Metal Chalcogenide and Pnictide OER Catalysts: The Impact of the Crystalline Precursor on the Active Amorphous Catalyst

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Metal Chalcogenide and Pnictide OER Catalysts: The Impact of the Crystalline Precursor on the Active Amorphous CatalystDeveloping earth-abundant, cheap materials that can chemically transform water into oxygen and hydrogen is an important goal in the quest to build a sustainable energy future. This catalytic process, referred to as water electrolysis or water-splitting, is used to produce hydrogen in an environmentally-friendly manner. Hydrogen is employed in many industries (e.g., petroleum processing) and could also be used as a fuel for transportation as well as other purposes. Currently metal-chalcogenide (e.g., nickel and sulfur) and metal-pnictide (e.g., cobalt and phosphorous) materials show great promise as earth-abundant compounds with good catalytic properties for the water oxidation reaction (which is one of the two reactions involved in water splitting) but their true chemical compositions and structures are not well-understood. In this project, Dr. Buddie Mullins is conducting experiments on metal-chalcogenide and metal-pnictide materials and studying their chemical and structural transformations during the water oxidation reaction. Dr. Mullins is actively involved in scientific public awareness and promotion activities through his research that encourage the participation and intellectual development of students in science, technology, engineering and mathematics (STEM) disciplines. These activities include laboratory internships for high school students and college undergraduates with the aim of encouraging these students (especially women and those historically underrepresented in STEM) to pursue careers in the STEM fields.With funding from the Chemical Catalysis Program of the Chemistry Division, Professor Buddie Mullins is working to verify or disprove the hypothesis that (i) metal-chalcogenide (MC) and metal-pnictide (MP) electrocatalysts are simply precursors to highly active metal-oxide (MO) electrocatalysts and (ii) that the underlying layers of MC or MP don't influence the catalytic performance. It is clear that the outer layers of MCs and MPs transform into MOs under water oxidation conditions. During this transformation an amorphous high surface area film is created that is more catalytically active than its' crystalline oxide analog. Professor Mullins is studying the mechanism by which the amorphous film is created as well as its enhanced activity. He is also synthesizing both nanocolumnar and dense films of MCs and MPs for use as model electrocatalysts by glancing angle physical vapor deposition, which can reproducibly create electrocatalyst films. Mullins is probing the films with many different ex situ characterization techniques, including molecular beams and thermal desorption mass spectrometry for characterization and measurement of the surface area. Dr. Mullins is actively involved in promoting science and science education to students of all ages and especially those historically underrepresented in the sciences. This is accomplished via videos, internships and public demonstrations; these activities support the broader impacts of the research project.