Efficient and Durable Solar Water Splitting by a Hybrid Nitride System

该项目与人工光合作用（AP）有关，这是一种将太阳能直接收集并储存在氢等化学物质中的过程。AP是一项关键的新兴技术，可确保美国未来对可持续能源和化学品的需求。目前，AP光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极降解背后的机制来解决这一挑战，同时通过将氮化钽（一种高效的AP光电极）与氮基有机涂层和催化剂材料相结合，努力提高其稳定性。这一结果将对采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。实验工作将辅以教育工作，旨在开发旨在教育非科学专业学生可再生能源重要性的新课程。该项目的灵感来自于首席研究员最近成功地理解了限制氮化钽（Ta3N5）性能的因素。先前的结果表明，需要非氧化物材料的表面钝化，以及催化剂，才能充分发挥Ta3N5在高效太阳能水分解中的潜力。石墨C3N4 （g-C3N4）是一种罕见的满足要求的材料选择。该项目也是在g-C3N4已被证明有效促进水氧化的2电子途径的背景下构思的。总之，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不稳定机制产生重要的见解。它们还有望产生实际有用的策略，以解决诸如低光电压和差稳定性等关键问题。最重要的成果将是首次展示通过光电极/水结以10%的效率分解水。具体目标将指向1)证明g-C3N4在Ta3N5表面的保形和均匀覆盖，碳纳米点（CDots）沉积在g-C3N4上作为助催化剂，使水氧化过程中形成的过氧化氢不成比例；2)表征杂化材料的结构；3)进行电化学和光谱表征，探究g-C3N4的引入是否减轻了Ta3N5典型的费米能级钉钉效应；4)测量有g-C3N4和不含g-C3N4在Ta3N5上光电极/水界面的电荷转移动力学，了解g-C3N4如何影响电荷转移速率。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劳动力，并在首席研究员团队在教育推广方面取得成功的基础上再创辉煌。将与教育专家建立新的合作关系，以定量评估这些努力的效力。

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.