解决能源问题的新途径--光解水制氢的研究

面对日益枯竭的能源危机,氢能是一种洁净、最有前景的替代能源。目前在各种制氢的方法中光催化分解水制氢的研究最多,光解水过程中催化剂最关键,本文对利用太阳能光解水的途径、提高光催化反应效率以及光催化剂的开发研究进行了综述。     

高压下TiSi2可见光光热催化分解水制氢的研究

系统地研究了高压下一系列TiSi2催化剂的可见光光热催化分解水制氢行为.研究结果表明,压力增加显著提高了TiSi2催化剂光催化分解水制氢速率.添加NaOH和Na2CO3有利于水分解制氢的反应进行,在一定范围内,NaOH和Na2CO3浓度增加,放氢速率增加.研究还发现,担载贵金属Pt或Ru对反应速率没有显著影响.本文还采...     

催化剂筛选：火山型曲线成因理论解析及其在多相催化中的应用

多相催化对于现代社会来说具有极其重要的意义,催化剂的理性设计/筛选是现代催化化学研究者的一个重要的目标。其中,火山型曲线是一个的重要工具。它指出对于一个催化反应来说,其催化活性针对关键物种吸附能来说呈一条先上升后下降的曲线,要求最佳催化剂对中间体的吸附能不能太高也不能太低。近几十年来,密度泛函理论等第一性原理计算方法的发展让许多催化剂表面反应微观物理量的计算成为了可能,这极大地拓展了火山型曲线的应用范围。 然而,对于火山型曲线根源的解释,人们却并非了解得十分清楚;一些基本科学概念的理解很多还是基于经验性的Sabatier原理：吸附太弱不利于吸附、太强不利于脱附。针对该问题的科学解析,本文进行了详细的动力学探究,试图以完全数学解析的方式回答催化反应中火山型曲线的必然存在性、产生根源及在催化活性预测中的内涵。本文采用了两步催化模型以及微动力学来进行速率方程的推导,并考虑BEP关系(基元反应的能垒与其反应焓存在线性关系)的应用,最终将整体反应速率转化为中间体吸附能相关的单值函数。基于对该函数的系列推导和分析,得到如下基本结论：(1)从数学上以一个完全的解析形式证明了催化反应中火山型曲线的存在。(2)通过对比催化反应与与之对应的气相反应,我们证明了：若无催化剂参与反应,则火山型曲线不会产生;由于催化剂表面的参与,随着催化剂吸附能力的增强,其表面会因为吸附作用而被占据毒化,导致反应速率存在一个最大值,即形成火山型曲线。从概念上讲,火山型曲线的根源是由“吸附过程引发表面活性位占据”这一自毒化效应造成的,它的存在可能体现为多相催化的基本属性。(3)数值模拟解析展示了表面反应与气相反应的区别,印证了我们的数学解析结论。同时,通过一定的简化,我们对火山型曲线中各部分的斜率进行了研究。结果发现,对于吸附决速过程,催化反应和气相反应斜率相同,其差别主要出现在脱附决速过程。在此阶段由于吸附能过大,表面被毒化,表面反应速率开始下降;而气相反应的速率依然上升。(4)表面反应速率方程的分解和简化结果表明,最佳催化剂在反应中的空活性位点覆盖度和其BEP关系的斜率存在内在关联关系(θ*opt=1–α),据此讨论了其在催化剂寻优过程中的意义。尝试解释了(a)合成氨反应中正逆反应所需最佳催化剂不同的现象;(b)合成氨或CO甲烷化反应最佳催化剂为前过渡金属、而CO/NO氧化等为后过渡金属这一典型催化现象的物理图像。最后,针对火山型曲线理论框架在实际催化剂理论筛选寻优中的应用,我们简要综述了本课题组近年来在光解水制氢Pt基助催化剂和染料敏化太阳能电池的对电极材料设计方面的理论进展。     

控制氢气反应方向有新法

华东理工大学材料学院教授杨化桂和化学学院副教授王海丰在一项最新研究中,首次提出以一种新型共催化剂材料——一氧化铂团簇来控制氢气反应方向,这一发现将对太阳能光解水制氢领域及相关清洁能源领域产生积极的影响。近日,相关成果在线发表于《自然-通讯》。在太阳能光解水制氢领域中,金属铂一直被视为最有效的共催化剂之一,不过,它同样也会高效催化氢气的氧化反应,这就限制了催化剂光能转换效率的提升。因此,如何有效地抑制氢气氧化反应,     

