Ferrous-immobilized iron saccharide complexes for electro-synthesis of ammonia via NORR

We report iron (Fe) saccharide complexes based on sucrose and fructose ligands (Fe[S] and Fe[F]) as an efficient electrocatalyst for electrochemical nitric oxide reduction reaction (e-NORR) in ambient conditions. The prepared catalysts were mixed with Vulcan (C) and loaded on a gas diffusion electrode (GDE) to circumvent the mass transport limitation. Fe[S]/C demonstrates high reaction yield for NO-to-NH3 conversion with Faradaic efficiency (FENH3) of 97.2 % and conversion efficiency (CENH3) of 95.2% with 1% NO, while N-N dimerization leading to N2 formation mainly occurs on Fe[F]/C catalyst. The dominant number of Fe2+ active sites over Fe3+ in Fe[S], confirmed by Mössbauer spectroscopy, enables drastically increased charge-transferring ability and high current density (90.83 mA/cm2) via redox coupling at Fe2+. Gaseous nitric oxide (NO) adsorption on the catalyst was monitored via DRIFT analysis. The DRIFT results clearly show that the adsorption of gaseous nitric oxide (NO) increases more rapidly on Fe[S] than on Fe[F], which is in good agreement with the high content of Fe2+ active sites in Fe[S] obtained by Mössbauer results. The NH3 production rate was accelerated even with increasing NO concentration up to 10%, reaching 1175.7 μmol/(h·cm2) with FENH3 of 91.7 % and CENH3 of 47.2%. Fe[S] catalyst exhibits high NORR performance with promising stability during long-term reaction test. Our findings show that the saccharide-based Fe2+-immobilized complex can be an ideal catalyst candidate with superior catalytic performance producing green ammonia as a carbon–neutral fuel source.