Morphological engineering of Cu2S electrodes to enhance pseudocapacitance through redox mediator integration

Abstract

Redox mediators (RMs) have emerged as a promising strategy for enhancing electrochemical performance by enabling additional redox reactions within the electrolyte. However, most studies on RMs have focused on electric double-layer capacitors, leaving their potential in pseudocapacitor systems largely unexplored. This study addresses this gap by systematically investigating the interaction mechanisms between RMs and pseudocapacitor electrodes with distinct morphologies. Cu2S-based electrodes were synthesized in one-dimensional nanorod (1D-CNR) and two-dimensional nanosheet (2D-CNS) configurations. Potassium ferricyanide (K3Fe(CN)6) was employed as the RM to activate surface redox reactions and enhance charge storage at the electrode–electrolyte interface. Electrochemical analyses revealed that introducing 0.1 M RM significantly increased areal capacitance at a current density of 10 mA cm–2—from 0.76 to 1.80 F cm–2 for 1D-CNR and from 0.63 to 2.36 F cm–2 for 2D-CNS. This performance enhancement was attributed to the surface adsorption of [Fe(CN)6]3–/4– ions, which suppressed OH– intercalation into the Cu2S lattice and promoted a transition toward electric double-layer (EDL)-dominated charge storage. In 1D-CNR electrodes, the RM preferentially adsorbed at the nanorod tips, resulting in localized EDL enhancement and improved structural stability. In contrast, 2D-CNS electrodes exhibited uniform surface activation, yielding a larger active area and higher overall capacitance. These findings underscore the role of RMs as active contributors to charge storage, particularly when combined with morphology-engineered electrodes. This work offers new insights into integrating redox-active electrolytes in pseudocapacitor systems, enabling surface-controlled, stable, and high-performance energy storage.