Surface deterioration dependent on the crystal facets of spinel LiNi_(0.5)Mn_(1.5)O_(4) cathode active material

The spinel LiNi_(0.5)Mn_(1.5)O_(4)(LNMO)cathode active materials(CAMs)are considered a promising alternative to commercially available cathodes such as layered and polyanion oxide cathodes,primarily due to their notable safety and high energy density,particularly in their single-crystal type.Nevertheless,the industrial application of the LNMO CAMs is severely inhibited due to the interfacial deterioration and corrosion under proton-rich and high-voltage conditions.This study successfully designed and synthesized two typical types of crystal facets-exposed single-crystal LNMO CAMs.By tracking the electrochemical deterioration and chemical corrosion evolution,this study elucidates the surface degradation mechanisms and intrinsic instability of the LNMO,contingent upon their crystal facets.The(111)facet,due to its elevated surface energy,is found to be more susceptible to external attack compared to the(100)and(110)facets.Our study highlights the electrochemical corrosion stability of crystal plane engineering for spinel LNMO CAMs.

Crystal Facet Engineering of TiO_(2) Nanostructures for Enhancing Photoelectrochemical Water Splitting with BiVO_(4) Nanodots

Although bismuth vanadate(BiVO4)has been promising as photoanode material for photoelectrochemical water splitting,its charge recombination issue by short charge diffusion length has led to various studies about heterostructure photoanodes.As a hole blocking layer of BiVO4,titanium dioxide(TiO_(2)) has been considered unsuitable because of its relatively positive valence band edge and low electrical conductivity.Herein,a crystal facet engineering of TiO_(2) nanostructures is proposed to control band structures for the hole blocking layer of BiVO4 nanodots.We design two types of TiO_(2) nanostructures,which are nanorods(NRs)and nanoflowers(NFs)with different(001)and(110)crystal facets,respectively,and fabricate BiVO4/TiO_(2) heterostructure photoanodes.The BiVO4/TiO_(2) NFs showed 4.8 times higher photocurrent density than the BiVO4/TiO_(2) NRs.Transient decay time analysis and time-resolved photoluminescence reveal the enhancement is attributed to the reduced charge recombination,which is originated from the formation of type II band alignment between BiVO4 nanodots and TiO_(2) NFs.This work provides not only new insights into the interplay between crystal facets and band structures but also important steps for the design of highly efficient photoelectrodes.

Crystal facet effect induced by different pretreatment of Cu_(2)O nanowire electrode for enhanced electrochemical CO_(2) reduction to C_(2+) products

Electrocatalytic CO_(2) conversion has been considered as a promising way to recycle CO_(2) and produce sustainable fuels and chemicals.However,the efficient and highly selective electrochemical reduction of CO_(2) directly into multi‐carbon(C_(2+))products remains a great challenge.Herein,we synthesized three type catalysts with different morphologies based on Cu_(2)O nanowires,and studied their morphology and crystal facet reconstruction during the pre‐reduction process.Benefiting from abundant exposure of Cu(100)crystal facet,the nanosheet structure derived Cu catalyst showed a high faradaic efficiency(FE)of 67.5%for C_(2+)products.Additionally,electrocatalytic CO_(2) reduction studies were carried out on Cu(100),Cu(110),and Cu(111)single crystal electrodes,which verified that Cu(100)crystal facets are favorable for the C_(2+)products in electrocatalytic CO_(2) reduction.Our work showed that catalysts would reconstruct during the CO_(2) reduction process and the importance in morphology and crystal facet control to obtain desired products.

