• Long, Jeffrey W.
• Parker, Joseph F.
• Nelson, Eric S.
• Chervin, Christopher N.
• Miller, Bryan W.
• Desario, Paul
• Rolison, Debra

Abstract

Nickel–iron oxides and oxyhydroxides are among the most active oxygen-evolution reaction (OER) catalysts in alkaline electrolytes. Compositions rich in Ni are reported to show superior activity, but the establishment of competitive OER activity with lower cost, Fe-rich analogues is more desirable for metal–air batteries and other devices that will see large-scale production. Herein, we demonstrate that by controlling pore–solid architecture and the degree of crystallinity, we achieve a single-phase, Fe-rich NiFe2Ox catalyst that matches the OER performance metrics previously demonstrated for compositions with higher Ni-to-Fe ratios. We also show that OER activity linearly tracks increases in the catalyst surface area, whereas the degree of ex situ surface hydroxylation does not play a significant role. To prepare the pore–solid structured forms, NiFe2Ox gels were synthesized by using an epoxide-initiated sol–gel method and subsequently processed to aerogels or xerogels. The activities of these two sol–gel-derived nanostructures were compared with a nanoparticulate analogue with lower specific surface area, prepared by using conventional precipitation methods. The higher surface area and larger pore volume expressed by the NiFe2Ox formed as an aerogel result in a performance-competitive OER overpotential of 356 mV at a current density of 10 mA cm−2, with an approximately 140 mV improvement relative to the low-surface-area, precipitated analogue.

Topics

• density
• impedance spectroscopy
• pore
• surface
• nickel
• phase
• Oxygen
• precipitation
• iron
• current density
• crystallinity