What Elements Really Intercalate into Pd Lattice When Heated in Dimethylformamide?

Palladium hydrides (PdHx) are pivotal in both fundamental research and practical applications across a wide spectrum. PdHx nanocrystals, synthesized by heating in dimethylformamide (DMF), exhibit remarkable stability, granting them widespread applications in the field of electrocatalysis. However, this stability appears inconsistent with their metastable nature. The substantial challenges in characterizing nanoscale structures contribute to the limited understanding of this anomalous phenomenon. Here, through a series of well-conceived experimental designs and advanced characterization techniques, including aberration-corrected scanning transmission electron microscopy (AC-STEM), in situ X-ray diffraction (XRD), and time-of-flight secondary ion mass spectrometry (TOF-SIMS), we have uncovered evidence that indicates the presence of C and N within the lattice of Pd (PdCxNy), rather than H (PdHx). By combining theoretical calculations, we have thoroughly studied the potential configurations and thermodynamic stability of PdCxNy, demonstrating a 2.5:1 ratio of C to N infiltration into the Pd lattice. Furthermore, we successfully modulated the electronic structure of Pd nanocrystals through C and N doping, enhancing their catalytic activity in methanol oxidation reactions. This breakthrough provides a new perspective on the structure and composition of Pd-based nanocrystals infused with light elements, paving the way for the development of advanced catalytic materials in the future.

Comprehensive Understanding of the Kinetic Behaviors of Main Protease from SARS-CoV-2 and SARS-CoV: New Data and Comparison to Published Parameters.

The main protease (Mpro) is a promising drug target for inhibiting the coronavirus due to its conserved properties and lack of homologous genes in humans. However, previous studies on Mpro's kinetic parameters have been confusing, hindering the selection of accurate inhibitors. Therefore, obtaining a clear view of Mpro's kinetic parameters is necessary. In our study, we investigated the kinetic behaviors of Mpro from SARS-CoV-2 and SARS-CoV using both FRET-based cleavage assay and the LC-MS method, respectively. Our findings indicate that the FRET-based cleavage assay could be used for preliminary screening of Mpro inhibitors, while the LC-MS method should be applied to select the effective inhibitors with higher reliability. Furthermore, we constructed the active site mutants (H41A and C145A) and measured the kinetic parameters to gain a deeper understanding of the atomic-level enzyme efficiency reduction compared to the wild type. Overall, our study provides valuable insights for inhibitor screening and design by offering a comprehensive understanding of Mpro's kinetic behaviors.

Progress and Perspective for In Situ Studies of Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells.

Proton exchange membrane fuel cell (PEMFC) is one of the most promising energy conversion devices with high efficiency and zero emission. However, oxygen reduction reaction (ORR) at the cathode is still the dominant limiting factor for the practical development of PEMFC due to its sluggish kinetics and the vulnerability of ORR catalysts under harsh operating conditions. Thus, the development of high-performance ORR catalysts is essential and requires a better understanding of the underlying ORR mechanism and the failure mechanisms of ORR catalysts with in situ characterization techniques. This review starts with the introduction of in situ techniques that have been used in the research of the ORR processes, including the principle of the techniques, the design of the in situ cells, and the application of the techniques. Then the in situ studies of the ORR mechanism as well as the failure mechanisms of ORR catalysts in terms of Pt nanoparticle degradation, Pt oxidation, and poisoning by air contaminants are elaborated. Furthermore, the development of high-performance ORR catalysts with high activity, anti-oxidation ability, and toxic-resistance guided by the aforementioned mechanisms and other in situ studies are outlined. Finally, the prospects and challenges for in situ studies of ORR in the future are proposed.

Bifunctional Ultrathin RhRu0.5 -Alloy Nanowire Electrocatalysts for Hydrazine-Assisted Water Splitting.

