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

非技术总结：清洁氢的生产是大规模和长期实施氢燃料经济的主要挑战之一。利用水裂解反应生产氧气和氢气是目前最有前途的清洁氢气生产技术之一。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，这就需要使用能够降低活化能势垒的催化剂。OER催化剂的设计需要使其能够在低应用电位下促进反应，以提高整体能量转换效率，同时无毒、廉价、丰富和耐用。通过这项由材料研究部固态与材料化学项目和化学部化学催化项目共同资助的资助，PIs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族化合物（硒化物和碲化物）的高效OER电催化剂，该催化剂含有第一排过渡元素。其良好的定制电子和结构特性表明，这些硫族化合物基电催化剂优于传统的OER电催化剂，后者基于贵金属或过渡金属氧化物，仅显示适度的催化活性。这种含有地球上丰富的非贵重元素的高效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，以可持续和非成本高昂的方式生产替代能源是人类主要关注的问题之一。这个多学科项目涉及本科生、研究生和博士后研究人员，他们在化学、电化学、物理和表面科学领域的前沿方法上合作，发现新的催化剂成分。为了传播有关替代能源生产的知识，我们设计了示范实验，并通过在圣路易斯科学中心开展的外展活动、密苏里州S&amp；T开办的少数民族工程介绍营（MITE）以及在夏季为当地高中教师组织的讲习班与公众分享，其中包括利用该项目成果的活性水电解器的现场演示。技术摘要：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，具体目的如下：(1)通过组合方法确定新的高效OER电催化剂组合；(2)通过实验测量和电子能带结构计算了解它们的催化活性，并对结构-性能相关性有适当的认识；(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研究了一个假设，即过渡金属硫族化合物比常用的贵金属氧化物对OER具有更好的催化效率，这是由于以下几个因素：(i)金属-硫键的共价程度增加，这将改变金属原子的化学势；（ii）广泛的金属-金属键导致硫族化合物结构丰富，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）过渡金属硫族化合物所表现出的金属-硫族配位几何的多样性，可以影响催化活性位点的性质，并产生阴离子空位；（iv）复杂的电子特性以及较小的带隙使其在可见区域更具吸收性。过渡金属硫族化合物（硒化物和碲化物），二元，NixEy [E = Se, Te]，三元[Ni1-xMxEn；M = Fe, Co, Mn]，和季元[NixMIyMIIzEn；MI = Fe, MII = Al, Co， Mn]合成物（主要通过电沉积），并通过详细的电化学研究研究了它们的催化活性。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，并为这些新催化剂的结构-性能关系创造了深入的知识。特别强调的是对催化剂表面化学成分的解释。采用各种表面分析技术揭示了关于这些硫系催化剂在OER条件下稳定性的有价值的见解，并允许鉴定实际的催化活性物质。

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.