FeS2@Ti3C2Tx Pseudocapacitive Anode for Supercapacitors: Effect of Counter-Electrode Electrochemical Behavior on Supercapacitor Metrics

Understanding the impact of electroactive material charge storage behavior on the supercapacitor performance is important to mitigate the multifaceted issues of supercapacitors. Aqueous hybrid supercapacitors (AHSCs) employ an energy-dense and another power-dense electrode to balance energy and power. Herein, two AHSC device architectures using a pseudocapacitive FeS2@Ti3C2Tx anode in both a capacitive high-surface-area carbon (HSAC) in one and a pseudocapacitive VO2 in another are rationally studied. The growth of FeS2 on metallic MXenes (FeS2@Ti3C2Tx) improves its capacitance from 285 to 437 F g–1 in a stable potential window of 0 to −0.8 V. FeS2@Ti3C2Tx||VO2 demonstrates a wider voltage window (1.8 V) and higher energy density (29.2 Wh kg–1) than FeS2@Ti3C2Tx||HSAC, owing to the higher oxygen evolution reaction onset potential of the VO2 (0.9 V) than the HSAC (0.65 V), whereas FeS2@Ti3C2Tx||HSAC demonstrates a higher power density owing to the power-dense HSAC. FeS2@Ti3C2Tx||VO2 delivers a higher self-discharge voltage of 1.27 V and a lower leakage current than FeS2@Ti3C2Tx||HSAC, originating from all pseudocapacitive electrodes and demonstrating the benefits of all pseudocapacitive-based AHSCs.