Hydrazine-assisted water electrolysis offers a feasible path for low-voltage green hydrogen production. Herein, the design and synthesis of ultrathin RhRu0.5 -alloy wavy nanowires as bifunctional electrocatalysts for both the anodic hydrazine oxidation reaction (HzOR) and the cathodic hydrogen evolution reaction (HER) is reported. It is shown that the RhRu0.5 -alloy wavy nanowires can achieve complete electrooxidation of hydrazine with a low overpotential and high mass activity, as well as improved performance for the HER. The resulting RhRu0.5 bifunctional electrocatalysts enable, high performance hydrazine-assisted water electrolysis delivering a current density of 100 mA cm-2 at an ultralow cell voltage of 54 mV and a high current density of 853 mA cm-2 at a cell voltage of 0.6 V. The RhRu0.5  electrocatalysts further demonstrate a stable operation at a high current density of 100 mA cm-2 for 80 hours of testing period with little irreversible degradation. The overall performance greatly exceeds that of the previously reported hydrazine-assisted water electrolyzers, offering a pathway for efficiently converting hazardous hydrazine into molecular hydrogen.

Graphene-nanopocket-encaged PtCo nanocatalysts for highly durable fuel cell operation under demanding ultralow-Pt-loading conditions.

The proton exchange membrane fuel cell (PEMFC) as an attractive clean power source can promise a carbon-neutral future, but the widespread adoption of PEMFCs requires a substantial reduction in the usage of the costly platinum group metal (PGM) catalysts. Ultrafine nanocatalysts are essential to provide sufficient catalytic sites at a reduced PGM loading, but are fundamentally less stable and prone to substantial size growth in long-term operations. Here we report the design of a graphene-nanopocket-encaged platinum cobalt (PtCo@Gnp) nanocatalyst with good electrochemical accessibility and exceptional durability under a demanding ultralow PGM loading (0.070 mgPGM cm-2) due to the non-contacting enclosure of graphene nanopockets. The PtCo@Gnp delivers a state-of-the-art mass activity of 1.21 A mgPGM-1, a rated power of 13.2 W mgPGM-1 and a mass activity retention of 73% after an accelerated durability test. With the greatly improved rated power and durability, we project a 6.8 gPGM loading for a 90 kW PEMFC vehicle, which approaches that used in a typical catalytic converter.

Silver nanoparticles boost charge-extraction efficiency in Shewanella microbial fuel cells.

Microbial fuel cells (MFCs) can directly convert the chemical energy stored in organic matter to electricity and are of considerable interest for power generation and wastewater treatment. However, the current MFCs typically exhibit unsatisfactorily low power densities that are largely limited by the sluggish transmembrane and extracellular electron-transfer processes. Here, we report a rational strategy to boost the charge-extraction efficiency in Shewanella MFCs substantially by introducing transmembrane and outer-membrane silver nanoparticles. The resulting Shewanella-silver MFCs deliver a maximum current density of 3.85 milliamperes per square centimeter, power density of 0.66 milliwatts per square centimeter, and single-cell turnover frequency of 8.6 × 105 per second, which are all considerably higher than those of the best MFCs reported to date. Additionally, the hybrid MFCs feature an excellent fuel-utilization efficiency, with a coulombic efficiency of 81%.

Chemical vapour deposition of Fe-N-C oxygen reduction catalysts with full utilization of dense Fe-N4 sites.

Replacing scarce and expensive platinum (Pt) with metal-nitrogen-carbon (M-N-C) catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells has largely been impeded by the low oxygen reduction reaction activity of M-N-C due to low active site density and site utilization. Herein, we overcome these limits by implementing chemical vapour deposition to synthesize Fe-N-C by flowing iron chloride vapour over a Zn-N-C substrate at 750 °C, leading to high-temperature trans-metalation of Zn-N4 sites into Fe-N4 sites. Characterization by multiple techniques shows that all Fe-N4 sites formed via this approach are gas-phase and electrochemically accessible. As a result, the Fe-N-C catalyst has an active site density of 1.92 × 1020 sites per gram with 100% site utilization. This catalyst delivers an unprecedented oxygen reduction reaction activity of 33 mA cm-2 at 0.90 V (iR-corrected; i, current; R, resistance) in a H2-O2 proton exchange membrane fuel cell at 1.0 bar and 80 °C.

