High Throughput Preparation of Ag-Zn Alloy Thin Films for the Electrocatalytic Reduction of CO2 to CO.

Ag-Zn alloys are identified as highly active and selective electrocatalysts for CO2 reduction reaction (CO2RR), while how the phase composition of the alloy affects the catalytic performances has not been systematically studied yet. In this study, we fabricated a series of Ag-Zn alloy catalysts by magnetron co-sputtering and further explored their activity and selectivity towards CO2 electroreduction in an aqueous KHCO3 electrolyte. The different Ag-Zn alloys involve one or more phases of Ag, AgZn, Ag5Zn8, AgZn3, and Zn. For all the catalysts, CO is the main product, likely due to the weak CO binding energy on the catalyst surface. The Ag5Zn8 and AgZn3 catalysts show a higher CO selectivity than that of pure Zn due to the synergistic effect of Ag and Zn, while the pure Ag catalyst exhibits the highest CO selectivity. Zn alloying improves the catalytic activity and reaction kinetics of CO2RR, and the AgZn3 catalyst shows the highest apparent electrocatalytic activity. This work found that the activity and selectivity of CO2RR are highly dependent on the element concentrations and phase compositions, which is inspiring to explore Ag-Zn alloy catalysts with promising CO2RR properties.

Dealloying-Derived Nanoporous Bismuth for Selective CO2 Electroreduction to Formate.

Electrochemical CO2 reduction (CO2ER) to formate is an attractive approach for CO2 utilization. Here, we report a nanoporous bismuth (np-Bi) catalyst fabricated by chemically dealloying a rapidly solidified Mg92Bi8 alloy for CO2ER. The np-Bi catalyst exhibits a three-dimensional interconnected ligament-channel network structure, which can efficiently convert CO2 to formate with a selectivity of ≤94% and an activity of 62 mA cm-2 in a wide potential range. Remarkably, the np-Bi catalyst delivers an industry-level current density of ∼500 mA cm-2 for formate production at a low overpotential of 420 mV in the flow cell. The outstanding CO2ER performance can be attributed to the enlarged surface area with abundant accessible active sites and highly curved surfaces with enhanced intrinsic activity. This work highlights the structural synergies for enhancing CO2ER.

Formation, lithium storage properties, and mechanism of nanoporous germanium fabricated by dealloying.

Germanium (Ge) has become a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity and decent electron/ion conductivity, but it exhibits inferior lifespan caused by dramatic volume variations during the (de)lithiation process. Herein, hierarchically, nanoporous Ge (np-Ge) was fabricated by the combination of selective phase corrosion with chemical dealloying. As an anode for LIBs, the np-Ge electrode exhibits marvelous cycling stability with capacity retentions of 1060.0 mA h g-1 at 0.2 A g-1 and 767.1 mA h g-1 at 1 A g-1 after 100 cycles. Moreover, the electrode shows excellent rate capability with a capacity retention of 844.2 mA h g-1 at 5 A g-1. Noticeably, the (de)lithiation mechanisms of np-Ge and porous Si-Ge (p-Si6Ge4) were unveiled by operando X-ray diffraction.

Tailoring P2/P3 Biphases of Layered Nax MnO2 by Co Substitution for High-Performance Sodium-Ion Battery.

P-type layered oxide is a promising cathode candidate for sodium-ion batteries (SIBs), but faces the challenge of simultaneously realizing high rate capability and long cycle life. Herein, Co-substituted Nax MnO2 nanosheets with tunable P2/P3 biphase structures are synthesized by a novel dealloying-annealing strategy. The optimized P2/P3-Na0.67 Mn0.64 Co0.30 Al0.06 O2 cathode delivers an excellent rate capability of 83 mA h g-1 at a high current density of 1700 mA g-1 (10 C), and an outstanding cycling stability over 500 cycles at 1000 mA g-1 . This excellent performance is attributed to the unique P2/P3 biphases with stable crystal structures and fast Na+ diffusion between open prismatic Na sites. Moreover, operando X-ray diffraction is applied to explore the structural evolution of Na0.67 Mn0.64 Co0.30 Al0.06 O2 during the Na+ extraction/insertion processes, and the P2-P2' phase transition is effectively suppressed. Operando Raman technique is utilized to explore the structural superiority of P2/P3 biphase cathode compared with pure P2 or P3 phase. This work highlights precisely tailoring the phase composition as an effective strategy to design advanced cathode materials for SIBs.

