Photocatalytic water splitting for hydrogen production

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Simultaneous hydrogen and peroxide production by photocatalytic water splitting

Photocatalytic oxidation of water is a promising method to realize large-scale H₂O₂ production without a hazardous and energy-intensive process. In this study, we introduce a Pt/TiO₂(anatase) photocatalyst to construct a simple and environmentally friendly system to achieve simultaneous H₂ and H₂O₂ production. Both H₂ and H₂O₂ are high-value chemicals, and their separation is automatic. Even without the assistance of a sacrificial agent, the system can reach an efficiency of 7410 and 5096 μmol g^–1 h^–1 (first 1 h) for H₂ and H₂O₂, respectively, which is much higher than that of a commercial Pt/TiO₂(anatase) system that has a similar morphology. This exceptional activity is attributed to the more favorable two-electron oxidation of water to H₂O₂, compared with the four-electron oxidation of water to O₂.     

Bridging electrocatalyst and cocatalyst studies for solar hydrogen production via water splitting

Solar-driven water-splitting has been considered as a promising technology for large-scale generation of sustainable energy for succeeding generations. Recent intensive efforts have led to the discovery of advanced multi-element-compound water-splitting electrocatalysts with very small overpotentials in anticipation of their application to solar cell-assisted water electrolysis. Although photocatalytic and photoelectrochemical water-splitting systems are more attractive approaches for scaling up without much technical complexity and high investment costs, improving their efficiencies remains a huge challenge. Hybridizing photocatalysts or photoelectrodes with cocatalysts has been an effective scheme to enhance their overall solar energy conversion efficiencies. However, direct integration of highly-active electrocatalysts as cocatalysts introduces critical factors that require careful consideration. These additional requirements limit the design principle for cocatalysts compared with electrocatalysts, decelerating development of cocatalyst materials. This perspective first summarizes the recent advances in electrocatalyst materials and the effective strategies to assemble cocatalyst/photoactive semiconductor composites, and further discusses the core principles and tools that hold the key in designing advanced cocatalysts and generating a deeper understanding on how to further push the limits of water-splitting efficiency.

This perspective briefly reviews recently developed water splitting electrocatalyst materials and discusses their utilization as cocatalysts for photocatalytic and photoelectrochemical water splitting systems.     

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.     

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.     

Nanostructured materials for photocatalytic hydrogen production

Photocatalytic hydrogen (H₂) production represents a very promising but challenging contribution to a clean, sustainable and renewable energy system. The photocatalyst material plays a key role in photocatalytic H₂ production, and it has proven difficult to obtain corrosion resistant, chemically stable, visible light harvesting and highly efficient photocatalysts, which have their band edges matching the O₂ and H₂ production levels. Nanoscience and nanotechnology are opening a new vista in the development of highly active, nanostructured photocatalysts with large surface areas for optimized light absorption, minimized distances (or times) for charge-carrier transport, and further favorable properties. Our focus here is on recently developed nanostructured photocatalysts. In particular, the particle size, chemical composition (including dopants), microstructure, crystal phase, morphology, surface modification, bandgap and flat-band potential of the nanophotocatalysts have shown a visible effect on photocatalytic H₂ production rates, which may be further increased by adding sensitizers, cocatalysts or scavengers. Finally, potential directions required to push this research field a step further are highlighted.     

Heterostructured MOFs photocatalysts for water splitting to produce hydrogen

Metal-organic frameworks (MOFs) with high designability and structure diversity have been widely developed as promising photocatalytic materials,but most of the...     

Conversion of solid amorphous mixed zirconium-titanium phosphates into crystalline from by molten oxalic acid

Solid amorphous mixed zirconium-titanium phosphates, with general formula Zr_xTi_/1–x//HPO₄/₂.n H₂O/ where x=0.1–1, and n=3–5/, are mixed with an excess of solid oxalic acid dihydrate and digested in molten oxalic acid. Then oxalic acid is removed by extraction and the residue washed with dilute /O.OlM/ HCl solution and bidistilled water. As a result of this method, crystalline mixed zirconium-titanium phosphate is formed.     

