Periodic Reporting for period 1 - BICATC2 (Bioinspired bimetallic catalysts for CO2 reduction beyond C1 products)
Berichtszeitraum: 2024-05-02 bis 2026-05-01
The global economy has a strong dependence of chemicals for diverse uses including polymers, pharmaceuticals and agrochemicals. 90% of chemical feedstocks currently derive from gas and oil and as such, chemical industry is set to become the biggest driver of new oil demand by 2030. Therefore finding alternative chemical feedstocks is a key sustainability goal. Most projections for Net Zero include plans for Carbon Capture and Storage. However, in order to close the loop and build a circular economy, Carbon Capture and Utilization, in which the waste CO2 is chemically transformed and used as a source for chemical production. CO2 is a kinetically inert molecule containing two strong C=O bonds, making the task of activating and transforming this simple molecule highly challenging. Low cost, renewable electricity can be used in conjunction with suitable electrocatalysts to drive this reaction. The technology to produce C1 products such as formate, methanol and CO is quite advanced and widely achievable. To fully harness the potential of CO2 as a building block, it is necessary to move beyond C1 products to C2+ products, which have higher energy densities and a wider range of uses. C2+ products such as ethanol and propanol can be used as liquid fuels, which are crucial in hard to decarbonise areas such as aviation and shipping.
The production of C2+ products directly from CO2 is a gap in the current technology, the realisation of which would greatly reduce emissions.
Few systems can successfully produce C2+ coupled products and those which can suffer from selectivity issues
The key aim of this project is develop bimetallic electrocatalysts for the multielectron reduction of CO2 to form C2+ products and to immobilise these species onto surfaces such as carbon nanotubes to improve catalyst stability and facilitate device integration.
The production of C2+ products directly from CO2 is a gap in the current technology, the realisation of which would greatly reduce emissions.
Few systems can successfully produce C2+ coupled products and those which can suffer from selectivity issues
The key aim of this project is develop bimetallic electrocatalysts for the multielectron reduction of CO2 to form C2+ products and to immobilise these species onto surfaces such as carbon nanotubes to improve catalyst stability and facilitate device integration.
The first work package was dealing with the synthesis of bimetallic complexes.
The work began with a thorough literature review to establish a solid foundation and formulate an experimental plan. Synthetic procedures were then initiated, leading to the successful synthesis of ligands and their subsequent use in the preparation of bimetallic complexes. All synthesised compounds were fully characterised to confirm their structures and properties.Four homobimetallic complexes without linkers were synthesised to facilitate studies under homogeneous conditions. A novel approach was developed to append a pyrene moiety to the ligand using an ether linker, and this ligand was successfully metalated with cobalt, iron, nickel, and copper. A heterobimetallic Cu/Fe complex based on an N2S2 bpy ligand was also synthesised. This complex exhibited intriguing fluxional properties, warranting extensive characterisation. In response to findings from WP2, a new bimetallic ligand scaffold incorporating an amine group was synthesised to enhance CO2 binding capabilities.
The second work package explored the reactivity of the synthesized complexes towards CO2 and the study of the related mechanism
This was assessed using standard electrochemical techniques such as cyclic voltammetry and controlled potential electrolysis. Special focus was given to cobalt complexes to enable comparisons with previously studied monometallic catalysts. Bulk electrolysis was performed, and the products were analysed using gas chromatography and ion chromatography. Mechanistic investigations were carried out using UV-vis spectroelectrochemistry and attempts to synthesise hydride complexes.
All complexes demonstrated measurable reactivity towards CO2 during cyclic voltammetry studies. However, cobalt complexes were prioritised for bulk electrolysis experiments. The electrolysis revealed no C2+ products, and challenges were encountered in detecting liquid products in organic electrolytes. The preference of the bimetallic complexes for proton reduction over CO2 reduction prompted the redesign of the ligand scaffold, incorporating an amine group as a linker. For the Cu/Fe complex, the reduced Cu(I) species, a likely catalytic intermediate, was successfully isolated and characterised using EPR, 1H^1H1H NMR, and IR spectroscopy. Preliminary experiments on this complex with CO2 showed some activity, though further investigations were limited due to the early termination of the project.
