(6dc) Development of Devices and Selective Catalysts for the Solar-Driven Electrochemical Reduction of CO2 to Fuels

The electrochemical and photoelectrochemical reduction of CO₂ presents an attractive route towards fuel formation from renewable energy. However, the dearth of selective, active and inexpensive catalyst materials remains a key challenge on the way to renewable production of hydrocarbon fuels. Here, we address these challenges through the design of novel devices and selective earth-abundant catalysts for the electrochemical^[1–3] and solar-driven^{[1,4–6]} reduction of CO₂. In addition, we provide insight into the origin of selectivity on electrocatalysts based on copper, paving the way towards more rational design of electrochemical fuel forming devices.

Copper-based catalysts derived from the reduction of CuO are known to reduce CO₂ but simultaneously exhibit poor selectivity. In tackling this issue, we pioneer the application of Atomic Layer Deposition (ALD) to direct the catalytic selectivity of copper materials. ALD coating of CuO nanowires with thin layers of SnO₂ leads to a catalyst which produces CO with high selectivity even at low overpotentials. This compares favorably to conventional gold catalysts, known to selectively convert CO₂ to CO. Unmodified CuO nanowires, in stark contrast, lead to a wide product distribution and yield considerable parasitic hydrogen. To gain insight into the origin of these striking changes, we perform kinetic studies, high resolution transmission electron microscopy and gas chemisorption measurements. These data serve to explain the observed selectivity changes on the basis of decreased binding strengths for both H and CO intermediates on the Sn-containing catalyst surface.

We subsequently combine our ALD-derived catalyst with an Earth-abundant oxide anode to effect overall splitting of CO₂ to CO and O₂. Driven by a 3-junction solar cell, this device achieves long-term solar splitting of CO₂ into CO and O₂ at an efficiency of 13.4 %, presently the state of the art.^[1]

Going beyond the production of CO, we investigate the further reduction of CO to hydrocarbons. Insights into the factors controlling the branching between different hydrocarbon species are scarce, precluding any rational design of selective catalysts. To remedy these shortcomings, we devise a platform allowing for the systematic study of the relevant reaction parameters. Exploiting non-aqueous electrolytes, we isolate activation-controlled kinetic data in electrochemical driving force, proton availability, solvent dielectric and reagent concentration. Our observations provide unique insight into the mechanism of hydrocarbon production on copper electrodes. We demonstrate that the competition between H and CO for surface sites plays an important role in governing the product selectivity between methane, ethylene and hydrogen. These results establish a new paradigm in controlling hydrocarbon product selectivity in electrochemical fuel formation.^[2]

Research Interests:

Future research directions will be presented, focusing on the design and careful study of electrochemical systems and surface processes that mediate the activation and selective catalytic turnover of weakly-reactive, industrially-relevant substrates. This research aims to employ electrochemical methods to understand the interaction of n-alkanes with catalyst surfaces, leading to their stepwise dehydrogenation to alkenes, and ultimately their total oxidation to CO₂. Scaling challenges related to the need for ion transport in electrochemical systems will be investigated both trough theory and experiment, leading to the development of more scalable electrochemical reaction systems, enabled by the advent of additive manufacturing technologies. This research holds the promise to provide substantial efficiency gains for industrial processes and will provide a cornerstone for the coupling of intermittent and renewably sourced electrical energy, decreasing the carbon footprint of industrial chemical processes. It will furthermore lead to novel insights into the factors governing bonding and reactivity of hydrocarbons on catalyst surfaces.

Teaching Interests:

Chemical engineering is diverse. Incorporating knowledge from a large variety of fields of study, it spans the scale from the reactions of molecules on a surface to the operations of entire an petrochemical production plant. My training as a chemical engineer, in combination with my Ph.D. and postdoctoral research in inorganic chemistry give me a broad overview of the pieces which constitute chemical systems and processes. Drawing from this background and my diverse interests, my students will learn to cross the bridge between fundamental understanding and real-world applications. I firmly believe that a high degree of integrated understanding provides the groundwork to truly innovative engineering solutions.

My main teaching interests lie in the field of electrochemistry, electrochemical engineering, catalysis, kinetics and photochemistry, as such, I look forward to developing programs in electrochemistry, electrocatalysis and solar energy conversion.