Simulation of Mode-Switching Methods' Effect on Mass Transfer in a Unitized Regenerative Fuel Cell

Unitized regenerative fuel cells are unique devices that combine the functions of fuel cells and water electrolysis in one system. The internal mass-transport mechanisms present in a unitized regenerative fuel cell are closely related to the mode-switching method of the cell. A two-dimensional, single-phase, isothermal, multicomponent, and transient model was developed to investigate the characteristics of mass transfer coupled with electrochemical reaction in a unitized regenerative fuel cell under interval and continuous mode-switching methods. Results indicate that the average gas mass fractions in the gas-flow channel, gas diffusion layer, and catalyst layer are the same under the two different mode-switching methods. Gas mass fractions in different layers exhibit the same variation trend and gradient during the first and second cycles of interval and continuous switching. Under the two different mode-switching methods, the gradient of the gas mass fraction in fuel cell mode is larger than that in water electrolysis mode. The transient response of these layers under two different mode-switching methods is delayed by approximately 0.2s compared with that of the operating voltage.