CAREER: Advanced Photochemical Paradigms for Enhanced Photovoltaics and Photocatalysis

太阳能的转换和利用可以通过光电化学（PEC）方案来实现，光电化学（PEC）方案将光能转换为电能，例如基于PEC的光电化学（PV），或化学能，例如太阳能燃料和使用光催化剂的太阳能环境净化。因此，了解定义和调节PEC系统中基本光捕获和电荷传输过程的基础科学对于PEC太阳能电池和太阳能电池的发展至关重要。该提案的总体目标是从根本上改变和增强当前最先进的基于PEC的光伏和光催化系统中的基本光捕获和电荷传输效率。具体而言，拟议的研究计划将针对以下子任务。将常规PEC太阳能电池的光阳极（通常为平面透明导电氧化物（TCO）上的厚PV层的形式）转换为一组3-D纳米结构的共形TCO/PV光阳极。这一创新将大大缩短PV层中的传输长度，将大部分传输留在接近金属的TCO层中以增强光电流收集，同时仍提供足够的PV材料以容纳太阳光子通量。PI将研究这些变革结构产生的基本运输机制。特别地，在TCO/PV层的界面处将PV层的厚度减小到大约空间电荷层的宽度（通常为30 nm）可以使整个光诱导电荷分离和传输过程受到该界面处的内置电势的强烈影响。因此，慢扩散传输机制可以被更有效的场驱动漂移传输机制取代，以抑制PV层中的电荷复合。反过来，具有较小过电位的替代性更快的氧化还原介体可以用于增强光伏性能。 2.协同地，从2-D到3-D TCO的转换使得能够将各种3-D光子晶体（PC）配置并入到3-D共形TCO/PV架构中，这可以通过光子的多次散射来捕获光，从而导致光收获和电荷传输过程之间的协同而不是冲突。因此，PEC太阳能电池可以更实惠，因为需要更少的PV材料来适应太阳能通量。 3. Ti 3+和/或氧空位自掺杂的TiO 2-x可以是一种有效的可见光活性光催化剂，不使用额外的掺杂剂，从而最大限度地减少环境问题。为了实现有效的可见光活性，Ti 3+的浓度必须足够高，以诱导一个连续的空位带的电子态正好低于TiO 2的导带边缘。与传统的TiO 2在苛刻条件下的还原反应（Ti4+-<$Ti3+）不同，我们提出了一种以TiH 2和H2 O2为前驱体的Ti 3+自掺杂TiO 2-x光催化剂的氧化转化（Ti 2 +-<$Ti3+）方案。该方法将提供一种容易的、低成本的和高浓度的Ti 3+掺杂在整个TiO 2-x基质的本体中。TiH 2和H2 O2的反应产生水解的溶胶-凝胶样的多孔TiO 2-x，允许方便地掺入等离子体纳米颗粒和形成用于增强太阳能光催化活性的通用纳米结构TiO 2-x。更广泛的影响作为纳米科学提供了更多的机会，更有效的PEC过程中，主要的教育目标是整合相关的介绍nanoscience实验，这两个项目和本科生化学到我们现有的课程与实验室作业，以便为学生提供动手理解课程工作和基本的nanoscience知识。其次，作为培养下一代科学家的有效途径，PI计划通过开发一个多功能项目：阿贡的北方学生科学家，扩大与阿贡科学家的研究合作。该计划将把PI与阿贡的研究合作纳入学生招募，教育和培训，研究，就业和社区推广。学生将接触到世界一流的研究环境，在他们年轻的时候参与前线研究项目，并接受尖端研究设施，跨学科知识，批判性思维和解决问题的方法以及团队合作技能的培训。随着人们对石油和核能带来的环境灾难的日益关注，PEC能量转换成为能源科学中一个极具吸引力的研究方向。由于能源科学是阿贡的核心研究领域，PI将利用阿贡的研究和NIU的网络，通过阿贡和北方伊利诺伊大学科学家的互动演示，为当地高中的学生和教师建立一个外展计划“能源和环境研讨会”。

Xu1150617 Intellectual MeritsSolar energy conversion and utilization can be implemented through photoelecrochemical (PEC) schemes that convert light energy to electricity, such as PEC-based photovoltaics (PV), or chemical energy such as solar fuels and solar environmental purification using photocatalysts. Therefore, understanding the basic science that defines and regulates the elementary light harvesting and charge transport processes in PEC systems is crucial for the advancement of PEC solar cells and photocatalysis. The overall goal of this proposal is to fundamentally transform and enhance the elementary light harvesting and charge transport efficiencies in current state-of-the-art PEC-based photovoltaic and photocatalytic systems. Specifically, the proposed research plan will aim to the following subtasks.1. Converting the photoanodes of conventional PEC solar cells, typically in the format of a thick PV layer on a planar transparent conducting oxide (TCO), to a set of 3-D nanoarchitectured conformal TCO/PV photoanodes. This innovation will drastically shorten the transport length in the PV layer, leaving the majority of the transport in the nearly metallic TCO layer for enhanced photocurrent collection, while still providing sufficient PV material to accommodate the solar photon flux. The PI will study the fundamental transport mechanisms resulting from these transformative structures. In particular, reducing the thickness of the PV layer to approximately the width of the space charge layer (typically 30 nm) at the interface of TCO/PV layer can subject the overall light-induced charge separation and transport processes to the strong influence of the built-in potential at this interface. As a result, the slow diffusive transport mechanism can be replaced by the more efficient field-driven drift transport mechanism to suppress charge recombination in the PV layer. In turn, alternative faster redox mediators with less overpotential can be applied for enhanced photovoltaic performance. 