Challenges in Catalyst Design for the Ammonia Oxidation Reaction in Aqueous Media: The Case of Metal Porphyrins
Year: 2026
Type: preprint
Abstract: Electrochemical ammonia oxidation (eAOR) in aqueous media is attractive for practical applications, yet molecular catalysts remain largely unexplored under these conditions, and only a few immobilized molecular eAOR catalysts operating in water have been reported.Here, we first establish a Pt/Vulcan carbon benchmark in alkaline aqueous media, combining cyclic voltammetry, controlled-potential electrolysis and gas chromatography.We then screen iron and manganese porphyrins -Fe(TPP)Cl and Mn(TPP)Cl as immobilized carbon-supported films, and the water-soluble Fe(TMPyP)Cl under homogeneous conditions -for eAOR activity in aqueous electrolytes.UV-vis spectral changes in homogeneous conditions, and shifts of the redox waves in cyclic voltammetry in both homogeneous and heterogeneous conditions suggest NH3 coordination to the metal center, but no clear catalytic oxidation response is observed.In concentrated aqueous ammonia, Fe(TMPyP)Cl in solution gives an anodic current enhancement compared with the bare electrode.We discuss possible factors limiting the catalytic activity, which may be relevant to future catalyst design.
Source: ChemRxiv
Authors: Nikolaos Kostopoulos, Alina Sekretareva
Institution: Uppsala University
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7221671070