Beyond Extended Surfaces: Understanding the Oxygen Reduction Reaction on Nanocatalysts.

Increasing the platinum utilization efficiency is the key to the advancement and broad dissemination of proton-exchange-membrane fuel cells (PEMFCs). Central to the task is the creation of highly active and durable Pt-based catalysts for the cathodic oxygen reduction reaction (ORR), which demands a comprehensive understanding of the ORR processes on these catalysts under reaction conditions. Past efforts have accumulated a vast wealth of knowledge of the ORR on extended Pt and Pt-alloy model surfaces. While the knowledge has been applied to understanding and designing ORR catalysts, it has also been recognized that these understandings cannot always translate into nanoscale systems. In this Perspective, we will review the progress that the theoretical descriptor has evolved to reconcile the observed differences between extended and nanoscale Pt surfaces, and we highlight the needs in advancing both characterizations and theories in order to understand ORR in the more complex Pt-alloy nanocatalysts. Particularly, understanding the dynamic structure-composition-function relation of Pt-alloy nanocatalysts during ORR demands concerted efforts in precision synthesis, advanced atomistic-scale in situ characterization, and comprehensive computational models.

A Polymerization-Assisted Grain Growth Strategy for Efficient and Stable Perovskite Solar Cells.

Intrinsically, detrimental defects accumulating at the surface and grain boundaries limit both the performance and stability of perovskite solar cells. Small molecules and bulkier polymers with functional groups are utilized to passivate these ionic defects but usually suffer from volatility and precipitation issues, respectively. Here, starting from the addition of small monomers in the PbI2 precursor, a polymerization-assisted grain growth strategy is introduced in the sequential deposition method. With a polymerization process triggered during the PbI2 film annealing, the bulkier polymers formed will be adhered to the grain boundaries, retaining the previously established interactions with PbI2 . After perovskite formation, the polymers anchored on the boundaries can effectively passivate undercoordinated lead ions and reduce the defect density. As a result, a champion power conversion efficiency (PCE) of 23.0% is obtained, together with a prolonged lifetime where 85.7% and 91.8% of the initial PCE remain after 504 h continuous illumination and 2208 h shelf storage, respectively.

Evolution Pathway from Iron Compounds to Fe1(II)-N4 Sites through Gas-Phase Iron during Pyrolysis.

Pyrolysis is indispensable for synthesizing highly active Fe-N-C catalysts for the oxygen reduction reaction (ORR) in acid, but how Fe, N, and C precursors transform to ORR-active sites during pyrolysis remains unclear. This knowledge gap obscures the connections between the input precursors and the output products, clouding the pathway toward Fe-N-C catalyst improvement. Herein, we unravel the evolution pathway of precursors to ORR-active catalyst comprised exclusively of single-atom Fe1(II)-N4 sites via in-temperature X-ray absorption spectroscopy. The Fe precursor transforms to Fe oxides below 300 °C and then to tetrahedral Fe1(II)-O4 via a crystal-to-melt-like transformation below 600 °C. The Fe1(II)-O4 releases a single Fe atom that diffuses into the N-doped carbon defect forming Fe1(II)-N4 above 600 °C. This vapor-phase single Fe atom transport mechanism is verified by synthesizing Fe1(II)-N4 sites via "noncontact pyrolysis" wherein the Fe precursor is not in physical contact with the N and C precursors during pyrolysis.

Ultra-high Areal Capacity Realized in Three-Dimensional Holey Graphene/SnO2 Composite Anodes.

