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Author ORCID Identifier

https://orcid.org/0000-0001-9869-7624

AccessType

Open Access Dissertation

Document Type

dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemical Engineering

Year Degree Awarded

2022

Month Degree Awarded

February

First Advisor

Ashwin Ramasubramaniam

Subject Categories

Catalysis and Reaction Engineering | Chemical Engineering | Nanoscience and Nanotechnology | Thermodynamics

Abstract

The electrochemical hydrogen evolution reaction (HER) and nitrogen reduction reaction (NRR) offer fossil-fuel-free routes for hydrogen and ammonia synthesis, respectively. However, currently, both processes lack suitable electrocatalysts for practical applications. Thus, this dissertation focuses on the computational rational design of HER and NRR electrocatalysts.

HER is most efficiently catalyzed by platinum (Pt), which is expensive. To reduce the catalyst cost, we investigate core-shell nanoparticles of inexpensive tungsten-carbide (WC) and Pt (WC@Pt). Using first-principles density functional theory (DFT) calculations, we compare the suitability of two WC phases, α-WC and β-WC as support materials for Pt overlayers. We dope WC with titanium and examine its effects on the thermodynamic stability and HER activity of WC and WC@Pt nanoparticles. We show that β-WC is more suited than α-WC for stabilizing Pt overlayers, and that moderate titanium doping of WC is an effective approach to stabilize β-WC and β-WC@Pt nanoparticles.

Thereafter, we investigate molybdenum diselenide (MoSe2) for HER. The catalytic activity of MoSe2 is limited because most of its electrochemical surface area—the basal plane—is inert towards HER. To activate the basal plane, we examine the effect of doping MoSe2 with electron-rich transition metals (Mn, Fe, Co, and Ni). Our DFT studies show that all selected dopants improve HER thermodynamics on the basal plane. We also find that all selected transition-metal dopants promote the formation of HER active Se-vacancy sites in MoSe2. Overall, our studies show that transition-metal-doping of MoSe2 is an effective strategy to activate MoSe2 for HER.

Finally, we investigate molybdenum disulfide (MoS2) for NRR. To overcome its low NRR activity and selectivity, we dope MoS2 with iron. With DFT calculations, we show that the formation of iron-doped edges is energetically preferred over undoped edges of MoS2. We show that catalytically active sulfur vacancies are more readily formed at iron-doped edges than at undoped edges of MoS2. We show that such defect-rich iron-doped edges can catalyze NRR at moderate cathodic potentials and we propose a new mechanism for NRR at these sites. Our studies show that iron-doping of MoS2 is a potentially viable strategy for producing inexpensive, active, and selective NRR electrocatalysts.

DOI

https://doi.org/10.7275/25104743

Creative Commons License

Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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