Periodic Reporting for period 1 - DimerCat (DimerCat: Isolated dimers for catalyzing CO2 electroreduction to higher carbon products)
Reporting period: 2020-10-19 to 2022-10-18
With increasing temperature, melting glaciers and drastic climate change, the need to move towards a net-zero world has accelerated. EU and most of the countries are trying to approach towards net-zero carbon emissions by 2050 through the reduction of greenhouse gas emissions and the use of renewable energy. This project aims towards converting CO2 to useful chemicals such as ethanol, ethylene etc. which forms the basic building block of many industrial chemicals. This method has an advantage over the conventional method in that it may result in significantly higher energy efficiency due to its low operational temperature compared to the thermocatalytic CO2 reduction. Decline in the cost of renewable electricity further adds to its advantage.
The overall objective of the project is to synthesize metal-doped carbon catalysts, especially dual-atom catalysts (DACs) as they were predicted to form multi-carbon products (ethanol, ethylene) of high value during electrochemical CO2 reduction.
i) Synthesis and stabilization of DimerCat materials,
ii) Identification of the mechanism of ECO2RR and tuning the catalyst design to enhance the selectivity towards C2 products,
iii) Investigation of the behavior of the catalysts at high current densities
We could synthesize metal-doped carbon catalysts having dimeric metal sites. However, the number of dual-atomic sites were much lesser compared to the single-atomic sites and hence CO2 could be electrochemically reduced to carbon monoxide instead of the higher carbon products. It was really exciting to see that a very small percentage of metal doping on carbon could result in such a high activity, on-par with the state-of-the-art Au catalyst. Further we compared our synthesized catalyst with all the best reported catalysts and observed a general trend and limitations for all the catalysts, which is ascribed to the scaling-relationship between the intermediates.
The overall objective of the project is to synthesize metal-doped carbon catalysts, especially dual-atom catalysts (DACs) as they were predicted to form multi-carbon products (ethanol, ethylene) of high value during electrochemical CO2 reduction.
i) Synthesis and stabilization of DimerCat materials,
ii) Identification of the mechanism of ECO2RR and tuning the catalyst design to enhance the selectivity towards C2 products,
iii) Investigation of the behavior of the catalysts at high current densities
We could synthesize metal-doped carbon catalysts having dimeric metal sites. However, the number of dual-atomic sites were much lesser compared to the single-atomic sites and hence CO2 could be electrochemically reduced to carbon monoxide instead of the higher carbon products. It was really exciting to see that a very small percentage of metal doping on carbon could result in such a high activity, on-par with the state-of-the-art Au catalyst. Further we compared our synthesized catalyst with all the best reported catalysts and observed a general trend and limitations for all the catalysts, which is ascribed to the scaling-relationship between the intermediates.
Based on the literature, we selected Fe, Ni and Co atom for synthesizing the metal-doped carbon catalysts. These catalysts are known to produce carbon monoxide (CO) during electrochemical CO2 reduction. We presumed that dual-atomic Fe-Fe, Ni-Ni or Co-Co can facilitate the carbon-carbon coupling to form multi-carbon products such as ethanol or ethylene. Thus, we synthesized catalysts namely C2N900@Fe, C2N900@Ni, TAP 900@Fe and TAP 900@Ni. We observed that all of these catalysts mostly form single atomic sites with few dual-atomic sites as seen from HAADF-STEM images. Dual-atomic sites are very hard to stabilise and single-atomic sites are more thermodynamically favored. These materials exhibited excellent electrochemical CO2 reduction activity towards CO production and negligible amount of liquid products (formate, acetate, methanol, ethanol, propanol) were obtained.
Electrochemical facility was developed in the lab to screen the synthesized catalyst for the CO2 reduction. Due to COVID situation, the whole process took quite a long time from design to optimisation. Based on the literature, I have successfully designed an adaptable electrochemical cell for CO2 reduction testing. The surface area of the electrode was kept higher in comparison to the volume of the electrolyte used to detect even the minor liquid product formed. Benchmarking of the whole setup was carried out with the state-of-the-art Au/C (20 wt%) catalyst. GC was calibrated and optimised to analyse the gaseous products. Liquid 1H-NMR and High-performance liquid chromatography (HPLC) instrument was also optimised to analyse the liquid products formed during the CO2 reduction reaction.
