Activating the oxygen electrocatalytic activity of layer-structured Ca0.5CoO2 nanofibers by iron doping

Abstract

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−xFe_xO₂ (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 (O₂²⁻/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.