Acetaminophen: a novel redox-additive for snowballing the energy density of flexible supercapacitors

Increasing the energy density of carbon-based electrodes is one of the important missions in the field of supercapacitors. The best strategy to proliferate the energy density of a supercapacitor is harnessing redox additives with conventional electrolytes. Here, acetaminophen has been adopted as a redox additive with H2SO4 for the first time to increase the energy density of the supercapacitor electrode. The specific capacitance of the electrode increased 2 times after the addition of acetaminophen with H2SO4. A flexible supercapacitor (FSC) was fabricated using polyvinyl alcohol (PVA)/H2SO4 and acetaminophen/PVA/H2SO4 gel electrolytes. The energy density of the FSC with acetaminophen/PVA/H2SO4 (26.4 W h kg(-1)) was similar to 3-fold higher than that with PVA/H2SO4 (7 W h kg(-1)). Due to the reversible redox process of acetaminophen to N-acetyl-p-benzoquinone-imine in H2SO4, the electrochemical performance of the supercapacitor electrodes was boosted. The FSC retained 95% of its original capacitance even after 12 000 cycles. Moreover, the ionic conductivity of the PVA/H2SO4 gel electrolyte increased from 2.6 to 9.6 mS cm(-1) as a result of adding acetaminophen, which might also be the reason for the excellent energy density of FSC.