Quantifying Oxygen Ingress and Its Impact on Solution Chemistry for Flow Cells Operated in Air

A flow battery-adapted redox flow cell is designed to measure the rate of ambient oxygen diffusing into air-sensitive electrolytes. This simple method uses a viologen radical cation-mediated two-electron oxygen reduction reaction to quantify oxygen-related performance issues affecting myriad electrochemical applications where a glovebox is impractical. Generally, using low-oxygen-permeability materials in a typical bench-scale flow cell configuration, ambient oxygen can be expected to saturate the electrolyte after about 15 min, leading to self-discharge capacity losses on the order of 13 mAh d^–1, with additional losses of 2.4 mAh d^–1 cm_silicone^–2 when employing silicone. Th ORR redox mediator used for oxygen ingress measurements herein, dextrosil viologen, is an emerging organic flow battery anolyte with a molecular design that enables tolerance toward hydroxide and peroxide accumulation in solution.