表面缺陷与钯的沉积对硫化镉纳米晶粒的光催化制氢性能的影响（英文）

近年来,光解水制氢的发展引起了人们的高度关注。CdS是一种具有可见光响应的很有潜力光催化剂,但由于光生电子/空穴对的快速复合和表面上的析氢反应速率低,所以它仅表现出有限的光解水制氢活性。对CdS表面结构和性能的影响的研究仍然非常有限。在本工作中,我们制备了三种具有不同形貌的CdS纳米晶体(长棒状,短棒状和三角片状)用于光解水制氢。随着纵横比的增加,非极性表面暴露面积增大,表面缺陷程度也随之增加,而表面缺陷可以捕获光生电子/空穴,从而降低其复合机会。我们发现氢的生产率可能与表面缺陷的程度有关。另外,这些缺陷可以用来固定Pd粒子形成异质结结构,有利于光生电荷的分离。在1%(w,质量分数) Pd的协助下,所有CdS催化剂的氢气产率都大大提高。值得注意的是,sr-CdS/Pd的制氢产率达到了7884μmol·h~(-1)·g~(-1),与文献报道的最高值相当。希望本文能够为了解晶体结构和性能对光催化的影响提供认识。     

催化剂筛选:火山型曲线成因理论解析及其在多相催化中的应用（英文）

多相催化对于现代社会来说具有极其重要的意义,催化剂的理性设计/筛选是现代催化化学研究者的一个重要的目标.其中,火山型曲线是一个的重要工具.它指出对于一个催化反应来说,其催化活性针对关键物种吸附能来说呈一条先上升后下降的曲线,要求最佳催化剂对中间体的吸附能不能太高也不能太低.近几十年来,密度泛函理论等第一性原理计算方法的发展让许多催化剂表面反应微观物理量的计算成为了可能,这极大地拓展了火山型曲线的应用范围.然而,对于火山型曲线根源的解释,人们却并非了解得十分清楚;一些基本科学概念的理解很多还是基于经验性的Sabatier原理:吸附太弱不利于吸附、太强不利于脱附.针对该问题的科学解析,本文进行了详细的动力学探究,试图以完全数学解析的方式回答催化反应中火山型曲线的必然存在性、产生根源及在催化活性预测中的内涵.本文采用了两步催化模型以及微动力学来进行速率方程的推导,并考虑BEP关系(基元反应的能垒与其反应焓存在线性关系)的应用,最终将整体反应速率转化为中间体吸附能相关的单值函数.基于对该函数的系列推导和分析,得到如下基本结论:(1)从数学上以一个完全的解析形式证明了催化反应中火山型曲线的存在.(2)通过对比催化反应与与之对应的气相反应,我们证明了:若无催化剂参与反应,则火山型曲线不会产生;由于催化剂表面的参与,随着催化剂吸附能力的增强,其表面会因为吸附作用而被占据毒化,导致反应速率存在一个最大值,即形成火山型曲线.从概念上讲,火山型曲线的根源是由"吸附过程引发表面活性位占据"这一自毒化效应造成的,它的存在可能体现为多相催化的基本属性.(3)数值模拟解析展示了表面反应与气相反应的区别,印证了我们的数学解析结论.同时,通过一定的简化,我们对火山型曲线中各部分的斜率进行了研究.结果发现,对于吸附决速过程,催化反应和气相反应斜率相同,其差别主要出现在脱附决速过程.在此阶段由于吸附能过大,表面被毒化,表面反应速率开始下降;而气相反应的速率依然上升.(4)表面反应速率方程的分解和简化结果表明,最佳催化剂在反应中的空活性位点覆盖度和其BEP关系的斜率存在内在关联关系(θopt=1–α),据此讨论了其在催化剂寻优过程中的意义.尝试解释了(a)合成氨反应中正逆反应所需最佳催化剂不同的现象;*(b)合成氨或CO甲烷化反应最佳催化剂为前过渡金属、而CO/NO氧化等为后过渡金属这一典型催化现象的物理图像.最后,针对火山型曲线理论框架在实际催化剂理论筛选寻优中的应用,我们简要综述了本课题组近年来在光解水制氢Pt基助催化剂和染料敏化太阳能电池的对电极材料设计方面的理论进展.     

