NiFeOx

NiFeOx refers to mixed nickel-iron oxide materials, typically comprising nickel and iron in oxide or oxyhydroxide forms. These materials are studied chiefly as electrocatalysts for water splitting, with particular emphasis on the oxygen evolution reaction (OER) in alkaline environments. The active phase is often a Ni-Fe oxyhydroxide (NiFeOOH) that develops in situ under anodic conditions; other forms include crystalline spinels such as NiFe2O4 and various amorphous or nanostructured Ni-Fe oxide composites supported on substrates.

In composition and structure, NiFeOx materials exhibit a range of stoichiometries and structural motifs. The presence of iron typically enhances OER activity through synergistic electronic effects that modify nickel active sites and improve charge transfer. These materials can exist as layered double hydroxides, amorphous oxides, or converted oxide/hydroxide phases, with performance strongly influenced by composition, oxidation state, particle size, and the nature of the support.

Synthesis methods are diverse and include electrodeposition, co-precipitation, solvothermal or hydrothermal routes, and thermal or electrochemical oxidation. Activation procedures often involve applying oxidizing potentials to form the active NiFeOOH phase. Tuning the Ni:Fe ratio and synthesis conditions allows optimization of activity, stability, and conductivity for a given electrode configuration.

Applications of NiFeOx span renewable energy technologies, notably alkaline water electrolysis for hydrogen production. They are also explored in energy storage devices, such as supercapacitors and rechargeable metal-air batteries, where their pseudocapacitive and catalytic properties can be advantageous. Ongoing research focuses on understanding the mechanisms of synergistic activity and improving durability under harsh operating conditions.