Electrochemical promotion of nanostructured catalysts and electrocatalysts for environmentally important processes

近几十年来，世界能源需求和以化石燃料（主要是石油、天然气和煤炭）为基础的消费品材料生产呈指数级增长。由于不可能减少人类活动，因此全球能源需求不断增长，因此显然需要改变游戏规则的战略，以实施基于可再生原料的替代能源，以及温室气体排放的封存和回收的替代方法。现代非均相催化剂，强大的纳米结构系统，用于增强化学反应和显著减少能源需求，提供了出色的机会。典型的非均相催化剂由纳米级金属或金属氧化物颗粒沉积在高表面积载体上组成。催化剂经常失活或催化活性低。因此，采用了多种促进途径：(1)化学促进：在制备过程中向催化剂中加入化学物质，如K、Na、Ce、Sn等，以改善催化剂的催化行为，往往提高催化剂的稳定性和寿命。这些物质的加入改变了催化剂的电子或晶体结构，从而提高了所需化学反应的催化性能和选择性。（ii）金属-载体相互作用（MSI）定义为载体在改变催化剂性质方面起关键作用的效应，这是由于两种材料之间的相互作用，通常导致更高的催化活性；（iii）电化学促进催化（EPOC）或也称为非法拉第电化学修饰催化活性（NEMCA）是30年前发现的，是提高催化活性的另一种方法。EPOC在多相催化中引入了一类新的启动子，如O2-、H+、K+、Na+、OH-等。通过在催化剂工作电极和沉积在固体电解质上的对电极之间施加电流或电位，由于催化剂的电子性质的改变，催化活性和选择性可以显著改变。可以确定的是，上述三种现象之间存在着操作上的区别而不是功能上的区别。虽然化学促进和MSI在操作条件下难以控制，但EPOC现象提供了对表面上促进剂数量的原位控制，并提供了通过施加小电流或电位来改变催化剂性能的独特机会。尽管EPOC已经研究了30多年，并应用于100多种不同电解质、催化剂和反应的催化体系，但仍有几个重要的问题和应用需要解决：(i)用高度分散的纳米颗粒催化剂观察电化学促进的反应条件和电化学电池设计是什么？（ii）由离子导电支架支撑的NPs“自诱导”或“无线”提升的机制是什么，以及它与MSI的关系？（iii）利用质子或阴离子导体将EPOC现象应用于复杂有机燃料氧化的电催化有哪些新方法？该研究计划的长期目标是通过离子导电陶瓷和质子（阴离子）交换聚合物电解质支持的纳米结构催化剂，建立对EPOC的全面理解。为了合理设计燃料电池的高效催化系统和减少固定和汽车排放的温室气体，在纳米颗粒尺度上对EPOC和MSE之间的关系有一个基本的理解。

In recent decades, the world has witnessed an exponential increase in energy demand and consumer product materials production based on fossil fuels, mainly oil, gas and coal. Because it is not possible to decrease the human activity and therefore the growing global energy demand it is evident that the game-changing strategies are required to implement the alternative energy sources based on renewable feedstocks as well as the alternative approaches for sequestration and recycling of greenhouse gas emissions. Modern heterogeneous catalysts, powerful nanostructured systems used to enhance chemical reactions and significantly reducing energy demand, offer outstanding opportunities. A typical heterogeneous catalyst consists of a nanosized metal or metal oxide particle deposited on the high surface area supports. Catalysts often suffer from deactivation or low catalytic activity. Therefore, various promoting routes are used: (i) Chemical promotion: addition of chemical species to the catalyst during preparation, e.g., K, Na, Ce, Sn, etc., to improve its catalytic behavior and often its stability and a life-span. The addition of such species changes the electronic or crystal structure of the catalyst, thus improving catalytic performance and selectivity for the desired chemical reaction. (ii) Metal-support interaction (MSI) defined as the effect where the support plays a key role in changing the properties of the catalyst as a result of the interaction between the two materials, usually resulting in higher catalytic activity; (iii) Electrochemical promotion of catalysis (EPOC) or also referred to as non-Faradaic electrochemical modification of catalytic activity (NEMCA) was discovered 30 years ago and is an alternative approach to enhance catalytic activity. EPOC introduced a new class of promoters previously unknown in heterogeneous catalysis, e.g., O2-, H+, K+, Na+, OH-, etc. By applying electrical current or potential between the catalyst-working electrode and a counter electrode deposited on a solid electrolyte, catalytic activity and selectivity can be significantly altered due to modifications of electronic properties of the catalyst. It is well established that an operational and not a functional difference between the above three phenomena exists. Whereas chemical promotion and MSI are difficult to control under operating conditions, the EPOC phenomenon offers in-situ control of the amount of promoters on surfaces and offers a unique opportunity to modify catalyst properties via application of small electrical current or potential.Despite that EPOC has been investigated for more than 30 years and applied for over 100 catalytic systems with various electrolytes, catalysts and reactions, several important issues and applications remain and need to be addressed: (i) What are the reaction conditions and the electrochemical cell design to observe electrochemical promotion with highly dispersed nanoparticle catalysts? (ii) What is the mechanism of the “self-induced” or “wireless” promotion with NPs supported on ionically conductive supports and its relationship to MSI? (iii) What are new approaches for application of EPOC phenomenon in electocatalysis for oxidation of complex organic fuels using proton or anion conductors?The long-term objectives of the proposed research program are to establish a comprehensive understanding of the EPOC with nanostructured catalysts supported on ionically conductive ceramics and proton (anion) exchange polymer electrolytes. To develop a fundamental understanding and a relationship between EPOC and MSE at the nanoparticle scale for the rational design of the efficient catalytic systems for fuel cells and abatement of greenhouse gas from the stationary and automobile sources.