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 cmsilicone–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.