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

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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.