Electrooxidation of hydrazine hydrate using Ni–La catalyst for anion exchange membrane fuel cells

Carbon supported Ni, La, and Ni1−xLax (0.1 ≤ x ≤ 0.9) catalysts were synthesized by an impregnation/freeze-drying procedure followed by thermal annealing. The catalytic activity for electro-oxidation of hydrazine hydrate on anionic ionomer-coated catalysts was evaluated using a (4 × 4) 16-channel electrochemical electrode array in 1.0 M KOH + 1.0 M hydrazine hydrate solution at 60 °C. The Ni0.9La0.1/C catalyst oxidized hydrazine hydrate at a lower potential and exhibited higher mass activity in comparison with a similarly made Ni/C catalyst. Chemical insight suggests that the cause of improved performance for the Ni0.9La0.1/C catalyst is likely multifunctional synergism of the components. However, X-ray absorption fine structure (XAFS) and high voltage electron microscopy (HVEM) unexpectedly show some hcp−LaNi5 shells coating the fcc−Ni catalyst particles. As a result of the screening tests, an unsupported Ni0.9La0.1 catalyst was synthesized by spray pyrolysis and tested in a direct hydrazine hydrate fuel cell MEA (DHFC) producing 453 mW cm−2.

► Ni–La/C catalysts were synthesized and investigated for hydrazine oxidation. ► The Ni0.9La0.1/C catalyst exhibited the best onset potential and mass activity. ► HVEM suggested the metal particles are composed of Ni cores with NixLay shells.