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

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 O transport resistance (r) 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 in CCLs and therefore to clarify the intrinsic mechanism. Herein, we systematically explore the influences of the operating conditions, in terms of the dry O mole fraction, the relative humidity, the operating pressure and the temperature on r using limiting current measurements combined with mathematical calculations. The results show that, in contrary to the established rules, r in CCLs of PEMFCs is aggravated when the dry O mole fraction or the operating pressure are increased. It is also experimentally found that r 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 O transport behavior in CCLs of PEMFCs, and it accounts for the influence of the dry O mole fraction on r in CCLs.