Elena Pérez-Gallent

We performed H-cell and flow cell experiments to study the electrochemical reduction of CO₂ to oxalic acid (OA) on a lead (Pb) cathode in various nonaqueous solvents. The effects of anolyte, catholyte, supporting electrolyte, temperature, water content, and cathode potential on the Faraday efficiency (FE), current density (CD), and product concentration were investigated. We show that a high FE for OA can be achieved (up to 90%) at a cathode potential of -2.5 V vs Ag/AgCl but at relatively low CDs (10-20 mA/cm²). The FE of OA decreases significantly with increasing water content of the catholyte, which causes byproduct formation (e.g., formate, glycolic acid, and glyoxylic acid). A process design and techno-economic evaluation of the electrochemical conversion of CO₂ to OA is presented. The results show that the electrochemical route for OA production can compete with the fossil-fuel based route for the base case scenario (CD of 100 mA/cm², OA FE of 80%, cell voltage of 4 V, electrolyzer CAPEX of $20000/m², electricity price of $30/MWh, and OA price of $1000/ton). A sensitivity analysis shows that the market price of OA has a huge influence on the economics. A market price of at least $700/ton is required to have a positive net present value and a payback time of less than 10 years. The performance and economics of the process can be further improved by increasing the CD and FE of OA by using gas diffusion electrodes and eliminating water from the cathode, lowering the cell voltage by increasing the conductivity of the electrolyte solutions, and developing better OA separation methods.

Valorization of CO₂ and biomass waste streams via electrochemical conversions is a sustainable alternative for the production of fine chemicals and commodity chemicals. This topic has gained a lot of attention in the past decades and major research efforts have been put into it. Key advances has been achieved in the field of material development, where, novel catalysts have been synthesized, developed and have demonstrated to increase the efficiency and selectivity towards the targeted products. Relatively to the large number of studies focused on material development, limited studies are focused on process development, reactor optimization and product separation. Although material development is of paramount importance to achieve an adequate electrochemical reaction performance, it is only the first step needed in order to develop a competitive technology. Process development offers the possibility of enhancing the overall performance of the technology by looking not only at the reaction level, but finding engineering solutions to overcome critical limitations. Process development is essential in order to accelerate the technology towards its envisioned application and advance towards commercial realization. In this talk, we will present several optimization strategies (beyond material development) that helped increase the overall performance of several electrochemical conversion processes, as well as the economic profitability of the complete system. In addition, in order to advance the technology on the TRL scale and have a positive market potential, the technology needs to be evaluated in several aspects such as the scaling-up challenges, its cost competitiveness and its climate benefits. For this, it is crucial to consider the complete value chain, and evaluate not only the electrochemical reaction but also the upstream and the downstream processes. A complete system approach is paramount for the development of competitive technologies. In this talk we will also show several examples on different process intensification strategies and its benefits on the economic potential of them.

Recently, deep eutectic solvents (DES) have been considered as possible electrolytes for the electrochemical reduction of CO₂ to value-added products such as formic and oxalic acids. The applicability of pure DES as electrolytes is hindered by high viscosities. Mixtures of DES with organic solvents can be a promising way of designing superior electrolytes by exploiting the advantages of each solvent type. In this study, densities, viscosities, diffusivities, and ionic conductivities of mixed solvents comprising DES (i.e., reline and ethaline), methanol, and propylene carbonate were computed using molecular simulations. To provide a quantitative assessment of the affinity and mass transport of CO₂ and oxalic and formic acids in the mixed solvents, the solubilities and self-diffusivities of these solutes were also computed. Our results show that the addition of DES to the organic solvents enhances the solubilities of oxalic and formic acids, while the solubility of CO₂ in the ethaline-containing mixtures are in the same order of magnitude with the respective pure organic components. A monotonic increase in the densities and viscosities of the mixed solvents is observed as the mole fraction of DES in the mixture increases, with the exception of the density of ethaline-propylene carbonate which shows the opposite behavior due to the high viscosity of the pure organic component. The self-diffusivities of all species in the mixtures significantly decrease as the mole fraction of DES approaches unity. Similarly, the self-diffusivities of the dissolved CO₂ and the oxalic and formic acids also decrease by at least 1 order of magnitude as the composition of the mixture shifts from the pure organic component to pure DES. The computed ionic conductivities of all mixed solvents show a maximum value for mole fractions of DES in the range from 0.2 to 0.6 and decrease as more DES is added to the mixtures. Since for most mixtures studied here no prior experimental measurements exist, our findings can serve as a first data set based on which further investigation of DES-containing electrolyte solutions can be performed for the electrochemical reduction of CO₂ to useful chemicals.

Carbon dioxide (CO₂) is currently considered as a waste material due to its negative impact on the environment. However, it is possible to create value from CO₂ by capturing and utilizing it as a building block for commodity chemicals. Electrochemical conversion of CO₂ has excellent potential for reducing greenhouse gas emissions and reaching zero net emissions by 2050. To date, Carbon Capture and Utilization (CCU) technologies have been studied independently. We report a novel methodology based on the integration of CO₂ capture and conversion by the direct utilization of a CO₂ capture media as electrolyte for electrochemical CO₂ conversion. This has a high potential for reducing capital and operational cost when compared to traditional methodologies. A novel mixture of chemical and physical absorption solvents allowed for the captured CO₂ to be converted to formic acid with faradaic efficiencies up to 50 % and with carbon conversion of ca. 30 %. By increasing the temperature in the electrochemical reactor from 20 °C to 75 °C, the productivity towards formic acid increased by a factor of 10, reaching up to 0.7 mmol∙m^-2·s^-1. The direct conversion of captured CO₂ was also demonstrated for carbon monoxide formation with faradaic efficiencies up 45 %.