光催化分解水制氢反应中助催化剂的作用及机理（英文）

近年来,随着一次能源过度消耗所带来的能源和环境问题日益突出,开发廉价、可持续的清洁能源备受关注.光催化分解水制氢可利用太阳能普遍率高和几乎免费等特点制取燃烧热值高、燃烧产物无污染的氢气能源.自从1972年日本的Fujishima教授和Honda教授首次发现TiO2单晶电极光催化分解水可以产生氢气以来,光催化制氢被认为是实现可持续制氢最有潜力的方法之一.有效地将太阳能转换为化学能的关键是设计高效的电荷分离和运输结构.然而,现有的大多数半导体光催化剂因缺少活性位点、光生载流子易复合等缺点而无法达到较高的转换效率.因此,如何提高半导体光催化产氢的转换效率是现阶段面对的重要问题.在众多解决方法中,助催化剂的引入可以为光催化制氢反应增加活性位点,促进光生载流子的有效分离,进而有效地提高半导体光催化产氢速率.本文总结了多种不同类型的助催化剂应用于光催化产氢研究的最新进展,详细讨论了助催化剂在增强光吸收、提供活性位点、增加催化剂稳定性和促进电荷分离等方面的作用,阐明了助催化剂在光催化分解水制氢中的反应机理,同时还提出了光催化制氢的未来研究和预测.本文将助催化剂分为以下几种类别进行讨论:(1)单一助催化剂,包括金属/合金、金属氧化物/氢氧化物、金属磷化物、金属硫化物、碳基材料等助催化剂材料;(2)双助催化剂;(3)Z-Scheme助催化剂;(4)MOFs助催化剂.近年来,助催化剂材料在光催化产氢中应用的发展趋势从当初价格昂贵的贵金属趋于价格相对低廉的非贵金属,从单一体系趋于更复杂的体系.虽然现阶段关于助催化剂与基底之间的匹配还需要进一步研究,但我们相信随着技术的发展,这些问题都可以迎刃而解.希望在不久的将来,可以精确设计和构建出具有高效光催化产氢活性的催化剂体系,开发出更多新的可再生清洁能源,从而缓解能源紧缺和环境恶化等棘手问题.     

Pt基催化剂表面氢氧电催化反应的理论计算研究

氢氧电催化反应是氢能源体系的重要反应,其热力学和动力学直接影响水解制氢和燃料电池的能量效率和功率密度.过去十多年来,基于量子化学的理论计算在电催化剂设计及电催化反应机理研究中得到广泛应用.结合文献结果,本文介绍了近年来在Pt基催化剂表面氢、氧电催化反应理论计算研究中获得的结果和认识.在研究中重点对反应中间体吸附结构、覆盖度及其对反应路径和动力学的影响机制进行了分析.结果指出,反应中间体的吸附特性不仅会影响反应控制步骤的活化能,同时通过改变表面反应活性位的结构和数量影响表面反应速率.对火山顶点附近的Pt基催化剂,简单计算的吸附能不足以准确预测催化剂活性,必须考虑吸附质的覆盖度和吸附结构的影响.在此认识基础上,根据表面反应自由能及速率与关键中间体吸附能、覆盖度及电极电势的关系建立微观动力学模型,利用密度泛函理论计算获得关键吸附中间体在催化剂表面的电化学吸附等温线(吸附结构及覆盖度与电极电势的关系),确定反应活性位、反应路径和动力学,构建催化活性与吸附能的关系曲线,预测催化剂的表面结构及尺寸效应,并对一些重要实验结果进行解释.     

