A transition metal oxofluoride offering advantages in electrocatalysis and potential use in applications

Abstract

The recently described solid solution (Co,Ni,Mn)₃Sb₄O₆F₆ has proved stable and efficient as a catalyst for electrocatalytic water oxidation. The end component Co₃Sb₄O₆F₆ was found to be most efficient, maintaining a current density of j = 10 mA cm⁻² at an overpotential of 443 mV with good capability. At this current density, O₂ and H₂ were produced in the ratio 1 : 2 without loss of faradaic current against a Pt-cathode. A morphological change in the crystallite surface was observed after 0.5 h, however, even after 64.5 h, the overall shape and size of the small crystallites were unaffected and the electrolyte contained only 0.02 at% Co. It was also possible to conclude from in situ EXAFS measurements that the coordination around Co did not change. The oxofluorides express both hydrophilic and hydrophobic surface sites, incorporate a flexible metalloid element and offer the possibility of a mechanism that differs from other inorganic catalytic pathways previously described.