Lamella-heterostructured nanoporous bimetallic iron-cobalt alloy/oxyhydroxide and cerium oxynitride electrodes as stable catalysts for oxygen evolution.

Developing robust nonprecious-metal electrocatalysts with high activity towards sluggish oxygen-evolution reaction is paramount for large-scale hydrogen production via electrochemical water splitting. Here we report that self-supported laminate composite electrodes composed of alternating nanoporous bimetallic iron-cobalt alloy/oxyhydroxide and cerium oxynitride (FeCo/CeO2-xNx) heterolamellas hold great promise as highly efficient electrocatalysts for alkaline oxygen-evolution reaction. By virtue of three-dimensional nanoporous architecture to offer abundant and accessible electroactive CoFeOOH/CeO2-xNx heterostructure interfaces through facilitating electron transfer and mass transport, nanoporous FeCo/CeO2-xNx composite electrodes exhibit superior oxygen-evolution electrocatalysis in 1 M KOH, with ultralow Tafel slope of ~33 mV dec-1. At overpotential of as low as 360 mV, they reach >3900 mA cm-2 and retain exceptional stability at ~1900 mA cm-2 for >1000 h, outperforming commercial RuO2 and some representative oxygen-evolution-reaction catalysts recently reported. These electrochemical properties make them attractive candidates as oxygen-evolution-reaction electrocatalysts in electrolysis of water for large-scale hydrogen generation.

Surface-Alloyed Nanoporous Zinc as Reversible and Stable Anodes for High-Performance Aqueous Zinc-Ion Battery.

Metallic zinc (Zn) is one of the most attractive multivalent-metal anode materials in post-lithium batteries because of its high abundance, low cost and high theoretical capacity. However, it usually suffers from large voltage polarization, low Coulombic efficiency and high propensity for dendritic failure during Zn stripping/plating, hindering the practical application in aqueous rechargeable zinc-metal batteries (AR-ZMBs). Here we demonstrate that anionic surfactant-assisted in situ surface alloying of Cu and Zn remarkably improves Zn reversibility of 3D nanoporous Zn electrodes for potential use as high-performance AR-ZMB anode materials. As a result of the zincophilic ZnxCuy alloy shell guiding uniform Zn deposition with a zero nucleation overpotential and facilitating Zn stripping via the ZnxCuy/Zn galvanic couples, the self-supported nanoporous ZnxCuy/Zn electrodes exhibit superior dendrite-free Zn stripping/plating behaviors in ambient aqueous electrolyte, with ultralow polarizations under current densities up to 50 mA cm‒2, exceptional stability for 1900 h and high Zn utilization. This enables AR-ZMB full cells constructed with nanoporous ZnxCuy/Zn anode and KzMnO2 cathode to achieve specific energy of as high as ~ 430 Wh kg‒1 with ~ 99.8% Coulombic efficiency, and retain ~ 86% after long-term cycles for > 700 h.

Production of polyhydroxyalkanoate from acetate by metabolically engineered Aeromonas hydrophilia.

Aeromonas hydrophila 4AK4 normally produces the copolymer of 3-hydroxybutyrate and 3-hydroxyhexanoate (PHBHHx) using lauric acid as the carbon source. In this study we reported the metabolic engineering of A. hydrophila 4AK4 for the production of polyhydroxyalkanoate (PHA) using acetate as a main carbon source. Recombinant A. hydrophila overexpressing ß-ketothiolase and acetoacetyl-CoA reductase could accumulate poly-3-hydroxybutyrate (PHB) from acetate with a polymer content of 1.39 wt%. Further overexpression of acetate kinase/phosphotransacetylase and acetyl-CoA synthetase improved PHB content to 8.75 wt% and 19.82 wt%, respectively. When acetate and propionate were simultaneously supplied as carbon sources, the engineered A. hydrophila overexpressing ß-ketothiolase, acetoacetyl-CoA reductase, and acetyl-CoA synthetase was found able to produce the copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate (PHBV). The recombinant grew to 3.79 g/L cell dry weight (CDW) containing 15.02 wt% PHBV. Our proposed metabolic engineering strategies illustrate the feasibility for producing PHA from acetate by A. hydrophila.

Spontaneously separated intermetallic Co3Mo from nanoporous copper as versatile electrocatalysts for highly efficient water splitting.

Developing robust nonprecious electrocatalysts towards hydrogen/oxygen evolution reactions is crucial for widespread use of electrochemical water splitting in hydrogen production. Here, we report that intermetallic Co3Mo spontaneously separated from hierarchical nanoporous copper skeleton shows genuine potential as highly efficient electrocatalysts for alkaline hydrogen/oxygen evolution reactions in virtue of in-situ hydroxylation and electro-oxidation, respectively. The hydroxylated intermetallic Co3Mo has an optimal hydrogen-binding energy to facilitate adsorption/desorption of hydrogen intermediates for hydrogen molecules. Associated with high electron/ion transport of bicontinuous nanoporous skeleton, nanoporous copper supported Co3Mo electrodes exhibit impressive hydrogen evolution reaction catalysis, with negligible onset overpotential and low Tafel slope (~40 mV dec-1) in 1 M KOH, realizing current density of -400 mA cm-2 at overpotential of as low as 96 mV. When coupled to its electro-oxidized derivative that mediates efficiently oxygen evolution reaction, their alkaline electrolyzer operates with a superior overall water-splitting output, outperforming the one assembled with noble-metal-based catalysts.

