Abstract The exploitation of state‐of‐the‐art Pt/C electrocatalysts for polymer electrolyte membrane fuel cells (PEMFCs) is mostly limited, due to high Pt loading and durability issues caused by electrochemical instability of the carbon support in high potential regimes. In this study, the authors report that high‐compressive 3D Pt nanostructured thin films can considerably increase the catalytic activity and electrochemical durability of electrocatalysts under PEMFC device operating conditions. The nanostructure fabrication relies on the dealloying or selective leaching of solid alloys of Pt–C binary film to produce a residual 3D nanoporous thin‐film structure. A very rich structural behavior from the dealloying is shown, in which stress relief plays a governing role; the films possess a 3D structure of randomly interpenetrating ligaments and hierarchical pores with sizes between less than 50 nm and several tens of micrometers. In addition, a significant change is observed in the average lattice constant (1.55% compressive strain), which can tune the structural and electronic states of catalytic sites for enhancing the activity of the Pt electrocatalysts. Electrochemical performance of the fabricated porous strained Pt thin‐film electrocatalysts in both half‐cell and single‐cell analyses has demonstrated activity and durability superior to benchmark carbon support Pt catalysts.
Compared to Ru single atom catalyst, hetero-RuM (M = Fe, Os, and Ir) double atom catalysts showed improved N 2 RR activity with the help of d xz and d xy bonding orbital, caused by strain, dopant and configurational effects.
Oxygen-based electrocatalysis is an integral aspect of a clean and sustainable energy conversion/storage system. The development of economic bifunctional electrocatalysts with high activity and durability during reversible reactions remains a great challenge. The tailored porous structure and separately presented active sites for oxygen reduction and oxygen evolution reactions (ORR and OER) without mutual interference are most crucial for achieving desired bifunctional catalysts. Here, we report a hybrid composed of sheath–core cobalt oxynitride (CoOx@CoNy) nanorods grown perpendicularly on N-doped carbon nanofiber (NCNF). The brush-like CoOx@CoNy nanorods, composed of metallic Co4N cores and oxidized surfaces, exhibit excellent OER activity (E = 1.69 V at 10 mA cm–2) in an alkaline medium. Although pristine NCNF or CoOx@CoNy alone had poor catalytic activity in the ORR, the hybrid showed dramatically enhanced ORR performance (E = 0.78 V at −3 mA cm–2). The experimental results coupled with a density functional theory (DFT) simulation confirmed that the broad surface area of the CoOx@CoNy nanorods with an oxidized skin layer boosts the catalytic OER, while the facile adsorption of ORR intermediates and a rapid interfacial charge transfer occur at the interface between the CoOx@CoNy nanorods and the electrically conductive NCNF. Furthermore, it was found that the independent catalytic active sites in the CoOx@CoNy/NCNF catalyst are continuously regenerated and sustained without mutual interference during the round-trip ORR/OER, affording stable operation of Zn–air batteries.
In this letter, new two-way and four-way power dividers are proposed using quarter-wave long multi-conductor coupled lines. The design equations for a two-way power divider are derived by analyzing a three-conductor coupled line. Then, the structure is extended to propose a planar four-way power divider with compact size. The fabricated two-way and four-way power dividers at 2.0 GHz show an excellent performance in the insertion loss, impedance matching at all ports and isolation between output ports.
In article number 2009241, Docheon Ahn, Pil Kim, Sung Jong Yoo, and co-workers synthesize monolithic antiperovskite crystals through atomic-scale engineering. The nitride PdNi alloy achieves excellent catalytic activity and durability under acidic media, resulting from the synergistic effect of nitride and intermetallic structures. This strategy will pave the way for overcoming the catalytic performance of potential materials.
