Titanium dioxide nanomaterials in electrocatalysis for energy

Over the last two decades, researchers have found many strategies to obtain high surface area nanostructured titanium dioxide. These nanostructures have recently found application as supports for the fabrication of electrodes for electrochemical energy conversion and storage devices. The properties that make titanium dioxide appealing for these applications are as follows: (i) stability in a variety of conditions relevant to electrocatalysis, (ii) electronic conductivity, (iii) synergistic effects with metal catalysts. The work splits TiO₂ nanomaterials into the following two classes: (i) powders and (ii) embedded nanoarchitectures (e.g. titania nanotubes on titanium support). We give an overview of the latest applications, with a special emphasis on fuel cells, electrolysis, and carbon dioxide electroreduction. We conclude with a list of the research needs that, in the opinion of the authors, will support the exploration and consolidation of the use of titania in electrocatalysis for energy.     

电催化剂设计中表面和界面工程的最新进展

电催化已发展为一种涉及电化学、表面科学、材料科学和催化科学等众多科学分支的交叉学科和综合技术,在工农业生产、经济和国防建设、能源开发和环境保护等方面发挥了不可或缺的作用。金属纳米催化剂的可控合成和创新构建,极大地推动了电催化的广泛应用和巨大进展。过渡金属尤其是贵金属Pt、Pd等电催化剂,在电催化中表现出良好的选择性、活性和稳定性,很难完全被其他材料所取代。制约电催化可持续发展的瓶颈问题是,如何设计、合成和构建高性能低成本的金属纳米催化剂。为实现这一目标,人们付出了大量的努力并取得了一些可喜的进展。电催化是发生在电解质与电极材料表面和界面的异相催化反应,金属纳米电催化剂的性能与其形貌、结构、尺寸和组成相关。本文着力总结和探讨如何从表面工程和界面工程角度设计、合成和构筑金属纳米结构及其复合结构,以实现金属电催化剂性能和成本的双优化。本文提出了在金属纳米结构及其复合结构的设计、合成和构筑过程中需要考虑的几个重要的表面和界面因素,即表面面积、表面晶面、活性位点和界面结构等。首先,有效表面面积越大,越有利于电催化反应。我们总结了增大催化剂有效活性面积的四种有效方法,包括减小颗粒尺寸、制成薄层二维纳米结构、增大粗糙度、形成中空、多孔或介孔及框架结构等。其次,表面晶面也可决定电催化的性能。我们简单总结了低指数晶面和高指数晶面在表面能、晶面形成和催化活性上的“挑战与机遇”矛盾关系,并简要阐述了晶面选择性即晶面效应以及晶面与尺寸的依赖关系。再次,活性位点一般指的是低配位表面原子位点,是电催化反应的决定因素之一。我们描述了活性位点与表面和界面结构特征、纳米晶表面晶面、表面缺陷和空穴、表面面积和粒子尺寸等的依赖关系。最后,界面结构工程是调控电催化性能的最丰稔因素。我们简述了界面结构的形成、分类及其对优化界面活性位点的成分和几何结构、表面悬键和原子配位数、电子结构与电子传递、质子传输和物种交换等方面调控作用,并在界面工程的基础上推介了贵金属基复合结构的合成、组装的几种典型方式。本文以具体示例的形式,分别从表面工程和界面工程的角度,扼要介绍了本课题组最近在甲酸氧化、氧还原、析氢等电催化反应体系中贵金属基纳米结构及其复合纳米结构电催化剂的设计、合成与构筑的具体做法。我们分别介绍了低指数晶面和高指数晶面的表面设计对于提高催化剂性能的关键作用。对于低指数晶面,我们重点介绍了如何获得相似尺寸的不同表面晶面以研究其晶面效应,如何维持相同晶面调节尺寸以研究其尺寸效应,如何建造与电极有良好电学接触的低指数晶面纳米结构,以利于提升其电催化性能。对于高指数晶面,介绍了几种形成高指数晶面的途径,并阐明了其晶面对电催化性能的影响。另一方面,我们从金属纳米结构及其复合结构的成分和结构调控策略介绍了界面构建对于提升电催化性能的奇妙作用,包括建造多金属纳米结构、与二维材料负载组装和利用界面极化。由此,本文总结了表面和界面工程对于电催化剂设计、合成和构筑目前面临的三个关键挑战。     