新型产氢催化剂的合成及其光催化产氢性能研究

<正>太阳能光解水制氢被认为是人类解决能源危机的有效途径之一,高效稳定廉价产氢催化剂的研究一直是太阳能光解水制氢领域的难点和热点。本论文设计合成了多种类型的产氢催化剂,在多组分体系中研究了催化剂活性与结构间的依赖关系。主要研究结果如下:1.设计合成了两种双核Rh配合物[Rh2(bpy)2(μ-O2CCH3)2]2+和[Rh2(phen)2(μ-O2CCH3)2]2+,     

光催化完全分解水制氢研究进展

由完全分解水的特殊性出发,从材料的结构和能带设计以及材料的表面修饰等方面对完全分解水光催化剂的研制及其分解水产氢产氧性能进行了评述.介绍了Z型体系在完全分解水制氢方面的原理,以及目前已经开发出来的几个Z型体系.对光催化完全分解水研究中存在的问题进行了简单分析.     

表面组装钴物种同时促进Cd0.9Zn0.1S光催化剂的界面电荷分离和表面反应

利用人工光合成将太阳能转化为化学燃料是太阳能利用的重要途径,具有广阔的应用前景,其中,太阳能光催化分解水制氢是最为关键的反应之一.但是,大多数半导体光催化材料面临着光生电荷分离困难和表面催化反应速率慢等挑战.本文以具有可见光响应的半导体光催化剂Cd_0.9Zn_0.1S(CZS)纳米棒为研究模型,利用水热法成功在其表面上均匀地组装氧化钴物种(CoO_x),构建了多级异质结构CZS@CoO_x.扫描电子显微镜和透射电子显微镜显示,表面组装的CoO_x物种均匀地覆盖在CZS纳米棒的整个表面上,形成了有序的CZS@CoO_x核壳多级异质结构.高分辨率透射电子显微镜进一步确认了氧化钴晶格间距与六方CZS的(002)晶面高度匹配,利于光生电荷在界面的分离和转移.稳态荧光光谱测试表明,与物理混合的样本相比,CZS@CoO_x多级异质结构表现出明显降低的荧光强度,说明多级异质结构能有效促进光生电子-空穴对的分离.时间分辨荧光光谱结果显示,CZS@CoO_x多级异质结构的平均光生电荷寿命明显增长,进一步确认了多级异质结构对光生电荷分离的作用.此外,电化学开路电位测量显示,增强的开路电压响应归因于多级异质结构CZS@CoO_x中致密的界面接触.电化学阻抗谱进一步确认,与没有形成致密界面结构的CZS-CoO_x和CZS/CoO_x相比,多级异质结构CZS@CoO_x的电荷转移电阻大幅度降低,从而确保了更快的界面电荷分离和转移.最后对CZS@CoO_x多级异质结构的光催化产氢活性进行了评价,发现其光催化产氢的性能远高于贵金属Pt/CZS光催化剂;进一步测量了CZS@CoO_x的表观量子效率,在420 nm处光催化产氢的表观量子效率为20%.此外,在多级异质结构CZS@CoO_x上进一步引入Pt助催化剂,可将表观量子效率进一步提升至37%.本文报道的这一简易可行的表面组装构建多级异质结构的策略有望在太阳能光催化领域发挥重要作用.     

Inorganic Photocatalysts for Overall Water Splitting

Photocatalytic water splitting using semiconductor photocatalysts has been considered as a “green” process for converting solar energy into hydrogen. The pioneering work on electrochemical photolysis of water at TiO₂ electrode, reported by Fujishima and Honda in 1972, ushered in the area of solar fuel. As the real ultimate solution for solar fuel‐generation, overall water splitting has attracted interest from researchers for some time, and a variety of inorganic photocatalysts have been developed to meet the challenge of this dream reaction. To date, high‐efficiency hydrogen production from pure water without the assistance of sacrificial reagents remains an open challenge. In this Focus Review, we aim to provide a whole picture of overall water splitting and give an outlook for future research.     

Low Catalyst Loading Enhances Charge Accumulation for Photoelectrochemical Water Splitting

Solar water oxidation is a critical step in artificial photosynthesis. Successful completion of the process requires four holes and releases four protons. It depends on the consecutive accumulation of charges at the active site. While recent research has shown an obvious dependence of the reaction kinetics on the hole concentrations on the surface of heterogeneous (photo)electrodes, little is known about how the catalyst density impacts the reaction rate. Using atomically dispersed Ir catalysts on hematite, we report a study on how the interplay between the catalyst density and the surface hole concentration influences the reaction kinetics. At low photon flux, where surface hole concentrations are low, faster charge transfer was observed on photoelectrodes with low catalyst density compared to high catalyst density; at high photon flux and high applied potentials, where surface hole concentrations are moderate or high, slower surface charge recombination was afforded by low-density catalysts. The results support that charge transfer between the light absorber and the catalyst is reversible; they reveal the unexpected benefits of low-density catalyst loading in facilitating forward charge transfer for desired chemical reactions. It is implied that for practical solar water splitting devices, a suitable catalyst loading is important for maximized performance.     

