Redox-active ligand-mediated assembly for high-performance transition metal oxide nanoparticle-based pseudocapacitors

Abstract

The important issues in preparing transition metal oxide nanoparticle (TMO NP)-based energy storage electrodes, such as pseudocapacitor electrodes, are to effectively minimize the amount of electrochemically inactive organics (i.e., polymeric binders and ligands stabilizing NPs) and simultaneously increase the amount of high-energy TMO NPs within a limited electrode area/volume without a significant loss in charge transfer kinetics. Herein, we introduce a redox-active ligand-mediated layer-by-layer (LbL) assembly as a novel approach for significantly enhancing the energy storage performance of TMO NP-based pseudocapacitor electrodes. In this study, high-energy TMO NPs and conductive NPs are periodically LbL-assembled using redox-active porphyrin ligands instead of polymeric binders. During LbL deposition, the insulating native ligands on the NP surface are successfully exchanged with carboxylic acid-functionalized porphyrin ligands, forming a densely NP-packed structure that can minimize the mass and volume of electrochemically inactive components. Based on this redox-active ligand-mediated LbL approach, the resultant pseudocapacitor electrodes exhibit much higher energy capacities (areal, volumetric, and specific capacities) and superior rate capability than insulating polymeric ligand-mediated electrodes as well as previously reported electrodes. Our approach can provide a fundamental basis for fully exploiting the energy efficiency of components and further designing a variety of high-performance electrochemical electrodes. © 2022 Elsevier B.V. All rights reserved.