Sol-flame synthesis of cobalt-doped TiO2 nanowires with enhanced electrocatalytic activity for oxygen evolution reaction

Abstract

Doping nanowires (NWs) is of crucial importance for a range of applications due to the unique properties arising from both impurities' incorporation and nanoscale dimensions. However, existing doping methods face the challenge of simultaneous control over the morphology, crystallinity, dopant distribution and concentration at the nanometer scale. Here, we present a controllable and reliable method, which combines versatile solution phase chemistry and rapid flame annealing process (sol-flame), to dope TiO₂ NWs with cobalt (Co). The sol-flame doping method not only preserves the morphology and crystallinity of the TiO₂ NWs, but also allows fine control over the Co dopant profile by varying the concentration of Co precursor solution. Characterizations of the TiO₂:Co NWs show that Co dopants exhibit 2+ oxidation state and substitutionally occupy Ti sites in the TiO₂ lattice. The Co dopant concentration significantly affects the oxygen evolution reaction (OER) activity of TiO₂:Co NWs, and the TiO₂:Co NWs with 12 at% of Co on the surface show the highest OER activity with a 0.76 V reduction of the overpotential with respect to undoped TiO₂ NWs. This enhancement of OER activity for TiO₂:Co NWs is attributed to both improved surface charge transfer kinetics and increased bulk conductivity.