Investigation of Semiconductor Surfaces and Catalyst Interfaces for Water Oxidation with Solar Energy

阳光是地球上可用的最大能源。即使收集一小部分照射到美国的阳光也会帮助我们的国家实现能源独立。有几个因素限制了充分利用阳光来满足我们的能源需求。例如，阳光是断断续续的，而我们的能源需求几乎是恒定的。此外，直接使用太阳能来满足我们的一些需求是很困难的，比如运输燃料。这些因素促使人们努力将太阳能转化为化学燃料，通常称为太阳能燃料。水是地球上可用的最丰富的化学物质之一，一种被称为氧化的反应使太阳的能量将水转化为有用的能量形式（电子和质子）。科学家们目前还没有完全了解控制太阳能水氧化的过程。在这个项目中，哈曼博士正在研究吸收阳光的半导体表面的水氧化的基本步骤。沉积在这些表面上的催化剂利用吸收的太阳能氧化水。哈曼博士还参与了一些利用他的研究活动的外展活动。这些活动吸引了各级公众和学生参与与太阳能捕获和转化为有用能源形式（如太阳能燃料）相关的科学挑战。这些活动包括参加密歇根州立大学科学节，一系列以可持续发展为重点的科学研讨会，中西部本科生研究研讨会，以及美国化学学会（ACS）为经济困难的高中生提供的SEED项目。在化学部化学催化项目的资助下，密歇根州立大学（MSU）的哈曼博士正在研究光诱导金属氧化物半导体水氧化。金属氧化物半导体表面缺陷态和光致态在水氧化效率中起着主导作用。一套电化学、光电化学、光谱和operando测量正在进行，以阐明在包括钨酸铜、CuWO4在内的三元金属氧化物电极上太阳水氧化过程中这些表面状态的性质和行为。在半导体表面集成水氧化催化剂是一种很有前途的提高水氧化效率的方法，然而，半导体与催化剂之间形成的界面的性质及其对发生在该界面上的电子转移反应的影响尚不清楚。一些半导体/催化剂组合也正在研究中，以发展对界面在控制整个水氧化反应中的作用的一般和详细的了解。从这项研究中获得的知识允许将太阳能有效地转化为高能量密度的化学燃料，这对社会来说是一个重大的利益。这项研究的其他更广泛的影响来自于哈曼博士在各个层面的推广和教育活动。这些活动增加了代表性不足的少数群体对这一科学领域的兴趣、理解和参与。具体的推广工作包括参加密歇根州立大学科学节，中西部本科生研究研讨会，一系列关注可持续性的科学研讨会，以及ACS项目SEED。

Sunlight is the largest energy resource available on Earth. Harvesting even a small fraction of the sunlight striking the United States would help our country become energy independent. There are several factors which limit full utilization of sunlight to meet our energy needs. For example, sunlight is intermittent while our energy demands are nearly constant. Also, it is difficult to use solar energy directly to meet some of our needs, such as transportation fuels. These factors motivate efforts to convert solar energy into chemical fuels, often referred to as solar fuels. Water is one of the most abundant chemicals available on Earth, and a reaction known as oxidation enables the energy of the sun to convert water into useful forms of energy (electrons and protons). Scientists currently do not fully understand the processes which control solar-powered water oxidation. In this project, Dr. Hamann is investigating the fundamental steps of water oxidation on semiconductor surfaces that absorb sunlight. Catalysts deposited on those surfaces use the absorbed solar energy to oxidize water. Dr. Hamann is also engaged in several outreach activities that leverage his research activities. These activities engage the public and students at all levels in the scientific challenges associated with solar energy capture and conversion to useful forms of energy (like solar fuels). These activities include participation in the Michigan State University Science Festival, a series of Science Café's focused on sustainability, the Midwestern Symposium on Undergraduate Research, and the American Chemical Society (ACS) Project SEED for economically disadvantaged high school students.With funding from the Chemical Catalysis Program of the Chemistry Division, Dr. Hamann of Michigan State University (MSU) is investigating photo-induced water oxidation with metal oxide semiconductors. Surface states, both defect and photo-induced species, play a dominant role in controlling the efficiency of water oxidation on metal oxide semiconductors. A suite of electrochemical, photoelectrochemical, spectroscopic and operando measurements are being carried out to elucidate the nature and behaviour of these surface states during solar water oxidation on ternary metal oxide electrodes, including copper tungstate, CuWO4. Integration of water oxidation catalysts on semiconductor surfaces is a promising method to improve the water oxidation efficiency, however the nature of the interface that develops between semiconductor and catalyst, and its effect on the electron-transfer reactions occurring at this interface, is not well understood. Several semiconductor/catalyst combinations are also being investigated to develop a general and detailed understanding of the role of the interface in controlling the overall water oxidation reaction. The knowledge gained from this research allows the development of efficient conversion of solar energy to high energy density chemical fuels, which is a significant benefit to society. Additional broader impacts of this research derive from Dr. Hamann's outreach and educational activities at all levels. These activities increases interest, understanding and participation of underrepresented minorities in this area of science. Specific outreach efforts include participation in the MSU Science Festival, the Midwestern Symposium on Undergraduate Research, a series of Science Café's focused on sustainability, and the ACS Project SEED.