Nanostructured alloy-type electrode materials and its composites have shown extraordinary promise for lithium-ion batteries (LIBs) with exceptional gravimetric capacity. However, studies to date are usually limited to laboratory cells with too low mass loading (and thus too low areal capacity) to exert significant practical impact. Herein, by impregnating micrometer-sized SnO2/graphene composites into 3D holey graphene frameworks (HGF), we show that a well-designed 3D-HGF/SnO2 composite anode with a high mass loading of 12 mg cm-2 can deliver an ultra-high areal capacity up to 14.5 mAh cm-2 under current density of 0.2 mA cm-2 and stable areal capacity of 9.5 mAh cm-2 under current density of 2.4 mA cm-2, considerably outperforming those in the state-of-art research devices or commercial devices. This robust realization of high areal capacity defines a critical step to capturing the full potential of high-capacity alloy-type electrode materials in practical LIBs.

Enhanced adsorptive desulfurization by iso-structural amino bearing IRMOF-3 and IRMOF-3@Al2O3versus MOF-5 and MOF-5@Al2O3 revealing the predominant role of hydrogen bonding.

Desulfurization of oragnosulfur-containing fuels signify a great importance in improving the quality of fuel and is also beneficial to the environment. In this work, we report two new composites, namely, MOF-5@γ-Al2O3 and IRMOF-3@γ-Al2O3, synthesized by loading iso-structural MOF-5 and amino bearing IRMOR-3 onto the γ-Al2O3 beads (the loading amount of MOF-5 and IRMOF-3 are 13.4 wt% and 16.3 wt%, respectively). The composites are fully characterized by IR spectroscopy, XRD, SEM, BET and XRF. These iso-structural MOFs and their composites exhibit substantially high adsorptive desulfurization capacities for benzothiophene (BT), 3-methylthiophene (3-MT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The adsorption capacities of amino bearing IR-MOF-3 and IRMOF-3@γ-Al2O3 are significantly greater than those of MOF-5 and MOF-5@γ-Al2O3, e.g., the adsorption capacities for DBT of IRMOF-3@γ-Al2O3, IRMOF-3, MOF-5@γ-Al2O3 and MOF-5 are 54.9, 45.1, 31.4 and 24.1 mg S g-1 MOFs, respectively, under optimal conditions (time 60 min, temperature 30 °C, MOFs@γ-Al2O3/Moil = 1/40). The adsorption results revealed the predominant role of hydrogen bonding between the Lewis basic S atoms of the organo sulfurs and -NH2 groups in IR-MOF-3 and also the π-π interactions that works well in MOF-5. The enhancement in the desulfurization capability of MOFs@γ-Al2O3versus the corresponding pristine MOFs shall be attributed to the advantage of the confinement effect of the γ-Al2O3 pores that results in larger specific surface area, much more exposed active sites, and shorter diffusion channels of the MOFs. The kinetics and thermodynamic parameters indicate that the adsorption process is spontaneous and endothermic, and the increase in entropy is the primary driving force for the desulfurization. In addition, it is found that the composites possess good reusability and can be regenerated by simple washing due to enhanced mechanical strength.

Pt-Based Nanocrystal for Electrocatalytic Oxygen Reduction.

Currently, Pt-based electrocatalysts are adopted in the practical proton exchange membrane fuel cell (PEMFC), which converts the energy stored in hydrogen and oxygen into electrical power. However, the broad implementation of the PEMFC, like replacing the internal combustion engine in the present automobile fleet, sets a requirement for less Pt loading compared to current devices. In principle, the requirement needs the Pt-based catalyst to be more active and stable. Two main strategies, engineering of the electronic (d-band) structure (including controlling surface facet, tuning surface composition, and engineering surface strain) and optimizing the reactant adsorption sites are discussed and categorized based on the fundamental working principle. In addition, general routes for improving the electrochemical surface area, which improves activity normalized by the unit mass of precious group metal/platinum group metal, and stability of the electrocatalyst are also discussed. Furthermore, the recent progress of full fuel cell tests of novel electrocatalysts is summarized. It is suggested that a better understanding of the reactant/intermediate adsorption, electron transfer, and desorption occurring at the electrolyte-electrode interface is necessary to fully comprehend these electrified surface reactions, and standardized membrane electrode assembly (MEA) testing protocols should be practiced, and data with full parameters detailed, for reliable evaluation of catalyst functions in devices.

