Efficient Photocatalytic Conversion of CO2 and Water Vapor to Hydrocarbon Fuels Using Sunlight

小行星0927262 该奖项是根据2009年美国复苏和再投资法案资助的在最初的工作中，PI已经实现了使用氮掺杂的二氧化钛纳米管阵列将二氧化碳和水蒸气有效地太阳能转化为甲烷和其他烃，其中壁厚足够低以促进有效的载流子转移到吸附物质，用助催化剂铂和/或铜的纳米尺寸岛敏化。 所有实验均在宾夕法尼亚州大学公园的户外阳光下进行。中间反应产物，氢气和一氧化碳，也被检测到，其相对浓度的基础上的烃生产率取决于在纳米管阵列表面上的助催化剂的性质。使用功率密度在75至102 mW/cm 2之间的室外阳光，标准化为100 mW/cm 2的全球AM 1.5阳光，烃生产率为111 ppm cm-2 hr-1（约160微升/g hr）当纳米管阵列样品用Cu和Pt纳米颗粒两者敏化时，获得。至少比以前发表的报告高20倍，这些报告是在实验室条件下使用紫外线照射进行的。 PI试图了解其高光催化CO2转化率所固有的反应，并进一步提高其目的。初始目标包括：{1}一致的敏感性。在初步的努力中，纳米管阵列样品的顶表面用Cu和Pt助催化剂颗粒敏化。PI认为纳米管阵列样品在其整个表面积上的均匀敏化将显著提高光催化转化率。他们试图使用原子层沉积或溶液化学技术均匀地敏化纳米管阵列样品，其中直接变量包括纳米颗粒类型（Cu、CuO、Cu 2 O、Pt）、负载、间距、尺寸和与纳米管壁厚相关的尺寸分布。他们将阐明助催化剂的作用，以及相关的潜在物理机制，包括半反应，从而使光催化材料的设计能够提高性能。{2}增强可见光吸收。将CO2大规模太阳能转化为烃燃料需要对可见光有响应的光催化剂。PI提出了两条路线来实现这一目标。首先，通过扩展他们在二氧化钛的氮掺杂上的初步努力，这可以通过修改结晶退火的条件以将氮保持在晶格内并使与掺杂相关的载流子陷阱态的密度最小化来最容易地实现。另一种方法是通过阳极氧化组成分级的金属膜以获得相应金属氧化物的纳米管阵列来合成设计用于广谱太阳能吸收的组成分级的Ti-Cu-O纳米管阵列。 {3}光催化膜。通过增强敏化纳米管阵列的光催化性能，并通过减小孔径来增加表面积，PI寻求实现机械稳健的高表面积光催化膜，CO2和水蒸气流入该膜中，并且烃离开，从而减少逆反应的机会，从而提高转化率，因为产物不会在纳米管表面附近积聚。纳米管的孔径将被优化，以限制CO2和H2O蒸气物种的流入，从而实现完全（或接近完全）转化为碳氢化合物和中间体，从而获得完全的反应产物分离。更广泛的影响：一种可行的方法，利用太阳能和CO2产生碳氢化合物燃料，从而提供一种以化学燃料的形式储存太阳能的方法。博士的跨学科培训学生在这一至关重要领域，并显着REU参与。知识专长：提高对光催化材料和反应的理解，从而能够设计先进的光催化剂，提高对氧化物材料及其带隙工程的理解，提高对三元氧化物半导体的合成，材料特性和性能的理解。

0927262 Grimes This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).In initial work the PIs have achieved efficient solar conversion of carbon dioxide and water vapor to methane and other hydrocarbons using nitrogen doped titania nanotube arrays, with a wall thickness low enough to facilitate effective carrier transfer to the adsorbing species, sensitized with nano dimensional islands of co-catalysts platinum and/or copper. All experiments have been conducted in outdoor sunlight at University Park, PA. Intermediate reaction products, hydrogen and carbon monoxide, are also detected, with their relative concentrations underlying hydrocarbon production rates as dependent upon the nature of the co-catalysts on the nanotube array surface. Using outdoor sunlight with a power density between 75 to 102 mW/cm2, normalized to global AM 1.5 sunlight at 100 mW/cm2, a hydrocarbon production rate of 111 ppm cm-2 hr-1 (about 160 microliters/g hr) is obtained when the nanotube array samples are sensitized with both Cu and Pt nanoparticles.1 This rate of CO2 to hydrocarbon production obtained under outdoor sunlight is at least 20 times higher than previous published reports, which were conducted under laboratory conditions using UV illumination. The PIs seek to understand the reactions inherent in their high rates of photocatalytic CO2 conversion, with a further aim of significantly improving them. Initial objectives include: {1} Uniform sensitization. In preliminary efforts the top surface of the nanotube array samples were sensitized with Cu and Pt co-catalyst particles. The PIs believe uniform sensitization of the nanotube array samples over their entire surface area would significantly enhance photocatalytic conversion rates. They seek to uniformly sensitize the nanotube array samples using atomic layer deposition, or solution chemistry techniques, with immediate variables including nanoparticle type (Cu, CuO, Cu2O, Pt), loading, spacing, size, and size distribution in relationship to the nanotube wall thickness. They will elucidate the role(s) the co-catalysts play, and the associated underlying physical mechanisms including half-reactions, thereby enabling design of photocatalytic materials for enhanced performance. {2} Enhanced Visible Light Absorption. Useful, scale solar conversion of CO2 to hydrocarbon fuels will require photocatalysts responsive to visible light. The PIs propose two routes to achieve this. First, by extending their preliminary efforts on nitrogen doping of titania, which can most readily be accomplished by modifying the conditions of the crystallization anneal to maintain nitrogen within the lattice and minimize the density of carrier trap states associated with doping. Another approach is the synthesis of compositionally graded Ti-Cu-O nanotube arrays designed for broad spectrum solar energy absorption, by anodization of compositionally-graded metal films to achieve nanotube arrays of the corresponding metal oxides. {3} Photocatalytic Membranes. By enhancing the photocatalytic properties of the sensitized nanotube arrays, and increasing the surface area through decreased pore size the PIs seek to achieve a mechanically robust high-surface area photocatalytic membrane into which CO2 and water vapor flow, and hydrocarbons exit reducing the chances of back reactions, thereby enhancing the conversion rate, as the products will not accumulate near the nanotube surface. The nanotube pore size will be optimized to limit the inflow of CO2 and H2O vapor species to achieve a complete (or nearly complete) conversion to hydrocarbons and intermediates, thus obtaining a complete reactant-product separation.Broader Impacts: A viable means to generate hydrocarbon fuels using solar energy and CO2, thereby providing a means to store solar energy in the form of chemical fuel. Interdisciplinary training of a Ph.D. student in this vitally important field, and significant REU participation. Intellectual Merit:Improved understanding of photocatalytic materials and reactions enabling design of advanced photocatalysts, enhanced understanding of oxide materials and their bandgap engineering, enhanced understanding of the synthesis, material properties and performance of ternary oxide semiconductors.