Ag2-xO with highly exposed{111}crystal facets for efficient electrochemical oxygen evolution:Activity and mechanism

A series of Ag2–xO/FTO-i electrodes(where i denotes the current density during the electrodeposition, and i = 0.5, 1, 2, 3, 4, or 7) was fabricated in 0.1 M K2B4O7 electrolyte containing Ag+ ions by galvanostatic electrocrystallization. The electrode composition and morphology were characterized using X-ray powder diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The results reveal that the electrode films consist of Ag2O, but some of the Ag+ ions on the {111} crystal facets are oxidized into Ag2+ ions. Furthermore, the Ag2–xO/FTO-1 electrode shows a triangular slice shape of a parallel matrix with a larger exposed area of {111} crystal facets than other Ag2–xO/FTO-i(i = 0.5, 2, 3, 4, or 7) electrodes. Electrocatalytic experiments prove that the Ag2–xO/FTO-1 electrode produces the highest oxidative current density, has an overpotential of 417 m V at 10 m A cm–2, and has a Tafel slope of 47 m V dec–1 in 0.1 M K2B4O7. Electrochemical impedance spectra indicate that Ag2–xO/FTO-1 electrodes have the best ability for charge transfer. In addition, in the I-t test over 10 h, the current density decreased 4%. Fortunately, both O–O and Ag2+ species were detected after electrocatalysis and a possible mechanism for the oxygen evolution reaction is proposed in which the formation of Ag2+ and O–O species on {111} facets plays a critical role.

Facet effects on bimetallic ZnSn hydroxide microcrystals for selective electrochemical CO_(2)reduction

Employing crystal facets to regulate the catalytic properties in electrocatalytic carbon dioxide reduction reaction(eCO_(2)RR)has been well demonstrated on electrocatalysts containing single metals but rarely explored for bimetallic systems.Here,we synthesize ZnSn(OH)_(6)(ZSO)microcrystals(MCs)with distinct facets and investigate the facet effects in eCO_(2)RR.Electrochemical studies and in situ Fourier Transform Infrared Spectroscopy(in situ-FTIR)reveal that ZSO MCs produce mainly C1 products of HCOOH and CO.The{111}facet of the ZSO MCS exhibits higher selectivity and faradaic efficiency(FE)than that of the{100}facet over a wide range of potentials(-0.9 V∼-1.3 V versus RHE).Density Functional Theory(DFT)calculations elucidate that the{111}facet is favorable to the adsorption/activation of CO_(2)molecules,the formation of intermediate in the rate-determining step,and the desorption of C1 products of CO and HCOOH molecules.

Synergistic effect of atomic layer deposition-assisted cocatalyst and crystal facet engineering in SnS2 nanosheet for solar water oxidation

The severe bulk recombination and sluggish oxygen evolution reaction(OER)dynamics of photoanodes severely restrict the application of photoelectrochemical(PEC)devices.To solve these two problems,crystallographic facet orientation and cocatalyst emergence with a high-quality photoanode/cocatalyst interface were realized through an air annealing-assisted strategy to treat atomic layer deposition(ALD)-modified SnSnanosheet arrays.Based on experimental observations and theoretical calculations,the reduced(001)crystal facet of SnSdecreases the recombination of photogenerated carriers in the bulk and improves the carrier separation of the photoanode.Moreover,the unexpectedly formed ZnTiOSfilm decreases the overpotential of the surface OER,reduces interface recombination,and extends the carrier lifetime.These synergistic effects lead to significantly enhanced PEC performance,with a high photocurrent density of 1.97 mA cm^(-2)at 1.23 V vs.reversible hydrogen electrode(RHE)and a low onset potential of 0.21 V vs.RHE,which are superior to reported mostly SnS-based photoanodes.