Double-negative-index ceramic aerogels for thermal superinsulation.

Ceramic aerogels are attractive for thermal insulation but plagued by poor mechanical stability and degradation under thermal shock. In this study, we designed and synthesized hyperbolic architectured ceramic aerogels with nanolayered double-pane walls with a negative Poisson's ratio (-0.25) and a negative linear thermal expansion coefficient (-1.8 × 10-6 per °C). Our aerogels display robust mechanical and thermal stability and feature ultralow densities down to ~0.1 milligram per cubic centimeter, superelasticity up to 95%, and near-zero strength loss after sharp thermal shocks (275°C per second) or intense thermal stress at 1400°C, as well as ultralow thermal conductivity in vacuum [~2.4 milliwatts per meter-kelvin (mW/m·K)] and in air (~20 mW/m·K). This robust material system is ideal for thermal superinsulation under extreme conditions, such as those encountered by spacecraft.

Unifying the Hydrogen Evolution and Oxidation Reactions Kinetics in Base by Identifying the Catalytic Roles of Hydroxyl-Water-Cation Adducts.

Despite the fundamental and practical significance of the hydrogen evolution and oxidation reactions (HER/HOR), their kinetics in base remain unclear. Herein, we show that the alkaline HER/HOR kinetics can be unified by the catalytic roles of the adsorbed hydroxyl (OHad)-water-alkali metal cation (AM+) adducts, on the basis of the observations that enriching the OHad abundance via surface Ni benefits the HER/HOR; increasing the AM+ concentration only promotes the HER, while varying the identity of AM+ affects both HER/HOR. The presence of OHad-(H2O) x-AM+ in the double-layer region facilitates the OHad removal into the bulk, forming OH--(H2O) x-AM+ as per the hard-soft acid-base theory, thereby selectively promoting the HER. It can be detrimental to the HOR as per the bifunctional mechanism, as the AM+ destabilizes the OHad, which is further supported by the CO oxidation results. This new notion may be important for alkaline electrochemistry.

Nanoscale Structure Design for High-Performance Pt-Based ORR Catalysts.

Proton-exchange-membrane fuel cells (PEMFCs) are of considerable interest for direct chemical-to-electrical energy conversion and may represent an ultimate solution for mobile power supply. However, PEMFCs today are primarily limited by the sluggish kinetics of the cathodic oxygen reduction reaction (ORR), which requires a significant amount of Pt-based catalyst with a substantial contribution to the overall cost. Hence, promoting the activity and stability of the needed catalyst and minimizing the amount of Pt loaded are central to reducing the cost of PEMFCs for commercial deployment. Considerable efforts have been devoted to improving the catalytic performance of Pt-based ORR catalysts, including the development of various Pt nanostructures with tunable sizes and chemical compositions, controlled shapes with selectively displayed crystallographic surfaces, tailored surface strains, surface doping, geometry engineering, and interface engineering. Herein, a brief introduction of some fundamentals of fuel cells and ORR catalysts with performance metrics is provided, followed by a detailed description of a series of strategies for pushing the limit of high-performance Pt-based catalysts. A brief perspective and new insights on the remaining challenges and future directions of Pt-based ORR catalysts for fuel cells are also presented.

Tailored Phase Conversion under Conjugated Polymer Enables Thermally Stable Perovskite Solar Cells with Efficiency Exceeding 21.

The precise control of stoichiometric balance and ionic defects on the surface of solution-processed perovskite is critical to the performance and stability of perovskite solar cells (pero-SCs). Here, we introduce a low-cost and stable conjugated donor polymer (PTQ10) as interfacial layer in the planar n-i-p structured pero-SCs. The polymer was applied to the perovskite intermediate phase before the thermal annealing. This treatment significantly reduced the loss of surface organic cation during thermal annealing. Importantly, the kinetics of phase conversion of perovskite was influenced, and perovskite crystal showed a more preferential orientation. Moreover, the polymer proved to be an effective hole extraction layer due to the proper energy alignment with perovskite. Finally, a champion power conversion efficiency of the planar pero-SCs was achieved at 21.2% with a high fill factor of 81.6%. The devices also showed great ambient and thermal stability. This work presents a facile way of perovskite surface control to achieve high-performance pero-SCs.

