Improving the Longevity of Li-Mediated Ammonia Synthesis via Pulsed Electrolysis under High Current Densities

Ammonia synthesis via lithium-mediated nitrogen reduction reaction (Li-NRR) has emerged as a promising electrochemical alternative to the Haber-Bosch process, enabling decentralized, sustainable ammonia production under ambient conditions. Despite this, barriers linger in advancing its efficiency, reaction kinetics, and sustainable operational stability. In this context, we present a high-performance Li-NRR system characterized by a recyclable NiCu₁Ru_100h foam cathode and a pulsed-voltage operation within a single-cell reactor configuration. Constructed from a Ni foam coated with Cu and Ru, the NiCu₁Ru₁₀₀ electrode presents a large active surface area and catalytic spots, enabling strong lithium plating, nitridation, and protonation functions. Under potentiostatic operation at an optimal cathode potential (-12 V vs Ag/Ag⁺), the NiCu₁Ru₁₀₀ cathode attained an ammonia yield rate approaching ca. 24 nmol s^-1 cm_geo^-2 at a current density of -80.5 mA cm^-2, alongside a Faradaic efficiency of ca. 9% reaching 20% after constant potentiostatic recycling. The single-compartment cell design, in contrast to a conventional H-cell, indicated that ammonia crossover and anodic ammonia oxidation could substantially influence the apparent performance; we verified this by incorporating an ion-exchange separator and conducting control experiments focused on ammonia oxidation. Significantly, a pulsed operational technique that alternates rapid, intense negative cathodic pulses with anodic stripping pulses markedly reduced the rate of current density loss during recycling of the working electrode, suggesting improved control of solid-electrolyte interphase stability in the Li-NRR process. The cathode was successfully recycled across seven consecutive Li-NRR cycles with minimal structural degradation. This study provides insights into cell configurations and operational strategies that could improve the lifespan and selectivity of lithium-mediated ammonia synthesis.