Activating the oxygen electrocatalytic activity of layer-structured Ca_0.5CoO₂ nanofibers by iron doping

The development of low-cost, highly efficient and stable electrocatalysts for the oxygen evolution reaction (OER) is of great significance for many promising energy storage and conversion applications, including metal-air batteries and water splitting technology. Here we report a layer-structured Ca_0.5CoO₂ nanofibers composed of interconnected ultrathin nanoplates, synthesized using an electrospinning process. The OER activity of Ca_0.5CoO₂ can be dramatically improved by iron doping, and the overpotential of Ca_0.5Co_1-FeO₂ (x = 0.25) is only 346 mV at a current density of 10 mA cm^-2. The mass activity and intrinsic activity of Ca_0.5Co_0.75Fe_0.25O₂ at 1.6 V are, respectively, ∼18.7 and ∼11.4 times higher than those of Ca_0.5CoO₂. Iron doping modifies the electronic structure of Ca_0.5CoO₂, resulting in partial oxidation of the surface cobalt and increased amount of highly oxidative species (O₂^2-/O₂). Consequently, Ca_0.5Co_0.75Fe_0.25O₂ nanofibers with tuned electronic states have shown great potential as cost-effective and efficient electrocatalysts for OER.