Exploration of significant influences of the operating conditions on the local O2 transport in proton exchange membrane fuel cells (PEMFCs)

Abstract

A drastic reduction of the Pt loading in the cathode catalyst layers (CCLs) of proton exchange membrane fuel cells (PEMFCs) is much desired. However, a decrease in Pt loading inevitably leads to an unexpected increase of local O₂ transport resistance (r_Local) and severely weakens the fuel cell performance, particularly at high current densities. Thus, it is both urgent and meaningful to explore the impacts of the operating conditions on r_Local in CCLs and therefore to clarify the intrinsic mechanism. Herein, we systematically explore the influences of the operating conditions, in terms of the dry O₂ mole fraction, the relative humidity, the operating pressure and the temperature on r_Local using limiting current measurements combined with mathematical calculations. The results show that, in contrary to the established rules, r_Local in CCLs of PEMFCs is aggravated when the dry O₂ mole fraction or the operating pressure are increased. It is also experimentally found that r_Local in CCLs is alleviated with the increase in the relative humidity or the operating temperature. Moreover, an adsorption controlled solution-diffusion model is proposed to illuminate the local O₂ transport behavior in CCLs of PEMFCs, and it accounts for the influence of the dry O₂ mole fraction on r_Local in CCLs.