Surface - Gated Charge Carrier - Selective Nanocontacts in Photoelectrochemical Catalysis

从化石燃料向可持续能源基础设施的过渡因缺乏由可再生能源制成的高能源重量比的化学燃料而受阻。能量密集型燃料需要长期储存能量(从四季到数年)和长距离或重载运输。光电化学分解水是一种直接将太阳光能量储存在化学燃料氢气和氧气中的途径。最近，来自美国(加州理工学院)和德国(TU Ilmenau，Fraunhofer ISE，柏林亥姆霍兹中心)的一个跨学科团队实现了一个令人印象深刻的太阳能-氢能转换系统，其效率达到了19%，即使用了半导体所能达到的最大理论效率的85%。目前的结果清楚地证明了将太阳光直接高效地转化为氢气和氧气的可行性，但它们缺乏应用所需的一个重要因素：长期稳定性。为了稳定运行，半导体必须在严酷的水溶液中免受腐蚀，同时保持催化剂的完整性。稳定性问题是实际设备面临的最大挑战。为了防止腐蚀，半导体表面通常被涂覆一层热力学稳定的氧化膜。这种薄膜不仅必须提供化学保护，而且还必须在半导体和电催化剂之间提供电传输。这产生了一个基本的权衡：厚膜或非导电膜可以防止腐蚀，但那些膜不能充分传导电流。在我的博士学位期间，我基于表面栅极/夹断效应开发了用于纳米线太阳能电池的新的电荷载流子选择接触。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(通过捐赠或接受载流子)，而金属点触点本身有助于载流子提取。在这里，我建议将这些纳米级的点接触用于水分离设备。这种接触预计会产生很大的光伏，因此由于“夹断”效应，性能会很高。重要的是，它们可以被厚的(100 nm-1微米)甚至不导电的氧化层包围，以提供坚固的化学保护，同时保证足够的电子传输，这一特性的组合似乎是传统几何结构所无法企及的。这项工作由两个具体目标组成。首先，我将研究模型系统中“夹点”效应的基本方面。在第二部分中，我将应用新的基础知识，使用区域选择性氧化物沉积方法，开发一种高性能、但在化学上坚固的载流子收集纳米结构界面。为了完成这项工作，我将把我在博士学位上在纳米制造和纳米尺度界面性质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.