Application of an electrochemical membrane reactor to the thermochemical water splitting IS process for hydrogen production

The Bunsen reaction (SO₂ + I₂ + 2H₂O = H₂SO₄ + 2HI) in the thermochemical IS process to produce hydrogen was successfully employed using an electrochemical membrane reactor. H₂SO₄ and HI were concentrated in the anode side and the cathode side of the reactor, respectively. I₂ is the dominant bulk of the recycling chemicals in this process, and I₂ concentration at the outlet of the reactor was reduced ca. 93% by using this technique. The electric energy consumption for the reaction was about 50% smaller by reducing the concentration of I₂ indicating that the IS process can be operate efficiently at low I₂ concentration. The reaction was carried out for 4 h, and the HI concentration was increased by 26%. This amount was the same within 10% as the values calculated from the total loaded electricity. In order to decrease the overpotential at the anode side, small amount of HI was added to the anode side solution. The total voltage was reduced by 0.03 V by the addition of HI.     

Catalytic activity of Pt-promoted CdS nanocrystals covered with a polymer in photoelectrochemical hydrogen production by water splitting

Photocatalytic properties of Pt-promoted CdS nanocrystals functionalized by the polymer coating were investigated. Deposition of Pt on the surface of the nanoparticles followed by polymer functionalization provides a high photocatalytic activity (1.45 mmol h^–1 mg^–1 at 0.93 W cm^–2) and apparent quantum yield (7%, λ = 445 nm) of the particles. Dependence of the rate of H₂ evolution on Pt loading is described by a curve with the maximum, whereas the quantum yield decreases with an increase in the light flux density. The photocatalytic activity of the nanocrystals increases more than 2 times with polymer coatining.     

A mechanism for water splitting and hydrogen absorbing functions of metal–oxide layered hydrogen storage materials studied by means of ion beam analysis

This review describes a study of catalytic functions of water splitting at the surface and hydrogen gas emitting from the bulk of metal–oxide layered materials as well as hydrogen storage materials as its application by means of the ion beam analysis techniques. First are described a microscopic model for water splitting at the oxide surface and mass balance equations for hydrogen atoms in the bulk. The latter is a mathematical expression of a one‐way diffusion model proposed for an anomalous isotope effect in D–H and H–D replacements of both deuterium (D) implanted into perovskite oxide ceramics by protium (H) in H₂O vapour and the vise versa. The latter model brings about finding of catalytic functions of water splitting at the surface and hydrogen gas emitting from the bulk. Second, experimental results on the anomalous isotope effect are presented and the D–H replacement rates are described in detail. Subsequently are shown results on H₂ gas emission measured with a Bach method, which give a clear evidence for the water splitting and hydrogen gas emitting catalytic functions of the oxide surface. Finally, we present experimental data on the hydrogen absorption and emission characteristics of the metal–oxide layered hydrogen storage materials as an application of the water splitting and hydrogen absorbing catalysts. Copyright © 2014 John Wiley & Sons, Ltd.     

Homogeneous catalytic system for photoinduced hydrogen production utilizing iridium and rhodium complexes

An efficient homogeneous catalytic system for the visible-light-induced production of hydrogen from water utilizing cyclometalated iridium(III) and tris-2,2'-bipyridyl rhodium(III) complexes is described. Synthetic modification of the photosensitizer Ir(C--N) 2(N--N) (+) and water reduction catalyst Rh(N--N) 3 (3+) creates a family of catalysts with diverse photophysical and electrochemical properties. Parallel screening of the various catalyst combinations and photoreaction conditions allows the rapid development of an optimized photocatalytic system that achieves over 5000 turnovers with quantum yields ( (1)/ 2 H 2 per photon absorbed) greater than 34%. Photophysical and electrochemical characterization of the optimized system reveals that the reductive quenching pathway provides the necessary driving force for the formation of [Rh(N--N) 2] (0), the active catalytic species for the reduction of water to produce hydrogen. Tests for system poisoning with mercury or CS 2 provide strong evidence that the system is a true homogeneous system for photocatalytic hydrogen production.     

