Hybridization of Fe-O in iron doped hydroxyapatite for superior electrochemical charge storage

Hydroxyapatite (HAp) is an interesting phosphate candidate with a weak electrical conductivity that can be tuned by doping metal ions to enhance the active sites for electrochemical charge storage. HAp and Fe-doped HAp were prepared by a wet chemical method. On doping, the crystallite size reduces to 9.56 nm. The surface area of 0.01FH (0.01% Fe) is 152.17 m(2)/g which is similar to 3 times higher compared to PH. The 0.01FH sample shows the highest specific capacitance of 351.3 F/g at 30 mA/g. While X-ray photoemission spectroscopy shows the oxidation states of Fe in 2(+) and 3(+), X-ray absorption indicates (i) the enhancement of unoccupied density of states of Fe, and (ii) reduced interatomic distance of Fe-O in 0.01FH. These results show that the augmentation of surface properties and hybridization of Fe-O and the modification of its local atomic structures are responsible for high electrochemical charge storage in 0.01FH.

Automated summary

By doping metal ions, the weak electrical conductivity of hydroxyapatite (HAp) can be enhanced to improve its electrochemical charge storage. HAp and Fe-doped HAp were synthesized using a wet chemical method, resulting in a reduction in crystallite size to 9.56 nm. The 0.01FH sample, with a specific capacitance of 351.3 F/g at 30 mA/g, exhibited the highest performance. X-ray photoemission spectroscopy revealed Fe oxidation states of 2+ and 3+, while X-ray absorption indicated enhanced unoccupied density of states and reduced Fe-O interatomic distance in 0.01FH. These findings suggest that surface properties, Fe-O hybridization, and modifications in local atomic structures contribute to the high electrochemical charge storage in 0.01FH.