Effect of liquid water accumulation in electrolytic cell mode on start-up performance of fuel cell mode of unitized regenerative fuel cells

Abstract

Due to the increased popularity of hydrogen-based electricity generation technology, unitized regenerative fuel cells can be regarded as an electricity conversion device coupling two-phase behaviors. Water management inside the cell is important to complete a suitable start-up characteristic of unitized regenerative fuel cells when changing the working modes. In this study, investigations on fundamental of water expelling principles and influence of residual liquid water on cell behavior are performed numerically utilizing a three-dimensional two–phase model. The model involves in charge, gaseous species, liquid water, dissolved water and heat transfer. Experiments are conducted to validate reaction modes through voltage-current density curves. Dynamic responses of water in various phases (liquid and dissolved phase) are obtained in a purging mode, which is initiated by an electrolytic cell mode. Gas purging procedure has various of impacts on the performance under different purging time conditions. Under the same purging result condition, operational voltage exhibits significant influence on cell performance at the start-up stage. The relative humidity has an important influence on output performance. Those results originate from the complex effects of the residual water in a purging mode, as well as the liquid water condensed in during the fuel cell operation procedure.