Periodic Reporting for period 1 - CO2Polymerisation (Conversion of CO2/H2O to Polyethylene through Cascade Electro-reduction–Polymerisation Catalysis)
Reporting period: 2020-11-01 to 2022-10-31
The increasing concentration of CO2, the main long-lived greenhouse gas in the Earth's atmosphere, is causing global warming and climate change. In today's world of high energy demand, converting CO2 into renewable fuels through clean and economical chemical processes seems to be a more rewarding approach than its geological sequestration. The development of electrochemical CO2 reduction has recently emerged as a promising and environmentally friendly approach for recycling carbon resources and producing value-added chemical feedstocks such as CH4, C2H4, and CH3OH. Reducing the concentration of CO2 in the atmosphere by using CO2 for sustainable energy or producing low-carbon fuels such as polyethylene can simultaneously solve two global problems: Energy scarcity and environmental pollution. Due to the great importance of this issue in our modern society, the impact of the proposed research on the scientific community and industry will be enormous, both in Europe and worldwide. Therefore, there is a need to develop a novel sustainable process to produce hydrocarbons from renewable carbonaceous resources, such as sustainable CO2. The development of processes to produce hydrocarbons from CO2 would be a significant breakthrough that would complement the conversion of today's global economy from eventually depleted petrochemical feedstocks to carbonaceous resources. Such progress could mitigate the volatility of global chemical prices and would lead to a more sustainable technological solution. The main objective of the proposal is to theoretically develop a novel catalyst for the direct conversion of CO2 to hydrocarbons such as CH4, C2H4, and CH3OH by electrolytic reduction of CO2 that can achieve higher efficiency under relatively mild operating conditions. To this end, a multiscale framework for ab initio simulation of direct CO2 electroreduction to CO intermediates and then to hydrocarbons using computational chemistry is presented.
Here we modeled the electrochemical reduction of CO2 to CO with a promising copper electrocatalyst both in vacuum (without solvation) and with solvation using extensive density functional theory (DFT) and kinetic Mont Carlo (KMC) multiscale simulations. The dependence of Gibbs free energy on pH and applied potential (U) parameters was investigated for all elementary reactions involved in the conversion of CO2 to CO. Barrier energies, adsorption energies, vibrational frequencies, zero-point energies, kinetic rates, thermodynamic parameters, and transition states were calculated in vacuum and solvation cases to determine the reaction pathways leading to the production of CO from CO2. The results from DFT were used as input values in the KMC scale to calculate the detailed surface coverage, catalytic performance, and turnover frequency. This is the only study that considers the three facets (100), (110), and (111) of the copper electrocatalyst as well as the solvation effect in the CO2 electroreduction reaction. In addition, the contribution of zero-point energy to the energy parameters in both vacuum and solvation was considered by performing calculations of the vibrational modes of surface species with the phonon code to obtain more accurate results. This work provides a deeper understanding and suggestions for the development of high-performance electrocatalysts for the electrochemical reduction of CO2. The Quantum Espresso and ZACROS packages were used for density functional theory and kinetic Monte Carlo simulations to calculate electronic parameters and simulate catalytic processes. The entire reaction pathways of the production of CO (the crucial intermediate in the production of hydrocarbons) from the CO2 reduction reaction on the copper electrocatalyst (the only catalyst for this conversion) were mapped, and all structures of the relevant intermediates and transition states were determined. Energetic parameters, vibrational frequencies, ZPE energies, kinetic rates (reaction rate constants and equilibrium constants) from transition state theory, and thermodynamic parameters (entropies, Gibbs free energies) were calculated to distinguish the reaction pathways leading to the production of CO from CO2. At an applied potential (U) of less than (-1.60 V, RHE) and a pH of 6.0 all elementary reactions of CO2RR were thermodynamically favorable, which was in excellent agreement with other theoretical and experimental works. In addition, the dependence of Gibbs free energy on pH and applied potential parameters was investigated for all primary reactions. Most importantly, the role of water solvation in CO2RR was investigated by forming a 1.0 ML water layer on the Cu catalyst. The adsorption sites of the adsorbates and the reaction mechanism were almost identical in both vacuum and solvation cases. Detailed analysis showed that solvation had significant effects on the stability of the adsorbents and intermediates compared to vacuum. In addition, the activation energies of all elementary reactions were reduced by solvation, making CO2RR more favorable and environmentally friendly. The DFT-scale results were used as input values for the kinetic Monte Carlo scale to calculate the detailed surface coverage, catalytic performance, and turnover frequency. It was investigated that CO is formed via the carboxyl pathway (CO2-->trans-COOH*-->cis-COOH*-->CO*+OH*-->CO*-->CO), while C1 hydrocarbon is formed via the HCOO pathway. Direct CO2 dissociation was not worth mentioning due to its high activation barrier compared to other pathways. KMC simulations of CO2RR in vacuum at an applied potential of -2, -1, 0, +1, and +2V were performed. It was found that CO2 essentially dissociates into CO and O at an applied potential of -2 or -1V. In other cases, the CO begins to form, with CO2, H, and OH bound to Cu.
In this project, we continued research on the conversion of CO2 to chemicals using DFT and KMc simulations. CO was identified as a key intermediate for this conversion via the copper electrocatalyst. All reaction mechanisms for the conversion of CO2 to CH3OH, CH4, C2H4, etc. on copper catalysts were proposed. The adsorption energies of adsorbents and intermediates, activation energies (transition states) and reaction energies of all elementary reactions were calculated. The vibrational frequencies (zero-point energies) and other thermodynamic properties were calculated. All these parameters were calculated for both vacuum and solvation to show the importance of the solvation effect on the CO2 reduction reaction process. Furthermore, the effects of the applied potential and pH on the Gibbs free energies of the elementary steps of CO2 reduction to produce CO using the Cu catalyst were investigated. Because of the great importance of this topic, the impact of the proposed research on the scientific community and industry both in Europe and worldwide will be enormous. In addition, as part of the "Science Days", I visited local schools in Ljubljana (Livada Elementary School, QSI School, etc.) to talk about the importance of preventing pollution while generating energy through this project and to inspire young people about basic research.