Heterogeneous Catalyst-Modified Anode in Solid Oxide Fuel Cells for Simultaneous Ammonia Synthesis and Energy Conversion

An innovative and cost-efficient method of coproduction of electricity and ammonia through solid oxide fuel cells (SOFCs) by implementing a transition metal nitride (Mn_xN_y) catalyst on the fuel electrode is the focus of the work. Breaking molecular nitrogen (N≡N) with a simultaneous enhancement in the electrochemical performance of the Ni-ScSZ-supported-SOFC was achieved by using transition metal nitride (Mn₄N) catalysts on the fuel electrode. Ex situ X-ray diffraction and X-ray photoelectron spectroscopy revealed the chemical stability of the Mn_xN_y catalyst under H₂ and N₂ atmospheres under cell operating conditions. The nitrogen reduction reaction (NRR) at the Mn₄N active sites was measured via hydrogenation of lattice nitrogen and formation of metallic Mn followed by renitrification of the catalyst. Electrochemical impedance spectroscopy analysis of the catalyst-modified cell revealed improved hydrogen oxidation reaction activity and NRR during cell operation. The cell exhibited peak power densities of 539 and 374 mW·cm^-2 for humidified (3 wt %) H₂ and a dry N₂/H₂ (1:1) mixture, respectively. Furthermore, a high rate of ammonia production of 1.63 × 10^-9 mol·cm^-2·s^-1 and a power density of 348 mW·cm^-2 were achieved when the cell was operated at 800 °C.