The third work package consisted in the immobilisation of the pyrene-appended complexes synthesised in WP1 on carbon electrodes through non-covalent interactions. The carbon nanotubes were drop-cast onto electrodes and incubated with solutions of the catalysts. Both bimetallic and homometallic complexes bearing the pyrene group were immobilised and evaluated. The immobilisation process was successful, and comparative studies were conducted to evaluate CO2 reduction on the electrode surface. Turn Over Numbers (TON) were significantly higher for immobilised complexes than for those in homogeneous conditions. The monometallic complexes were more active for CO2 reduction, producing primarily CO, while the bimetallic complexes favoured hydrogen evolution. Attempts to study the reaction mechanism using surface spectroelectrochemical IR were made, though these proved to be technically challenging.
Despite its early termination, this research project demonstrated the successful synthesis of innovative bimetallic complexes, explored their reactivity towards CO2, and advanced the study of their immobilisation on electrode surfaces. The findings provide a foundation for future studies on improving CO2 reduction catalysts and understanding their mechanisms.
The work began with a thorough literature review to establish a solid foundation and formulate an experimental plan. Synthetic procedures were then initiated, leading to the successful synthesis of ligands and their subsequent use in the preparation of bimetallic complexes. All synthesised compounds were fully characterised to confirm their structures and properties.Four homobimetallic complexes without linkers were synthesised to facilitate studies under homogeneous conditions. A novel approach was developed to append a pyrene moiety to the ligand using an ether linker, and this ligand was successfully metalated with cobalt, iron, nickel, and copper. A heterobimetallic Cu/Fe complex based on an N2S2 bpy ligand was also synthesised. This complex exhibited intriguing fluxional properties, warranting extensive characterisation. In response to findings from WP2, a new bimetallic ligand scaffold incorporating an amine group was synthesised to enhance CO2 binding capabilities.
The second work package explored the reactivity of the synthesized complexes towards CO2 and the study of the related mechanism
This was assessed using standard electrochemical techniques such as cyclic voltammetry and controlled potential electrolysis. Special focus was given to cobalt complexes to enable comparisons with previously studied monometallic catalysts. Bulk electrolysis was performed, and the products were analysed using gas chromatography and ion chromatography. Mechanistic investigations were carried out using UV-vis spectroelectrochemistry and attempts to synthesise hydride complexes.
All complexes demonstrated measurable reactivity towards CO2 during cyclic voltammetry studies. However, cobalt complexes were prioritised for bulk electrolysis experiments. The electrolysis revealed no C2+ products, and challenges were encountered in detecting liquid products in organic electrolytes. The preference of the bimetallic complexes for proton reduction over CO2 reduction prompted the redesign of the ligand scaffold, incorporating an amine group as a linker. For the Cu/Fe complex, the reduced Cu(I) species, a likely catalytic intermediate, was successfully isolated and characterised using EPR, 1H^1H1H NMR, and IR spectroscopy. Preliminary experiments on this complex with CO2 showed some activity, though further investigations were limited due to the early termination of the project.
The third work package consisted in the immobilisation of the pyrene-appended complexes synthesised in WP1 on carbon electrodes through non-covalent interactions. The carbon nanotubes were drop-cast onto electrodes and incubated with solutions of the catalysts. Both bimetallic and homometallic complexes bearing the pyrene group were immobilised and evaluated. The immobilisation process was successful, and comparative studies were conducted to evaluate CO2 reduction on the electrode surface. Turn Over Numbers (TON) were significantly higher for immobilised complexes than for those in homogeneous conditions. The monometallic complexes were more active for CO2 reduction, producing primarily CO, while the bimetallic complexes favoured hydrogen evolution. Attempts to study the reaction mechanism using surface spectroelectrochemical IR were made, though these proved to be technically challenging.
Despite its early termination, this research project demonstrated the successful synthesis of innovative bimetallic complexes, explored their reactivity towards CO2, and advanced the study of their immobilisation on electrode surfaces. The findings provide a foundation for future studies on improving CO2 reduction catalysts and understanding their mechanisms.
The project was terminated after only 6 months. Despite its early termination, this research project demonstrated the successful synthesis of innovative bimetallic complexes, explored their reactivity towards CO2, and advanced the study of their immobilisation on electrode surfaces. The findings provide a foundation for future studies on improving CO2 reduction catalysts and understanding their mechanisms.