Wide-temperature activated carbon-based symmetric supercapacitors with impressive performance empowered by H3PO4 electrolyte

As a commercial electrode material, activated carbon (AC) has been widely used in electrochemical energy storage systems. However, the electrochemical performance of AC for supercapacitors has not been well developed due to the absence of an ideal electrolyte. In this paper, we report on the all-temperature impressive performance of AC‖AC symmetric supercapacitors with commercial loading level (>10 mg cm−2) empowered by H3PO4 electrolyte. The physicochemical properties of H3PO4 electrolytes with different weight ratios of H3PO4 to H2O have been characterized. The H3PO4 electrolyte with H3PO4/H2O weight ratio of 1 endows AC‖AC supercapacitors with enhanced performance at a wide temperature range of –45–55 °C, compared with the counterparts with H3PO4/H2O weight ratio being 0.5 and 2. The electrochemical performance of AC‖AC supercapacitors operating with the H3PO4 electrolyte (H3PO4/H2O = 1:1, w/w) is increased as the temperature increases from −45 to 55 °C. The impressive performance of AC‖AC supercapacitors operating with H3PO4/H2O weight ratio of 1 is attributed to the high conductivity and reduced water activity of the electrolyte, as confirmed by instrumental analysis and molecular dynamic simulations.