Patent attributes
A method of operating an electrochemical conversion assembly is provided. According to the method, an assembly warm-up operation is executed by increasing the temperature TSTACK of the membrane electrode assembly. Next, stoichiometry-based control of the relative humidity (RH) of one of the reactant flowfields is initiated when the temperature TSTACK exceeds a threshold temperature T0. The stoichiometry-based RH control comprises a reduction in the relative humidity from a value RHWET exceeding 100% relative humidity to a value RHDRY less than 100% relative humidity. The relative humidity value RHDRY is sufficiently low to permit reduction of an initial membrane hydration λWET in the membrane electrode assembly. The reduction in the relative humidity to RHDRY is achieved by controlling the stoichiometry of the reactant flowfield and the temperature of the membrane electrode assembly such that the reduction to RHDRY decreases substantially continuously, relative to portions of the RH profile of the reactant flowfield prior to initiation of the stoichiometry-based control. The cell transitions from the stoichiometry-based RH control to generally elevated-temperature, temperature-based RH control when membrane hydration in the membrane electrode assembly falls below a target membrane hydration value λDRY. Additional methods and corresponding systems are contemplated.