The electrochemical nitrogen reduction reaction (NRR) for ammonia production is one of the most spotlighted chemical process for hydrogen storage and transportation. We investigated NRR on the ruthenium-based subnano-clustered catalysts embedded in modified defective graphene (Ru x /YC, Ru : ruthenium, x : 1 to 3, Y : boron, carbon, and nitrogen, C : graphitic carbon) using density functional theory (DFT) calculation. We identified the energetically optimized structures of Ru x /YCs among all possible geometries. Also we calculated the dissociative adsorption free energy of nitrogen (ΔG Diss ) to determine which mechanism to follow for NRR on Ru x /YCs. We also calculated the adsorption energy (ΔE Ads ) of all possible reaction intermediates to identify the detailed mechanism and the limiting potential for NRR on each catalyst. Additionally, we compared the reaction potential for NRR and hydrogen evolution reaction (HER) by calculating the adsorption free energy of H * . In the Ru x /C catalysts, ΔE Ads of N * tend to become stronger and the ΔG Diss decreased, as the number of Ru atoms increased. In contrast, the reverse tendency was shown in Ru x /BC catalysts between ΔG Diss and the number of Ru atoms. In the Ru x /NCs, ΔG Diss for the two Ru atoms was lowest. Overall, NRR follow the dissociative mechanism on the Ru 3 /C, Ru 1 /BC, and Ru 2 /BC catalysts, and association mechanism on the others. As shown in figure below, single-atomic Ru 1 /YCs showed obviously lower NRR potential than double- and triple-atomic Ru x /YCs. In the case of Ru x /C and Ru x /NC, it was due to the relatively weak adsorption of N 2 H * . However, in Ru 1 /BC, the ΔE Ads of N 2 H * was so strong that the reaction potential was relatively higher than Ru 2 /BC and Ru 3 /BC due to the strong B-N bonding. It was found that the ΔE Ads of N 2 H * can be used as an indicator to predict NRR potential on Ru x /YCs. We compared the reaction potential for NRR and HER on each catalysts. In Ru 2 /NC catalyst, HER potential was lower than NRR potential, and it was found that Ru 2 /NC with good activity and selectivity is the most promising candidate for NRR catalyst. Figure 1
Systematic ab initio SCF calculations have been performed on the hydrogen-bonded dimers of fluoromethanes involving with ammonia and water applying basis sets of 9s5p/5s and 9s5p1d/5p1d. Various ground state properties of these stable dimeric complexes have been evaluated. We compared these with corresponding properties of isolated monomers. We report equilibrium geometries, stabilization energies, dipole moments and force constants of intermolecular bonds. The effects arising as a consequence of the non-additive behavior of hydrogen bonding in chain-like oligomers are discussed. Systematic, methodical errors due to the use of the SCF approximation and the basis set dependence of the computed results are pointed out.
Abstract Owing to their remarkable electrochemical activities, 1T phase transition metal dichalcogenide (TMD) materials have attracted considerable interest in recent decades. However, metastable 1T phases are difficult to prepare and readily change phases. Therefore, for the first time, a monolayer nanotubular 1T Ru dichalcogenide comprising 92% of the 1T phase is synthesized, which is the highest value ever obtained using solvothermal methods. In the tubular geometry, the 1T phase exhibits superior durability against various external stimuli and electrocatalytic activity toward the oxygen reduction reaction. According to density‐functional‐theory‐based and molecular dynamics calculations, sufficiently curved architectures can change their bond identities to safely maintain 1T phases, hence providing a strategy for stabilizing metastable phases. The study results form a basis for extensively applying 1T phases and will stimulate interest for applying tubular structures for stabilizing metastable materials.
Single-Atom Sites Catalysts In article number 2300673, Dongmok Whang, Sung Jong Yoo, Namgee Jung, Joseph T. Hupp, and co-workers present a strategy to enhance the efficiency and durability of sub-nanometer catalysts for electrochemical reactions. The cover art depicts the strong interaction between single-atom site Ru catalysts and chemically stable ZrO2-x nanoparticles, enabling superior stability and improved activity of the catalysts for hydrogen evolution reactions.
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