Impact of Platinum Loading and Layer Thickness on Cathode Catalyst Degradation in PEM Fuel Cells

Abstract

We investigated the effect of platinum loading and layer thickness on cathode catalyst degradation by a comprehensive in-situ and scanning tunneling electron microscopy energy dispersive spectroscopy (STEM-EDS) characterization. To decouple the effect of platinum loading and layer thickness, the experiments were categorized in two sets, each with cathode loadings varying between 0.1 and 0.4 mgPt cm-2: (i) Samples with a constant Pt/C ratio and thus varying layer thickness, and (ii) samples with varying Pt/C ratios, achieved by dilution with bare carbon, to maintain a constant layer thickness at different platinum loadings. Every MEA was subjected to an accelerated stress test, where the cell was operated for 45,000 cycles between 0.6 and 0.95 V. Regardless of the Pt/C ratio, a higher relative loss in electrochemically active surface area was measured for lower Pt loadings. STEM-EDS measurements showed that Pt was mainly lost close to the cathode – membrane interface by the concentration driven Pt2+ ion flux into the membrane. The size of this Pt-depletion zone has shown to be independent on the overall Pt loading and layer thickness, hence causing higher relative Pt loss in low thickness electrodes, as the depletion zone accounts for a larger fraction of the catalyst layer

Does the platinum-loading in proton-exchange membrane fuel cell cathodes influence the durability of the membrane-electrode assembly?

“…S1† and Table 1), overall leading to a high oxygen transport resistance in the MEA at BOT. On the contrary, the high cathode Pt loading MEA (0.3-Pt/C) initially exhibits a low oxygen transport resistance at BOT; this trend overall agrees with the literature 24,27 and notably the seminal study of Greszler et al : “ the electrode oxygen transport resistance is inversely proportional to platinum loading or, equivalently, platinum surface area ”. 7 …”

“…S1,† related to the EIS diagrams recorded for the four x -Pt/C MEAs at 1 A cm −2 ), in agreement with the literature. 24–26…”

“…S1, † related to the EIS diagrams recorded for the four x-Pt/C MEAs at 1 A cm −2 ), in agreement with the literature. [24][25][26] Comparing BOT vs. EOT, all the polarization curves exhibit significant voltage losses for all the investigated MEAs, which seems inversely correlated to the cathode Pt loading: the larger the loading the smaller the losses. It is more explicit in Fig.…”

Catalyst Development for High‐Temperature Polymer Electrolyte Membrane Fuel Cell (HT‐PEMFC) Applications

“…[65] Efforts to enhance the intrinsic activity of pure Pt and reduce the content of precious group metal (PGM) catalysts, while maintaining fuel cell (FC) performance, have been ongoing to achieve large-scale technology commercialization. [66][67][68] Aiming at high activity, DFT studies show that a pure Pt catalyst with maximized surface sites of generalized coordination number (GCN) between 7.5 and 8.3 could be ideal. [69] The above would tailor Pt particle size in the range within 1.8-3 nm.…”

Multigram-Scale Synthesis of High-Pt-Content PtCo Intermetallic Catalysts for Proton Exchange Membrane Fuel Cells

“…This means that the cathode catalyst applied to HDVs needs a high Pt content 23 to make the cathode layer not too thick to ensure efficient mass transport. 24 Note that several approaches have been proposed recently to address the sintering issue of IMC catalysts, 25 such as KCl matrix-assisted annealing, 26 anchoring preparation with heteroatom-doped carbons, 27 surface coating of IMC nanoparticles with carbons 28 or metal oxides, 29 and thermal decomposition of bimetallic organic compounds. 30 Nevertheless, these methods either challenge achieving size control for PtCo IMC catalysts with a high-Pt content or involve tedious preparation processes, posing a barrier to large-scale production.…”