Improvement of low-humidity performance of PEMFC by addition of hydrophilic SiO₂ particles to catalyst layer

Hydrophilic SiO₂ particles are added to the catalyst layer of a fuel cell membrane-electrode assembly (MEA) to improve wettability and performance at low-humidity conditions. The SiO₂ added MEAs are prepared by spraying technique and the contact angle is measured by the sessile drop method. The effects of SiO₂ additions of 0, 20, 40 and 60 wt.% (based on Pt/C) are investigated for various relative humidity levels in the anode and the cathode. The increased wettability of the cathode catalyst layer exerts an adverse effect on cell performance by causing flooding; this result demonstrates the hydrophilicity of SiO₂. With 40 wt.% addition of SiO₂ to the anode catalyst layer, the current density at 0.6 V and 0% relative humidity of the anode is 93% of that at 100% relative humidity. By comparison, the performance of a cell using a MEA with no added SiO₂ is only 85% of that at 0% relative humidity. A MEA with SiO₂ addition in the anode gives a higher performance at 60% relative humidity of the cathode than one with an undoped MEA. Increased wettability of the anode catalyst layer caused by SiO₂ addition renders it easy to absorb water from back diffusion.