Increasing Current Density of Li-Mediated Ammonia Synthesis with High Surface Area Copper Electrodes
Katja Li, Sarah G. Shapel, Degenhart Hochfilzer, Jakob B. Pedersen, Kevin Krempl, Suzanne Z. Andersen, Rokas Sažinas, Mattia Saccoccio, Shaofeng Li, Debasish Chakraborty, Jakob Kibsgaard, Peter C. K. Vesborg, Jens K. Nørskov, Ib Chorkendorff
Abstract
The lithium-mediated ammonia synthesis is so far the only proven electrochemical way to produce ammonia with promising faradaic efficiencies (FEs). However, to make this process commercially competitive, the ammonia formation rates per geometric surface area need to be increased significantly. In this study, we increased the current density by synthesizing high surface area Cu electrodes through hydrogen bubbling templating (HBT) on Ni foam substrates. With these electrodes, we achieved high ammonia formation rates of 46.0 ± 6.8 nmol s–1 cmgeo–2, at a current density of −100 mA/cmgeo–2 at 20 bar nitrogen atmosphere and comparable cell potentials to flat foil electrodes. The FE and energy efficiency (EE) under these conditions were 13.3 ± 2.0% and 2.3 ± 0.3%, respectively. Additionally, we found that increasing the electrolyte salt concentration improves the stability of the system, which is attributed to a change of Li deposition and/or solid electrolyte interphase.