Defective Indium/Indium Oxide Heterostructures for Highly Selective Carbon Dioxide Electrocatalysis.

Electrochemical CO2 reduction to fuels and chemicals is a promising approach for CO2 utilization. Developing highly active, selective, and cost-effective electrocatalysts is the key to the large-scale application of this technology. Here, we report that defective indium/indium oxide heterostructures selectively catalyze CO2 electroreduction into C1 products in a broad potential range from -0.7 to -1.2 V vs RHE in aqueous media with the faradaic efficiency approaching 100%. This electrocatalyst enables an efficient CO2-to-formate conversion with excellent selectivity (up to 93%), activity (up to 50.8 mA cm-2), and durability (>25 h). The collaboration between metallic In and In oxide of the heterostructures attributes to the boosted electrochemical CO2 reduction: Metallic In mainly facilitates formate production, while In oxide suppresses the competing hydrogen evolution reaction. This study highlights the integration of different functional components/defects into heterostructures as an effective strategy for enhancing CO2 electrocatalysis.

Surface Reconstruction of Ultrathin Palladium Nanosheets during Electrocatalytic CO2 Reduction.

A surface reconstructing phenomenon is discovered on a defect-rich ultrathin Pd nanosheet catalyst for aqueous CO2 electroreduction. The pristine nanosheets with dominant (111) facet sites are transformed into crumpled sheet-like structures prevalent in electrocatalytically active (100) sites. The reconstruction increases the density of active sites and reduces the CO binding strength on Pd surfaces, remarkably promoting the CO2 reduction to CO. A high CO Faradaic efficiency of 93 % is achieved with a site-specific activity of 6.6 mA cm-2 at a moderate overpotential of 590 mV on the reconstructed 50 nm Pd nanosheets. Experimental and theoretical studies suggest the CO intermediate as a key factor driving the structural transformation during CO2 reduction. This study highlights the dynamic nature of defective metal nanosheets under reaction conditions and suggests new opportunities in surface engineering of 2D metal nanostructures to tune their electrocatalytic performance.

Isolated Diatomic Ni-Fe Metal-Nitrogen Sites for Synergistic Electroreduction of CO2.

Polynary single-atom structures can combine the advantages of homogeneous and heterogeneous catalysts while providing synergistic functions based on different molecules and their interfaces. However, the fabrication and identification of such an active-site prototype remain elusive. Here we report isolated diatomic Ni-Fe sites anchored on nitrogenated carbon as an efficient electrocatalyst for CO2 reduction. The catalyst exhibits high selectivity with CO Faradaic efficiency above 90 % over a wide potential range from -0.5 to -0.9 V (98 % at -0.7 V), and robust durability, retaining 99 % of its initial selectivity after 30 hours of electrolysis. Density functional theory studies reveal that the neighboring Ni-Fe centers not only function in synergy to decrease the reaction barrier for the formation of COOH* and desorption of CO, but also undergo distinct structural evolution into a CO-adsorbed moiety upon CO2 uptake.

Ligament size-dependent electrocatalytic activity of nanoporous Ag network for CO2 reduction.

Electrochemical CO2 reduction (ECR) depends significantly on the nanostructures of electrocatalysts. Here we show a nanoporous Ag network catalyst (np-Ag) for efficient electrochemical reduction of CO2. The np-Ag samples with an average ligament size of 21 nm (denoted by np-Ag (21 nm)) and 87 nm (denoted by np-Ag (87 nm)) were fabricated by dealloying the rapidly solidified Mg80Ag20 (wt%) alloy ribbons in 1 wt% citric acid and 5 wt% phosphoric acid, respectively. The ligament size effect on the electrocatalytic activity and selectivity of CO2 conversion into CO is investigated. When catalysing CO2 reduction in 0.1 M KHCO3, the np-Ag (21 nm) catalyst exhibits a significantly enhanced selectivity with a faradaic efficiency for CO formation of 85.0% at -0.8 V versus RHE, about two times that (41.2%) over the np-Ag (87 nm). Additionally, a superior catalytic activity is also achieved over the np-Ag (21 nm), with a >2.5-fold increase in the CO partial current density relative to the np-Ag (87 nm). The improved selectivity and activity of np-Ag (21 nm) are attributed to the enhanced electrochemical surface area, higher local pH derived from ligament size effect, as well as more defect sites (i.e., grain boundaries) in ligaments.

