THE SYNTHESIS AND MODIFICATION OF 2D MATERIALS FOR APPLICATION IN WATER OXIDATION CATALYSIS

Abstract

The unifying goal of this work is the design of a heterogeneous catalyst that can facilitate the energy intensive oxygen evolution reaction (OER) in water splitting, considered one of the ‘holy grails’ in catalytic science. In order for this process to be industrially feasible, an efficient catalyst composed of first row transition metal based materials must be used. To accomplish this, existing systems must be studied in order to determine which properties are important and subsequent creation and modification of new systems based on lessons learned must be employed. Birnessite, a 2D layered manganese dioxide, comprises the majority of the effort. In the studies leading to this work, this material was primarily studied by mineralogists with the majority focusing on structural characterization. However, the material’s moderate activity toward performing the OER has revived interest. In this work, we look to determine important species, the role dopants play in activity, and the function of the interlayer and surface chemistry. From these findings, an enhanced, earth abundant OER catalyst will be designed. We determine that Mn3+ in the system plays and important role in producing a catalytic species with large oxygen production capabilities. By increasing the amount of Mn3+ in the system via a simple comproportionation reaction by exposing the Mn4+ to Mn2+ ion, we increase the total turnover of birnessite 50-fold. Additionally, the addition of dopants to the system , both within and between the sheets, has a positive effect on the activity of birnessite. In particular, incorporation of cobalt into the lattice of birnessite brings the activity level on par to that of precious metal oxide catalysts due to the cobalt offering a deeper electron acceptor than in birnessite alone. In conjunction with these studies, the role of the interlayer species and catalyst confinement has demonstrated the ability to greatly enhance a catalyst’s ability to perform the OER by ordering and orienting the water around the active confined catalyst. Combining confinement effects with the cobalt-doped birnessite sheets resulted in further enhancement in the material’s OER capabilities. This system mimics that of an enzyme where the cobalt-doped birnessite sheets facilitate greater electron-hole transfer to the interlayer active site, where the confinement effects enhance electron transfer kinetics and water organization for O-O bond formation. Additionally, metal chalcogenide OER catalysts were explored with mattagamite phase cobalt pertelluride. Through the work, we determine the formation of a Te-Co-O heterostructure as the catalytically active phase, where the metallic nature of the cobalt pertelluride facilitates charge mobility between the electrode and catalyst’s cobalt oxide surface functioning as the active OER species.