Impact of ultra-low Pt loadings on the performance of anode/cathode in a proton-exchange membrane fuel cell

摘要

This study focuses on the elaboration of PEMFC electrodes containing ultra-low platinum (Pt) loadings by direct liquid injection metal organic chemical vapor deposition (DLI-MOCVD). DLI-MOCVD offers a large number of advantages for the elaboration of model PEMFC electrodes. First, by using different metal precursors or elaboration temperature, the size of the Pt nanoparticles and thus the intrinsic catalytic activity can easily be tailored in the nanometer range. In this work, Pt nanoparticles (1-5 nm) with remarkable low degree of agglomeration and uniform distribution were deposited onto the microporous side of a commercial gas-diffusion layer (GDL). Second, reduction of the Pt loading is made possible by varying the Pt deposition time and its influence of the cell performance can be extracted without variation of the thickness of the catalytic layer (in previous studies, a decrease of the catalyst utilization was observed when increasing the Pt loading, i.e. the thickness of the catalytic layer (CL)). The electrocatalytic activity of home-made Pt nanoparticles elaborated by DLI-MOCVD was measured in liquid electrolyte or in complete fuel cell operating on H_2/O_2 or H_2/air and compared vs. that of a commercially available electrode containing 500 μg_(Pt) cm~(-2) (Pt_(Ref500)). At the cathode, the performance of the electrodes containing 104-226 μg of Pt per cm~2 of electrode compares favorably with that of the Pt_(Ref500)) in H_2 /O_2 conditions. In H_2/air conditions, additional mass-transport losses are detected in the low-current density region but the high effectiveness of our electrodes improves the performance in the high-current density region. At the anode, the Pt loading can be reduced to 35 μg_(pt) cm~(-2) without any voltage loss in agreement with previous observations.