Mechanistic Understanding of Electrocatalytic Bio-oil Hydrogenation Rates: Towards a Cost-effective Electrochemical System

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The transportation sector of the U.S. economy generates a large portion of greenhouse gas emissions. Increased use of renewable fuels is one option to reduce transportation-related greenhouse gas emissions and also to secure domestic, sustainable resources for fuel. One promising strategy to help meet transport needs is to synthesize transportation-grade fuels (e.g. liquid hydrocarbons) from biomass waste using renewable electricity, thereby enabling a CO2-neutral fuel source. Bio-oil hydrogenation is known to be the most capital- and energy-intensive steps for biofuel production. One promising approach to address this challenge is to use electrocatalytic hydrogenation (ECH) of biomass because it provides a sustainable method of fuel production and enables the use of renewable electricity. However, improved electrochemical systems and electrocatalysts are needed to make ECH economically competitive. This fundamental research project will address energy efficiency, product yield challenges, and economic analysis of ECH. The project will focus on the molecular pathways and reaction bottlenecks for hydrogenation reactions on metals in the aqueous phase. The research project will provide multidisciplinary training to two PhD students at the University of Michigan and enable them to conduct cutting-edge research in materials synthesis and characterization, computational modeling, and electrocatalysis. Underrepresented minority and female students will be engaged in research and outreach at both the high school and undergraduate level. This fundamental research project will focus on the hypothesis-directed study of electrochemical hydrogenation reactions on platinum group metals and bimetallic alloys in aqueous phase. The research will advance knowledge of metals and bimetallic alloys for use in selective hydrogenation of biomass waste using renewable electricity for sustainable fuel production. The project's goal is to help engender the widespread use of electrocatalytic hydrogenation by focusing on three main areas, the adsorption of organics and hydrogen on metal surfaces, electrocatalytic hydrogenation rates on metals and bimetallics, and using a combination of theory and experiment to understand the link between adsorption and reaction rates and selectivity to predict more active and selective alloys. The team will measure and compute intrinsic reaction rates under controlled conditions on different metals, and then find correlations with adsorption energies and reaction intermediates. The project?s guiding hypothesis is that by starting with metals having moderate activity for hydrogenation and modifying to create bimetallics (e.g., Pt-alloys), one can tune the oxygenated aromatic and hydrogen adsorption energies to increase reaction rates and energy efficiency. To probe the reaction pathway and intermediates, the project will measure adsorption isotherms and use surface-enhanced Raman spectroscopy under reaction conditions to selectively probe species near the electrocatalyst surface. To complement the experimental work, the project includes density functional theory modeling of hydrogen and oxygenated aromatic adsorption energies and ECH activity at applied potentials in water. Fundamental knowledge will result of molecular-level reaction mechanisms for electrocatalytic hydrogenation systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.