Transition Metal-containing Compounds For Electrocatalytic Hydrazine Oxidation

The fuel cell field is of great significance to the development of environmental protection and sustainable energy.The fuel cell with hydrazine as raw materials has a lot of advantages,such as easy to transport and storage,high theoretical electromotive force.Hydrazine electric oxidation in direct hydrazine fuel cell is essential,but the catalyst widely used are most of the precious metal catalyst,and the high prices and limited storage severely hampered its large scale application,thus developing high activity and low price catalyst become a research hotspot.Inspired by the relatively recognized performance of transition metal sulfides in the oxidation of hydrazine,the catalytic properties of Fe S₂ and Fe₃S₄were compared via the density functional theory calculations,therein,the Fe centres were identified as the catalytic sites of all possible active locations.Due to the different coordination numbers of iron-sulfur,the free energies of the dehydrogenation steps on Fe S₂ are far less than those on Fe₃S₄,which led to the much better catalytic performance of Fe S₂.Accordingly,Fe S₂ microspheres were rationally proposed as a more efficient electrocatalyst for hydrazine oxidation,which was then prepared by a facile one-step hydrothermal strategy.Such Fe S₂ microspheres show great activity for hydrazine oxidation with an onset oxidation potential of 0.22 V vs.reversible hydrogen electrode,and a peak current density of 16 m A cm^-2 using the electrolyte containing 100 m M hydrazine and 1 M KOH.Meanwhile,stability and high faradaic efficiency（3.5 e^-/N₂H₄）was obtained for hydrazine oxidation to N₂.Mono-atomic catalysts have attracted much attention in the field of catalysis because of their remarkable catalytic activity and maximum atomic utilization.Metal catalysts loaded with atomically dispersed atoms can provide efficient and highly active surface sites for sustainable and benign catalytic transformation.Based on the large area and many active sites of two-dimensional materials,polydopamine（PDA）was synthesized from dopamine by stirring method and nitrogen-doped graphene nanosheets with iron atoms dispersed（Fe-PDA 800）were prepared by high temperature annealing method（800℃）as electrocatalyst for hydrazine oxidation.The excellent Hz OR activity was achieved by taking advantage of the excellent conductivity of two-dimensional carbon materials and the stability in the electrocatalytic process as the substrate of electrocatalyst,which was loaded with dispersed iron atoms.The synthesized Fe-PDA800 catalyst has a peak current density of 15.5 m A cm^-2 and a starting potential of 0.20V at p H 14.It has excellent electrocatalytic stability and controls the irreversible process of N₂ diffusion.