Heterogeneous Catalyst-Modified Anode in Solid Oxide Fuel Cells for Simultaneous Ammonia Synthesis and Energy Conversion
Or Rahumi, Manasa K. Rath, Alexey Kossenko, Michael Zinigrad, Konstantin Borodianskiy
Abstract
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 x N 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 (Mn 4 N) catalysts on the fuel electrode. Ex situ X-ray diffraction and X-ray photoelectron spectroscopy revealed the chemical stability of the Mn x N y catalyst under H 2 and N 2 atmospheres under cell operating conditions. The nitrogen reduction reaction (NRR) at the Mn 4 N 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 %) H 2 and a dry N 2 /H 2 (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.