Jeff Blackburn

A practical field guide to thermoelectrics: Fundamentals, synthesis, and characterization

The study of thermoelectric materials spans condensed matter physics, materials science and engineering, and solid-state chemistry. The diversity of the participants and the inherent complexity of the topic mean that it is difficult, if not impossible, for a researcher to be fluent in all aspects of the field. This review, which grew out of a one-week summer school for graduate students, aims to provide an introduction and practical guidance for selected conceptual, synthetic, and characterization approaches and to craft a common umbrella of language, theory, and experimental practice for those engaged in the field of thermoelectric materials. This review does not attempt to cover all major aspects of thermoelectric materials research or review state-of-the-art thermoelectric materials. Rather, the topics discussed herein reflect the expertise and experience of the authors. We begin by discussing a universal approach to modeling electronic transport using Landauer theory. The core sections of the review are focused on bulk inorganic materials and include a discussion of effective strategies for powder and single crystal synthesis, the use of national synchrotron sources to characterize crystalline materials, error analysis, and modeling of transport data using an effective mass model, and characterization of phonon behavior using inelastic neutron scattering and ultrasonic speed of sound measurements. The final core section discusses the challenges faced when synthesizing carbon-based samples and the measuring or interpretation of their transport properties. We conclude this review with a brief discussion of some of the grand challenges and opportunities that remain to be addressed in the study of thermoelectrics.

Merging [FeFe]-Hydrogenases with Materials and Nanomaterials as Biohybrid Catalysts for Solar H2 Production

The catalysts commonly used for the H2 producing reaction in artificial solar systems are typically platinum or particulate platinum composites. Biological catalysts, the hydrogenases, exist in a wide-variety of microbes and are biosynthesized from abundant, non-precious metals. By virtue of a unique catalytic metallo-cluster that is composed of iron and sulfur, [FeFe]-hydrogenases are capable of catalyzing H2 production at turnover rates of millimoles-per-second. In addition, these biological catalysts possess some of the characteristics that are desired for cost-effective solar H2 production systems, high solubilities in aqueous solutions and low activation energies, but are sensitive to CO and O2. We are investigating ways to merge [FeFe]-hydrogenases with a variety of organic materials and nanomaterials for the fabrication of electrodes and biohybrids as catalysts for use in artificial solar H2 production systems. These efforts include designs that allow for the integration of [FeFe]-hydrogenase in dye-solar cells as models to measure solar conversion and H2 production efficiencies. In support of a more fundamental understanding of [FeFe]-hydrogenase for these and other applications the role of protein structure in catalysis is being investigated. Currently there is little known about the mechanism of how these and other enzymes couple multi-electron transfer to proton reduction. To further the mechanistic understanding of [FeFe]-hydrogenases, structural models for substrate transfer are being used to create enzyme variants for biochemical analysis. Here results are presented on investigations of proton-transfer pathways in [FeFe]-hydrogenase and their interaction with single-walled carbon nanotubes.