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

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

Stable mass-selected AuTiO_x nanoparticles for CO oxidation

Stability under reactive conditions poses a common challenge for cluster- and nanoparticle-based catalysts. Since the catalytic properties of &lt;5 nm gold nanoparticles were first uncovered, optimizing their stability at elevated temperatures for CO oxidation has been a central theme. Here we report direct observations of improved stability of AuTiOx alloy nanoparticles for CO oxidation compared with pure Au nanoparticles on TiO2. The nanoparticles were synthesized using a magnetron sputtering, gas-phase aggregation cluster source, size-selected using a lateral time-of-flight mass filter and deposited onto TiO2-coated micro-reactors for thermocatalytic activity measurements of CO oxidation. The AuTiOx nanoparticles exhibited improved stability at elevated temperatures, which is attributed to a self-anchoring interaction with the TiO2 substrate. The structure of the AuTiOx nanoparticles was also investigated in detail using ion scattering spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The measurements showed that the alloyed nanoparticles exhibited a core-shell structure with an Au core surrounded by an AuTiOx shell. The structure of these alloy nanoparticles appeared stable even at temperatures up to 320 °C under reactive conditions, for more than 140 hours. The work presented confirms the possibility of tuning catalytic activity and stability via nanoparticle alloying and self-anchoring on TiO2 substrates, and highlights the importance of complementary characterization techniques to investigate and optimize nanoparticle catalyst designs of this nature.</p

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

Cost and lifetime currently hinder widespread commercialization of polymer electrolytemembrane fuel cells (PEMFCs). Reduced electrode Pt loadings lower costs; however, the impactof metal loading (on the support) and its relation to degradation (lifetime) remain unclear. Thelimited research on these parameters stems from synthetic difficulties and lack of in situanalytics. This study addresses these challenges by synthesizing 2D and 3D Pt/C model catalystsystems via two precise routes and systematically varying the loading. Pt dissolution wasmonitored using on-line inductively coupled plasma mass spectrometry (on-line-ICP-MS), whileX-ray spectroscopy techniques were applied to establish the oxidation states of Pt in correlationwith metal loading. Dissolution trends emerge which can be explained by three particleproximity dependent mechanisms: (1) shifts in the Nernst dissolution potential, (2) redeposition,and (3) alteration of Pt oxidation states. These results identify engineering limitations, whichshould be considered by researchers in fuel cell development and related fields. <br /