Direct Nitrogen Oxidation via Pd Nanoparticle Electrocatalysis

Palladium nanoparticles with two different ligands were used as electrocatalysts at low temperature in a hermetic one-pot electrochemical cell with either a LiOH or a LiOD electrolyte. During initial low-pressure experiments involving Pd nanoparticle electrocatalysts with epigallocatechin gallate (EGCG) ligands, an abrupt, significant pressure drop occurred in the cell headspace air from 1.59 to 0.055 bar. This astounding, repeatable, and unexplained result initiated further experimentation. Synthetic methods for bifunctional Pd nanoparticle electrocatalysts with EGCG ligands and poly(vinylpyrrolidone) (PVP) ligands are described. These Pd nanoparticles are capable of simultaneously generating ammonium, nitrite, and nitrate ions. Ion chromatography was used for quantification of nitrogen-containing anions and cations in an alkaline electrolyte. The Pd nanoparticles with PVP ligands and a 5 bar 3:1 H2/N2 gas mixture resulted in a nitrate yield rate of 1.16 μg h–1 mgcat–1 with current applied for 132 h. The Pd–PVP nanoparticles also achieved the highest ammonium and nitrite ion yield rates at 10 bar under similar conditions, while the Pd–EGCG nanoparticles achieved lower yield rates and Faradaic efficiency (FE) values. This study demonstrates that direct generation of nitrite and nitrate salts avoids the need to further process ammonia to produce ammonium nitrate.