Recent advances in energy chemistry of precious-metal-free catalysts for oxygen electrocatalysis

The rational design and effective construction of precious-metal-free materials for OER and ORR, respectively, are reviewed in the respects of electronic structure regulation, nanostructure tailor, and freestanding electrode fabrication. This affords fresh concepts for oxygen electrocatalysis and is also enlightening for other energy catalysis with targeted optimization.     

Recent Progress on Two-dimensional Electrocatalysis

Due to their unique electronic and structural properties triggered by high atomic utilization and easy surface modification, two-dimensional(2D) materials have prodigious potential in electrocatalysis for energy conversion technology in recent years. In this review, we discuss the recent progress on two-dimensional nanomaterials for electrocatalysis. Five categories including metals, transition metal compounds, non-metal, metal-organic framework and other emerging 2D nanomaterials are successively introduced. Finally, the challenges and future development directions of 2D materials for electrocatalysis are also prospected. We hope this review may be helpful for guiding the design and application of 2D nanomaterials in energy conversion technologies.     

Hydrogen energy currency: Beyond state-of-the-art transition metal oxides for oxygen electrocatalysis

In this opinion piece, we highlight and discuss beyond state-of-the-art transition metal oxide materials for the oxygen evolution reaction and oxygen reduction reaction, which are essential for the renewable energy conversion and storage of H₂ to electricity. We pinpoint some of the synthetic routes taken and discuss essential measurements required in the highlighted works, which others should undertake to achieve highly active and stable oxygen evolution reaction and oxygen reduction reaction catalysts in both acidic and alkaline media.     

Recent advances in surface x-ray diffraction and the potential for determining structure-sensitivity relations in single-crystal electrocatalysis

Determining how electrode structure governs the performance of an electrocatalyst requires techniques capable of probing structure at the atomic scale, often in situ and operando. In recent years, there have been numerous advances in the main experimental techniques for determining the structure of the electrochemical interface. In situ/operando synchrotron surface x-ray diffraction measurements are key to investigate the atomic structure of the electrode surfaces as well as understand the structure-reactivity relations in electrocatalysis. Here we discuss some recent improvements that have taken place in surface x-ray diffraction and how we expect them to lead to an enhanced understanding of electrocatalysis.     

