(241f) Coupling Water Electrolysis and Hydrogenation Chemistries Using Metal Oxide Bronzes

Industrial hydrogenations rely on energy- and carbon-intensive steam methane reformation (SMR) as a hydrogen source. Water electrolysis is a more sustainable hydrogen source, but remains economically infeasible. To address this challenge, we are investigating a reactor scheme that integrates electrochemical and thermochemical steps¹ to extract and activate hydrogen from water and deliver it directly to the active sites of a hydrogenation reactor. This approach decouples the overall process from the thermodynamic and kinetic constraints of water electrolysis, providing an avenue towards improved sustainability for catalytic hydrogenations of CO, CO₂, N₂, and biofuel oxygenates. Furthermore, this scheme presents an opportunity for energy and cost savings via (a) combining two process units into one, (b) decreasing the energetic requirement of sourcing hydrogen from water, and (c) attaining selectivity toward, e.g., partial hydrogenation reactions through electrochemical control of hydrogen chemical potential at a catalyst surface.

The approach centers on a hydrogen-conducting membrane composed of a metal oxide bronze (MOB, H_xMO_y). Using density functional theory calculations, we investigated hydrogen intercalation in W, Mo, Ti, and V binary MOBs. We developed a kernel ridge regression (KRR) model to accelerate the prediction of intercalation potentials in the MOBs using acid-base properties as descriptors.² Cyclic voltammetry and chronopotentiometry measurements agreed well with the KRR predictions. Interestingly, hydrogen intercalation was found to be feasible at several hundred mV positive of 0 V vs. RHE, indicating that reactive hydrogen could be generated from water at applied potentials smaller than the ~1.5 V required for water electrolysis. In further experiments, the reaction of Pt/H_xWO₃ with acetylene in a quartz tube reactor at 200 °C resulted in clear evidence of ethylene and ethane products.

[1] Miu, E.V., & McKone, J.R. (2019). Journal of Materials Chemistry A, 7(41), 23756-23761.
[2] Miu, E.V., Mpourmpakis, G. and McKone, J.R. (2020). In preparation.