FeCo nanoparticles with different compositions as electrocatalysts for oxygen evolution reaction in alkaline solution

[Display omitted] •Core and surface composition is easily tuned via Co–Fe molar concentration ratio.•Intrinsic activity is enhanced by improved conductivity and Fe doping into CoOOH.•Fe59Co41 (S4) shows overpotential of 285 mV at 10 mA/cm2 current density in 1 M KOH.•S4 shows long-term stability during oxygen evolution reaction for 24 h. FeCo nanoparticles with different surface-layer compositions were synthesized using the polyol method. The compositional difference between the surface layer and the core arises from the dissimilarity in the reduction potentials of Fe and Co at the synthesis temperature. The FeCo nanoparticles consisted of an Fe-rich FeCo alloy core and a Co-rich FeCo oxide layer. The size of the FeCo nanoparticles was approximately 207 nm, and Fe59Co41 (S4) showed optimal intrinsic catalytic activity for an oxygen evolution reaction. The overpotential of S4 was 285 mV at 10 mA/cm2 in 1 M KOH solution, which is much lower than that of the other samples. In addition, after chronopotentiometry at 10 mA/cm2 for 24 h in 1 M KOH, the overpotential at 10 mA/cm2 increased from 285 to 294 mV. The enhancement of the catalyst properties was attributed not only to the synergetic effect of the metal core and oxide layer, but also to the optimal iron doping effect.