Towards High-Energy-Density Pseudocapacitive Flowable Electrodes by the Incorporation of Hydroquinone

This study reports an investigation of hydroquinone (HQ) as a multielectron organic redox molecule to enhance the performance of flowable electrodes. Two different methods to produce high-performance pseudocapacitive flowable electrodes were investigated for electrochemical flow capacitors. First, HQ molecules were deposited on carbon spheres (CSs) by a self-assembly approach using various HQ loadings. In the second approach, HQ was used as a redox-mediating agent in the electrolyte. Flowable electrodes composed of HQ showed a capacitance of 342 F g^-1, which is >200 % higher than that of flowable electrodes based on nontreated CSs (160 F g^-1), and outperformed (in gravimetric performance) many reported film electrodes. A similar trend in capacitance was observed if HQ was used as a redox agent in the electrolyte; however, its poor cycle life restricted further consideration. In addition, a twofold increase in capacitance was observed under flow conditions compared to that of previous studies.