Date of Award

2022-12-01

Degree Name

Doctor of Philosophy

Department

Chemistry

Advisor(s)

Dino D. Villagran

Abstract

Hydrogen fuel generation through electrochemical water splitting is considered as an advanced energy conversion technology driven by sustainable energy. High activity and cost effective electrocatalysts that are able to drive down the energy cost needed for both two half reactions, namely, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are required to fulfill the energy transfer process. Exploring new electrocatalysts with enhanced OER and HER activity and stability is crucial for renewable energy applications. Porphyrin and macrocycle derivatives are versatile and can electrochemically catalyze water splitting efficiently. In our work, we use porphyrin as platform for both HER and OER catalysis. As a homogeneous electrocatalyst, free base porphyrins are able to afford up to two electrons redox transfer. In addition, the four-nitrogen cavity inside the porphyrin provides two protonation sites, this makes it feasible for facilitating HER. Rational design: the substituent group with -Br, -F, F2 and F3 on the meso-position results in regulatable hydrogen production under different mechanisms. We also developed a heterogenized porphyrin framework with Kevlar structure, which results in efficient and sturdy bifunctional electrocatalysis that can operate in both neutral and pH dependent solutions are comparable with most of the metal-based materials. The catalytic activity can hold for 60 hours under all the electrolysis conditions. We found that when porphyrins are metalated with first-row transition metals, i.e., Co and Fe, with linkers that have different electron negativity, they show different performance towards OER. On the other hand, intercalated porphyrin into electrochemically inert layered structure material can prevent catalyst degradation and serve for water oxidation. Beside these, we were also working on high surface area Ni based MoS2 that is synthesized with pre-treated amine and carbon for water splitting electrocatalysis. As for catalyzing HER, pre-treatment with carbon nanotubes during the synthesis can largely enhance the exposure of MoS2 HER active basal plane; when using as OER catalyst, the DETA pre-treated NiMoS2 has the best performance. All these works provide insight into the rational electrocatalyst design for eco-friendly fuel generation and more importantly, for the practical large-scale industrial production in an environmentally benign and cost-effective way.

Language

en

Provenance

Received from ProQuest

File Size

96 p.

File Format

application/pdf

Rights Holder

Yulu Ge

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Chemistry Commons

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