Joseph Yoo – Cobalt Dithiolene-like Metal Organic Surfaces for Efficient Hydrogen Evolution

Project Summary: This project focuses on developing catalysts that make the evolution of hydrogen efficient in order to counteract the storage issue with solar energy. We focus on a previously reported cobalt dithiolene catalysts and incorporate it into metal-organic surfaces which can be deposited onto a variety of supports.

Main Issue: Our hypothesis was that film surfaces that are modeled under previously reported catalysts for hydrogen evolution, namely Eisenberg's molecular catalyst for cobalt, would retain much of its catalytic properties while becoming much more stable and robust. Our goals are to create two-dimensional and one-dimensional films which would incorporate this Eisneberg motif and test the films made from various ligands for their potential to reduce water and potential for further modifications.

Learning Outcomes: I learned about having a repertoire of information and known syntheses that I had done, and applying that knowledge in order to predict outcomes on novel experiments. Furthermore I am more thoroughly able to understand how the development of an idea works, being grounded on previously done work and further testing the limits of the information that is currently known to see the boundaries of that knowledge

Student Contribution: I mainly focused on optimizing the synthetic conditions and methods for the ligand and its precursors, as well as isolating crystals of intermediates. Basic electrochemical studies were also done and film growth optimization was also performed and I helped develop the primary method for bulk film synthesis. Currently my individual project is developing more novel ligands which will mimic the Eisenberg molecular catalyst and eventually synthesize and analyze my own films.

Abstract: Cobalt dithiolene species, among the most efficient catalysts for hydrogen evolution reactions, were synthesized into metal- organic surfaces using trinucleating conjugated ligands. Benzenehexathiol and triphenylenehexathiol were reacted with cobalt (II) at a liquid-liquid interphase in order to produce a stable film, which upon analysis via powder x-ray diffraction (PXRD) and x-ray photoelectron spectroscopy (XPS), supported the presence of cobalt bisdithiolene complexes.
Electrochemical studies, via cyclic voltammograms, showed a separation of oxidation and reductive peaks, which is indicative of surface level redox reactions. This current steadily increased as the pH of the solution was lowered, and was confirmed to be solely from the film by repeating the experiments on bare electrodes and obtaining negligible current. These complexes do not tend to decompose to form active heterogeneous materials as experiments in pH 1.3 solutions of H2SO4 and 0.1 M KNO3 did not lead to significant current after being rinsed and transferred to a clean solution.
The current development is to synthesize one-dimensional metal-organic wires, which would be done via dinucleating conjugated ligands such as 1,4 diamino 2,3,5,6 tetrathiol phenylene and 4,5,9,10 tetrathiol pyrene. These species are desirable to study for the open positions that may be further modified to alter ligand environments, allowing for the optimization of overpotential and the possibility of functionalization to align wires via a condensation reaction, or possibly add a photosensitizer to directly couple photocatalysis.

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