Synthesis of Metal Pnictides and Exploration of Their Thermoelectric and Catalytic Potential

Synthesis of complex solids is often a bottleneck of the materials by design concept. The limitations of conventional synthetic approaches resulted in inability to synthesize predicted materials in ternary and quaternary systems with drastically different reactivities of the constituent elements. Several strategies to advance synthesis and produce challenging phases will be discussed, such as averaging precursor reactivity by atomic mixing of refractory components; and prebuilding chemical bonds in the precursor. In-situ studies are crucial for the development of effective synthesis, especially when backed-up with ex-situ synthetic explorations and DSC results. Synthesis enabled exploration of clathrates with potential for thermoelectric applications will be discussed.

The second project is devoted to improving electrocatalysts based on 3d transition metal phosphides for water splitting. We performed systematic studies of the polycrystalline and facet-selective single crystal of metal phosphide electrocatalysts. In-situ studies at SLAC SSRL show that P in phosphide plays an important role in H adsorption. At hydrogen evolution reaction (HER) applied bias the surface of the catalysts is reduced, and oxidation of the surface occurs only after the reducing bias is turned off, explaining common ex-situ observation of oxidized surface of the used catalysts. Studies of M₂P (M = Fe, Co, Ni) single crystals show that crystal facets have drastically different reactivity thus paving the way to enhance activity of nanocrystalline catalysts via shape control. Finally, tuning of electronic structure and chemical bonding between M and P sublattices via aliovalent substitution allow to enhance activity and stability of ternary ordered phosphide electrocatalysts.

Kirill Kovnir works on synthetic solid state chemistry of emergent energy materials including the development of innovative synthetic routes towards metastable compounds. Kirill grew up in Ukraine. After receiving graduate studies and a couple of postdoctoral stints in Europe he moved to the US. Kirill started his independent career in 2011 at UC Davis where he received tenure. Soon after that, in 2017, Kirill relocated his group to Iowa State University. Kirill’s research interests are in the broad field of solid-state and materials chemistry. Understanding the synthesis-structure-property relationship is a key to the rational design of such materials.