Activity of carbon-encapsulated Ni_12−xFe_xP₅ catalysts for the oxygen evolution reaction: Combination of high activity and stability

Rational design of efficient, earth-abundant, and durable electrocatalysts to accelerate the oxygen evolution reaction (OER) is critical for hydrogen ion by water electrolysis. In the present work, nanostructured Ni_12−xFe_xP₅ (x = 1.2, 2.4, 3.6) OER electrocatalysts synthesized by a colloidal method is reported. For x = 1.2, an alloy of Ni, Fe, and P is formed. For x = 2.4 or x = 3.6, a core-shell NiFeP@Fe₃O₄ structure is formed. The nanoparticles are encapsulated in a self-generated carbon layer. The carbon layer is formed during synthesis from synthesis residues. The carbon-encapsulated Ni_9.6Fe_2.4P₅ catalyst offers the outstanding mass activity of 0.1 A mg⁻¹ and overpotential of 220 mV at 10 mA cm⁻², assigned to a combination of enhanced electrical conductivity provided by the carbon shell, a large surface area, and a high specific catalytic activity. Post-mortem characterization indicates that the carbon encapsulation remains intact under conditions of the OER.