7 Search Results

Successful development of catalysts for electrochemical formic acid oxidation (FAO) requires finding an optimal balance between catalytic performance (activity, stability, and selectivity) and catalyst cost. While platinum is one of the most active catalyst materials for FAO, it suffers from performance loss at low overpotentials due to poisoning with CO, which is one of the intermediates formed in the so-called indirect path of FAO. In this work, we explored the synergistic effects of the supporting material and annealing temperature on the performance of Pt thin films for FAO in acidic media. Compared to the as-prepared Pt films, the annealed filmsmore » show up to 5-fold and 15-fold improvement for FAO on Pt@Ni and Pt@Cr, respectively. In conclusion, while the most active Pt@Ni thin film shows the lowest stability, the most active Pt@Cr thin film is also the most stable, challenging conventional trade-offs in electrocatalysis and providing a promising candidate for FAO nanocatalyst synthesis.« less

Intrinsically stable materials are desirable for constructing energy storage devices, which aim to demonstrate durability under the harsh electrochemical conditions that are detrimental to their lifespan. However, in this study it is demonstrated that the intrinsic instability of an electrochemical interface can be converted from an obstacle into an advantage. In aqueous zinc-ion batteries, manganese oxide (MnO₂) exhibits considerable dissolution even in electrolyte containing Mn²⁺ salt. Balancing with redeposition alleviates the harmful impact of dissolution on performance and alters the trajectory of the active phase. Inclusion of Mn²⁺ salt in the electrolyte induces MnO₂ deposition on all conductive surfaces, requiringmore » that distracting side reactions be eliminated to isolate the dynamics of the active phase. Under conditions favoring dissolution, capacity decreases dramatically and a highly crystalline tetragonal ZnMn₂O₄ phase forms, while redeposition helps maintain capacity and promotes a disordered cubic Zn-rich phase. Ultimately, this work aims to illuminate a path forward to unlock the potential of batteries made with materials that are fundamentally unstable in their operating environment.« less

The feasible commercialization of alkaline, phosphoric acid and polymer electrolyte membrane fuel cells depends on the development of oxygen reduction reaction (ORR) electrocatalysts with improved activity, stability, and selectivity. The rational design of surfaces to ensure these improved ORR catalytic requirements relies on the so-called "descriptors" (e.g., the role of covalent and noncovalent interactions on platinum surface active sites for ORR). Here, we demonstrate that through the molecular adsorption of melamine onto the Pt(111) surface [Pt(111)-M_ad], the activity can be improved by a factor of 20 compared to bare Pt(111) for the ORR in a strongly adsorbing sulfuric acid solution.more » Additionally, the M_ad moieties act as "surface-blocking bodies," selectively hindering the adsorption of (bi)sulfate anions (well-known poisoning spectator of the Pt(111) active sites) while the ORR is unhindered. This modified surface is further demonstrated to exhibit improved chemical stability relative to Pt(111) patterned with cyanide species (CN_ad), previously shown by our group to have a similar ORR activity increase compared to bare Pt(111) in a sulfuric acid electrolyte, with Pt(111)-M_ad retaining a greater than ninefold higher ORR activity relative to bare Pt(111) after extensive potential cycling as compared to a greater than threefold higher activity retained on a CN_ad-covered Pt(111) surface. We suggest that the higher stability of the Pt(111)-M_ad interface stems from melamine's ability to form intermolecular hydrogen bonds, which effectively turns the melamine molecules into larger macromolecular entities with multiple anchoring sites and thus more difficult to remove.« less

Perovskite oxides are an important class of oxygen evolution reaction (OER) catalysts in alkaline media, despite the elusive nature of their active sites. In this work, we demonstrate that the origin of the OER activity in a La_1-xSrxCoO₃ model perovskite arises from a thin surface layer of Co hydr(oxy)oxide (CoO_xH_y) that interacts with trace-level Fe species present in the electrolyte, creating dynamically stable active sites. Generation of the hydr(oxy)oxide layer is a consequence of a surface evolution process driven by the A-site dissolution and O-vacancy creation. In turn, this imparts a 10-fold improvement in stability against Co dissolution and amore » 3-fold increase in the activity-stability factor for CoO_xH_y/ LSCO when compared to nanoscale Co-hydr(oxy)oxides clusters. Our results suggest new design rules for active and stable perovskite oxide-based OER materials.« less

Deployment of proton-exchange membrane fuel cells is limited by the durability of Pt-nanoscale catalysts during cathodic oxygen reduction reactions. Dissolution processes on single crystalline and thin film surfaces are now correlated leading to the design of PtAu catalysts with suppressed dissolution. A remaining challenge for the deployment of proton-exchange membrane fuel cells is the limited durability of platinum (Pt) nanoscale materials that operate at high voltages during the cathodic oxygen reduction reaction. In this work, atomic-scale insight into well-defined single-crystalline, thin-film and nanoscale surfaces exposed Pt dissolution trends that governed the design and synthesis of durable materials. A newly definedmore » metric, intrinsic dissolution, is essential to understanding the correlation between the measured Pt loss, surface structure, size and ratio of Pt nanoparticles in a carbon (C) support. It was found that the utilization of a gold (Au) underlayer promotes ordering of Pt surface atoms towards a (111) structure, whereas Au on the surface selectively protects low-coordinated Pt sites. Finally, this mitigation strategy was applied towards 3 nm Pt₃Au/C nanoparticles and resulted in the elimination of Pt dissolution in the liquid electrolyte, which included a 30-fold durability improvement versus 3 nm Pt/C over an extended potential range up to 1.2 V.« less