Research in the Dempsey group aims to address challenges associated with developing efficient solar energy conversion processes. We are particularly interested in charge transfer processes associated with solar fuel production, including proton-coupled electron transfer reactions and electron transfer across interfaces. Our research program bridges molecular and materials chemistry and relies heavily on methods of physical inorganic chemistry, including transient absorption spectroscopy and electrochemistry.

 

Proton-Coupled Electron Transfer

Central to photosynthesis and solar fuel production is a process known as proton-coupled electron transfer (PCET). PCET is a fundamental charge transfer reaction wherein the reaction pathways of protons and electrons are intimately coupled. Solar fuel generating reactions rely on this fundamental process, as both protons and electrons must be managed for light-driven water splitting. Revealing exactly how PCET proceeds in systems like these is vital for advancing sustainable energy technologies.

In one project, we are probing the pathways by which molecular transition metal-based catalysts mediate the electrochemical reduction of protons to hydrogen. Specifically, how do these coordination complexes choreograph the movement of protons and electrons to generate fuels? To accomplish this, we use a combination of inorganic synthesis, electrochemical techniques, and time-resolved spectroscopies to measure electron and proton transfer kinetics, detect intermediates, and resolve the mechanisms by which these catalysts operate. Through careful studies, we hope to understand what factors influence PCET reaction mechanism and to learn how we can design better catalysts that produce fuels like hydrogen with enhanced efficiency.

In a second project, we are interested in discovering how light absorption can be coupled to proton-coupled electron transfer processes. By integrating the capture of solar photons with fuel-forming PCET reactions, we hope to realize new ways by which solar energy can be utilized to directly drive the production of fuels. To accomplish this, we are using a combination of inorganic synthesis and photochemistry to interrogate how electronic structure can be used to influence PCET reactivity. The details revealed by these studies will ultimately provide a better understanding of the role PCET plays in solar fuel producing reactions and allow us to harness light-driven PCET reactions for energy conversion.

 

Interfacial Electron Transfer

Interfacial electron transfer processes will dictate efficiency in devices proposed for energy capture and conversion. By improving our understanding of both semiconductor nanocrystal surfaces and electron transfer processes across the interfaces of these nanocrystal building blocks, our work will help realize new nanoparticle-based materials.

In one project, we are exploring the composition of semiconductor quantum dot surfaces and probing their reactivity using a combination of NMR, UV-Vis absorption spectroscopy, inductively-coupled plasma mass spectrometry, and luminescence spectroscopy. We are also studying how the addition of charge carriers to these materials (doping) influences their surface composition and are employing a suite of physical methods to reveal the mechanisms of doping.

In a second project, we are studying the electronic structure of core/shell metal oxide nanomaterials to understand how these materials improve performance of dye-sensitized photoelectrosynthesis cells. This highly collaborative work is part of the Alliance for Molecular PhotoElectrode Design (AMPED) for Solar Fuels Energy Frontier Research Center.