Discovery and high-throughput screening of heteroleptic iridium complexes for photoinduced hydrogen production

The catalytic process of photoinduced hydrogen generation via the reduction of water has been investigated. The use of parallel synthetic techniques has facilitated the synthesis of a 32 member library of heteroleptic iridium complexes that was screened, using high-throughput photophysical techniques, to identify six potential photosensitizers for use in catalytic photoinduced hydrogen production. A Pd/Ni thin film hydrogen selective sensor allowed for rapid quantification of hydrogen produced via illumination of aqueous systems of the photosensitizer, tris(2,2'-dipyridyl)dichlorocobalt ([Co(bpy)(3)]Cl(2)), and triethanolamine (a sacrificial reductant) with ultra-bright light emitting diodes (LEDs). The use of an 8-well parallel photoreactor expedited the investigation of the hydrogen evolution process and facilitated mechanistic studies. All six compounds investigated produced considerably more hydrogen than commonly utilized photosensitizers and had relative quantum efficiencies of hydrogen production up to 37 times greater than that of Ru(bpy)(3)(2+).     

增强UiO-66-NH2光催化水分解制氢性能的研究进展

氢能是一种能量密度高、储量大、可再生、零污染的新能源。光催化水分解制氢是一种绿色、清洁的能源转换技术,被认为是一种有效的制氢方法。UiO-66-NH2是一种可见光响应、稳定性良好的金属有机骨架材料,但存在可见光响应范围有限、导电性差、载流子复合率高等问题。研究者们采用金属粒子掺杂、染料敏化、金属纳米粒子负载等多种方法对UiO-66-NH2进行改性,提升UiO-66-NH2在光催化水分解制氢反应中的性能,并报道了许多研究成果。因此,本文对近年来报道的有关增强UiO-66-NH2光催化水分解制氢性能的方法进行了综述,并对后续的发展提出了建议,以期为UiO-66-NH2在光催化水分解制氢中应用研究提供参考。     

First-principle investigation of TcSe2 monolayer as an efficient visible light photocatalyst for water splitting hydrogen production

Research on Chemical Intermediates - One typical two-dimensional transition metal dichalcogenide (TMDC) called the TcSe2 monolayer has been predicted to be a potential photocatalyst for water...     

Cyclodextrin-based systems for photoinduced hydrogen evolution

Light-driven catalytic three component systems for the reduction of protons, consisting of a cyclodextrin-appended iridium complex as photosensitizer, a viologen-based electron relay, and cyclodextrin-modified platinum nanoparticles as the catalyst, were found to be capable of producing molecular hydrogen effectively in water, using a sacrificial electron donor. The modular approach introduced in this study allows the generation of several functional photo-active systems by self-assembly from a limited number of building blocks. We established that systems with polypyridine iridium complexes of general formula [Ir(ppy)(2)(pytl-R)]Cl (ppy, 2-phenylpyridine; pytl, 2-(1-substituted-1H-1,2,3-triazol-4-yl)pyridine) as photosensitizers are active in the production of H(2), with yields that under our experimental conditions are 20-35 times higher than those of the classical system with [Ru(bpy)(3)]Cl(2) (bpy, 2,2'-bipyridine), methyl viologen, and Pt. By investigating different photocatalytic systems, it was found that the amount of hydrogen produced was directly proportional to the emission quantum yield of the photosensitizer.     

CdS的结构参数对其可见光分解水产氢性能的影响

采用水热/溶剂热法合成了球形、棒状和叶子状的CdS,并采用扫描电子显微镜(SEM)、X射线粉末衍射仪(XRD)、紫外-可见漫反射光谱(UV-vis DRS)、荧光光谱(PL)、比表面积及孔隙率分析仪(BET)等技术对其结构和光吸收特性进行了表征.考察了4种CdS光催化剂的可见光分解水产氢性能,并考察了CdS的结构参数对其活性的影响.结果表明,当Pt的负载量为1.2%(质量分数)时,L-CdS产氢速率最高,为47.77 mmol·h~(-1)·g~(-1).结构表征显示,L-CdS(002)晶面衍射峰强度特别强.(002)晶面是高指数晶面,比表面能大,这可能是其活性高的主要原因.紫外-可见漫反射光谱和荧光光谱结果也表明,L-CdS具有很好的可见光响应和较弱的荧光强度.