The Promise and Challenges of Ammonia Electrosynthesis From Dinitrogen and Water Using an Electrochemical Palladium Membrane.

Sustainable ammonia production can be achieved via an electrochemical process coupling the lithium redox-mediated nitrogen reduction (Li-NRR) with hydrogen oxidation, but a more practical approach uses water oxidation (the oxygen evolution reaction; OER) as the anode reaction. However, coupling the Li-NRR and the OER is restricted by incompatibility of the anhydrous conditions required for nitrogen reduction with water. Aiming to resolve this, we investigated an electrolyser with an electrochemical palladium-based membrane, which transforms protons generated by the OER to palladium hydride in aqueous media and releases protons into non-aqueous Li-NRR media to sustain ammonia production. The hydride formation/oxidation mechanism, validated through experiments with deuterated water, ensures exclusive membrane selectivity to protons, and is facilitated by the palladium-gold electrocatalysts. We demonstrate ammonia electrosynthesis from nitrogen (15 bar) and water at a faradaic efficiency of 59 ± 4%, yield rate of 20 ± 1 nmol s-1 cm-2 and energy efficiency of 9.0 ± 0.7% over more than two days. However, deeper investigation of the system revealed ammonia-promoted corrosion of the palladium-based membrane-a challenge that needs to be addressed in the future developments of this technology.