Tailoring Morphology and Electronic Structure of Cobalt Iron Oxide Nanowires for Electrochemical Oxygen Evolution Reaction

The influence of iron on nanocasting of cobalt oxide nanowires and the performance of these materials for the oxygen evolution reaction (OER) are investigated. Pristine Co3O4 and mixed cobalt iron oxide nanowires with a diameter of 7 nm have been synthesized via a nanocasting route by using SBA-1S silica as a template. A small amount of iron added during the synthesis results in a decrease in the nanowires' array length and induces the formation of a bimodal pore size distribution. Raman spectroscopy, X-ray emission, and high-energy resolution X-ray absorption spectroscopies further show that Fe incorporation alters the electronic structure by increasing the average distortion around the cobalt centers and the amount of Co2+ in tetrahedral sites. These affect the OER activity significantly; the overpotential of pristine Co3O4 at 10 mA/cm(2) decreases from 398 to 378 mV, and the current density at 1.7 V increases from 107 to 150 mA/cm(2) with the addition of iron at the Co/Fe atomic ratio of 32. Furthermore, post-reaction characterization confirmed that both the morphology and electronic structure of nanowires remain intact after a long-term stability test.