The Dissolution Dilemma for Low Pt Loading Polymer Electrolyte Membrane Fuel Cell Catalysts

Abstract

Cost and lifetime currently hinder widespread commercialization of polymer electrolyte membrane fuel cells (PEMFCs). Reduced electrode Pt loadings lower costs; however, the impact of metal loading (on the support) and its relation to degradation (lifetime) remain unclear. The limited research on these parameters stems from synthetic difficulties and lack of in situ analytics. This study addresses these challenges by synthesizing 2D and 3D Pt/C model catalyst systems via two precise routes and systematically varying the loading. Pt dissolution was monitored using on-line inductively coupled plasma mass spectrometry (on-line-ICP-MS), while X-ray spectroscopy techniques were applied to establish the oxidation states of Pt in correlation with metal loading. Dissolution trends emerge which can be explained by three particle proximity dependent mechanisms: (1) shifts in the Nernst dissolution potential, (2) redeposition, and (3) alteration of Pt oxidation states. These results identify engineering limitations, which should be considered by researchers in fuel cell development and related fields.

Beyond Active Site Design: A Surfactant‐Free Toolbox Approach for Optimized Supported Nanoparticle Catalysts

“…Pt dissolution studies obtained at a constant loading of 30 wt.% of precious metal and show that without further effort to improve the stability of the smallest NPs, high‐power performance devices obtained by increasing Pt utilization and dispersion will not be possible by further decreasing particle sizes. However, similar Pt dissolution studies performed with constant particle size, but decreasing interparticle distance showed a trend of decreasing detected Pt dissolution at decreasing interparticle distance [56] . Such studies had not been possible using commercial catalyst materials.…”

“…Finally, with an optimized control of the size and the conditioning steps, the toolbox was recently used to independently investigate the influence of NP size and metal loading (interparticle distance) on the stability of electrocatalysts against metal dissolution [46,56] . Pt dissolution studies obtained at a constant loading of 30 wt.% of precious metal and show that without further effort to improve the stability of the smallest NPs, high‐power performance devices obtained by increasing Pt utilization and dispersion will not be possible by further decreasing particle sizes.…”

Platinum Dissolution in Realistic Fuel Cell Catalyst Layers

“…When aiming at ultra-low Pt loadings for PEMFC,i ti s crucial to discuss the impact of the catalyst loading on Pt dissolution. Previous works in this field [10,11,17] have always been conducted on model surfaces.Realistic catalyst layers on gas diffusion layers (GDL) with relevant loadings for fuel cell applications have not yet been directly investigated. Figure 2 shows the impact of catalyst loading on the dissolution of Pt in realistic catalyst layers studied with the novel GDE-ICP-MS setup.T he corresponding additional structural characterization and electrochemical data can be found in Figures S4-S8.…”

“…When aiming at ultra‐low Pt loadings for PEMFC, it is crucial to discuss the impact of the catalyst loading on Pt dissolution. Previous works in this field [10, 11, 17] have always been conducted on model surfaces. Realistic catalyst layers on gas diffusion layers (GDL) with relevant loadings for fuel cell applications have not yet been directly investigated.…”

The Oxygen Reduction Reaction on Pt: Why Particle Size and Inter-particle Distance Matter

“…Follow up work has demonstrated an improvement in ORR activity at small interparticle distance also for carbon supported high surface area electrocatalysts 36 . Very recently, it has been shown that the inter-particle distance of Pt nanoparticles deposited on two dimensional as well as three dimensional carbon supports influences the amount of dissolved Pt detected in scanning flow cell (SFC) measurements coupled to online ICP-MS 12 . Density functional theory modeling indicates that proton accumulation caused by the overlap of the EDL (at high particle density) competes with proton depletion caused by the proximity of the nanoparticles to the carbon support 37 .…”