter-chain ionic liquid [Emim][BF₄] had a specific capacitance of 92.99 F g^-1 (an increase of approximately 6.7%), whereas AC modified with the longer-chain ionic liquid [Bmim][BF₄] exhibited a specific capacitance of 94.39 F g^-1 (an increase of approximately 8.3%). Regarding long-term cycling performance(10 000 cycles), the capacitance retention rates of the modified materials were 96.64% and 92.83%, respectively, both higher than that of the original material (capacitance retention rate of 91.73%).