Study On Low-temperature Fabrication And Electrocatalytic Properties Of Composite Anodes Integrating Cobalt-based Compounds For Water Oxidation

Energy harvesting and storage through means of efficient hydrogen utilization either via traditional water electrolyzer or photoelectrochemical water splitting based on semiconductors is an essential route for future renewable energy landscape. One of the two half reactions that constitute the dissociation of water, namely oxygen evolution reaction(OER) has long been identified as the critical step responsible for major system energy loss, and thus poses great limitation of the scalable hydrogen production and solar fuel development. The OER is a demanding thermodynamic uphill reaction, in that two water molecules need to be simultaneously oxidized and form a weak O-O bond, the driving bias of which normally far exceeds its theoretical potential. Electrocatalysts that bear prospects in massive application need to demonstrate efficacy in mediating such multielectron reactions, reasonable selectivity, corrosion resistance and durability for long-time operation in strongly oxidizing aqueous conditions.This thesis focuses on extending the present library of first-row transitional metal-based electrocatalysts and photo-electrocatalysts. We endeavored to demonstrate that cobalt hydroxide derivatives are effective OER catalysts due to structural similarities with those of electrodeposited amorphous Co-Pi and cobaltates probed during electrocatalytic turnovers. We successfully fabricated hexagonal layered double hydroxide sheets containing cobalt and explored their OER catalytic performance in near-neutral buffer solutions, and the OER catalysis mechanism was discussed regarding their crystal structures.Using low-temperature hydrothermal synthesis, we were able to obtain morphologically intriguing hierarchical-structured cobalt hydroxide carbonate microclusters. The interplay of different precursors and product morphology was systemically investigated. We also probed and elucidated the growth mechanism of the products by interrupting the course of complete reaction. Further we integrated strongly electronegative Au nanoparticles onto cobalt hydroxide matrix by forming a binary entity with a self-assembled wreath-like structure. Au incorporation massively enhanced the roughness factor and a much improved OER catalytic performance was found.In addition to singular electrocatalytic properties, we managed to have fabricated visible-light sensitive composite electrode by gluing a novel family of amorphous cobalt phosphate obtained from a precipitation m ethod under the coordination protection of ammonia with proton conductor Naf ion onto FTO substrates. The amorphous KCPO materials exhibit optimal energy alignment with appropriate band structures for photoelectrochemical water oxidation.This dissertation represents an experimental study on the synthesis, growth mechanism, functionality and structure-property relationship of cobalt-based hydroxides and the application possibility as OER catalysts. Our work lies at the heart of future hydrogen energy utilization and provides instructive reference for future water oxidation catalysis development based on earth-abundant elements.