Charge‐Transfer Effects of Organic Ligands on Energy Storage Performance of Oxide Nanoparticle‐Based Electrodes

Abstract

One of the most difficult challenges related to pseudocapacitive nanoparticle (PC NP)‐based energy storage electrodes with theoretically high capacity is to overcome the sluggish charge‐transfer kinetics that result from the poorly conductive PC NPs and bulky/insulating organics (i.e., organic ligands and/or polymeric binders) within the electrodes. Herein, it is reported that physical/chemical functionalities of organic ligands and their molecular‐scale coating onto NPs have considerable effects on the rate capability and capacity of oxide NP‐based pseudocapacitor electrodes. For this study, pseudocapacitive iron oxide (Fe3O4) NPs are layer‐by‐layer (LbL)‐assembled with conductive indium tin oxide (ITO) NPs using various types of organic ligands (or linkers). In particular, hydrazine ligands, which have extremely small molecular size and strong chemical reducing properties, can effectively remove bulky organic ligands from the NP surface, and thus reduce the separation distance between neighboring NPs. Simultaneously, the hydrazine ligands significantly increase the number of oxygen vacancies on Fe3O4 and ITO NPs during LbL deposition, which markedly enhances the rate capability and capacitance of the electrodes compared to other organic ligands with bulky size and/or without reducing properties. This approach can provide a fundamental basis for developing and designing various high‐performance electrochemical electrodes based on metal oxide NPs.

Overcoming the Trade‐Off between Optical Transmittance and Areal Capacitance of Transparent Supercapacitors for Practical Application

“…In fact, it has been reported that capacitive TMOs, including Mn 3 O 4 , do not exhibit their theoretically expected performance due to their inherently low electrical conductivity (on the order of 10 −7 -10 −8 S cm −1 ). [31,32] On the other hand, SnO 2 with excellent conductivity of 0.21 S cm −1 and bulk electron mobility of 240 cm 2 V −1 s −1 would promote charge transport in the TMO electrodes. [33,34] The gradual increase in electrical conductivity by incorporating SnO 2 NPs was confirmed by I-V measurements (Figure 3i).…”

Carbon Nanocluster‐Mediated Nanoblending Assembly for Binder‐Free Energy Storage Electrodes with High Capacities and Enhanced Charge Transfer Kinetics

“…We examined the electrical properties of the (Fe 3 O 4 NP/CCN) 20 composites to verify the roles of CCNs as conductive linkers (Figure 1f; Figure S10, Supporting Information). In this case, the CCN-mediated Fe 3 O 4 NP films exhibited high current levels (≈10 −1 mA) with ohmic conduction behaviors (𝛼 = 1.10) in the relationship between current density (J) and electric field (E) [J ∝ E 𝛼 ]; [41] this result was in stark contrast to the pristine OA-Fe 3 O 4 NP film showing insulating properties (current levels of ≈10 −8 mA with 𝛼 = 0.01). These improvements in the electrical properties of the CCN-mediated films occurred mainly due to the formation of a uniformly nanoblended/interconnected structure and the effective removal of insulating native ligands by conductive CCNs during the LbL assembly, which markedly reduced the contact resistance at the interfaces between adjacent Fe 3 O 4 NPs.…”

Emerging Challenges in Textile Energy Electrodes: Interfacial Engineering for High‐Performance Next‐Generation Flexible Energy Storage Devices

“…In particular, the presence of polymeric ligands and linkers on the surface of TMO NPs can act as insulating barriers that hinder the access and transfer of charge carriers (electrons and ions) at the interfaces of adjacent electrode components, such as current collector/TMO NP, TMO NP/TMO NP, and TMO NP/electrolyte. [153][154][155] Therefore, a crucial strategy for achieving high-performance textile energy electrodes with densely packed TMO NP arrays lies in the ligand-controlled interfacial design of TMO NPs.…”