Search for: All records

As the development of polymer electrolyte membrane fuel cells (PEMFCs) has sped up in recent years, producing active and durable electrocatalysts has become an increasingly important technical challenge. Platinum–cobalt (Pt–Co) alloy electrocatalyst has been commercially applied to hydrogen-powered fuel cell vehicles, and their intermetallic forms promise better durability, which is crucial to satisfy the 8000 h lifetime target of heavy-duty vehicles and other transportation options. In this feature article, we first present the atomically ordered structures of Pt–Co intermetallic, then discuss the thermodynamic and kinetic driving forces for making the PtCo-based intermetallic nanoparticles with desired structural attributes, followed by recent examples to illustrate how to achieve better control in composition, size, and shape. Discussion on the relationship between the key structural features and catalytic performance is focused on the application of Pt–Co intermetallic nanostructures as oxygen reduction reaction (ORR) electrocatalysts for hydrogen-powered PEMFCs. We emphasize specifically the importance of intermetallic structures for enhancing the durability and summarize the characterizations of their electrocatalytic performance in both three-electrode system and full cell studies. Finally, we provide our perspectives on the design, synthesis, characterization, and property studies of Pt–Co intermetallic nanoparticles as ORR electrocatalysts. This article should provide a new understanding on the design of ORR electrocatalytic applications using this class of intermetallics. 

This paper describes the development of mixed B-site pyrochlore Y₂MnRuO₇electrocatalyst for oxygen evolution reaction (OER) in acidic media, a challenge for the development of low-temperature electrolyzer for green hydrogen production. Recently, several theories have been developed to understand the reaction mechanism for OER, though there is an  uncertainty in most of the cases, due to the complex surface structures. Several key factors such as lattice oxygen, defect, electronic structure, oxidation state, hydroxyl group and conductivity were identified and shown to be important to the OER activity. The contribution of each factor to the performance however is often not well understood, limiting their impact in guiding the design of OER electrocatalysts. In this work, we showed mixed B-site pyrochlore Y₂MnRuO₇catalyst exhibits 14 times higher turnover frequency (TOF) than RuO₂while maintaining a low overpotential of ~ 300 mV for the entire testing period of 24 h in acidic electrolyte. X-ray photoelectron spectroscopy (XPS) analysis reveals that this B-site mixed pyrochlore Y₂MnRuO₇has a higher oxidation state of Ru than those of Y₂Ru₂O₇, which could be crucial for improving OER performance as the broadened and lowered Ru 4d band resulted from the B-site substitution by Mn is beneficial to the OER kinetics.

 

The world-renowned Miocene Clarkia paleolake in northern Idaho (USA) is closely associated with Columbia River Basalt Group volcanism. The flood basalt dammed a local drainage system to form the paleolake, which preserved a plant fossil Lagerstätte in its deposits. However, the precise age and temporal duration of the lake remain unsettled. We present the first unequivocal U-Pb zircon ages from interbedded volcanic ashes at the P-33 type location, constraining the deposition to 15.78 ± 0.039 Ma. Using micro–X-ray fluorescence and petrographic and spectral analyses, we establish the annual characteristics of laminations throughout the stratigraphic profile using the distribution of elemental ratios, mineral assemblages, and grain-size structures, as well as organic and fossil contents. Consequently, the ~7.5-m-thick varved deposit at the type location P-33 represents ~840 yr of deposition, coincident with the end of the main phase of Columbia River Basalt Group eruptions during the Miocene Climate Optimum. The timing and temporal resolution of the deposit offer a unique opportunity to study climate change in unprecedented detail during global warming associated with carbon-cycle perturbations.