Electrochemical promotion of nanostructured catalysts and electrocatalysts for environmentally important processes

近几十年来，全球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产量呈指数级增长。由于人类活动不可能减少，因此全球能源需求不断增长，显然需要改变游戏规则的战略来实施以可再生原料为基础的替代能源，以及温室气体排放的封存和再循环的替代办法。 现代多相催化剂，强大的纳米结构系统，用于加强化学反应和显著减少能源需求，提供了绝佳的机会。典型的多相催化剂是由沉积在高比表面积载体上的纳米金属或金属氧化物颗粒组成的。催化剂经常失活或催化活性低。因此，使用了各种促进途径：(I)化学促进：在制备过程中向催化剂中添加化学物种，如K、Na、Ce、Sn等，以改善其催化性能，通常是其稳定性和寿命。这些物种的加入改变了催化剂的电子或晶体结构，从而提高了催化性能和所需化学反应的选择性。(Ii)金属-载体相互作用(MSI)的定义是，由于两种材料之间的相互作用，载体在改变催化剂的性质方面起着关键作用，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催化活性修饰(NEMCA)是30年前发现的，是提高催化活性的另一种方法。EPOC引入了一类以前在多相催化中未知的新的促进剂，例如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。众所周知，上述三种现象之间存在业务上的差异，而不是功能上的差异。虽然在操作条件下很难控制化学促进剂和MSI，但EPOC现象提供了就地控制表面促进剂的量，并提供了通过施加小电流或小电位来改变催化剂性能的独特机会。 尽管EPOC已经被研究了30多年，并应用于100多个具有不同电解液、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)观察高分散纳米粒子催化剂的电化学促进的反应条件和电化学池设计是什么？(Ii)以离子导电载体为载体的NPs“自诱导”或“无线”促进的机制是什么？它与MSI的关系是什么？(3)使用质子或阴离子导体将EPOC现象应用于复合有机燃料的电催化氧化有哪些新方法？ 拟议研究计划的长期目标是建立对以离子导电陶瓷和质子(阴离子)交换聚合物电解质为载体的纳米结构催化剂的EPOC的全面理解。在纳米粒子尺度上对EPOC和MSE之间的关系有一个基本的认识，为合理设计燃料电池的高效催化系统以及减少固定来源和汽车来源的温室气体提供依据。

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.