Revealing structure–activity links in Hydrazine Oxidation: Doping and nanostructure in Carbide–Carbon Electrocatalysts

Electrocatalysis of the hydrazine (N₂H₄) oxidation reaction (HzOR) is an important challenge for fuel cell technologies and hydrazine sensors. As an alternative to non-fossil-derived fuels, hydrazine is found to be a promising candidate, offering high theoretical voltage (1.56 V vs. RHE at pH=14), easy transport, and clean emissions (N₂ and H₂O). Though the HzOR is thermodynamically favored, its kinetics are sluggish, calling for electrocatalysts for expand the use of hydrazine-based technologies. Metals such as Pd and Au are known to be stable and efficient electrocatalysts for the HzOR, though their costliness remains a problem. Abundant metals such as Ni, Fe, Co manage to catalyze the HzOR with low overpotentials of 150-300 mV, yet are quickly deactivated by a passivating hydroxide layer.

Carbon-based electrocatalysts offer mechanical and chemical stability, cheap starting materials, easy doping of the carbon matrix, and tunable porosity for maximum exposure of active sites and efficient flow of reaction reagents and products. We have recently reported the first carbide-carbon composite electrocatalyst for the HzOR. This Fe₂MoC-embedded, N-doped carbon materials gave the lowest reported overpotential for carbon-based catalysts at pH=14.

Following this discovery, we were interested in investigating the effect of dopants on HzOR activity. Thus, we used an easily-tuned, multi-doped organometallic precursor, containing cyanide-bridged iron to (1) copper, (2) zinc or (3) iron. Pyrolysis and washing of these precursors yielded an Fe₃C-embedded, N-doped carbon, which proved to be an excellent electrocatalyst for HzOR, though with differences in peak current densities.¹ To elucidate the source of the differences, we studied these catalysts using a variety of materials and electrochemical characterization techniques, which revealed the important link of carbon nanostructure, induced by the metal dopants through different pathways, and HzOR activity.

[Burshtein et al. J. Mater. Chem. A 7, 23854–23861 (2019)]