Pacific Northwest National Laboratory

About: Pacific Northwest National Laboratory is a facility organization based out in Richland, Washington, United States. It is known for research contribution in the topics: Catalysis & Aerosol. The organization has 11581 authors who have published 27934 publications receiving 1120489 citations. The organization is also known as: PNL & PNNL.

Using nature's blueprint to expand catalysis with Earth-abundant metals

Abstract: BACKGROUND Catalysis has had a transformative impact on society, playing a crucial role in the production of modern materials, medicines, fuels, and chemicals. Precious metals have been the cornerstone of many industrial catalytic processes for decades, providing high activity, stability, and tolerance to poisons. In stark contrast, redox catalysis essential to life is carried out by metalloenzymes that feature exclusively Earth-abundant metals (EAMs). The terrestrial abundance of some EAMs is 104 times that of precious metals, and thus their increased use would lead to reduced cost and environmental footprint. In addition to these practical considerations, EAMs display distinct reactivity profiles that originate from their characteristic electronic structure, thermochemistry, and kinetics. The behavior of EAMs provides compelling scientific opportunities for catalyst design. We assert that nature’s blueprint provides essential principles for vastly expanding the use of EAMs in sustainable catalysis. ADVANCES Exquisite tuning of the local environment around EAM active sites is key to enabling their use in catalysis. Such control is achieved in enzymatic catalysis by directed evolution of the amino acid environment, resulting in engineered enzymes with extraordinary catalytic performance. Similarly in molecular catalysis, modifying the steric and electronic properties of ligands can lead to some EAM catalysts with performance superior to that obtained from precious metal catalysts. In addition, for heterogeneous catalysts, the local environment and electronic structure of active sites can be modified by bonding to other metals or main-group elements, facilitating reaction pathways distinct from those involving precious metals. Innovations in the design of EAM catalysts demonstrate their potential to catalyze many of the reactions that traditionally relied on precious metals, although further improvements are needed in activity, selectivity, lifetime, or energy efficiency. The characteristics of EAMs point to an overarching need for improved theories and computational methods that accurately treat their multiconfigurational electronic structure. OUTLOOK The remarkable ability of enzymes to catalyze a variety of reactions under mild conditions, using only EAMs, highlights compelling opportunities for the discovery of new catalysis. Although enzymes are versatile platforms for harnessing the properties of EAMs, they are insufficiently robust under the harsh pH, temperature, pressure, and solvent conditions required for some industrial catalytic processes. Thus, systematic strategies are needed for directed evolution to extend the reactivity and persistence of engineered enzymes. For molecular catalysts, the tunability of the ligands provides opportunities for systematically varying the activities of EAMs. Key challenges include enhancing metal-ligand cooperativity, controlling transport to EAM active sites, and mastering the interactions of EAM centers with both metal-based and organic-based redox-active ligands. In heterogeneous catalysis, tuning the lattice environment of EAMs offers new opportunities for catalyst discovery, but for practical applications EAM catalysts should exhibit long-term stability and high active-site density. Thus, advances are needed in the synthesis of materials with tunable phase and nanostructure, as well as insights into how EAM catalysts undergo electronic and structural changes under sustained catalytic turnover. Strategies for controlling EAM reactivity patterns, coupled with advances in synthetic methods and spectroscopic and computational techniques, are critical for the systematic use of EAMs in sustainable catalysis.

Thermal Growth and Performance of Manganese Cobaltite Spinel Protection Layers on Ferritic Stainless Steel SOFC Interconnects

Abstract: To protect solid oxide fuel cells (SOFCs) from chromium poisoning and improve metallic interconnect stability, manganese cobaltite spinel protection layers with a nominal composition of Mn 1 . 5 Co 1 . 5 O 4 were thermally grown on Crofer22 APU, a ferritic stainless steel. Thermal, electrical, and electrochemical investigations indicated that the spinel protection layers not only significantly decreased the contact area specific resistance (ASR) between a LSF cathode and the stainless steel interconnect, but also inhibited the subscale growth on the stainless steel by acting as a barrier to the inward diffusion of oxygen. A long-term thermal cycling test demonstrated excellent structural and thermomechanical stability of these spinel protection layers, which also acted as a barrier to outward chromium cation diffusion to the interconnect surface. The reduction in the contact ASR and prevention of Cr migration achieved by application of the spinel protection layers on the cathode side of ferritic stainless steel interconnects resulted in improved stability and electrochemical performance of SOFCs.

The Relationship between Overlying Synoptic-Scale Flows and Winds within a Valley

Abstract: The relationship between winds above and within the Tennessee Valley is investigated climatologically and with an atmospheric numerical model. For the climatological analyses, winds above the valley were determined by interpolation from four surrounding rawinsonde stations, while winds within the valley were measured on four 100-m towers. Tennessee Valley winds are generally weak and bidirectional, oriented along the valley's axis. The valley wind direction depends strongly on the component of the synoptic-scale pressure gradient that is superimposed along the valley's axis at ridge-top level, with winds blowing along the valley's axis from high toward low pressure. This relationship between winds above and within the valley can result in countercurrents similar to those observed in the Rhine Valley. While winds in the Tennessee Valley are driven primarily by this pressure-driven channeling mechanism, downward momentum transport can cause afternoon winds within the valley to approach the wind dir...

Nanoscale Strontium Titanate Photocatalysts for Overall Water Splitting

Abstract: SrTiO3 (STO) is a large band gap (3.2 eV) semiconductor that catalyzes the overall water splitting reaction under UV light irradiation in the presence of a NiO cocatalyst. As we show here, the reactivity persists in nanoscale particles of the material, although the process is less effective at the nanoscale. To reach these conclusions, Bulk STO, 30 ± 5 nm STO, and 6.5 ± 1 nm STO were synthesized by three different methods, their crystal structures verified with XRD and their morphology observed with HRTEM before and after NiO deposition. In connection with NiO, all samples split water into stoichiometric mixtures of H2 and O2, but the activity is decreasing from 28 μmol H2 g–1 h–1 (bulk STO), to 19.4 μmol H2 g–1 h–1 (30 nm STO), and 3.0 μmol H2 g–1 h–1 (6.5 nm STO). The reasons for this decrease are an increase of the water oxidation overpotential for the smaller particles and reduced light absorption due to a quantum size effect. Overall, these findings establish the first nanoscale titanate photocatalys...