Mitigation strategy of organic redox mediator crossover in chemically regenerative redox fuel cells

A modified (2, 2, 6, 6-tetramethylpiperidin-1-yl) oxyl (TEMPO) was developed for use as an organic mediator in chemically regenerative redox fuel cells (CRRFC). The main challenge of CRRFC is to determine the optimal redox molecule in terms of redox potential, stability, and fast regeneration kinetics. In order to avoid crossover of the TEMPO-based organic mediator through the membrane, the electroactive specie was functionalized with polyethylene glycol (PEG) chains of different lengths and the electrochemical properties of the synthesized species were assessed. Such chemical modification prevents the crossover of the redox mediators through the membrane, as demonstrated by ex situ analytical electrochemistry. The developed fuel cell provided a maximum power density of 110 mW cm-2 (150 mA cm-2 at 0.6 V) with TEMPO-based mediators bearing PEG chains, while exhibiting a higher stability than a cell using a commercial reference mediator. This study opens the route to design and select new organic mediators for applications in CRRFC and further improvements to enhance their stability over time.