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 (rLocal) 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 rLocal 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 rLocal using limiting current measurements combined with mathematical calculations. The results show that, in contrary to the established rules, rLocal in CCLs of PEMFCs is aggravated when the dry O2 mole fraction or the operating pressure are increased. It is also experimentally found that rLocal 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 rLocal in CCLs.