Efficient and Durable Solar Water Splitting by a Hybrid Nitride System

该项目涉及人工光合作用(AP)--太阳能被直接收集并储存在氢气等化学物质中的过程。AP是一项关键的新兴技术，可确保国家未来对可持续能源和化学品的需求。目前，AP光电电极材料缺乏维持稳定高效的能力。该项目将通过研究光电电极降解背后的机理，以及通过将氮化钽(一种有效的AP光电电极)与氮化物有机涂层和催化剂材料相结合来提高其稳定性的努力来应对这一挑战。这一结果将对使用人工光合作用作为大规模太阳能存储解决方案的最终目标做出重大贡献。与实验工作相辅相成的是旨在开发新课程的教育努力，旨在教育非理科专业的学生了解可再生能源的重要性。该项目的灵感来自首席研究员最近在了解限制氮化钽(Ta3N5)性能的因素方面取得的成功。以前的结果表明，需要用非氧化物材料和催化剂进行表面钝化，才能充分发挥Ta3N5用于高效太阳能分解水的潜力。石墨化C3N4(g-C3N4)代表了一种满足要求的稀有材料选择。该项目也是在g-C3N4已被证明在促进水氧化的2电子途径方面有效的背景下构思的。总而言之，该系统为研究太阳能应用中光电极/水界面的材料相关问题提供了一个独特的机会。这些实验将对光电极失稳机理产生重要的影响。预计它们还将产生实用的战略，以解决诸如光伏低和稳定性差等关键问题。最重要的成果将是首次展示光电极/水结以10%的效率分解水。具体目标将针对1)展示g-C3N4在Ta3N5表面的共形且均匀的覆盖，并在g-C3N4上沉积碳纳米点(CDots)作为助催化剂，以歧化水氧化生成的过氧化氢；2)表征杂化材料的结构；3)进行电化学和光谱表征，以探索g-C3N4的引入是否减轻了Ta3N5的典型的费米能级钉扎效应；以及4)测量g-C3N4和g-C3N4对Ta3N5上光电极/水界面的电荷转移动力学，以了解g-C3N4对电荷转移速率的影响。除了技术目标之外，该项目还将提供一个机会，通过研究生和本科生教育扩大可持续能源工作队伍，并在主要研究小组以往在教育推广方面的成功的基础上再接再厉。将与教育专家建立新的合作关系，以量化评估这些努力的成效。

This project relates to artificial photosynthesis (AP) - the process by which solar energy is directly harvested and stored in chemicals such as hydrogen. AP is a critical emerging technology for ensuring the Nation's future needs for sustainable energy and chemicals. Presently, AP photoelectrode materials lack the ability to sustain stable high efficiency. The project will address this challenge by studying the mechanisms behind photoelectrode degradation, along with efforts to improve the stability of tantalum nitride (an efficient AP photoelectrode) by integrating it with a nitride-based organic coating and catalyst material. The results will contribute significantly to the eventual goal of employing artificial photosynthesis as a large-scale solar energy storage solution. The experimental efforts will be complemented by educational efforts designed to develop novel curricula aimed at educating non-science majors on the importance of renewable energy. The project is inspired by the principal investigator's recent success in understanding the factors that limit the performance of tantalum nitride (Ta3N5). The previous results suggest that surface passivation by a non-oxide material, together with a catalyst, is needed to actualize the full potential of Ta3N5 for high-efficiency solar water splitting. Graphitic C3N4 (g-C3N4) represents a rare material choice that meets the requirement. The project is also conceived within the context that g-C3N4 has been shown effective in promoting a 2-electron pathway for water oxidation. Together, the system presents a unique opportunity to study material-related issues at the photoelectrode/water interface for solar energy applications. The experiments will generate important insight into photoelectrode destabilization mechanisms. They are also expected to yield practically useful strategies to address critical issues such as low photovoltage and poor stability. The most significant outcome will be the first demonstration of water splitting at efficiencies 10% by a photoelectrode/water junction. Specific aims will be directed at 1) demonstrating conformal and uniform g-C3N4 coverage on the surface of Ta3N5, with carbon nanodots (CDots) deposited on the g-C3N4 as a co-catalyst to disproportionate the hydrogen peroxide formed during water oxidation; 2) characterizing the structure of the hybrid material; 3) conducting electrochemical and spectroscopic characterization to probe whether the introduction of g-C3N4 mitigates the Fermi level pinning effect that is typical to Ta3N5; and 4) measuring the charge transfer kinetics at the photoelectrode/water interface on Ta3N5 with and without g-C3N4 to understand how g-C3N4 influences the charge transfer rates. Beyond the technical objectives, the project will provide an opportunity to expand the sustainable-energy workforce through graduate and undergraduate student education, and build upon previous successes by the principal investigator's team in educational outreach. A new collaboration with educational experts will be formed to quantitatively assess the effectiveness of these efforts.