Investigating Mixed Metal Chalcogenides for Electrocatalytic Water Oxidation: An Integrated Experimental and Theoretical Approach towards Materials Innovation

非技术性总结：清洁氢气的生产是大规模和长期实施氢燃料经济的主要挑战之一。利用水裂解反应制备氧气和氢气是目前最有前途的清洁氢气制备技术之一。然而，水裂解反应的效率受到动力学缓慢的水氧化过程（也称为析氧反应，OER）的限制，这需要使用可以降低活化能势垒的催化剂。OER催化剂需要被设计成使得其可以在低施加电势下促进反应以增加总能量转化效率，并且同时是无毒的、廉价的、丰富的和耐用的。通过这项赠款，由材料研究部的固态和材料化学计划以及化学部的化学催化计划共同资助，PI采用假设驱动的综合实验和基于DFT的理论方法来设计基于混合金属硫属化物（硒化物和碲化物）的高效OER电催化剂含有第一行过渡元素。它们有利地定制的电子和结构性质表明，这些硫族化物基电催化剂优于传统的OER电催化剂，其基于贵金属或过渡金属氧化物，并且仅显示出适度的催化活性。这种含有地球上丰富的非贵元素的高效OER电催化剂在全球范围内具有巨大的社会影响，特别是在可预见的未来，当以可持续和无成本限制的方式产生替代能源是人类的主要关注点之一时。这个多学科项目涉及本科生，研究生和博士后研究人员在化学，电化学，物理学和表面科学的前沿方法合作，以发现新的催化剂组合物。为了传播有关替代能源发电的知识，设计了示范实验，并通过在圣路易斯科学中心设立的外联活动与公众分享，通过由密苏里州ST运行的少数民族介绍工程（MITE）营地，并通过夏季为当地高中教师组织的研讨会，其中包括利用该项目成果的活性水电解器的现场演示。 本项目由材料研究部固体与材料化学项目和化学部化学催化项目共同资助，主要研究三元和四元过渡金属硫族化合物对OER的电催化活性，具体目标如下：（1）通过组合方法鉴定新的高效OER电催化剂组合物;（二）通过实验测量和电子能带结构计算了解它们的催化活性，并形成适当的见解（3）研究了这些电催化剂在OER条件下的稳定性。从材料化学的角度来看，PI研究了过渡金属硫属化物比常用的贵金属氧化物具有更好的OER催化效率的假设，这是由于几个因素，包括：（i）金属-硫属元素键中的共价程度增加，这将改变金属原子的化学势;（ii）硫族化物的结构丰富性，这是由于广泛的金属-金属键合引起的，从而产生可变的氧化态，这将影响催化剂位点的氧化还原电位;（iii）过渡金属硫属化物所表现出的多种金属-硫属元素配位几何形状，其可以影响催化活性位点的性质以及产生阴离子空位;以及（iv）复杂的电子性质，沿着的带隙更小，使得其在可见光区更有吸收性。过渡金属硫族化合物（硒化物和碲化物），二元，NixEy [E = Se，Te]，三元[Ni 1-xMxEn; M = Fe，Co，Mn]，和四元[NixMIyMIIzEn; MI = Fe，MII = Al，Co，Mn]组合物的合成（主要通过电沉积）和它们的催化活性进行了研究，通过详细的电化学研究与此授权的支持。系统的电子能带结构计算提供了对活性催化剂位点的深入了解，并深入了解这些新催化剂的结构-性能关系。特别强调的是放在催化剂表面上的化学组成的说明。采用各种表面分析技术揭示了有价值的见解，这些硫属化物催化剂的OER条件下的稳定性，并允许识别的实际催化活性物种。

Non-technical Summary:The production of clean hydrogen is one of the main challenges for large-scale and long-term implementation of a hydrogen fuel economy. Using water splitting reactions to produce oxygen and hydrogen is currently one of the most promising technologies for generating clean hydrogen. However, the efficiency of the water splitting reaction is limited by the kinetically slow water oxidation process (also referred to as oxygen evolution reaction, OER) which necessitates the use of catalysts that can lower the activation energy barrier. The OER catalyst needs to be designed such that it can facilitate the reaction at low applied potential to increase the overall energy conversion efficiency and, at the same time, be non-toxic, cheap, abundant, and durable. Through this grant, co-funded by the Solid State and Materials Chemistry Program in the Division of Materials Research and the Chemical Catalysis Program in the Division of Chemistry, the PIs employ a hypothesis-driven integrated experimental and DFT-based theoretical approach to design highly efficient OER electrocatalysts based on mixed metal chalcogenides (selenides and tellurides) containing first row transition elements. Their favorably tailored electronic and structural properties suggest that these chalcogenide-based electrocatalysts outperform the conventional OER electrocatalysts, which are based on precious metal or transition metal oxides and show only modest catalytic activity. Such high-efficiency OER electrocatalysts containing earth-abundant non-precious elements have a large societal impact globally, especially in the foreseeable future, when alternative energy generation in a sustainable and non-cost-prohibitive way is one of the primary concerns of mankind. This multidisciplinary project involves undergraduate, graduate and postdoctoral researchers collaborating on cutting edge approaches in chemistry, electrochemistry, physics, and surface science for discovery of new catalyst compositions. To disseminate knowledge about alternative energy generation, demonstration experiments are designed and shared with the public through outreach activities set up at the St. Louis Science Center, through Minority Introduction to Engineering (MITE) camps run by Missouri S&T, and through workshops organized during the summer for local high school teachers, which include live demonstrations of an active water electrolyser utilizing results from this project. Technical Summary:This project, which is co-funded by the Solid State and Materials Chemistry Program in the Division of Materials Research and the Chemical Catalysis Program in the Division of Chemistry, is centered on investigating electrocatalytic activities of ternary and quaternary transition metal chalcogenides towards OER with the following specific aims: (1) identifying new efficient OER electrocatalyst compositions through combinatorial approach; (2) understanding their catalytic activities through experimental measurements as well as electronic band structure calculations and developing a proper insight of the structure-property correlation; (3) studying stability of these electrocatalysts under conditions of OER. From a materials chemistry point of view, the PIs investigate the hypothesis that transition metal chalcogenides have better catalytic efficiency than the commonly used precious metal oxides for OER due to several factors including: (i) increased degree of covalency in the metal-chalcogen bonds which will alter the chemical potential of the metal atom; (ii) structural richness of the chalcogenides resulting from extensive metal-metal bonding giving rise to variable oxidation states, which will affect redox potential of the catalyst site; (iii) variety of metal-chalcogen coordination geometry exhibited by the transition metal chalcogenides that can affect the nature of active sites for catalysis as well as creating anion vacancies; and (iv) intricate electronic properties along with a smaller bandgap making it more absorptive in the visible region. Transition metal chalcogenides (selenides and tellurides), of binary, NixEy [E = Se, Te], ternary [Ni1-xMxEn; M = Fe, Co, Mn], and quaternary [NixMIyMIIzEn; MI = Fe, MII = Al, Co, Mn] compositions are synthesized (mainly by electrodeposition) and their catalytic activities are investigated through detailed electrochemical studies with support from this grant. Systematic electronic band structure calculations provide an insight into the active catalyst sites and create in-depth knowledge regarding structure-property relationships for these new catalysts. Special emphasis is placed on the elucidation of the chemical composition on the catalyst surface. Employing a variety of surface analytical techniques reveals valuable insights regarding the stability of these chalcogenide catalysts under conditions of OER and allows the identification of the actual catalytically active species.