Photolysis by Oxides with Internal Dipolar Fields

某些过渡金属氧化物陶瓷可以催化水光解，从水和阳光中产生氢。催化这一过程的颗粒系统仍然不切实际，因为它们的能量转换效率低，这受到载流子重组和还原和氧化中间体在形成更稳定的分子物种之前的反反应的限制。本研究的基本思路是利用体光伏效应在颗粒催化剂的每个微晶中建立一个内部场，使光生的载流子分离，在不同的位置形成还原和氧化产物。内部场可以通过使用铁电材料并入单个晶体内。因此，将进行实验来验证内部偶极场可以用来提高粒子系统中水光解的量子效率的假设。具体而言，将比较铁电态和准电态催化剂的光解效率。偶极场对铁电体（如TiO2对BaTiO3）上的催化薄膜反应性的影响也将被探讨。复合材料将使电荷分离和催化功能分别得到优化。效率可能会受到铁电粒子大小和薄膜厚度的影响。这些长度尺度现象将通过比较不同粒径催化剂的效率和在平面几何结构中测试不同厚度薄膜的反应性来独立探索。作为未来的燃料，氢很有吸引力，因为它的能量密度是石油的三倍，而且它的燃烧不会产生危险的排放物、温室气体或放射性副产品。目前有可能从阳光和水中生产出这种可持续的、清洁燃烧的燃料。然而，这种能源的潜在社会效益将不会实现，直到其成本成为具有竞争力的既定燃料来源（化石和核）。因此，本研究的首要目标是开发新材料，使光解氢在经济上可行。

Certain transition metal oxide ceramics can catalyze water photolysis and produce hydrogen from water and sunlight. Particulate systems that catalyze this process remain impractical because of their low energy conversion efficiency, which is limited by carrier recombination and the back reaction of reduced and oxidized intermediates before they can form more stable molecular species. The basic idea of this research is use the bulk photovoltaic effect to build an internal field into every crystallite in a particulate catalyst, so that the photogenerated charge carriers will be separated and the reduced and oxidized products formed at different locations. An internal field can be incorporated within the individual crystallites by using a ferroelectric material. Thus, experiments will be conducted to test the hypothesis that internal dipolar fields can be used to increase the quantum efficiency of water photolysis in particulate systems. Specifically, the photolysis efficiency of catalysts in the ferroelectric and paraelectric state will be compared. The influence of dipolar fields on the reactivity of thin catalytic films on ferroelectrics, such as TiO2 on BaTiO3, will also be explored. A composite will allow the charge separating and catalytic functions to be optimized separately. The efficiency will probably be affected by the size of the ferroelectric particle and by the thickness of the film. These length scale phenomena will be explored independently by comparing the efficiencies of catalysts with different particle sizes and by testing the reactivity of films of different thicknesses in a planar geometry.As a fuel for the future, hydrogen is attractive because it has three times the energy density of oil and its combustion does not create dangerous emissions, greenhouse gases, or radioactive byproducts. It is currently possible to produce this sustainable, clean burning fuel from sunlight and water. However, the potential societal benefits of this energy source will not be realized until the cost become competitive with established fuel sources (fossil and nuclear). Therefore, the overarching goal of this research is to develop new materials that will make photolytic hydrogen economically feasible.