A mathematical model for the iron/chromium redox battery

A mathematical model has been developed to describe the isothermal operation of a single anode-separator-cathode unit cell in a redox-flow battery and has been applied to the NASA iron/chromium system. The model, based on porous electrode theory, incorporates redox kinetics, mass transfer, and ohmic effects as well as the parasitic hydrogen reaction which occurs in the chromium electrode. A numerical parameter study was carried out to predict cel performance to aid in the rational design, scale-up, and operation of the flow battery. The calculations demonstrate: an optimum electrode thickness and electrolyte flow rate exist; the amount of hydrogen evolved and, hence, cycle faradaic efficiency, can be affected by cell geometry, flow rate, and charging procedure; countercurrent flow results in enhanced cell performance over cocurrent flow; and elevated temperature operation enhances cell performance.