PATEL, PRASAD
(2018)
Fundamental Study of 1-D Semiconductor and Nanoscale Electrode Architectures for Photo-Electrochemical Water Splitting.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Photoelectrochemical (PEC) water splitting is a promising technology for the production of clean hydrogen, long identified as a potential energy carrier for the much awaited hydrogen economy. Clean hydrogen is indeed capable of meeting the global energy demand placing minimal stress on the environment compared to hitherto combustion based technologies. Generation of clean hydrogen however, represents major challenges. Identification and development of suitable semiconductor materials as photoanodes exhibiting narrow band gap and superior solar-to-hydrogen efficiency (STH) combined with the desired PEC stability would represent a major breakthrough in the arduous path towards identifying and economically manufacturing commercially viable PEC water splitting systems. In addition to the photoanode, engineering of novel non-noble based cathode electro-catalysts with superior electrochemical activity for hydrogen evolution reaction (HER) compared to expensive state of the art noble metal electro-catalyst (e.g. Pt) will significantly contribute towards further lowering the cost of PEC water splitting cells.
Keeping in line with these goals, a co-doping strategy was adopted in this study for generating photoanodes with systematic band gap engineering. Accordingly, the co-doping strategy was implemented to modify the band gaps of ZnO and SnO2, which exhibit good electron mobility but possess wide band gaps yielding poor PEC activity. It was demonstrated that by synergistically co-doping Co and N into the ZnO lattice, and Nb and N co-doping into SnO2 crystalline structure resulted in significantly improved light absorption properties offering 4-5 orders of magnitude higher carrier density contributing to remarkably higher PEC activity with the highest applied bias photon-to-current efficiency (ABPE) (~4.1%) obtained for (Sn0.95Nb0.05)O2:N-600 nanotubes (NTs). The optoelectronic and PEC properties of (Sn0.95Nb0.05)O2:N-600 NTs are further improved by developing novel 1-D bilayer structures of WO3 and (Sn0.95Nb0.05)O2:N-600. The novel bilayer composite heterostructures offered improved light absorption, high carrier density and efficient separation of photogenerated carriers leading to long carrier lifetimes. As a result, superior PEC activity and STH (~3.83%) under zero applied bias was achieved, which is the highest STH obtained so far compared to other well-studied materials such as TiO2, ZnO, -Fe2O3, to the best of our knowledge. The composite bilayer structure also showed superior PEC stability in electrolyte solution under illumination.
Furthermore, ultra-low noble metal containing non-noble metals based Co1-x(Irx) (x=0.3, 0.4) and completely noble metal free (Cu0.83Co0.17)3P:x at. %S (x=10, 20, 30) solid solution electro-catalyst systems have been studied as cathode electro-catalyst for HER. The synergistic interaction of Co and Ir as well as Cu, Co, P and S offered excellent electrochemical properties. Accordingly, Co1-x(Irx) (x=0.3, 0.4) displayed ~40% and ~93% improved electrocatalytic response compared to Pt/C. On the other hand, (Cu0.83Co0.17)3P:30 at. %S showed HER response similar to that of Pt/C. These results together indeed reflect the significant advances made in the pursuit of non-noble metal electro-catalyst for HER replacing Pt/C, the expensive albeit, the prevalent gold standard HER electrocatalyst.
This thesis provides a detailed account of the fundamental study conducted into the synthesis, materials, characterization, photoelectrochemical and electrochemical response ably supported by first principles theoretical studies as required.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
20 June 2018 |
| Date Type: |
Publication |
| Defense Date: |
3 January 2018 |
| Approval Date: |
20 June 2018 |
| Submission Date: |
27 December 2017 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
331 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Chemical and Petroleum Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Photoelectrochemical water splitting, nanowires, hydrothermal, cobalt doping, doped zinc oxide, nitrogen doping, Hydrogen evolution reaction, Copper phosphide, Phosphosulfide, Sulfur doping, Iridium, Cobalt, Nanostructured solid solution |
| Date Deposited: |
20 Jun 2018 18:20 |
| Last Modified: |
20 Jun 2018 18:20 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/33723 |
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