Redox-active polymer-grafted particles as redox mediators for enhanced charge transport in solution-state electrochemical systems

Abstract

Efficient charge transport pathways in solutions of redox-active polymers are essential for advancing next-generation energy storage systems. Herein, we report the grafting of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA) polymer brushes onto silica particles with different molecular weights and grafting densities, and the impact of these composite particles in solutions of PTMA. The polymer-grafted particles are characterized using Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS) techniques. The grafted polymers have molecular weights of 2.5 kDa and 5.0 kDa, with corresponding grafting densities of 0.688 and 0.378 chains nm−2 for SiO2-PTMA-2.5k and SiO2-PTMA-5k, respectively, with the grafting density decreasing with increasing graft length. To investigate the effect of these composite particles on charge transport in solutions of PTMA, different concentrations of the grafted particles were added to solutions of PTMA of different concentrations (near overlap concentration, C*) in 0.1 M LiTFSI in acetonitrile. Electrochemical analysis reveals that below C* the addition of SiO2-PTMA-5k increases the apparent diffusion coefficient (Dapp) 15.2% to 1.041 × 10−6 cm2 s−1, the exchange rate constant (kex,app) by 9.5% to 1.546 × 1011 L mol−1 s−1, and the heterogeneous electron transfer rate constant (k0) by 24.6%, to 5.526 × 10−4 cm s−1. These results indicate that the synergistic interactions between unbound PTMA polymer chains in solution and PTMA-grafted particles facilitate interchain charge transfer kinetics. This highlights that grafted redox-active particles can enhance charge transport without the limitations of polymer-only solutions (e.g., chain entanglement) and presents a promising design strategy for high-performance electrochemical applications, such as redox flow batteries (RFBs).

Graphical abstract: Redox-active polymer-grafted particles as redox mediators for enhanced charge transport in solution-state electrochemical systems

Supplementary files

Article information

Article type
Edge Article
Submitted
03 Jan 2025
Accepted
27 Mar 2025
First published
27 Mar 2025
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2025, Advance Article

Redox-active polymer-grafted particles as redox mediators for enhanced charge transport in solution-state electrochemical systems

M. Avais, R. M. Thakur, E. Fox, J. L. Lutkenhaus and E. B. Pentzer, Chem. Sci., 2025, Advance Article , DOI: 10.1039/D5SC00051C

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