Steric Hindrance in Sulfur Vacancy of Monolayer MoS2 Boosts Electrochemical Reduction of Carbon Monoxide to Methane.

The efficient generation of methane by total electroreduction of carbon monoxide (CO) could be of benefit for a more sustainable society. However, a highly efficient and selective catalyst for this process remains to be developed. In this study, density functional theory calculations indicate that steric hindrance in monolayer molybdenum sulfide with 2 S vacancies (DV-MoS2 ) can facilitate the conversion of CO into CH4 with high activity and selectivity under electrochemical reduction at a low potential of -0.53 V vs. RHE and ambient conditions. The potential is a significant improvement on the state-of-the-art Cu electrode (-0.74 V vs. RHE), with less electrical energy. Moreover, the results suggest that such steric hindrance effects are important for structure-sensitive catalytic reactions.

Anchoring and Upgrading Ultrafine NiPd on Room-Temperature-Synthesized Bifunctional NH2 -N-rGO toward Low-Cost and Highly Efficient Catalysts for Selective Formic Acid Dehydrogenation.

Hydrogen is widely considered to be a sustainable and clean energy alternative to the use of fossil fuels in the future. Its high hydrogen content, nontoxicity, and liquid state at room temperature make formic acid a promising hydrogen carrier. Designing highly efficient and low-cost heterogeneous catalysts is a major challenge for realizing the practical application of formic acid in the fuel-cell-based hydrogen economy. Herein, a simple but effective and rapid strategy is proposed, which demonstrates the synthesis of NiPd bimetallic ultrafine particles (UPs) supported on NH2 -functionalized and N-doped reduced graphene oxide (NH2 -N-rGO) at room temperature. The introduction of the NH2 N group to rGO is the key reason for the formation of the ultrafine and well-dispersed Ni0.4 Pd0.6 UPs (1.8 nm) with relatively large surface area and more active sites. Surprisingly, the as-prepared low-cost NiPd/NH2 -N-rGO dsiplays excellent hydrophilicity, 100% H2 selectivity, 100% conversion, and remarkable catalytic activity (up to 954.3 mol H2 (mol catalyst)-1 h-1 ) for FA decomposition at room temperature even with no additive, which is much higher than that of the best catalysts so far reported.

Metabolic Engineering of Escherichia coli for Poly(3-hydroxybutyrate) Production under Microaerobic Condition.

The alcohol dehydrogenase promoter PadhE and mixed acid fermentation pathway deficient mutants of Escherichia coli were employed to produce poly(3-hydroxybutyrate) (P3HB) under microaerobic condition. The E. coli mutant with ackA-pta, poxB, ldhA, and adhE deletions accumulated 0.67 g/L P3HB, up to 78.84% of cell dry weight in tube cultivation. The deletion of pyruvate formate-lyase gene pflB drastically decreased P3HB production and P3HB content to 0.09 g/L and 24.44%, respectively. Overexpressing pflB via the plasmid in its knocked out mutant restored cell growth and P3HB accumulation, indicating the importance of the pyruvate formate-lyase in microaerobic carbon metabolism. The engineered E. coli BWapld (pWYC09) produced 5.00 g/L P3HB from 16.50 g/L glucose in 24 h batch fermentation, and P3HB production yield from glucose was 0.30 g/g, which reached up to 63% of maximal theoretical yield.

Transmission electron microscopy finds plenty of room on the surface.

The atomic features of materials' surfaces have fundamental importance for applications in numerous fields, such as heterogeneous catalysis, energy conversion and thin-film growth. Now transmission electron microscopy (TEM) and affiliated techniques have thoroughly revolutionized many disciplines of natural sciences, and are becoming some of the best solutions for surface exploration. In this Perspective, we try to summarise the important progress in surface elucidation by applying the state-of-the-art TEM, which covers (1) from the essential features of oxides to their dynamic behaviors, and the interactions between surfaces and gases; (2) the visualization of emerging materials from zero-dimensional single atoms to two-dimensional materials, and the development towards an ultimate integration of three-dimensional surfaces. Plenty of room has been made for TEM exploration of a material's surface, and the surface-integral frontiers are being pushed further.

Density functional theory calculations for two-dimensional silicene with halogen functionalization.

The electronic structures and band gaps of silicene (the Si analogue of graphene) adsorbed with halogen elements are studied using the density functional theory based screened exchange local density approximation method. It is found that the band gaps of silicene adsorbed with F, Cl, Br and I have a nonmonotonic change as the periodic number of the halogen elements increases. This is attributed to the transfer of contributions to band gaps from Si-Si bonding to Si-halogen bonding.

Effect of N/B doping on the electronic and field emission properties for carbon nanotubes, carbon nanocones, and graphene nanoribbons.

Carbon nanotubes, carbon nanocones, and graphene nanoribbons are carbon-based nanomaterials, and their electronic and field emission properties can be altered by either electron donors or electron acceptors. Among both donors and accepters, nitrogen and boron atoms are typical substitutional dopants for carbon materials. The contribution of this paper mainly provides a comprehensive overview of the theoretical topics. The effect of nitrogen/boron doping on the electronic and field emission properties for carbon nanotubes, carbon nanocones, and graphene nanoribbons is reviewed. It is also suggested that nitrogen is more an n-type donor. The discussion about the mechanism of field emission for N-doped carbon nanotubes and electronic structures of N-doped graphene nanoribbons is interesting and timely.