Activating the oxygen electrocatalytic activity of layer-structured Ca 0.5 CoO 2 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 0.5 CoO 2 nanofibers composed of interconnected ultrathin nanoplates, synthesized using an electrospinning process. The OER activity of Ca 0.5 CoO 2 can be dramatically improved by iron doping, and the overpotential of Ca 0.5 Co 1- x Fe x O 2 ( x = 0.25) is only 346 mV at a current density of 10 mA cm -2 . The mass activity and intrinsic activity of Ca 0.5 Co 0.75 Fe 0.25 O 2 at 1.6 V are, respectively, ∼18.7 and ∼11.4 times higher than those of Ca 0.5 CoO 2 . Iron doping modifies the electronic structure of Ca 0.5 CoO 2 , resulting in partial oxidation of the surface cobalt and increased amount of highly oxidative species (O 2 2- /O 2 ). Consequently, Ca 0.5 Co 0.75 Fe 0.25 O 2 nanofibers with tuned electronic states have shown great potential as cost-effective and efficient electrocatalysts for OER.