Selective Electrocatalytic Nitrate Reduction to Ammonia Using Nafion-Covered Cu Electrodeposits

Electrocatalytic NH3 production from NO3– reduction is a promising alternative to traditional Haber-Bosch NH3 synthesis. Although Nafion is commonly employed as a separator in two-compartment electrochemical cells and as a binder in catalyst inks, in this manuscript, we use Nafion as an overlayer on top of Cu electrodeposits to enhance NH3 selectivity. Faradaic efficiencies for NH3 and NO2– generation were evaluated as a function of electrodeposit morphology with and without the Nafion layer. These studies reveal that the combination of Cu (220) faces in the electrodeposits and activation of a NO intermediate by Nafion enables NH3 production with a high Faradaic efficiency of (97.0 ± 0.3) %. This optimized architecture also exhibits the fastest rate of NH3 production among the catalysts studied even after normalizing for its rough electrochemical active surface area. In addition to voltammetry, the electrocatalysts were characterized using a variety of techniques including atomic force microscopy, scanning electron microscopy, X-ray diffraction, and water contact angle measurements. Insights garnered about the parameters needed for selective NH3 production will inform future research on nonprecious metal NO3– reduction catalysts.