Quantum interference mediated vertical molecular tunneling transistors.

Molecular transistors operating in the quantum tunneling regime represent potential electronic building blocks for future integrated circuits. However, due to their complex fabrication processes and poor stability, traditional molecular transistors can only operate stably at cryogenic temperatures. Here, through a combined experimental and theoretical investigation, we demonstrate a new design of vertical molecular tunneling transistors, with stable switching operations up to room temperature, formed from cross-plane graphene/self-assembled monolayer (SAM)/gold heterostructures. We show that vertical molecular junctions formed from pseudo-p-bis((4-(acetylthio)phenyl)ethynyl)-p-[2,2]cyclophane (PCP) SAMs exhibit destructive quantum interference (QI) effects, which are absent in 1,4-bis(((4-acetylthio)phenyl)ethynyl)benzene (OPE3) SAMs. Consequently, the zero-bias differential conductance of the former is only about 2% of the latter, resulting in an enhanced on-off current ratio for (PCP) SAMs. Field-effect control is achieved using an ionic liquid gate, whose strong vertical electric field penetrates through the graphene layer and tunes the energy levels of the SAMs. The resulting on-off current ratio achieved in PCP SAMs can reach up to ~330, about one order of magnitude higher than that of OPE3 SAMs. The demonstration of molecular junctions with combined QI effect and gate tunability represents a critical step toward functional devices in future molecular-scale electronics.

Surface-Engineered PtNi-O Nanostructure with Record-High Performance for Electrocatalytic Hydrogen Evolution Reaction.

Hydrogen holds the potential of replacing nonrenewable fossil fuel. Improving the efficiency of hydrogen evolution reaction (HER) is critical for environmental friendly hydrogen generation through electrochemical or photoelectrochemical water splitting. Here we report the surface-engineered PtNi-O nanoparticles with enriched NiO/PtNi interface on surface. Notably, PtNi-O/C showed a mass activity of 7.23 mA/µg at an overpotential of 70 mV, which is 7.9 times higher compared to that of the commercial Pt/C, representing the highest reported mass activity for HER in alkaline conditions. The HER overpotential can be lowered to 39.8 mV at 10 mA/cm2 when platinum loading was only 5.1 µgpt/cm2, showing exceptional HER efficiency. Meanwhile, the prepared PtNi-O/C nanostructures demonstrated significantly improved stability as well as high current performance which are well over those of the commercial Pt/C and demonstrated capability of scaled hydrogen generation.

Microwave-Assisted Rapid Synthesis of Graphene-Supported Single Atomic Metals.

Graphene-supported single atomic metals (G-SAMs) have recently attracted considerable research interest for their intriguing catalytic, electronic, and magnetic properties. The development of effective synthetic methodologies toward G-SAMs with monodispersed metal atoms is vital for exploring their fundamental properties and potential applications. A convenient, rapid, and general strategy to synthesize a series of monodispersed atomic transition metals (for example, Co, Ni, Cu) embedded in nitrogen-doped graphene by two-second microwave (MW) heating the mixture of amine-functionalized graphene oxide and metal salts is reported here. The MW heating is able to simultaneously induce the reduction of graphene oxide, the doping of nitrogen, and the incorporation of metal atoms into the graphene lattices in one simple step. The rapid MW process minimizes metal diffusion and aggregation to ensure exclusive single metal atom dispersion in graphene lattices. Electrochemical studies demonstrate that graphene-supported Co atoms can function as highly active electrocatalysts toward the hydrogen evolution reaction. This MW-assisted method provides a rapid and efficient avenue to supported metal atoms for wide ranges of applications.