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Encapsulating cobalt phthalocyanine (CoPc) within the coordinating polymer poly-4-vinylpyridine (P4VP) results in a catalyst–polymer composite (CoPc–P4VP) that selectively reduces CO 2 to CO at fast rates at low overpotential. In previous studies, we postulated that the enhanced selectively for CO over H 2 production within CoPc–P4VP compared to the parent CoPc complex is due to a combination of primary, secondary, and outer-coordination sphere effects imbued by the encapsulating polymer. In this work, we perform in situ electrochemical X-ray absorption spectroscopy measurements to study the oxidation state and coordination environment of Co as a function of applied potential for CoPc, CoPc–P4VP, and CoPc with an axially-coordinated py, CoPc(py). Using in situ X-ray absorption near edge structure (XANES) we provide experimental support for our previous hypothesis that Co changes from a 4-coordinate square-planar geometry in CoPc to a mostly 5-coordinate species in CoPc(py) and CoPc–P4VP. The coordination environment of CoPc–P4VP is potential-independent but pH-dependent, suggesting that the axial coordination of pyridyl groups in P4VP to CoPc is modulated by the protonation of the polymer. Finally, we show that at low potential the oxidation state of Co in the 4-coordinate CoPc is different from that in the 5-coordinate CoPc(py), suggesting that the primary coordination sphere modulates the site of reduction (metal-centered vs. ligand centered) under catalytically-relevant conditions.
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Mitigating Cobalt Phthalocyanine Aggregation in Electrocatalyst Films through Codeposition with an Axially Coordinating Polymer
Abstract Cobalt phthalocyanine (CoPc) is a promising molecular catalyst for aqueous electroreduction of CO2, but its catalytic activity is limited by aggregation at high loadings. Codeposition of CoPc onto electrode surfaces with the coordinating polymer poly(4‐vinylpyridine) (P4VP) mitigates aggregation in addition to providing other catalytic enhancements. Transmission and diffuse reflectance UV–vis measurements demonstrate that a combination of axial coordination and π‐stacking effects from pyridyl moieties in P4VP serve to disperse cobalt phthalocyanine in deposition solutions and help prevent reaggregation in deposited films. Polymers lacking axial coordination, such as Nafion, are significantly less effective at cobalt phthalocyanine dispersion in both the deposition solution and in the deposited films. SEM images corroborate these findings through particle counts and morphological analysis. Electrochemical measurements show that CoPc codeposited with P4VPonto carbon electrode surfaces reduces CO2with higher activity and selectivity compared to the catalyst codeposited with Nafion.
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- Award ID(s):
- 1751791
- PAR ID:
- 10630200
- Publisher / Repository:
- John Wiley & Sons, Inc.
- Date Published:
- Journal Name:
- Small
- Volume:
- 21
- Issue:
- 7
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/smll.202402293
