Ultra-low voltage bipolar hydrogen production from biomass-derived aldehydes and water in membrane-less electrolyzers

Water electrolysis using renewable energy inputs is being actively pursued as a green route for hydrogen production. However, it is limited by the high energy consumption due to the sluggish anodic oxygen evolution reaction (OER) and safety issues associated with H-2 and O-2 mixing. Here, we replaced the OER with an electrocatalytic oxidative dehydrogenation (EOD) of aldehydes for bipolar H-2 production and achieved industrial-level current densities at cell voltages much lower than during water electrolysis. Experimental and computational studies suggest a reasonable barrier for C-H dissociation on Cu surfaces, mainly through a diol intermediate, with a potential-dependent competition with the solution-phase Cannizzaro reaction. The kinetics of the EOD reaction was further enhanced using a porous CuAg catalyst prepared from a galvanic replacement method. Through Ag incorporation and its modification on the Cu surface, the geometric current density and electrocatalyst durability were significantly improved. Finally, we engineered a bipolar H-2 production system in membrane-electrode assembly-based flow cells to facilitate mass transport, achieving maximum current densities of 248 and 390 mA cm(-2) at cell voltages of 0.4 V and 0.6 V, respectively. The faradaic efficiency of H-2 from both the cathode and anode reactions attained similar to 100%. Taking advantage of the bipolar H-2 production without the issues associated with H-2/O-2 mixing, an inexpensive, easy-to-manufacture dialysis porous membrane was demonstrated to substitute the costly anion exchange membrane, achieving an energy-efficient and cost-effective process in a simple reactor for H-2 production. An estimated H-2 price of $2.51/kg from an initial technoeconomic assessment is competitive with US DoE's Green H-2 targets.

Automated summary

This article introduces a new method for hydrogen production through water electrolysis using renewable energy sources. By replacing the sluggish oxygen evolution reaction with an electrocatalytic oxidative dehydrogenation of aldehydes, industrial-level hydrogen production is achieved at lower voltages. The use of a porous CuAg catalyst further enhances the reaction kinetics and a simple reactor with a dialysis porous membrane is demonstrated as a cost-effective and energy-efficient process for hydrogen production.