高效氧催化反应中的金属有机骨架材料（英文）

氧电催化反应包括氧气还原反应(ORR)和氧气析出反应(OER).作为核心电极反应,这两个反应对诸多能源存储与转换技术(比如燃料电池、金属空气电池以及全水分解制氢等)的能量效率起决定性作用.然而,ORR和OER涉及多个反应步骤、多个电子转移过程以及多相界面传质过程.这些复杂的过程较大程度上限制了ORR和OER的反应速率.从理论和实践两个方面来看,ORR和OER都需要高效电催化剂的参与来促进其反应速率,从而能够最终提高上述能源存储与转换技术的能量转换或利用效率.目前,以Pt,Pd,Ir,Ru为代表的贵金属基电催化剂具有十分突出的电催化性能.但是,过高的成本和过低的储量始终制约着贵金属基电催化剂在催化ORR和OER反应方面,乃至在能源存储与转换技术领域的规模化应用.因而,开发高效非贵金属基氧电催化剂成为近年来能源存储与转换领域的研究重点之一.在众多已经报道的非贵金属基氧电催化剂中,金属有机骨架材料(MOFs)备受瞩目.MOFs是一类由有机配体和金属节点通过配位键自组装而成的晶态多孔材料.它们具备超高比表面积、超高孔隙率以及规则性纳米孔道.相比较其他传统的多孔材料(比如活性炭、分子筛、介孔炭、介孔氧化硅等),MOFs最主要的优势在于它们的结构和功能可以依据需求通过选择合适的有机配体和金属节点进行便利地设计,或通过后处理进行必要的改性和调节.基于独特的多孔特性以及结构与功能的可设计、可调节性,MOFs在气体分离与存储、异相催化、化学传感、药物输送、环境保护以及能源存储与转化等领域都具有潜在的应用价值.因而,近年来,MOFs备受基础研究领域和工业界的青睐.针对MOFs开展的基础研究和应用开发逐渐成为诸多领域的研究焦点.也正由于MOFs具有的上述优异特性,尤其是结构与功能的可设计、可调节性,使得设计制备基于单纯MOFs以及MOFs衍生材料成为开发高效非贵金属基氧电催化剂的新途径.本综述首先论述了基于单纯MOFs的氧电催化剂(包括纯MOFs、活性物种修饰的MOFs以及与导电材料构成的复合MOFs)的合成以及它们在ORR或OER催化反应中应用的研究进展.在第二部分论述中,本综述主要针对MOFs衍生的各类氧电催化剂(包括无机微米-纳米结构/多孔碳复合材料、纯多孔碳材料、纯无机微米-纳米结构材料以及单原子型电催化材料)的研究进展进行了简要介绍和讨论.最后,本综述对MOFs基氧电催化剂目前存在的挑战进行了简要分析;同时,也对这类氧电催化剂的通用设计准则以及未来发展方向进行了展望.尽管存在诸多挑战,MOFs始终被认为是极好的"平台"材料.充分利用它们将有利于开发高效且实用的非贵金属基氧电催化剂.     

Recent advances in bismuth vanadate-based photocatalysts for photoelectrochemical water splitting

Photoelectrochemical(PEC) technology is considered to be a promising approach for solar-driven hydrogen production with zero emissions. Bismuth vanadate(BiVO_4) is a kind of photocatalytic material with strong photoactivity in the visible light region and appropriate band gap for PEC water splitting.However, the solar-to-hydrogen efficiency(STH) of BiVO_4 is far away from the 10% target needed for practical application due to its poor charge separation ability. Therefore, this review attempts to summarize the strategies for improving the photocurrent density and especially hydrogen production of BiVO_4 materials through PEC techniques in the last three years, such as doping nonmetal and metal elements, depositing noble metals, constructing heterojunctions, coupling with carbon and metalorganic framework(MOF) materials to further enhance the PEC performance of BiVO_4 photoanode. This review aims to serve as a general guideline to fabricate highly efficient BiVO_4-based materials for PEC water splitting.     

High-entropy transition metal chalcogenides as electrocatalysts for renewable energy conversion

High-entropy transition metal chalcogenides (HE-TMCs) are advantageous in electrocatalytic applications compared to other entropy-stabilized systems owing to the greater orbital extension and energetic match of p-orbitals in chalcogenides with d-orbitals of the transition metals providing additional space to tailor their electronic structure. The high-configurational entropy of HE-TMCs leads to stabilization of cubic rock salt, wurtzite-type and hexagonally packed 2D structures. Due to the multi-element nature of HE-TMCs, the synergy among different elements results in tunable d- and p-band positions. As a consequence, the adsorption energies of electrocatalytic reaction intermediates can be tailored to enhance catalytic performance in water splitting and CO₂ reduction. Furthermore, the entropy-stabilized disordered microstructural state of the material endows HE-TMCs with improved corrosion resistance. Despite recent advances in HE-TMC electrocatalysis, challenges such as identification and synthesis of efficient HE-TMCs as well as the identification of catalytically active sites and reaction mechanisms on HE-TMCs remain to be investigated.     