光催化制氢研究进展

The photocatalytic hydrogen evolution reaction (PHER) has gained much attention as a promising strategy for the generation of clean energy. As opposed to conventional hydrogen evolution strategies (steam methane reforming, electrocatalytic hydrogen evolution, etc.), the PHER is an environmentally friendly and sustainable method for converting solar energy into H₂ energy. However, the PHER remains unsuitable for industrial applications because of efficiency losses in three critical steps: light absorption, carrier separation, and surface reaction. In the past four decades, the processes responsible for these efficiency losses have been extensively studied. First, light absorption is the principal factor deciding the performance of most photocatalysts, and it is closely related to band-gap structure of photocatalysts. However, most of the existing photocatalysts have a wide bandgap, indicating a narrow light absorption range, which restricts the photocatalytic efficiency. Therefore, searching for novel semiconductors with a narrow bandgap and broadening the light absorption range of known photocatalysts is an important research direction. Second, only the photogenerated electrons and holes that migrate to the photocatalyst surface can participate in the reaction with H₂O, whereas most of the photogenerated electrons and holes readily recombine with one another in the bulk phase of the photocatalysts. Hence, tremendous effort has been undertaken to shorten the charge transfer distance and enhance the electric conductivity of photocatalysts for improving the separation and transfer efficiency of photogenerated carriers. Third, the surface redox reaction is also an important process. Because water oxidation is a four-electron process, sluggish O₂ evolution is the bottleneck in photocatalytic water splitting. The unreacted holes can easily recombine with electrons. Sacrificial agents are widely used in most catalytic systems to suppress charge carrier recombination by scavenging the photogenerated holes. Moreover, the low H₂ evolution efficiency of most photocatalysts has encouraged researchers to introduce highly active sites on the photocatalyst surface. Based on the abovementioned three steps, multifarious strategies have been applied to modulate the physicochemical properties of semiconductor photocatalysts with the aim of improving the light absorption efficiency, suppressing carrier recombination, and accelerating the kinetics of surface reactions. The strategies include defect generation, localized surface plasmon resonance (LSPR), element doping, heterojunction fabrication, and cocatalyst loading. An in-depth study of these strategies provides guidance for the design of efficient photocatalysts. In this review, we focus on the mechanism and application of these strategies for optimizing light absorption, carrier separation and transport, and surface reactions. Furthermore, we provide a critical view on the promising trends toward the construction of advanced catalysts for H₂ evolution.     

Single‐Crystal Semiconductors with Narrow Band Gaps for Solar Water Splitting

Solar water splitting provides a clean and renewable approach to produce hydrogen energy. In recent years, single‐crystal semiconductors such as Si and InP with narrow band gaps have demonstrated excellent performance to drive the half reactions of water splitting through visible light due to their suitable band gaps and low bulk recombination. This Minireview describes recent research advances that successfully overcome the primary obstacles in using these semiconductors as photoelectrodes, including photocorrosion, sluggish reaction kinetics, low photovoltage, and unfavorable planar substrate surface. Surface modification strategies, such as surface protection, cocatalyst loading, surface energetics tuning, and surface texturization are highlighted as the solutions.     