Both TAP 900@Fe and TAP 900@Ni showed good CO2RR activity at lesser negative potential and approached a high CO selectivity (mean FECO ~ 95 %) at -0.55 V vs RHE. Bare TAP 900 showed very poor selectivity towards CO indicating the activity in TAP 900@M resulting predominantly from the M-Nx sites.
Despite the continuous effort towards improving the catalyst, we still have inconclusive idea about the actual improvement in catalyst activity through a proper comparison of the intrinsic activity. To understand this, we compared our synthesized catalyst with the best-reported catalysts for CO2 to CO production. We observed that all the best-reported catalysts seem to have similar TOF limitations and cannot exceed a particular TOF order range. Diving deeper we find a correlation between the observed limitations and the linear scaling relationship between the intermediates. Due to the existence of a scaling relationship between both the C-binding species (*CO and *COOH), tuning of only one intermediate is quite impossible. This is responsible for the persistent overpotential and limitation observed. Thus, it is quite difficult to achieve a high intrinsic activity/TOF and so all the best catalysts always overlapped each other.
During the course of MSCA fellowship, 3 articles were published in peer-reviewed journals, 2 manuscripts under communication and the results were presented in 2 conferences. Main manuscript related to this manuscript is still under communication and once the article is published, the results will be disseminated through youtube and twitter.
Electrochemical facility was developed in the lab to screen the synthesized catalyst for the CO2 reduction. Due to COVID situation, the whole process took quite a long time from design to optimisation. Based on the literature, I have successfully designed an adaptable electrochemical cell for CO2 reduction testing. The surface area of the electrode was kept higher in comparison to the volume of the electrolyte used to detect even the minor liquid product formed. Benchmarking of the whole setup was carried out with the state-of-the-art Au/C (20 wt%) catalyst. GC was calibrated and optimised to analyse the gaseous products. Liquid 1H-NMR and High-performance liquid chromatography (HPLC) instrument was also optimised to analyse the liquid products formed during the CO2 reduction reaction.
Both TAP 900@Fe and TAP 900@Ni showed good CO2RR activity at lesser negative potential and approached a high CO selectivity (mean FECO ~ 95 %) at -0.55 V vs RHE. Bare TAP 900 showed very poor selectivity towards CO indicating the activity in TAP 900@M resulting predominantly from the M-Nx sites.
Despite the continuous effort towards improving the catalyst, we still have inconclusive idea about the actual improvement in catalyst activity through a proper comparison of the intrinsic activity. To understand this, we compared our synthesized catalyst with the best-reported catalysts for CO2 to CO production. We observed that all the best-reported catalysts seem to have similar TOF limitations and cannot exceed a particular TOF order range. Diving deeper we find a correlation between the observed limitations and the linear scaling relationship between the intermediates. Due to the existence of a scaling relationship between both the C-binding species (*CO and *COOH), tuning of only one intermediate is quite impossible. This is responsible for the persistent overpotential and limitation observed. Thus, it is quite difficult to achieve a high intrinsic activity/TOF and so all the best catalysts always overlapped each other.
During the course of MSCA fellowship, 3 articles were published in peer-reviewed journals, 2 manuscripts under communication and the results were presented in 2 conferences. Main manuscript related to this manuscript is still under communication and once the article is published, the results will be disseminated through youtube and twitter.
Through this project, we could establish some fundamental understanding of the electrochemical CO2 reduction on metal-doped carbon catalysts, which will help a lot in the progress of the field. We made some general observations for all the metal and metal-doped carbon catalysts which can contribute a lot towards catalyst development. We also developed a decoupled approach for the synthesis, which was never reported before and helped us in achieving highly accessible active site with a very high utilisation ratio. We believe that metal-doped carbon catalyst can prove to be a potential catalyst for electrochemical CO2 reduction with a very high tunability.