Crystal facet engineering of perovskite cobaltite with optimized electronic regulation for water splitting

The correlation between crystal facets and electronic configurations of perovskite is closely related to the intrinsic activity for water splitting.Herein,we proposed a unique molten-salt method(MSM)to manipulate the electronic properties of LaCoO_(3) by fine-tuning its crystal facet and atomic doping.LaCoO_(3) samples with oriented(110)(LCO(110))and(111)(LCO(111))facets were motivated by a capping agent(Sr^(2+)).Compared with the LCO(111)plane,the LCO(110)and Sr-doped LCO(111)(LSCO(111))planes possessed higher O 2p positions,stronger Co 3d-O 2p covalencies,and higher Co spin states by inducing CoO_(6) distortion,thus leading to superior oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)performances.Specifically,the overpotentials at 10 mA cm^(−2) were 299,322,and 289 mV for LCO(110),LCO(111),and LSCO(111),respectively.In addition,the(110)crystal facet and Sr substitution bestowed enhanced stability on LaCoO_(3) due to the strengthened Co-O bonding.The present work enlightens new avenues of regulating electronic properties by crystal facet engineering and atom doping and provides a valuable reference for the electron structure-electrocatalytic activity connection for OER and HER.

Facet Engineering of Advanced Electrocatalysts Toward Hydrogen/Oxygen Evolution Reactions

The electrocatalytic water splitting technology can generate highpurity hydrogen without emitting carbon dioxide,which is in favor of relieving environmental pollution and energy crisis and achieving carbon neutrality.Electrocatalysts can effectively reduce the reaction energy barrier and increase the reaction efficiency.Facet engineering is considered as a promising strategy in controlling the ratio of desired crystal planes on the surface.Owing to the anisotropy,crystal planes with different orientations usually feature facet-dependent physical and chemical properties,leading to differences in the adsorption energies of oxygen or hydrogen intermediates,and thus exhibit varied electrocatalytic activity toward hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).In this review,a brief introduction of the basic concepts,fundamental understanding of the reaction mechanisms as well as key evaluating parameters for both HER and OER are provided.The formation mechanisms of the crystal facets are comprehensively overviewed aiming to give scientific theory guides to realize dominant crystal planes.Subsequently,three strategies of selective capping agent,selective etching agent,and coordination modulation to tune crystal planes are comprehensively summarized.Then,we present an overview of significant contributions of facet-engineered catalysts toward HER,OER,and overall water splitting.In particular,we highlight that density functional theory calculations play an indispensable role in unveiling the structure–activity correlation between the crystal plane and catalytic activity.Finally,the remaining challenges in facet-engineered catalysts for HER and OER are provided and future prospects for designing advanced facet-engineered electrocatalysts are discussed.

A Novel Method of Fabricating a Well-Faceted Large-Crystal Diamond Through MPCVD

A novel method was developed to deposit a large crystal diamond with good facets up to 1000 μm on a tungsten substrate using a microwave plasma enhanced chemical vapor deposition （MPCVD）. This method consists of two steps, namely single-crystal nucleation and growth. Prior to the fabrication of the well-faceted, large crystal diamond, an investigation was made into the nucleation and growth of the diamond which were affected by the O2 concentration and substrate temperature. Deposited diamond crystals were characterized by scanning electron microscopy and micro-Raman spectroscopy. The results showed that the conditions of single-crystal nucleation were appropriate when the ratio of H2/CH4/O2 was about 200/7.0/2.0, while the sub- strate temperature Ts of 1000℃ to 1050℃ was the appropriate range for single-crystal diamond growth. Under the optimum parameters, a well-faeeted large crystal diamond was obtained.

Synthesis of a Large Diamond Crystal with a Smooth(100) Facet at its Top Through MPCVD

A large diamond crystal up to 500 μm in diameter with a smooth （100） facet at its top has been synthesized on Mo substrate through microwave plasma chemical vapor deposition （MPCVD）. Its morphology and quality were characterized by scanning electron microscopy （SEM）, and the growth mechanism was roughly illustrated from both macroscopic and microscopic viewpoints. It was found that morphological instabilities are a major factor resulting in synthesis of large diamond crystals, moreover, high microwave power density （MPD）, high CH4 concentrations, high pressure, high substrate surface temperature and the addition of a small amount of O2 were also necessary for the synthesis of large diamond crystals.

