Electrochemical capacitive performance of free-standing polyindole film and effect of introducing alkyl chain connecting two indoles

Polyindole (PIn), combining the good properties of polypyrrole and poly(para-phenylene), has been gained significant attention. But the capacitive performances of PIn and its derivatives electropsynthesized in boron trifluoride diethyl etherate (BFEE) were unknown so far. So we first prepared the free-standing PIn film in BFEE and studied its capacitive property. The specific capacitance value of PIn could achieve 270.2 F g⁻¹ at high current density of 10 A g⁻¹. And the capacitance retained of PIn 84.06% after 3000 cycles. For further studying the effect of introducing alkyl chains on the electrochemical properties of PIn, poly1,3-di(1H-indol-1-yl)propane (P(IP-3)), poly1,6-di(1H-indol-1-yl)hexane (P(IH-6)), and poly1,12-di(1H-indol-1-yl)dodecane (P(ID-12)) bridged by alkyl chains with different lengths were electrosynthesized in BFEE. Through a series of experiments, we found that the specific capacitance performances of P(IP-3), P(IH-6), and P(ID-12) were poorer than PIn, indicating the introduction of alkyl chains altered the electrochemical properties of the π-conjugated backbone of PIn and lowered its the properties, which could be proved by scanning electron microscope.