Anodic Palladium Membrane Electrolysis in Molten Hydroxides Promotes Thermochemical Dehydrogenation Catalysis

Dehydrogenation reactions, which involve the removal of molecular hydrogen for a substrate, play a central role in fuel processing, commodity and fine chemical synthesis, and hydrogen storage and transport. Many dehydrogenation reactions are endothermic and kinetically inhibited by H2, leading to low single pass yields, particularly at moderate temperatures. Dehydrogenation reactions can be promoted by integrating the catalyst with a hydrogen-selective membrane, across which an H2 partial pressure differential is used to drive in-situ hydrogen removal. However, this pressure-driven approach often results in limited hydrogen flux, reduced mechanical stability and low recovered hydrogen partial pressures that requires downstream pressurization. Herein, we address these challenges by employing a hydrogen-selective Pd-based membrane as the anode of a molten hydroxide electrochemical cell along with a hydrogen evolving platinum or nickel cathode. This construct enables electrochemically-driven H2 separation at the temperatures required for thermochemical dehydrogenation catalysis in the absence of a pressure differential. We demonstrate that low applied anode potentials of < 0.3 V versus the reversible hydrogen electrode are sufficient to drive diffusion-limited H-transport across the Pd membrane. Compared to pressure-driven processes, this approach enables a 4-fold enhancement in hydrogen separation rate at 300 °C, with concomitant hydrogen concentration from 0.05 atm (balance Ar) to a pure H2 stream at 1.0 atm. Interfacing the anode with a dehydrogenation catalyst enables electrochemically-promoted ammonia and methylcyclohexane dehydrogenation. Electrochemical H2 separation enhances the rate of both reactions at low temperatures (200-250 °C), drives conversion beyond thermodynamic limits from 89.4% to 91% and 58.3% to 94%, respectively, and generates a concentrated, high purity stream of H2. This work advances a versatile strategy for the electrochemical promotion of thermocatalytic dehydrogenation reactions.