暴露不同晶面WO_(3)的简单合成及光催化性能

以二水钨酸钠和水合偏钨酸铵为前驱体,在没有模板剂和助剂的条件下,采用简单水热法合成暴露不同晶面的WO_(3)纳米短棒。通过XRD、TEM、FT-IR和UV-visDRS等手段对合成样品的晶型、微观结构、表面官能团和光吸收性能进行表征;通过可见光下降解罗丹明B考察样品的光催化活性。结果表明:以二水钨酸钠为前驱体所合成的WO_(3)(WO_(3)-ST)沿[001]轴生长,主要暴露(100)和(010)晶面;以水合偏钨酸铵为前驱体所合成的WO_(3)(WO_(3)-AT)沿[110]轴生长,主要暴露(001)晶面,并且拥有比前者更宽的可见光吸收范围和更窄的禁带宽度;可见光下对罗丹明B的降解速率为为0.018min^(-1),为前者的18倍。

Function-reversible facets enabling SrTiO_(3)nanocrystals for improved photocatalytic hydrogen evolution

It has been widely reported that,for faceted nanocrystals,the two adjacent facets with different band levels contribute to promoted charge separation,and provide active sites for photocatalytic reduction and oxidation reaction,respectively.In such cases,only one family of facets can be used for photocatalytic hydrogen evolution.Herein,by using SrTiO_(3)nanocrystals enclosed by{023}and{001}facets as a model photocatalyst,this paper proposed a strategy to achieve the full-facets-utilization of the nanocrystals for photocatalytic hydrogen via chemically depositing Pt nanoparticles on all facets.The photo-deposition experiment of CdS provided direct evidence to demonstrate that the{023}facets which were responsible for photooxidation reaction can be function-reversed for photocatalytic hydrogen evolution after depositing Pt nanoparticles,together with the{001}facets.Thus,the full-facets-utilization led to a much-improved activity for photocatalytic hydrogen,in contrast to those SrTiO_(3)nanocrystals with only{001}facets deposited by Pt nanoparticles via a photo-deposition method.

Fe稳固的FeOOH@NiOOH电催化剂的大电流极化设计与析氧研究

电解水技术是制取高纯度氢气的有效途径,为传统的氢气生产提供了一种可持续的替代方案.其中,开发性能优异的电催化材料是降低电解水制氢成本的关键.析氧反应(OER)由于涉及多个电子转移而导致的动力学缓慢,是克服高过电位的主要挑战.镍铁羟基/氢氧化物(NiFe(oxy)hydroxides)是近期研究的热点,其在碱性条件下具有极低的OER过电位,部分材料性能甚至超过了贵金属基催化剂,如IrO_(2)和RuO_(2).然而,NiFe(oxy)hydroxides的长期催化稳定性,尤其是在大电流下的长期催化稳定性,成为限制其实际应用的主要问题,这主要是由于铁元素的严重流失导致的.因此,如何有效控制和利用电化学溶解/沉积动力学成为稳定铁位点的关键.为克服该挑战,本文提出了一种大电流极化重构方法来固定活性铁位点.通过在大电流(1.5 A cm^(-2))下对材料进行表面快速极化重构,成功制备了FeOOH@NiOOH(eFNO_(L))电催化剂.eFNO_(L)不仅具有稳定的铁位点,还暴露出高指数晶面,因此eFNO_(L)同时展现出较好的OER催化活性和稳定性.同时,密度泛函理论计算结果表明,与具有低指数晶面的FeNiOOH相比,大电流极化工程制备的分相eFNO_(L)对铁位点表现出更高的结合能,可以有效抑制OER过程中的铁流失,且高指数晶面在改变速率决定步骤和减少吸附能垒上具有更大的优势.电化学测试结果表明,经过优化后的eFNO_(L)催化剂在产生100和500 mA cm^(-2)大电流密度仅需234和27 mV的过电位,并且具有较小的Tafel斜率(35.2 mV dec^(-1)).由于铁位点结合能的提高,eFNO_(L)催化剂在500 mA cm^(-2)的电流密度下能够稳定催化超过100 h,且仅有1.5%的性能衰减,优于近期报道的大多数镍铁基OER催化剂.综上,本文为开发高活性和高稳定性能的催化剂提供了一种有效的大电流电化学重构策略,在电解水制氢领域实现其工业化的大规模应用方面显示出巨大潜力,有望降低可持续电解水制氢成本.

