High‐performance supercapacitor electrolytes based on high‐mole‐ratio phosphoric acid/lauryl ether surfactant liquid crystalline gel

Abstract

Proton-conducting gel electrolytes offer significant advantages for supercapacitors. Among various acids, phosphoric acid (H3PO4·H2O, PA) has the highest proton conductivity for use as a supercapacitor electrolyte. Compared with commonly used acidic and basic electrolytes (H2SO4 and KOH), a high specific capacitance of approximately 620 F g−1 was attained for PA under 0.1 A g−1 test conditions in combination with a reduced graphene oxide (rGO) symmetric electrode. Moreover, the PA electrolyte was further improved by confining it to a liquid crystal (LC) gel matrix. PA and a non-ionic surfactant (lauryl ether, C12H25[OCH2CH2]10OH) were used to form LC gels with PA:NI mole ratios 60 to 100:1, which had viscosity values in 800 to 5500 mPa s−1 range at a shear rate of 100 s−1 and provided a high gravimetric specific capacitance of approximately 1128 F g−1 when tested at 0.1 A g−1 with an rGO symmetric electrode. The mesophase of the LC gel at each PA:NI mole ratio was comprehensively analyzed using X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), and polarized optical microscopy (POM) to confirm that the mesostructure was responsible for the high specific capacitance. The electrochemical performance was studied using electrochemical methods and galvonastatic charge/discharge tests. Furthermore, to increase the energy density of supercapacitors, focusing on automotive applications, this LC gel electrolyte could be used in an asymmetrical pseudocapacitor design.