Controlled high-density interface engineering of Fe_(3)O_(4)-FeS nanoarray for efficient hydrogen evolution

The rational design of double active sites system is vital for constructing high-efficiency iron sulfides electrocatalysts towards hydrogen evolution reaction(HER) in alkaline media. However, it remains a challenge to controllably create the high-density interface of double sites for optimal synergistic effect.Herein, we reported a simple chemical oxidation-induced surface reconfiguration strategy to obtain the interface-rich Fe_(3)O_(4)-FeS nanoarray supported on iron foam(Fe_(3)O_(4)-FeS/IF) using FeS nanosheets as precursors. The abundant Fe_(3)O_(4)-FeS interfaces could improve the dispersion of active sites and facilitate the electron transfer, leading to enhanced hydrogen evolution efficiency. And meanwhile, by altering the oxidation temperature, the content of S and O could be effectively controlled, further achieving the ratio optimization of Fe_(3)O_(4)to FeS. Synchrotron-based X-ray absorption near-edge structure, X-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy consistently confirm the changes of electronic structure and d-band center of Fe_(3)O_(4)-FeS after chemical oxidation. Consequently, Fe_(3)O_(4)-FeS/IF exhibits excellent alkaline HER activity with a low overpotential of 120.8 mV to reach 20 mA cm^(-2),and remains stable ranging from 10, 20 to 50 mA cm^(-2) for each 20 h, respectively. Therefore, the facile and controllable chemical oxidation may be an effective strategy for designing high-density interfaces of transition metal-based sulfides towards alkaline HER.

Abnormal phenomenon of source-drain current of AlGaN/GaN heterostructure device under UV/visible light irradiation

We report an abnormal phenomenon that the source-drain current(I_(D))of AlGaN/GaN heterostructure devices decreases under visible light irradiation.When the incident light wavelength is 390 nm,the photon energy is less than the band gaps of GaN and AlGaN whereas it can causes an increase of ID.Based on the UV light irradiation,a decrease of I_(D) can still be observed when turning on the visible light.We speculate that this abnormal phenomenon is related to the surface barrier height,the unionized donor-like surface states below the surface Fermi level and the ionized donor-like surface states above the surface Fermi level.For visible light,its photon energy is less than the surface barrier height of the AlGaN layer.The electrons bound in the donor-like surface states below the Fermi level are excited and trapped by the ionized donor-like surface states between the Fermi level and the conduction band of AlGaN.The electrons trapped in ionized donor-like surface states show a long relaxation time,and the newly ionized donor-like surface states below the surface Fermi level are filled with electrons from the two-dimensional electron gas(2DEG)channel at AlGaN/GaN interface,which causes the decrease of ID.For the UV light,when its photon energy is larger than the surface barrier height of the AlGaN layer,electrons in the donor-like surface states below the Fermi level are excited to the conduction band and then drift into the 2DEG channel quickly,which cause the increase of ID.

Distribution of donor states on the surface of AlGaN/GaN heterostructures

The uniform distribution model of the surface donor states in AlGaN/GaN heterostructures has been widely used in the theoretical calculation.A common and a triple-channel AlGaN/GaN heterostructure Schottky barrier diodes have been fabricated to verify the models,but the calculation results show the uniform distribution model can not provide enough electrons to form three separate 2DEGs in the triple-channel Al GaN/GaN heterostructure.Our experiments indicate the uniform distribution model is not quite right,especially for the multiple-channel AlGaN/GaN heterostructures.Besides,it is found the exponential distribution model possibly matches the actual distribution of the surface donor states better,which allows the 2DEG to form in each channel structure during the calculation.The exponential distribution model would be helpful in the research field.

Microwave-assisted molybdenum-nickel alloy for efficient water electrolysis under large current density through spillover and Fe doping