Insights into facet-dependent reactivity of CuO–CeO2 nanocubes and nanorods as catalysts for CO oxidation reaction

Copper–ceria(Cu O–CeO2) catalysts have been known to be very effective for the oxidation of CO, and their chemical behavior has been extensively studied during the last decades. However, the effect of different CeO2 crystal surfaces on the catalytic activity of Cu O–CeO2 for the oxidation of CO is still unclear and should be further elucidated. In this study, we deposited 1 wt% Cu on mostly {100}-exposed CeO2 nanocubes(1 Cu Ce NC) and mostly {110}-exposed CeO2 nanorods(1 Cu Ce NR), respectively. Both 1 Cu Ce NC and 1 Cu Ce NR have been used as catalysts for the oxidation of CO and achieved 100% and 50% CO conversion at 130 ℃, respectively. The differences in the catalytic activity of 1 Cu Ce NC and 1 Cu Ce NR were analyzed using temperature-programmed reduction of H2 and temperature-programmed desorption of CO techniques. The results confirmed the excellent reducibility of the 1 Cu Ce NC catalyst, which was attributed to the weak interactions between Cu and the CeO2 support. Moreover, in situ diffuse reflectance infrared Fourier-transform spectroscopy studies indicated that the {100} planes of 1 Cu Ce NC facilitated the generation of active Cu(I) sites, which resulted in the formation of highly reactive Cu(I)-CO species during the oxidation of CO. Both the excellent redox properties and effective CO adsorption capacity of the 1 Cu Ce NC catalyst increased its catalytic reactivity.

ZnO单晶在天然有机质存在下溶解过程中的晶面效应

以极性氧化锌单晶(0001)面和非极性氧化锌单晶(101-0)面为研究对象,探究天然有机质(NOM)存在下不同晶面的溶解速率和腐蚀形貌的差异。实验结果表明,ZnO单晶特定晶面溶解的速率受其它晶面是否接触溶液影响,侧面接触溶液会加快顶面的溶解速率;NOM存在下(0001)面的溶解速率高于(101-0)面;不同NOM会对ZnO晶面的溶解腐蚀形貌产生不同的影响,与NOM本身性质有关。

赤铁矿在污染控制方面的晶面效应研究进展

赤铁矿(α-Fe_(2)O_(3))是热力学最稳定的氧化铁矿物,广泛存在于土壤和沉积物中,并在元素的生物地球化学循环中发挥重要作用.天然赤铁矿颗粒由于形成条件的差异而具有不同的形貌和暴露晶面.不同原子排列和电子结构的暴露面赋予赤铁矿特定的表面电荷性质和活性位点密度,使其反应性表现出晶面依赖性.综述了产生具有特定晶面的赤铁矿纳米颗粒的合成方法,重点探讨了赤铁矿在还原溶解、吸附、催化和水解反应中的晶面依赖效应以及对污染物去除的作用,还总结了赤铁矿晶面耦合Fe(Ⅱ)对污染控制的最新进展,并对赤铁矿未来的应用和发展进行了展望.为研究赤铁矿在元素的生物地球化学循环中的影响提供依据,并为污染控制和环境修复奠定理论基础.