Identification and molecular characterization of twin-arginine translocation system (Tat) in Xanthomonas oryzae pv. oryzae strain PXO99.

Xanthomonas oryzae pv. oryzae causes bacterial leaf blight, one of the most widespread and destructive bacterial diseases in rice. This study identified and characterized the contribution of the twin-arginine translocation (Tat) pathway to motility, chemotaxis, extracellular polysaccharide (EPS) production and virulence in X. oryzae pv. oryzae strain PXO99. The tatC disruption mutant (strain TCM) of strain PXO99 were generated, and confirmed both by PCR and Southern blotting. Strain PXO99 cells were highly motile in NYGB 0.3% soft agar plate. In contrast, the tatC mutation impaired motility. Furthermore, strain TCM cells lacked detectable flagella and exhibited almost no chemotaxis toward glucose under aerobic conditions, indicating that the Tat secretion pathway contributed to flagellar biogenesis and chemotactic responses. It was also observed that strain TCM exhibited a reductive production of extracellular polysaccharide (EPS) and a significant reduction of virulence on rice plants when compared with the wild type PXO99. However, the tatC mutation in strain PXO99 did not affect growth rate and the ability to induce hypersensitive response (HR) in nonhost tobacco (Nicotiana tabacum L. cv. Samsun). Our findings indicated that the Tat system of X. oryzae pv. oryzae played an important role in the pathogen's virulence.

[Cloning, sequencing and fuctional study of gacA gene from Xanthomonas oryzae pv. oryzicola].

A gacA homologue, designated gacA(Xooc), was cloned from Xanthomonas oryzae pv. oryzicola (Xooc), a bacterium that causes leaf streak of rice, with degenerated primers by polymerase amplification reaction (PCR). NCBI blast search indicated that GacA(Xooc) had a similar structure to that of other GacA proteins, and had a CheB (Chemotaxis response regulator containing a CheY-like receiver domain)domain. Sequence comparison showed that the gacA(Xooc) was conserved in the Xanthomonas genus. Homology search revealed that the gacA(Xooc) was 99.7% similarities to gacA (AY870457, this lab) of Xanthomonas oryzae pv. oryzae (Xoo). A gacA(Xooc), disruption mutant was successfully generated by a single cross-over event, and confirmed by PCR and Southern blot. But the mutant still had strong pathogenicity,and its virulence was not obviously different from that of wild type strain. The gacA did not globally regulate metabolism in Xooc, which was different from DC3000 of P. syringae pv. tomato, CHAO of P. fluorescens and IC1270 of Serratia plymuthica. Chemotaxis to 0.1% tryptone of the mutants was reduced compared to wild type strain. The results suggest that gacA(X00c) is involved chemotaxis of Xooc. Nevertheless, how gacA to regulate chemotaxis of Xooc, transcription and expression of genes involved in regulation still need to be further studied.

Zinc uptake regulator (zur) gene involved in zinc homeostasis and virulence of Xanthomonas oryzae pv. oryzae in rice.

Xanthomonas oryzae pv. oryzae causes bacterial leaf blight, one of the most widespread and destructive bacterial diseases in rice. In order to understand the gene of zinc uptake regulator (zur) involved in virulence of the pathogen in rice, we generated a mutant OSZRM by homologous suicide plasmid integration. The mutant failed to grow in NYGB medium supplemented with Zn(2+) or Fe(3+) at a concentration of 500 muM or 6 mM, whereas the wild-type strain grew well at the same conditions. The zur mutant was hypersensitive to hydrogen peroxide and exhibited reduction catalase activity and the production of extracellular polysaccharide (EPS). Interestingly, the mutant showed a reduction in virulence on rice but still kept triggering hypersensitive response (HR) in tobacco. When the mutant was complemented with the zur gene, the response was recovered to wild-type. These results suggested that zur gene is a functional member of the Zur regulator family that controls zinc and iron homeostasis, oxidative stress, and EPS production, which is necessary for virulence in X. oryzae pv. oryzae.