Surface - Gated Charge Carrier - Selective Nanocontacts in Photoelectrochemical Catalysis

由于缺乏由可再生能源制成的高能量重量比的化学燃料，阻碍了从化石燃料向可持续能源基础设施的过渡。能量密集的燃料需要长期的能量储存（从季节到年）和长途或重型运输。光电化学水分解是一种将太阳光能量储存在化学燃料氢气和氧气中的直接途径。最近，来自美国（加州理工学院）和德国（伊尔梅瑙工业大学，弗劳恩霍夫工业学院，柏林亥姆霍兹中心）的一个跨学科团队实现了一个系统，其太阳能到氢的效率令人印象深刻，达到19%，即所使用的半导体可实现的最大理论效率的85%。提出的结果清楚地证明了将阳光直接有效地转化为氢和氧的可行性，但是它们缺乏一个重要的应用所需的成分：长期稳定性。为了稳定运行，半导体必须在保持催化剂完整性的同时，防止在恶劣的电解质水溶液中受到腐蚀。稳定性问题是实际设备面临的最大挑战。为了防止腐蚀，半导体表面通常涂上一层热稳定的氧化膜。这种薄膜不仅要提供化学保护，还要提供半导体和电催化剂之间的电传输。这就产生了一个基本的权衡：厚的或不导电的薄膜可以防止腐蚀，但它们不能充分传导电流。在博士期间，我基于表面门控/掐断效应为纳米线太阳能电池开发了新的电荷载流子选择性触点。这些触点使用表面层来控制相邻金属纳米级点触点的载流子选择性（通过提供或接受载流子），而金属点触点本身则有利于载流子的提取。在这里，我建议在水分解装置中使用这些纳米级的点接触。预计这种接触将产生大的光伏，因此由于“掐断”效应而具有高性能。重要的是，它们可以被厚的（100 nm - 1 μ m）甚至非导电的氧化层包围，以提供强大的化学保护，同时保证足够的电传输，这是传统几何形状无法达到的性能组合。这项工作有两个具体目标。首先，我将研究模型系统中“掐断”效应的基本方面。其次，我将运用新的基础知识，利用区域选择性氧化沉积方法开发一种高性能，但化学坚固，载流子收集的纳米结构界面。为了完成这项工作，我将把我博士在纳米制造和纳米级界面特性方面的专业知识与美国主持人Shannon Boettcher教授在半导体-催化剂界面方面的世界领先专业知识结合起来。

The transition from fossil fuels to a sustainable energy infrastructure is impeded by the lack of chemical fuels with high energy-to-weight ratios made from renewable energies. Energy-dense fuels are needed for long-term energy storage (from seasons to years) and for long-distance or heavy-duty transportation.Photoelectrochemical water splitting is a direct route to store the sunlight’s energy in the chemical fuels hydrogen and oxygen gas. Recently, an interdisciplinary team from the USA (Caltech) and Germany (TU Ilmenau, Fraunhofer ISE, Helmholtz Zentrum Berlin) realized a system with an impressive solar-to-hydrogen efficiency of 19%, i.e. with 85% of the maximum theoretical efficiency achievable for the semiconductors used.The presented results clearly prove the feasibility of converting sunlight directly and efficiently into hydrogen and oxygen, however they lack one important ingredient required for an application: long-term stability. For stable operation the semiconductor must be protected from corrosion in harsh aqueous electrolyte solutions while the catalyst integrity is maintained. Stability issues represent the most significant challenge facing practical devices.To prevent corrosion, semiconductor surfaces are often coated conformably with a thermodynamically stable oxide film. This film must not only provide chemical protection but also electrical transport between semiconductor and electrocatalyst. This creates a fundamental trade-off: thick or non-conductive films can prevent corrosion but those do not sufficiently conduct current.During my PhD, I developed new charge carrier-selective contacts for nanowire solar cells based on the surface-gating/pinch-off effect. Those contacts use a surface layer to control the carrier-selectivity of an adjacent metal nanoscale point contact (by donating or accepting charge carriers), while the metal point contact itself facilitates the carrier extraction. Here I propose to use those nanoscale point contacts in water-splitting devices. Such contacts are predicted to generate large photovoltages, and hence high performances due to the “pinch-off” effect. Importantly, they can be surrounded by a thick (100 nm – 1 µm) and even non-conductive oxide layer for robust chemical protection while simultaneously guaranteeing sufficient electrical transport, a combination of properties that seems out of reach for conventional geometries. The work consists of two specific aims. In the first, I will study fundamental aspects of the “pinch-off” effect in model systems. In the second, I will apply the new fundamental knowledge to develop a high-performance, but chemically robust, carrier-collecting nanostructured interface using area-selective oxide deposition methods.To accomplish the work I will combine my expertise in nanofabrication and nanoscale interface properties from my PhD with the world-leading expertise on semiconductor-catalyst interfaces of the American host, Prof. Shannon Boettcher.