Understanding Active Sites in (photo)-Electrocatalysis of Two-Dimensional Metal Organic Frameworks via Raman Spectroelectrochemistry

Anna Maria Dominic

AutorIn

Anna Maria Dominic

Titel

Understanding Active Sites in (photo)-Electrocatalysis of Two-Dimensional Metal Organic Frameworks via Raman Spectroelectrochemistry

Zitierfähige Url:

https://nbn-resolving.org/urn:nbn:de:bsz:14-qucosa2-913594

Erstveröffentlichung

2024

Datum der Einreichung

14.12.2023

Datum der Verteidigung

16.04.2024

Abstract (EN)

In electrocatalysis, two-dimensional conjugated metal-organic frameworks (2D c-MOFs) are increasingly recognized as potential candidates for sustainable energy conversion, offering customizable active sites and electronic properties. This thesis presents a comprehensive investigation into the (photo)electrocatalytic active sites and mechanisms of 2D c-MOFs, with a particular focus on the interplay between their metal and organic components. Employing in situ Raman spectroscopy and electrochemical analyses, it was determined that within the copper-phthalocyanine-based MOF (CuPc-CuO4), the CuO4 nodes serve as the primary active sites for the Oxygen Reduction Reaction (ORR) below -0.2 V. Distinct redox potentials of -0.04 V for CuPc and +0.33 V for CuO4 versus Ag|AgCl were observed, further enhanced by Nickel-Nitrilotriacetic Acid (Ni-NTA) functionalization on the electrodes. Rotating Disk Electrode (RDE) testing revealed that CuPc-CuO4 MOFs exhibit an electron transfer number of 3.6 for ORR. The electrocatalytic activity was most favorable when both the phthalocyanine copper and the copper in the CuO4 linkage were in the +1 oxidation state (CuI/CuI), with the Cu in CuO4 primarily responsible for oxygen reduction. This state's effectiveness is attributed to a decrease in bandgap and an increase in π-conjugation, supported by Density Function Theory (DFT) calculations, which suggest that electron transfer rates in the mixed-valence state are critical for catalysis. Substitution of Cu with other metals (Zinc, Cobalt, Manganese, and Nickel) in CuPc-MO4 MOFs shifted the onset potentials and electron transfer number for ORR, as tested with RDE, underscoring the significant role of metal-oxygen linkages in the process. Remarkably, CuPc-CoO4 substitution exhibited lowest overpotential and highest electron transfer number for ORR, highlighting its potential for enhancing electrocatalytic processes. Additionally, this study explores a novel sp-carbon incorporated MOF with CuO4 linkages, Cu3HHAE2, demonstrating photocatalytic activity for Hydrogen Evolution Reaction (HER). This activity is primarily attributed to the acetylene units within the framework, evidenced by a shift in the C≡C band from 2116 to 2044 cm-1. However, the presence of CuO4 linkages is essential, indicating a synergistic effect crucial for enhanced catalytic performance. This research highlights the dependence of electrocatalytic activity on the structural configuration of the MOF, revealing that while certain components may act as primary active sites, other elements of the MOF structure play an indispensable role in facilitating overall catalysis.

Verweis

Link: https://pubs.acs.org/doi/10.1021/acs.jpcc.2c08819
Oxidation State Dependent Conjugation Controls Electrocatalytic Activity in a Two-Dimensional Di-Copper Metal–Organic Framework
DOI: https://doi.org/10.1021/acs.jpcc.2c08819

Freie Schlagwörter (EN)