光电催化分解水的光阳极改性策略

Photoelectrochemical water splitting is to utilize collected photo-generated carrier for direct water cleavage for hydrogen production. It is a system combining photoconversion and energy storage since converted solar energy is stored as high energy-density hydrogen gas. According to intrinsic properties and band bending situation of a photoelectrode, hydrogen tends to be released at photocathode while oxygen at photoanode. In a tandem photoelectrochemical chemical cell, current passing through one electrode must equals that through another and electrode with lower conversion rate will limit efficiency of the whole device. Therefore, it is also of research interest to look into the common strategies for enhancing the conversion rate at photoanode. Although up to 15% of solar-to-hydrogen efficiency can be estimated according to some semiconductor for solar assisted water splitting, practical conversion ability of state-of-the-art photoanode has yet to approach that theoretical limit. Five major steps happen in a full water splitting reaction at a semiconductor surface:light harvesting with electron excitations, separated electron-hole pairs transferring to two opposite ends due to band bending, electron/hole injection through semiconductor-electrolyte interface into water, recombination process and mass transfer of products/reactants. They are closely related to different proposed parameters for solar water splitting evaluation and this review will first help to give a fast glance at those evaluation parameters and then summarize on several major adopted strategies towards high-efficiency oxygen evolution at photoanode surface. Those strategies and thereby optimized evaluation parameter are shown, in order to disclose the importance of modifying different steps for a photoanode with enhanced output.     

A Hydrogen Farm Strategy for Scalable Solar Hydrogen Production with Particulate Photocatalysts

Scalable solar hydrogen production by water splitting using particulate photocatalysts is promising for renewable energy utilization. However, photocatalytic overall water splitting is challenging owing to slow water oxidation kinetics, severe reverse reaction, and H₂/O₂ gas separation. Herein, mimicking nature photosynthesis, a practically feasible approach named Hydrogen Farm Project (HFP) is presented, which is composed of solar energy capturing and hydrogen production subsystems integrated by a shuttle ion loop, Fe³⁺/Fe²⁺. Well‐defined BiVO₄ crystals with precisely tuned {110}/{010} facets are ideal photocatalysts to realize the HFP, giving up to 71 % quantum efficiency for photocatalytic water oxidation and full forward reaction with nearly no reverse reaction. An overall solar‐to‐chemical efficiency over 1.9 % and a solar‐to‐hydrogen efficiency exceeding 1.8 % could be achieved. Furthermore, a scalable HFP panel for solar energy storage was demonstrated under sunlight outdoors.     

光催化全解水助催化剂的设计与构建

能源和环境危机是当今社会面临的两大关键课题,利用太阳光驱动化学反应、将太阳能转化为化学能是解决上述问题的重要措施。通过光催化分解水是直接利用太阳能生产氢燃料的有效策略。光催化水分解过程可以分为三个基元步骤:光吸收、电荷分离与迁移、以及表面氧化还原反应。助催化剂可有效提高电荷分离效率、提供反应活性位点并抑制催化剂光腐蚀的发生,进而提高水分解效率。助催化剂也可以通过活化水分子以提高表面氧化还原动力学,进而提升整体光催化反应的太阳能转换效率。本文综述了助催化剂在光催化反应中的重要作用以及目前常用的助催化剂类型,详细说明了在光催化全解水过程中双助催化剂体系的构建及作用机理,并根据限制全解水的关键因素提出了新型助催化剂的设计策略。     

Emerging materials for plasmon-assisted photoelectrochemical water splitting

Energy production and environmental pollution are the two major problems the world is facing today. The depletion of fossil fuels and the emission of harmful gases into the atmosphere leads to the research on clean and renewable energy sources. In this context, hydrogen is considered an ideal fuel to meet global energy needs. Presently, hydrogen is produced from fossil fuels. However, the most desirable way is from clean and renewable energy sources, like water and sunlight. Sunlight is an abundant energy source for energy harvesting and utilization. Recent studies reveal that photoelectrochemical (PEC) water splitting has promise for solar to hydrogen (STH) conversion over the widely tested photocatalytic approach since hydrogen and oxygen gases can be quantified easily in PEC. For designing light-absorbing materials, semiconductors are the primary choice that undergoes excitation upon solar light irradiation to produce excitons (electron-hole pairs) to drive the electrolysis. Visible light active semiconductors are attractive to achieve high solar to chemical fuel conversion. However, pure semiconductor materials are far from practical applications because of charge carrier recombination, poor light-harvesting, and electrode degradation. Various heteronanostructures by the integration of metal plasmons overcome these issues. The incorporation of metal plasmons gained significance for improving the PEC water splitting performance. This review summarizes the possible main mechanisms such as plasmon-induced resonance energy transfer (PIRET), hot electron injection (HEI), and light scatting/trapping. It also deliberates the rational design of plasmonic structures for PEC water splitting. Furthermore, this review highlights the advantages of plasmonic metal-supported photoelectrodes for PEC water splitting.