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 ∼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.