Charge-Transfer-Modulated Transparent Supercapacitor Using Multidentate Molecular Linker and Conductive Transparent Nanoparticle Assembly

Abstract

One of the most critical issues in preparing high-performance transparent supercapacitors (TSCs) is to overcome the trade-off between areal capacitance and optical transmittance as well as that between areal capacitance and rate capability. Herein, we introduce a TSC with high areal capacitance, fast rate capability, and good optical transparency by minimizing the charge transfer resistance between pseudocapacitive nanoparticles (NPs) using molecular linker-and conductive NPmediated layer-by-layer (LbL) assembly. For this study, bulky ligand-stabilized manganese oxide (MnO) and indium tin oxide (ITO) NP multilayers are LbL-assembled through a ligand exchange reaction between native ligands and small multidentate linkers (tricarballylic acid). The introduced molecular linker substantially decreases the separation distance between neighboring NPs, thereby reducing the contact resistance of electrodes. Moreover, the periodic insertion of ITO NPs into the MnO NP-based electrodes can lower the charge transfer resistance without a meaningful loss of transmittance, which can significantly improve the areal capacitance. The areal capacitances of the ITO NP-free electrode and the ITO NP-incorporated electrode are 24.6 mF cm −2 (at 61.6% transmittance) and 40.5 mF cm −2 (at 60.8%), respectively, which outperforms state of the art TSCs. Furthermore, we demonstrate a flexible symmetric solid-state TSC that exhibits scalable areal capacitance and optical transmittance.

Nanoparticle‐Based Electrodes with High Charge Transfer Efficiency through Ligand Exchange Layer‐by‐Layer Assembly

“…Similarly, the areal capacitance of MnO NP‐based pseudocapacitor electrodes could be significantly increased by the insertion of OAm–ITO NPs using the abovementioned LE‐LbL assembly method (Figure 2e). [ 91 ] In this case, the charge transfer resistance ( R ct , a semicircle in the middle‐frequency region) and ion diffusion behavior (Warburg line in the low‐frequency region) of the OAm–ITO NP‐inserted electrode were significantly improved compared to the electrodes without OAm–ITO NPs (Figure 2f). That is, the periodic deposition of conductive ITO NP layers into a functional TMO NP (i.e., WO 2.72 or MnO 2 ) film through a ligand exchange reaction notably reduced the internal resistance of the electrodes, resulting in improved electrochemical performance.…”

“…Cho and co-workers reported that the modulation of surface ligands on TMO NPs can increase the electrical and electrochemical properties. [87,88,91] The removal of bulky ligands (i.e., oleylamine (OAm)) bound to the surface of electrochromic tungsten oxide (WO 2.72 ) nanorods (NRs) enhanced the coloration efficiency (CE) and response time of coloration/bleaching cycles. [88] They also showed that the electrochemical (or electrochromic) performance of WO 2.72 NR-based nanocomposites could be improved by reducing the ligand length or thickness of the ligand shell.…”

“…Recently, it was reported that the increased overall internal resistance of electrodes according to the increase in the mass loading of pseudocapacitive TMO NPs could be reduced through the periodic insertion of conductive NPs into LE-LbLassembled pseudocapacitive NP multilayers (Figure 8a−d). [91,191] In this case, the surfaces of the inserted conductive NP layers (i.e., TOA-Au NPs or OAm-ITO NPs) were covalently bonded to the amine groups of small-molecule ligands via the same ligand exchange reaction as that used for the TMO NP layers and acted as an electron transport layer between vertically adjacent TMO layers (Figure 8a,c). In addition, the periodically inserted conductive NPs were uniformly distributed within the electrodes without NP agglomeration or segregation, suggesting the formation of efficient electron paths (Figure 8b,d).…”

“…Adapted with permission. [ 91 ] Copyright 2019, American Chemical Society. b) Schematic illustration of the periodic insertion of the Au NP layer into Fe 3 O 4 NP‐based multilayer negative electrodes.…”

Transparent Electrodes for Energy Storage Devices

“…[2,23] The chargestorage capability of these conductive substrates is negligible so that they need to cooperate with other electroactive materials to gain a high FoM c . [26,[68][69][70][71][72][73] Owing to the high FoM e , the FoM c of ITO-based TESEs stands on a pole position among various types of TESEs (Figure 3a). For example, Yim et al fixed well-defined Mn 3 O 4 nanoparticles onto an ITO substrate in the presence of 1,2-ethanedithiol.…”