Effect of wide reactant relative humidity on PEMFC electrochemical and thermodynamic performance from both global and local perspectives

For realizing high-power and high-efficiency operation of proton exchange membrane fuel cell (PEMFC), influence mechanism of relative humidity (RH) on the fuel cell performance was explored in this study. Combining experimental and simulation methods, the effect of wide gas humidification on the fuel cell output power and irreversible losses was comprehensively studied. Rising RH negatively influenced PEMFC electrochemical and thermodynamic properties at I = 1.6 A/cm2. Humidification of the gas can lead to a maximum increase of 36 %, 43 % and 14.5 % in cell exergy efficiency at I = 0.2-0.4 A/cm2, I = 0.4-1.2 A/cm2 and I = 1.2-1.4 A/cm2, respectively. The effect of RH on the pressure drop at a wide current densities was identified using a two-phase multiplier, and further can be categorized into three zones. Electrochemical impedance spectroscopy (EIS) results showed that mass transfer losses and activation losses are keys to influence the characteristics of the above regions. Cathode catalyst layer (CCL) and proton exchange membrane (PEM) contributed more than 90 % to thermal irreversible loss, whose entropy generation rates change is consistent with activation loss. These study results can provide theoretical support for the development of PEMFC with high output power and high exergy efficiency at wide gas humidification conditions.