Block copolymer templated extended surface precious metal nanostructures as model electrocatalysts
Restricted (Penn State Only)
- Author:
- Bhattacharya, Deepra
- Graduate Program:
- Chemical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 17, 2023
- Committee Members:
- Robert Hickey, Outside Unit & Field Member
Enrique Gomez, Major Field Member
Seong Kim, Major Field Member
Christopher Arges, Chair & Dissertation Advisor
Seong Kim, Professor in Charge/Director of Graduate Studies - Keywords:
- Block copolymers
Nanofabrication
Lithography
Oxygen Reduction
Hydrogen Evolution
Electrocatalysis
Electrochemistry - Abstract:
- The development and commercialization of efficient electrochemical energy conversion devices such as electrolyzers and fuel cells is crucial to the realization of a carbon-neutral economy based on hydrogen. Electrochemical reactions underlying the operation of such devices are catalytic in nature, and because they operate under extreme electric potentials and pH, the choice of catalyst materials is limited to highly stable elements platinum and other platinum group metals (PGMs). The cost and scarcity of PGMs is, hence, a major bottleneck to the economic proliferation of fuel cells and electrolyzers. Electrocatalytic reaction systems, being constrained by the concurrence of electron and ion transport phases in addition to chemical species transport at the catalyst surface, are highly dependent on spatial synergy between an electrocatalyst material and its surroundings, and to this end, considerable research has been performed in the past decade on the nanostructuring and morphology control of electrocatalyst layers. However, the lack of suitable modes of fabrication that allow for the control of electrocatalyst nanostructure over experimentally relevant length scales (several millimeters) has limited systematic analyses of the dependence of electrocatalyst feature sizes and morphologies on their performance. This dissertation reports the development and subsequent testing of nanostructured PGM electrocatalysts of tunable feature size and morphology that can be fabricated with few or no defects over experimentally significant areas. The nanostructures, templated from the self-assembly of block copolymers, have been developed via liquid- and gas- phase fabrication pathways, as both free-standing and supported moieties of lamellar and cylindrical morphologies with features ranging from 11 nm – 35 nm. A combination of electron microscopy, atomic force microscopy, X-ray scattering, diffraction, and photoelectron spectroscopy have been used to obtain near-perfect pattern transfer of the block copolymer nanopatterns onto Platinum and Iridium oxide nanostructures on Si wafer and Glassy Carbon substrates. Testing for electrocatalytic performance for hydrogen evolution/oxidation and oxygen reduction has been carried out on interdigitated microelectrode arrays as two-point measurements as well as on a conventional three-electrode setup in 0.1 M perchloric acid with ultra-low PGM loadings (~5.8 µgPt cm-2). Catalyst performance probed as a function of nanoscale feature size and morphology reveals an inverse correlation between particle size and electroactivity, as well as the superiority of cylindrical morphologies over lamellae. Moreover, the results demonstrate electrocatalyst performance that rivals commercial platinum electrocatalysts in terms of mass activity (380 mA mgPt-1 at 0.9 V vs RHE), whilst surpassing commercial catalysts in terms of stability (mass activity loss: 11.45% at after 20,000 potential cycles). Overall, the dissertation presents BCP templating as a fabrication pathway towards stable, tunable nanostructured geometries for probing electrocatalyst functional response on model surfaces.