2. Synergistically, the transformation from 2-D to 3-D TCO enables the incorporation of a variety of 3-D photonic crystal (PC) configurations into the 3-D conformal TCO/PV architectures, which can trap light through multiple scattering of photons, resulting in synergy rather than conflict between the light harvest and charge transport processes. As such, PEC solar cells can be more affordable since less PV materials are needed for accommodating the solar flux. 3. Ti3+ and/or oxygen vacancy self-doped TiO2-x can be an effective visible-light active photocatalyst that using no additional dopants, thus to minimize the environmental concerns. In order to achieve efficient visible-light activity, the concentration of Ti3+ must be high enough to induce a continuous vacancy band of electronic states just below the conduction band edge of TiO2. Distinguished from the conventional reduction of TiO2 (Ti4+-¨Ti3+) under harsh conditions, we propose an oxidative conversion (Ti2+-¨Ti3+) scheme that uses TiH2 and H2O2 as precursors for Ti3+ self-doped TiO2-x photocatalysts. This process will provide a facile, low-cost and high-concentration doping of Ti3+ throughout bulk of the TiO2-x matrix. The reaction of TiH2 and H2O2 produces a hydrolyzed sol-gel-like precursory TiO2-x, allowing convenient incorporation of plasmonic nanoparticles and formation of versatile nanoarchitectured TiO2-x for enhanced solar photocatalytic activity. Broader ImpactsAs nanoscience provides more opportunities for more efficient PEC processes, the primary educational goal is to integrate introductory nanoscience experiments relevant to both this project and undergraduate chemistry into our existing curriculum with laboratory assignments, so as to provide students hands-on understanding in course work and basic nanoscience knowledge. Secondly, as an effective way to train the next generation scientists, the PI plans to broaden the research collaboration with Argonne scientists by developing a multifunctional program: Northern Student Scientists at Argonne. This program will incorporate PI's research collaborations with Argonne into student recruitment, education and training, research, employment and community outreach. The students will be exposed to world-class research environment, involved in frontline research projects at their young age, and trained with cutting-edge research facilities, cross-disciplinary knowledge, critical thinking and problem-solving methodologies, and team-work skills. Due to the growing concerns on environmental disasters related to petroleum and nuclear energy, PEC energy conversion becomes a highly attractive aspect of energy science. As energy science is Argonne's core research area, the PI will leverage Argonne'fs research and NIU's network to establish an outreach program Energy and Environment Workshop for students and teachers in local high schools via interactive presentations given by scientists at Argonne and Northern Illinois University.