Catalytic Water Oxidation Reaction at Nanostructured Titania Modified with Carbonized Metal Organic Framework

Abstract

Solar energy can be used for direct water splitting to produce hydrogen through a photoelectrochemical (PEC) reaction at semiconducting electrodes. Thus, the overall efficiency of the PEC system is dependent on electrocatalytic or photoelectrocatalytic electrode materials for efficient light absorption, charge separation and transport, in proton reduction and water oxidation half reactions. Herein, a new hybrid catalytic electrode comprised of NH2-MIL-125, a titanium-based metal organic framework (MOF), derived nanostructured Titania electrode material. XRD, SEM and EDX characterizations suggest that nanostructured Titania-MOF electrode is comprised of an underlying layer of TiO2nanorods and the upper layer of distributed clusters of MOF derived disk-shaped nanoparticles (NPs) with an island morphology. The NH2-MIL-125 NPs are formed through a colloid seed-assisted solvothermal reaction and afterwards carbonized while clustering during a pyrolysis process. The resulting nanostructure proved to be composed of C, O, N, and Ti elements. The Titania was employed as the anode substrate of the MOF NPs because it exhibits significantly improved activity for water oxidation and this reaction is greatly enhanced upon coating with carbonized MOF structure. The surface interrogation mode of scanning electrochemical microscopy (SI-SECM) is applied in this study to investigate reactive surface states (RSSs) on the nanostructured electrodes, owing to its selectivity to surface species, capability to in situ quantify for both surface coverage and reactivity of adsorbed RSSs, and usefulness to obtain spatially and temporally-resolved information.