(344b) Bipolar Hydrogen Production from Biorenewable Aldehydes and Water in Membrane-Less Electrolyzers

Water electrolysis using renewable energy inputs has been considered a green process to Hydrogen production. Conventional electrolysis is limited by the sluggish anodic oxygen evolution reaction (OER), leading to high energy input. In addition, the temporal spatial coupling of the production of H₂ and O₂ can cause issues associated with safety, economic feasibility, and system flexibility. Herein, we reported our recent work on replacing OER with an electrocatalytic oxidative dehydrogenation (EOD) of aldehydes for bipolar H₂ production with ultra-low cell voltages and high current densities. Experimental and DFT studies suggested a reasonable barrier for C-H dissociation on Cu surface, mainly through the diol intermediate, with the potential-dependent competition with Cannizzaro reaction. Based on the favorable thermodynamics of EOD reaction, we found that its occurrence on metallic Cu surface was linked to an autocatalytic Cu oxides reduction by aldehydes along with H₂ evolution. The kinetics of EOD reaction was further enhanced by a porous CuAg catalyst prepared from a galvanic replacement method. Through Ag incorporation and its modification of Cu surface, the reaction activity and durability were significantly improved. Finally, we engineered a bipolar H₂ production system in membrane-electrode assembly-based flow cells to facilitate mass transport, achieving a combined faradaic efficiency of ~200% and the maximum H₂ partial current density of 248 and 390 mA cm^−2 at cell voltages of 0.4 V and 0.6 V, respectively. Taking great advantage of the anodic H₂ production without the issues associated with H₂/O₂ mixing, an inexpensive, easy-to-manufacture dialysis membrane was demonstrated to substitute the costly anion exchange membrane, achieving an energy-efficient and cost-effective process in a simple reactor for H₂ production. Our technoeconomic analysis (TEA) study shows the estimated H₂ price of $2.51/kg is competitive with US DoE’s “Green H₂” targets.