Photolysis by Oxides with Internal Dipolar Fields

某些过渡金属氧化物陶瓷可以催化水的光解，并从水和阳光中产生氢气。 催化该过程的颗粒系统仍然不切实际，因为它们的能量转化效率低，这受到载流子复合以及还原和氧化中间体在它们可以形成更稳定的分子物质之前的逆反应的限制。 本研究的基本思想是利用体光伏效应在颗粒催化剂中的每个微晶内建立一个内场，使光生载流子分离，在不同的位置形成还原和氧化产物。 通过使用铁电材料，可以将内部场并入各个微晶内。 因此，实验将进行测试的假设，内部偶极场可以用来提高量子效率的水光解颗粒系统。 具体地，将比较铁电态和顺电态催化剂的光解效率。 偶极场对铁电体上的薄催化膜的反应性的影响，例如TiO 2对BaTiO 3，也将被探索。 复合材料将允许分别优化电荷分离和催化功能。 铁电粒子的尺寸和膜的厚度可能会影响效率。 这些长度尺度的现象将通过比较不同颗粒尺寸的催化剂的效率和通过测试平面几何形状中不同厚度的膜的反应性来独立地探索。作为未来的燃料，氢是有吸引力的，因为它的能量密度是石油的三倍，并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。 目前可以从阳光和水中生产这种可持续的清洁燃料。 然而，这种能源的潜在社会效益将无法实现，直到成本成为具有竞争力的现有燃料来源（化石和核）。 因此，这项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.