Activity of carbon-encapsulated Ni12−Fe P5 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 Ni12−xFexP5 (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 Ni9.6Fe2.4P5 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.