Gas Diffusion Electrodes for Electrocatalytic Oxidation of Gaseous Ammonia: Stepping Over the Nitrogen Energy Canyon

Abstract As ammonia continues to gain more and more interest as a promising hydrogen carrier compound, so does the electrochemical ammonia oxidation reaction (AmOR). To avoid the liberation of H 2 in a reverse Haber–Bosch reaction under release of the energetically more favorable N 2 , we propose the oxidation of ammonia to value‐added nitrite (NO 2 − ), which is usually obtained during the Ostwald process. We investigated the anodic oxidation of gaseous ammonia directly supplied to a gas diffusion electrode (GDE) using a variety of compositionally different multi‐metal catalysts coated on Ni foam under the simultaneous formation of H 2 at the cathode. This will double the amount of H 2 per ammonia molecule while applying a lower overpotential than that required for water electrolysis (1.4–1.8 V vs. RHE at 50 mA ⋅ cm −2 ). A selectivity study demonstrated that some of the catalyst compositions were able to produce significant amounts of NO 2 − , and further investigations using the most promising catalyst composition Ni f _AlCoCrCuFe integrated within a GDE demonstrated up to 88 % Faradaic efficiency for NO 2 − at the anode coupled to close to 100 % Faradaic efficiency for the cathodic H 2 production.