Membrane-Free Water Electrolysis for Hydrogen Generation with Low Cost

Conventional water electrolysis relies on expensive membrane-electrode assemblies and sluggish oxygen evolution reaction (OER) at the anode, which makes the cost of green hydrogen (H₂) generation much higher than that of grey H₂. Here, we develop an innovative and efficient membrane-free water electrolysis system to overcome these two obstacles simultaneously. This system utilizes the thermodynamically more favorable urea oxidation reaction (UOR) to generate clean N₂ over a new class of Cu-based catalyst (Cu_XO) for replacing OER, fundamentally eliminating the explosion risk of H₂ and O₂ mixing while removing the need for membranes. Notably, this membrane-free electrolysis system exhibits the highest H₂ Faradaic efficiency among reported membrane-free electrolysis work. In situ spectroscopic studies reveal that the new N₂H_y intermediate-mediated UOR mechanism on the Cu_XO catalyst ensures its unique N₂ selectivity and OER inertness. More importantly, an industrial-type membrane-free water electrolyser (MFE) based on this system successfully reduces electricity consumption to only 3.78 kWh Nm⁻³, significantly lower than the 5.17 kWh Nm⁻³ of commercial alkaline water electrolyzers (AWE). Comprehensive techno-economic analysis (TEA) suggests that the membrane-free design and reduced electricity input of the MFE plants reduce the green H₂ production cost to US$1.81 kg⁻¹, which is lower than those of grey H₂ while meeting the technical target (US$2.00–2.50 kg⁻¹) set by European Commission and United States Department of Energy.