CAREER: Aligned Tandem Semiconductor Microwire Slurries for Low-cost, High Efficiency Solar Hydrogen Generation

太阳能可以用来将水光化学“分解”成氢气和氧气。氢可以用作燃料电池的燃料，也可以用作制造化学产品和材料的积木分子。这项研究项目将研究用于生产太阳能裂水半导体微粒的新型催化剂和反应器设计，这些微粒能够在一定程度上提高太阳能到氢的转换效率，从而使浆态反应器设计适用于商业太阳能氢气生产。由此产生的发现将有助于推动太阳能技术沿着低成本太阳能储存和可持续燃料生产的道路前进。这种技术可能会给能源行业带来革命性的变化，并极大地增强美国的能源独立性。这项研究项目还包括一项教育和推广计划，使本科生和研究生以及更广泛的社区参与与太阳能和可再生资源有关的学习活动。在这项研究项目中，将寻求一种设计方法，用于设计理想匹配的顶部和底部电池带隙材料的单块单粒子。其目标是最大化光吸收和量子效率，同时最小化有害的欧姆电阻和反向反应。具体的研究目标是：(1)在硅微丝的基础上制作一种能够在1太阳能量通量下进行无辅助分水的串联式半导体光电极，并演示串联式单粒子浆料堆在24小时以上的太阳能转氢效率大于1%；(2)通过在运行过程中调用不同水平的磁取向和背反射来研究粒子取向和光散射对串联式单粒子浆料堆效率的基本影响；(3)研究了在不同光照强度和载气流量下，颗粒密度和单颗粒电流密度对水裂解反反应速率和氢氧共生浓度的影响：(4)通过对串联单颗粒的多物理模拟，预测了电流分布随颗粒取向和光散射的变化，以及电解液中氢、氧浓度随颗粒电流密度和载气流量变化的规律，并用实验结果验证了模型的正确性；(5)将优化带隙的三元III-V半导体作为串联粒子中的顶子电池，以生产能够超过8%的太阳能-氢气比的浆料反应器，并利用保护的二氧化钛涂层，将粒子的寿命延长到24小时以上。教育活动将包括太阳能和可再生能源课程的开发和广泛传播，材料和能源科学硕士学位计划和证书计划的孵化，以及直接将未被充分代表的本科生纳入研究过程。该项目由催化和电化学系统计划和既定的激励竞争研究计划(EPSCoR)共同资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Solar energy be used to photochemically "split" water into hydrogen and oxygen gases. Hydrogen can be used as a fuel to power fuel cells or as a building block molecule for the manufacture of chemical products and materials. This research project will study novel catalysts and reactor designs for producing solar water-splitting semiconductor microparticles that are capable of solar-to-hydrogen conversion efficiencies at a level that could make slurry reactor designs practical for commercial solar hydrogen production. The resulting discoveries will help advance solar energy technology along a path towards low-cost solar energy storage and sustainable fuel production. Such technologies potentially can revolutionize the energy industry and greatly enhance the energy independence of the United States. The research project is complemented by an educational and outreach plan that engages undergraduate and graduate students, as well as the wider community, in learning activities related to solar energy and renewable resources.In this research project, a design approach will be pursued for monolithic single-particles of ideally matched top and bottom cell bandgaps materials. The objective is to maximize light absorption and quantum efficiency while minimizing the deleterious ohmic resistances and back reactions. The specific research objectives are to: (1) Produce a tandem semiconductor photoelectrode on a base of silicon microwires capable of unassisted water-splitting under 1 Sun solar energy flux, and demonstrate a tandem single-particle slurry reactor at greater than 1 percent solar-to-hydrogen efficiency for more than 24 hours; (2) Investigate the fundamental effects of particle alignment and light scattering on the efficiency of a tandem single-particle slurry reactor by invoking variable levels of magnetic alignment and back reflection during operation; (3) Investigate the effects of particle density and single-particle current density on water-splitting back-reaction rates and co-evolved hydrogen and oxygen concentration with variable illumination intensity and carrier gas flow rate; (4) Perform mesoscale modeling via multi-physics simulations of tandem single particles to predict current distribution as a function of particle alignment and light scattering, as well as hydrogen and oxygen concentrations in the electrolyte as a function of particle current density and carrier gas flow rate, and validate the modeling by experimental results; (5) Incorporate a ternary III-V semiconductor of optimized bandgap as the top sub-cell in the tandem particles to produce a slurry reactor capable of solar-to-hydrogen in excess of 8 percent, and utilize a protective TiO2 coating to extend the particle lifetime beyond 24 hours. The educational activities will feature solar and renewable energy course development and broad dissemination, the incubation of a materials and energy science master’s degree program and certificate program, and direct inclusion of underrepresented undergraduates into the research process.This project is jointly funded by the Catalysis and Electrochemical Systems programs and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.