Efficient and Durable Solar Water Splitting by a Hybrid Nitride System

该项目涉及人工光合作用（AP）-直接收集太阳能并将其储存在氢等化学物质中的过程。 AP是确保国家未来对可持续能源和化学品需求的关键新兴技术。 目前，AP光电极材料缺乏保持稳定高效率的能力。 该项目将通过研究光电极退化背后的机制来应对这一挑战，沿着，并通过将其与氮化物基有机涂层和催化剂材料相结合来提高氮化钽（一种有效的AP光电极）的稳定性。 这些结果将大大有助于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。 实验工作将辅之以教育工作，旨在开发新的课程，旨在教育非科学专业的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理解限制氮化钽（Ta 3 N5）性能的因素方面取得的成功。 先前的结果表明，需要通过非氧化物材料与催化剂一起进行表面钝化，以实现Ta 3 N5用于高效太阳能水分解的全部潜力。 石墨C3 N4（g-C3 N4）代表了满足要求的罕见材料选择。 该项目也是在g-C3 N4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，该系统提供了一个独特的机会，研究材料相关的问题，在光电极/水界面的太阳能应用。 实验将产生重要的洞察光电极不稳定机制。 它们还有望产生实际有用的策略，以解决诸如低光电压和稳定性差等关键问题。 最重要的成果将是第一次演示水分解效率10%的光电极/水结。 具体目标将针对1）展示Ta 3 N5表面上的共形且均匀的g-C3 N4覆盖，其中沉积在g-C3 N4上的碳纳米点（CDots）作为助催化剂以使水氧化期间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以探测g-C3 N4的引入是否减轻了对于Ta 3 N5典型的费米能级钉扎效应;以及4）测量具有和不具有g-C_3 N_4的Ta_3 N_5上光电极/水界面处的电荷转移动力学，以了解g-C_3 N_4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，并在主要研究者团队先前在教育推广方面取得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，以定量评估这些努力的有效性。

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.