氧化锌形貌效应对光催化甲烷有氧偶联的影响

采用水热法并通过改变Zn前驱体、表面活性剂和水热温度等条件制备不同形貌的六方纤锌矿ZnO晶体,Au纳米颗粒作为助催化剂被负载在所合成的不同形貌的ZnO上。采用了FESEM、XRD、ICP方法对制备的光催化剂进行表征,并考察了其在光催化甲烷有氧偶联中的反应活性与反应选择性。结果表明,约30 nm的尖型ZnO纳米颗粒表现出显著提高的光催化甲烷转化活性;花型堆积的ZnO纳米片的催化活性略低于商业化的无规则ZnO纳米颗粒,但花型堆积的ZnO纳米片对C^(2+)高级烷烃的反应选择性更高;六棱柱形ZnO纳米棒则表现出极低的反应活性,但仍表现出相似的C^(2+)反应选择性。合适的主催化剂形貌与晶面调控对提高和改善光催化甲烷转化的性能具有重要且关键的影响。

基于光纤端面集成的液晶光束整形器件

光纤集成器件因其尺寸小、功能高度集成化等优点,近年来受到越来越多的关注。当前光纤集成器件通常由介质型或金属型微结构组成,其制备加工通常依赖于高精度的微纳加工技术,面临着成本高和工艺复杂等挑战。另外,静态、固定几何结构的光纤光学器件功能不可调,也在极大程度上限制了其应用范围。本文设计并验证了一种基于光纤端面集成的液晶光束整形器件。通过对单模光纤端面加工平行锚定和垂直锚定的液晶聚合物液滴,获得了可见光波段的光束整形器件。基于Q-张量模型和Rayleigh-Sommerfeld衍射理论,实现了具有特殊液晶指向矢排布的液晶聚合物液滴的模拟仿真。通过实验验证了不同锚定条件下液晶聚合物液滴的光学性能,实验结果与仿真结果基本吻合,证明了该液晶器件的光束整形能力。这种液晶器件为光纤光学器件的微型化与集成化提供了一种成本较低、高效便捷的全新途径。

Recent Advances in Structural Optimization and Surface Modification on Current Collectors for High‑Performance Zinc Anode:Principles,Strategies,and Challenges

The last several years have witnessed the prosperous development of zinc-ion batteries(ZIBs),which are considered as a promising competitor of energy storage systems thanks to their low cost and high safety.However,the reversibility and availability of this system are blighted by problems such as uncontrollable dendritic growth,hydrogen evolution,and corrosion passivation on anode side.A functionally and structurally well-designed anode current collectors(CCs)is believed as a viable solution for those problems,with a lack of summarization according to its working mechanisms.Herein,this review focuses on the challenges of zinc anode and the mechanisms of modified anode CCs,which can be divided into zincophilic modification,structural design,and steering the preferred crystal facet orientation.The possible prospects and directions on zinc anode research and design are proposed at the end to hopefully promote the practical application of ZIBs.

Construction of truncated-octahedral LiMn2O4 for battery-like electrochemical lithium recovery from brine

The extraction of lithium from salt lakes or seawater has attracted worldwide attention because of the explosive growth of global demand for lithium products. The LiMn_(2)O_(4)-based electrochemical lithium recovery system is one of the strongest candidates for commercial application due to its high inserted capacity and low energy consumption. However, the surface orientation of LiMn_(2)O_(4)that facilitates Li diffusion happens to be prone to manganese dissolution making it a great challenge to obtain high lithium inserted capacity and long life simultaneously. Herein, we address this problem by designing a truncated octahedral LiMn_(2)O_(4)(Tr-oh LMO) in which the dominant(111) facets minimize Mn dissolution while a small portion of(100) facets facilitate the Li diffusion. Thus, this Tr-oh LMO-based electrochemical lithium recovery system shows excellent Li recovery performance with high inserted capacity(20.25 mg g^(-1)per cycle) in simulated brine. In addition, the dissolution rate of manganese per 30 cycles is only 0.44% and the capacity maintained 85% of the initial after 30 cycles. These promising findings accelerate the practical application of LiMn_(2)O_(4)in electrochemical lithium recovery.