硫掺杂镍铁层状双氢氧化物的氧析出电催化性能

氧析出反应(OER)是裂解水、二氧化碳还原、以及可充电的锌空电池等许多技术中重要的半反应,但受限于其迟缓的反应动力学,开发高效的氧析出催化剂迫在眉睫.在OER出反应中,性能较好的非贵金属催化剂主要是第四周期过渡金属的一些化合物,如氧化物、氢氧化物、硫化物、硒化物、磷化物等等.在这些材料中,镍铁双金属化合物被认为是最优的氧析出材料,尤其是镍铁层状双氢氧化物(Ni Fe-LDHs)它拥有较大的电化学活性面积以暴露较多活性位点,同时镍铁两种过渡金属元素存在协同效应,使得其具有良好的催化性能.然而,这一类材料的OER性能仍然有优化的空间.研究表明,将硫化物氧化得到的氢氧化物会有少量的硫元素残留,这种硫残留的氢氧化物拥有十分优异的OER性能.为了进一步认识硫的引入对Ni Fe-LDHs的OER行为的影响,本文通过水热法合成了硫掺杂的Ni Fe-LDHs,考察了硫的掺杂量对催化剂性能的影响,验证了微量硫的存在对Ni Fe-LDHs的OER性能的贡献.扫描电镜图片显示,水热合成的催化剂是厚度为几十纳米的薄片,拥有较高的比表面积, X射线荧光光谱分析证明合成的硫掺杂Ni Fe-LDHs中镍铁的元素比例为4:1,而且硫的掺杂量并不影响催化剂的形貌和其中镍铁元素比.X射线光电子能谱分析表明,硫原子的引入使得铁原子结合能降低,即硫与铁的相互作用部分降低了铁的价态,这种硫和铁的相互作用能够优化OER反应中间体OH*与O*在铁活性位点上的吸附自由能,降低氧析出反应的过电势.电化学测试表明,拥有0.43%的硫掺杂Ni Fe-LDHs拥有最好的氧析出性能, 10 m A cm^-1下超电势仅有257 m V, Tafel斜率61.5 m V dec^-1.此后,随着硫掺杂量的提升,其性能先保持稳定,随后有所下降.在稳定测试中,硫掺杂的镍铁层状双氢氧化物在10 m Acm-1电流密度下循环30 h后过电位仅衰减14 m V.在对稳定性测试后的催化剂进行表征表明,催化剂发生了轻微了变形,但这对性能的影响不大.综上,本文提供了一种简便的通过非金属元素掺杂调控过渡金属氧化物的结构和电子态的方法,有望为设计高活性OER电催化剂提供新思路.     

二维材料用于电催化析氢的研究进展

电催化水分解因其丰富的原料来源和环境友好被认为是一种有前途的制氢技术. 开发用于电催化析氢反应的高效电催化剂是迫切需要的. 随着石墨烯的兴起, 二维(2D)材料因其独特的物理、 化学和电子特性, 已逐渐成为水电解的潜在候选材料. 本文介绍了二维材料用于电化学水分解产生氢气的最新进展, 概括了二维材料的合成方法, 总结了改善二维材料电化学析氢性能的策略, 讨论了该领域面临的挑战和未来的发展机遇.     

Low-temperature plasma technology for electrocatalysis

The latest applications of plasma in energy storage and conversion are summarized here, including using it as the preparation and modification technology of the various electrocatalysts and the usage of it as the synthesis technology directly. Also, the challenges and outlook of plasma technology in energy storage and conversion were summarized, and the solutions and prospected its development in the future were present.     

先进蛋黄-蛋壳结构能源转化纳米反应器

蛋黄-蛋壳结构独特的纳米结构及特性,使其在很多领域中具有潜在的应用价值,因此近年来受到了广泛关注.本综述总结了使用蛋黄-蛋壳纳米结构作为纳米反应器的研究进展.从合成策略出发,主要强调最近五年合成蛋黄-蛋壳纳米结构的最新研究进展.通过光催化,甲烷重整和电催化等反应作为典型的反应过程,重点讨论蛋黄-蛋壳结构纳米反应器在催化领域的应用,并对该领域未来的发展进行了展望.     

