CAREER: Hybrid Bronzes: Mixed-Valence Hybrid Metal Oxides as a Tunable Material Platform

第1部分：非技术概述可再生能源技术，如太阳能电池、电池和燃料电池，对于以可持续的方式解决紧迫的全球能源需求至关重要。这些系统依赖于高度稳定的材料，作为其有序结构的功能，显示出与能源相关的重要属性，如有效的光吸收和轻松传导电流的能力。然而，合成和修饰重要的结晶固体，如金属氧化物，是具有挑战性的，而且成本高昂。另一方面，分子的化学调谐更精确，能量密集度更低。在NSF材料研究部固态和材料化学项目的支持下，这位首席研究员和他的研究小组获得了这一职业奖项，研究如何通过为一种名为混合青铜器的新兴有机-无机材料开发设计原则，将分子和材料的最佳品质结合起来。这些易于合成、低成本且空气/水稳定的化合物实现了金属氧化层与具有可调功能的分子的原子级集成，从而提供了一种可调材料平台，可以满足多种期望的应用。这项工作阐明了控制混合青铜器电子行为的结构-性质关系，以指导它们在能源相关技术中的最终实施。此外，这一跨学科研究计划将本科生和研究生培养为未来STEM的多样化劳动力，并开发一个名为“Lab Hack”的多方面教学视频平台，旨在降低STEM教育和研究中的资源和知识障碍。第2部分：技术概述混合青铜是一种大块晶体材料，它结合了(1)具有可调载流子密度和带隙的混价金属氧化物薄片和(2)具有潜在化学、氧化还原和光活性的分子阵列的交替层。在这里，术语“青铜”指的是准自由电子赋予还原金属氧化物的金属光泽，正是这些移动载体最终实现了这种电子的多功能性。为了将混合青铜平台推向与能源相关的用途，有必要了解并随后控制它们的氧化还原活性、光吸收和电荷传输。混合青铜器也代表了多功能的模型系统，可以探索有关二维固态现象的问题。在NSF材料研究部固态和材料化学计划的支持下，这位首席研究员和他的研究小组利用温和的水自组装反应生产了具有良好合成控制程度的块状晶体混合青铜。然后使用一套基于衍射、光谱和电子表征技术，包括高压方法来阐明结构与性质之间的关系。具体地说，对系统变化的分子结构导向效应的评估阐明了无机层内的电荷传输是如何决定的。通过光电子学、电化学和电荷传输分析，探索了分子和层之间受刺激驱动的电荷转移现象的原理，随后进行了迭代的分子调谐。此外，压力/应变诱导的结构变化被用作指示混合青铜中电子性质转变的独特方法。总体而言，这项工作揭示了混合青铜的结构和电子行为之间的联系，包括紧急现象，以展示支持其定制的设计规则。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。

PART 1: Non-Technical SummaryRenewable energy technologies such as solar cells, batteries, and fuel cells are critical for addressing urgent global energy demand in a sustainable manner. These systems rely on materials that are highly stable and, as a function of their ordered structures, display important properties for energy-related use such as efficient light absorption and the ability to easily conduct electrical current. However, it is challenging and costly to synthesize and modify important crystalline solids such as metal oxides. The chemical tuning of molecules, on the other hand, is more precise and less energy intensive. With this CAREER award, supported by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, the principal investigator and his research group investigate how to combine the best qualities of molecules and materials by developing design principles for an emerging new class of organic-inorganic materials called hybrid bronzes. These easily synthesized, low-cost, and air-/water-stable compounds achieve atomic-level integration of metal oxide layers with molecules having adjustable functions, thereby providing a tunable material platform that can cater to numerous desired applications. This work elucidates structure-property relationships governing the electronic behavior of hybrid bronzes to inform their ultimate implementation in energy-related technologies. Furthermore, this interdisciplinary research program trains undergraduate and graduate students as the diverse future STEM workforce and develops a multi-faceted instructional video platform called "Lab Hacks" that seeks to lower resource and knowledge barriers in STEM education and research.PART 2: Technical SummaryHybrid bronzes are bulk crystalline materials that combine alternating layers of (1) mixed-valence metal oxide sheets featuring tunable charge-carrier densities and band gaps and (2) molecular arrays with the potential for chemical-, redox-, and photo-activity. Here, the term "bronze" refers to the metallic luster that quasi-free electrons impart to reduced metal oxides and it is these mobile carriers that ultimately enable such electronic versatility. To advance the hybrid bronze platform toward energy-related use, it is necessary to understand and subsequently control their redox activity, light absorption, and charge transport. Hybrid bronzes also represent versatile model systems that can probe questions regarding two-dimensional solid-state phenomena. With this CAREER award, supported by the Solid State and Materials Chemistry program in NSF’s Division of Materials Research, the principal investigator and his research group leverage mild aqueous self-assembly reactions to produce bulk crystalline hybrid bronzes with a fine degree of synthetic control. A suite of diffraction-based, spectroscopic, and electronic characterization techniques including high-pressure methods are then employed to elucidate structure-property relationships. Specifically, evaluation of systematically varied molecular structure-directing effects illuminates how charge transport is dictated within inorganic layers. Principles governing stimulus-driven charge transfer phenomena between molecules and layers are explored through optoelectronic, electrochemical, and charge transport analysis, followed by iterative molecular tuning. Further, pressure/strain-induced structure changes are employed as a unique approach to dictating electronic property transitions within hybrid bronzes. Overall, this work reveals connections between the structures and electronic behaviors of hybrid bronzes, including emergent phenomena, to demonstrate design rules enabling their customization.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.