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 (H) generation much higher than that of grey H. 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 N over a new class of Cu-based catalyst (CuO) for replacing OER, fundamentally eliminating the explosion risk of H and O mixing while removing the need for membranes. Notably, this membrane-free electrolysis system exhibits the highest H Faradaic efficiency among reported membrane-free electrolysis work. In situ spectroscopic studies reveal that the new NH intermediate-mediated UOR mechanism on the CuO catalyst ensures its unique N 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, significantly lower than the 5.17 kWh Nm 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 H production cost to US$1.81 kg, which is lower than those of grey H while meeting the technical target (US$2.00-2.50 kg) set by European Commission and United States Department of Energy.