Recent advances in photosynthetic energy conversion

Photosynthesis is one of the first natural processes evolved by cyanobacteria, algae and green plants to trap light and CO₂ in the form of reduced carbon compounds while simultaneously oxidizing water to oxygen. The photosynthetic energy conversion forms the basis for all the existing life today. The photosynthetic energy is being harnessed in many ways using modern technologies for the production of fuels using photosynthetic organisms, generation of direct electricity using photosystems/photosynthetic organisms in photo-bioelectrochemical cells or through photovoltaic systems. While the production of energy rich carbon fuels (ethanol, propanol) from photosynthetic organisms has already been accomplished due to advancement in understanding microbial physiology and metabolism, the photosynthetic hydrogen production as well as direct electricity generation from light is still at its infancy. Recent advances include combining photosystem complexes with hydrogenases for hydrogen production, using isolated thylakoids, photosystems on nanostructured electrodes such as gold nanoparticles, carbon nanotubes, ZnO nanoparticles for electricity generation. Many challenging optimizations on the immobilization methods, catalyst stability and isolation procedures, electron transfer strategies have acquired momentum leading to the production of more stable and higher current densities and power densities in photosynthetic devices. Further, the use of whole cell microorganisms (cyanobacteria, microalgae) rather than their isolated counterparts has produced promising results. The photosynthetic energy conversion has an enormous potential for renewable energy generation in a sustainable and environment friendly manner.     

铜基非贵金属氧还原电催化剂的研究进展

面对日益严重的全球能源危机,燃料电池作为一种清洁的能源转换装置在全世界范围内得到了广泛关注。燃料电池是一种能够使氢气、甲醇、甲酸和乙醇等小分子燃料和氧气发生氧化还原反应,并将其化学能转换为电能的新型装置。在燃料电池中,由于在阴极发生的氧气还原反应动力学速率缓慢而使得燃料电池的整体转换效率过低,目前商用的燃料电池一般采用贵金属铂作为催化剂来加速其反应。但由于铂的价格高昂且在反应过程中易被反应中间产物毒化而活性下降,使得燃料电池的整体成本过高,从而阻碍了燃料电池的实际商业化。为此,人们尝试利用非贵金属催化剂来替代铂基催化剂。找到一种廉价且高效的氧还原催化剂是目前燃料电池发展急需打破的瓶颈问题之一。近年来,人们发现铁、钴、锰等地表储量丰富的金属元素具有较高的氧还原催化活性。然而,作为一种最常见的金属元素,金属铜在氧还原催化剂方面研究较少。人们发现一些生物酶,如虫漆酶、细胞色素c氧化酶等能够高效地催化氧气还原,如虫漆酶在催化氧还原过程中仅表现出约20 mV的过电位,与金属铂(约200 mV)相比基本可忽略。通过研究这些活性生物酶,人们发现其活性中心均为含Cu的物质。进一步研究这些生物酶的活性位点,然后合成不同的铜基纳米材料去模拟酶的活性位点,以期望能够实现经济、高效催化氧还原反应。
　　本文总结了基于铜的纳米材料在催化氧还原方面的研究进展,首先介绍了一些氧还原实验测试中的基本概念,主要包括不同电解质条件下氧还原的反应机理以及常用的测试手段和性能评价指标。氧还原催化剂的性能应该综合活性、稳定性、抗毒化能力以及催化剂成本等多个方面来评价与比较。随后,我们概括性地介绍了铜基氧还原催化剂的发展现状。根据铜基催化剂的不同类型,我们主要分为三个部分进行介绍：(1)铜的复合物,这部分主要从模拟虫漆酶和模拟细胞色素c氧化酶两个方面分类介绍;(2)铜的化合物,这部分主要介绍了不同价态的铜的氧化物和铜的硫化物;(3)其它铜基催化剂,这部分主要介绍基于铜的尖晶石结构、有机框架材料及载体负载的铜纳米粒子作为氧还原催化剂,以及铜作为掺杂元素在提高锰的不同氧化物催化活性中的作用。最后,通过综合分析铜基氧还原催化剂的发展历程以及目前燃料电池的研究进展,我们对基于铜的氧还原催化剂的未来发展方向做了一些展望。继续研究、探索酶的氧还原活性位点以及机理依然是重中之重,只有完全理解了酶的催化机理,才能够很好的设计并合成材料来对其活性位点进行模拟,从而制备出高性能且低成本的铜基氧还原催化剂。希望本文能够使读者认识到燃料电池氧还原催化剂的发展现况,以及铜基氧还原催化剂目前存在的问题及其未来的发展方向。     

