Cobalt(III) complexes of pentadentate N5-donor ligands as precursors for proton reduction electrocatalysts

Abstract

Three new cobalt complexes of the general formula [CoIII(L)Cl]2+, where L is one of five pentadentate nitrogen-donor ligands based on the N4Py framework, have been synthesized and characterized fully by UV−visible and NMR spectroscopies, high-resolution electrospray ionization mass spectrometry (HRESI-MS), X-ray crystallography, and electrochemistry. The electrocatalytic capabilities of these complexes to form hydrogen via proton reduction has been evaluated in acetonitrile solutions with the presence of trifluoroacetic acid as a proton donor. Cyclic voltammetry studies indicated that all complexes catalyze H2 formation. DFT calculations indicate that the mechanism of hydrogen formation has the lowest activation energy when the reaction occurs between a H+ ion (oxonium ion H3O+) and a Co(II)-H hydride species.

Popular Abstract

The main source of energy has been for decades the use of non-renewable fossil fuels, which contribute strongly global pollution and are responsible for multiple problems such as: global warming, low air quality, destruction of ecosystems, etc. Many resources have been assigned to finding environmentally friendly and renewable energy sources for a sustainable future. One such promising energy source is the use of hydrogen as a fuel. The use of hydrogen as fuel generates only water as a byproduct, which means it does not release greenhouse gases. For hydrogen to be used as fuel it is needed in its reduced form as hydrogen gas, chemical formula H2. While hydrogen is the most abundant element on earth, it is usually found in its most stable form: water, which chemical formula is H2O. The transformation from H2O into H2 requires a lot of energy, which makes the process of generating H2 to use as fuel ultimately not sustainable. A way to reduce the energy needed to transform H2O into H2 is the use of catalysts. A catalyst is a substance which reduces the energy barrier needed to carry out a chemical reaction. The catalysts most used for the H2O → H2 reaction are made with noble metals such as platinum, rhodium, and iridium, which are expensive and have low abundance in earth. Additionally, these types of metals are hard to dispose of since they are toxic for many organisms. Recently, there has been much effort to use more environmentally friendly and cheaper metals, such as iron, cobalt, nickel, and manganese. The difficulty in using these metals is that they tend to not work as well as the commonly used noble metals so there needs to be many different catalysts developed and studied in order to be able to find some that match the common catalysts. This research focuses on investigating five different catalysts containing cobalt which are very similar but have slight modifications. The idea behind this work is to assess how the small modifications make the catalysts better or worse, so we can start to understand what parameters affect the effectiveness of cobalt catalysts and thus develop better catalysts in the future.

• author: Garcia Dominguez, Carmina
• supervisor: Yong Li
• organization: Department of Chemistry
• course: KEMR30 20231
• year: 2023
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: Hydrogen, Fuel cell, Catalysis, Electrocatalysis, Cobalt, Inorganic chemistry
• language: English
• additional info: Full text not available since the work is intended to be published in a scientific journal.
• id: 9141726
• date added to LUP: 2023-11-29 10:17:08
• date last changed: 2023-11-29 10:17:08