Continuous Ammonia Electrosynthesis from Nitrogen and Water in a Monolithic Pd Membrane-Based Flow Cell

Continuous electrochemical lithium-mediated ammonia production has shown promising performance. For this reaction, water oxidation could provide a direct route for proton supply, eliminating the need to generate molecular hydrogen. However, recent studies have reported low Faradaic efficiency for ammonia when water is used directly as the proton source. In this work, we integrate an electrically isolated Pd membrane to transfer protons generated from water oxidation into a nonaqueous lithium-mediated nitrogen reduction system. By employing Pd as a proton- and electron-conducting membrane rather than solely as a cathode, we enabled continuous operation in a flow-cell configuration, achieving a Faradaic efficiency of 36 ± 4% at a current density of -6 mA cm^-2 over 6 h. Online mass spectrometry confirmed that the produced ammonia contained protons generated by water oxidation. This approach to using Pd provides a practical strategy for proton transport and establishes a viable device configuration to advance electrochemical lithium-mediated nitrogen reduction toward sustainable green ammonia synthesis.