Spot the difference at the nanoscale: identical location electron microscopy in electrocatalysis

Identical location electron microscopy (IL-EM) offers a unique opportunity to track the morphological, compositional, and structural changes at the nanoscale in the systems where direct EM visualization is difficult or even currently impossible, for example, aqueous electrochemistry. Since its introduction by Mayrhofer and Arenz et al. in 2008 (Electrochemistry Communications 10 (2008) 1144–1147) to reveal degradation mechanisms in the state-of-the-art Pt/C catalyst in proton exchange membrane fuel cells, numerous electrochemical and nonelectrochemical systems were addressed by IL-EM. Thus, other types of fuel cells, water electrolysis, electrochemical synthesis, batteries, heterogeneous catalysis, and so on were addressed. In this short review, we highlight the most promising IL-EM applications focusing on the very recent studies. Moreover, we discuss the future perspectives of IL-EM, which, we believe, will benefit from the availability of the equipment that enables real atomic resolution and tomography, supported by computer simulations.     

瓜环基金属纳米催化剂的电化学研究进展（英文）

金属纳米材料在电催化应用中展示出良好的性能,但是它们依旧面临着稳定性差和调控策略有限的问题。引入第二组分是一种有效的策略,能够很好的改善其催化活性与稳定性。在这篇综述中,我们概述了结合金属纳米材料和瓜环（CB[n]）用于电催化应用。瓜环是一系列的具有刚性结构、高稳定性、与金属配位的官能团的大环,它们适合稳定金属纳米材料并对其进行调控。本文讨论按照瓜环的功能分类,包含瓜环作为保护剂、瓜环基的超分子自组装体以及瓜环作为前驱体制备氮掺杂多孔碳。多种金属纳米催化剂,包括金属纳米颗粒（Pt,Ir,Pd,Ru,Au）、金属单原子（Fe,Co,Ni）以及过渡金属碳化物（TMCs）成功与瓜环或瓜环衍生的碳材料复合,这些复合材料在许多电催化反应中展示出优异的性能和稳定性,反应包括了氧还原反应（ORR）、析氧反应（OER）、析氢反应（HER）、二氧化碳还原反应（CO2RR）、甲烷氧化反应（MOR）、乙醇氧化反应（EOR）。其中,一些金属-瓜环复合物可进一步作为双功能催化剂用于全水解和燃料电池中。瓜环基的纳米催化剂具有媲美商用催化剂的性能,甚至其稳定性可优于商用催化剂。实验分析以及密度泛函理论（DFT）计算...     

Underpotential deposit electrocatalysis of fast redox reactions for electrochemical energy storage systems

The electrocatalysis of the Fe^3+/2+ redox reaction at various electrode/electrolyte solution interfaces in the presence/absence of underpotential deposits of various metals has been investigated by the AC impedance method. Exchange current densities and double layer capacity data were obtained. On this basis, changes in the active surface area of the electrode and catalytic effects of the investigated metals were identified. Received: 27 May 1997 / Accepted: 29 July 1997