FeM/rGO (M = Ni and Cu) as bifunctional oxygen electrode

Three different iron-based electrocatalysts deposited on reduced graphene oxide (Fe/rGO, FeNi/rGO, and FeCu/rGO) were synthesized and examined for oxygen reduction and evolution reactions (ORR and OER, respectively) in alkaline media. X-ray powder diffraction analysis, Fourier transform infrared spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy were used for a thorough investigation of physico-chemical properties of FeM/rGO electrocatalysts. XPS analysis indicated the presence of transition metals in higher oxidation states. Onset potentials during OER were found to be 1.51, 1.64, and 1.71 V for FeNi/rGO, FeCu/rGO, and Fe/rGO, respectively. Moreover, FeNi/rGO showed the highest OER current density (∼40 mA cm−2 at 2 V), two times higher than the benchmark OER electrocatalyst, IrO2, and the lowest Tafel slope (88 mV dec-1), lower than IrO2. The somewhat better catalytic activity of Fe/rGO for ORR in alkaline media compared to FeNi/rGO and FeCu/rGO was noticed. Tafel slopes of 105, 112, and 113 mV dec-1 during ORR were found for Fe/rGO, FeCu/rGO, and FeNi/rGO, respectively. Almost constant ORR current densities during chronoamperometric measurements were noticed for Fe/rGO and FeCu/rGO indicating stable performance.