The development of high-efficiency electrocatalysts for overall water splitting under large current density is significant and challenging.Herein,a high-performing Fe-doped MoNi alloy catalyst(M-H-MoNiFe-50)abundant with flower-like nanorods assemblies has been prepared by high-pressure microwave reaction and hydrogen reduction.Firstly,Fe doped NiMoO_(4) precursor(M-MoNiFe-50)was synthesized by microwave fast heating,ensuring the robustness of nanorods,which owns larger area and improved catalytic activity than that by conventional hydrothermal method.Secondly,M-MoNiFe-50 was reduced in H_(2)/Ar to fabricate Fe-incorporated MoNi_(4) alloys(M-H-MoNiFe-50),greatly enhancing the conductivity and facilitating hydrogen/oxygen spillover.The final M-H-MoNiFe-50 exhibits remarkable activity for alkaline/acidic hydrogen evolution reaction and oxygen evolution reaction with low overpotential of 208(alkaline),254(acid)and 347 mV at 1,000 mA·cm^(−2).Moreover,an alkaline water electrolyzer is established using M-H-MoNiFe-50 as anode and cathode,generating a current density of 100 mA·cm^(−2) at 1.58 V with encouraging durability of 50 h at 1,000 mA·cm^(−2).The extraordinary water splitting performance can be chalked up to the large surface area,favorable charge transfer,modified electron distribution,intrinsic robustness as well as an efficient gas spillover of M-H-MoNiFe-50.The final electrocatalyst has great prospects for practical application and confirms the significance of Fe doping,microwave method and spillover effect for catalytic performance improvement.

Transition Metal Boride-Based Materials for Electrocatalytic Water Splitting

Electrocatalytic water splitting to produce hydrogen is an eco-friendly way to achieve sustainable utilization of renewable energy.The industrial application of water electrolysis, which is severely limited by slow kinetic reactions on electrode surfaces, requires the development of highly reactive, low-cost and stable electrocatalytic materials. Transition metal borides/borates have recently emerged as promising electrocatalytic materials for catalyzing hydrogen/oxygen evolution reactions(HER/OER) in inexpensive electrolyzers. However, so far, there has been little comprehensive summary of transition metal borides/borates. Here, this review provides the latest research progress on transition metal borides/borates for electrocatalytic water splitting. The structural characteristics of transition metal borides/borates and their synthesis methods in recent years are discussed. Then, the theoretical and experimental progress of transition metal borides including single-metal borides, multi-metal borides, borate derived and other nanocomposites containing boron(boron-doped nanocomposites/substrate with boron) in electrocatalytic reaction and the role of boron in regulating electrocatalytic performance are further emphasized. Finally, the potential challenges and future prospects of transition metal borides/borates in electrocatalysis are presented.

晶面工程优化钴基钙钛矿电子结构及其电解水性能

钴基钙钛矿催化剂的晶面和电子构型与其本征电解水活性密切相关.本文中,我们提出了一种独特的熔盐方法以调控LaCoO_(3)的晶面类型和原子掺杂,进而调制其电子结构.通过引入封端剂(Sr^(2+)),我们制备了具有特定(110)晶面(LCO(110))和(111)晶面(LCO(111))的LaCoO_(3)样品.与LCO(111)相比,CoO_(6)八面体的畸变使LCO(110)和LSCO(111)具有更高的O 2p位置、更强的Co 3d–O 2p共价性以及更高的Co自旋态,从而具有更优的析氧反应(OER)和析氢反应(HER)性能.其中,LCO(110)、LCO(111)和LSCO(111)在10 mA cm^(−2)处的过电位分别为299,322和289 mV.此外,(110)晶面和Sr掺杂使Co–O键能增强,进而提升了LaCoO_(3)的稳定性.本工作通过晶面工程和原子掺杂为电子结构的调控开辟了新的途径,并为阐明OER和HER催化剂的电子结构-电催化活性关系提供了参考.

Mapping of Defense Response Gene Homologs and Their Association with Resistance Loci in Maize

Defense response genes in higher plant species are involved in a variety of signal transduction pathways and biochemical reactions to counterattack invading pathogens. In this study, a total of 366 non-redundant defense response gene homologs （DRHs）, including 124 unigenes/expressed sequence tags, 226 tentative consensuses, and 16 DRH contigs have been identified by mining the Maize Genetics and Genomics and The Institute for Genomic Research maize databases using 35 essential defense response genes. Of 366 DRHs, 202 are mapped to 152 loci across ten maize chromosomes via both the genetic and in silico mapping approaches. The mapped DRHs seem to cluster together rather than be evenly distributed along the maize genome. Approximately half of these DHRs are located in regions harboring either major resistance genes or quantitative trait loci （QTL）. Therefore, this comprehensive DRH linkage map will provide reference sequences to identify either positional candidate genes for resistance genes and/or QTLs or to develop makers for fine-mapping and marker-assisted selection of resistance genes and/or QTLs.