DFG-RSF: Doped-graphene for electrochemical energy storage and conversion: Impact of the electronic structure on electrocatalytic activity in oxygen redox reactions

将能量储存在化学键中，使电力供应从亚瓦到数十兆瓦。将化学键的能量直接转化为电能的电化学系统可以存储GWh的能量并利用各种各样的化学系统。分子氧在环境大气中容易获得并且几乎不可替代，是用于电化学能量转换和存储系统的优异组分，因此氧氧化还原反应对于许多电化学装置如燃料电池或金属-空气电池具有决定性的重要性。在这样的系统中，在电极的表面处发生向氧/从氧的非均相电子转移。碳电极，重量轻，价格便宜，导电性好，是在大多数情况下的选择材料。碳电极的表面由石墨烯状结构域组成，然而，不同的碳显示出不同的氧氧化还原过程的效率。最近证明，用轻元素如N、B或S掺杂碳显著增强了电子向/从氧转移的动力学，并导致与贵金属相当的电催化活性。然而，其背后的物理原理尚未完全被理解。许多研究致力于这一主题遭受高复杂性的真实的碳电极，即电子结构，杂质，微观结构等的个体效应可以很难区分，我们建议使用外延石墨烯作为模型系统，以阐明掺杂碳中的电子结构和杂质在异质电子转移到氧和从氧的作用。我们将从外延石墨烯作为纯化学模型系统开始，计划以转移石墨烯为电极，开发越来越复杂的功能电化学电池。为了实现化学模型系统，将通过化学气相沉积在Ni（111）和Co（0001）表面原位生长掺杂石墨烯单层。N-、B-和S-石墨烯的电子性质将采用角度分辨光电子能谱（ARPES）和基于DFT的计算进行实验和理论探索。氢和碱金属在掺杂石墨烯层上的化学吸附将用于控制超高真空条件下的费米能级位置。然后，将使用ARPES、XPS和近环境压力XPS（NAP XPS）来追踪该系统在氧气暴露期间的演变。类似的方法将应用于利用掺杂石墨烯作为电极来操作电化学电池。石墨烯将在金属箔上生长，然后转移到固体电解质上或转移到Si 3 N4网格上，液体电解质从背面供应。石墨烯和氧之间的电子转移，以及新的含氧物种的形成将使用光电子能谱和X射线吸收光谱（NEXAFS）在操作条件下。

Storing energy in chemical bonds enables power supply from sub-W to tens of MW. Electrochemical systems that convert energy of chemical bonds directly to electric power can store GWh of energy and utilize a huge variety of chemical systems. Being easily accessible in ambient atmosphere and nearly inexhausable, molecular oxygen is an excellent component for electrochemical energy conversion and storage systems, so that oxygen redox reactions are of decisive importance for many electrochemical devices such as fuel cells or metal-air batteries. In such systems, heterogeneous electron transfer to/from oxygen occurs at the surface of an electrode. Carbon electrodes, being light-weight, cheap and well conductive, are the materials of choice in the most cases. The surface of carbon electrodes consists of a graphene-like domains, various carbons, however, reveal different efficiency for oxygen redox processes. It was recently demonstrated that doping of carbons with light elements like N, B or S enhances the kinetics of electron transfer to/from oxygen remarkably and leads to an electrocatalytic activity comparable to that of noble metals. However, the underlying physics has yet not been fully understood. A number of studies devoted to this topic suffer from high complexity of real carbon electrodes, i.e. individual effects of electronic structure, impurities, microstructure, etc. can be hardly distinguished.We propose to use epitaxial graphene as a model system to elucidate the role of electronic structure and impurities in doped carbons in heterogeneous electron transfer to and from oxygen. We will start from epitaxial graphene as purely chemical model system and are planning to develop functional electrochemical cells with increasing complexity using transferred graphene as electrode.To realize the chemical model systems monolayers of doped graphene will be grown in situ by chemical vapor deposition on Ni(111) and Co(0001) surfaces. The electronic properties of N-, B- and S-graphene will be explored experimentally and theoretically employing angle resolved photoemission spectroscopy (ARPES) and DFT-based calculations. Chemisorption of hydrogen and alkali metals on doped graphene layers will be used to control the Fermi level position under ultra-high vacuum conditions. The evolution of the system during oxygen exposure will then be traced using ARPES, XPS and near ambient pressure XPS (NAP XPS).A similar methodology will be applied to operating electrochemical cells utilizing doped graphene as an electrode. Graphene will be grown on metallic foils and then transferred onto solid electrolytes or onto Si3N4 grids with liquid electrolyte supplied from the back side. The electron transfer between graphene and oxygen as well as the formation of new oxygen-containing species will be followed using photoelectron spectroscopy and X-ray absorption spectroscopy (NEXAFS) under operando conditions.