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 ∼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. A unique electrocatalytic oxidative dehydrogenation of aldehydes and its facile kinetics on a Cu-based porous electrode enables an ultra-low voltage bipolar H 2 production system with industrial-relevant current densities.