Optimized Tandem Catalyst Patterning for CO2 Reduction Flow Reactors

This is the final scientific/technical report for a DOE project focused on the electrochemical conversion of CO₂ in non-aqueous solvents to novel products. Electrochemical reduction of CO₂ provides an attractive route to produce valuable fuels and chemicals that can simultaneously lower greenhouse gas emissions when powered by renewable electricity. While recent technological advances have shown the feasibility of industrial CO₂ electroreduction, many challenges remain to improve this technology and expand the list of economically viable products. The vast majority of electrochemical CO₂ reduction research has been conducted in aqueous media under neutral to alkaline conditions, leading to commonly reported products including carbon monoxide, formic acid, methane, methanol, ethylene, acetic acid, and ethanol. In comparison, non-aqueous media for CO₂ reduction has been underexplored but represents a possible avenue to yield new products and improved operating conditions. The aim of the project was to convert waste CO₂ in the form of flue gas to a multicarbon C2 - C4 chemical product in a reactor designed to achieve economically competitive values of current density and selectivity. The project strived to advance the technology readiness of an electrochemical CO₂ reduction process in alcohol solvents from the proof-of-concept stage to a device capable of meeting performance metrics for commercial viability. In the initial plan, the University of Louisville researchers were to focus on investigating the electrochemical process and improving the faradaic efficiency for novel C2 – C4 species, while also working on a parallel effort to build a practical electrolysis reactor to markedly increase the CO₂ reduction current density. The reactor development effort also aimed to engineer a dual-electrolyte feed strategy with non-aqueous catholyte and aqueous anolyte to promote water oxidation as the coupling anodic half-reaction to enable a sustainable and economical overall process. At the outset, the University of North Dakota was to investigate the feasibility of operating directly from coal-derived flue gas without separate capture and purification. The research team sought to determine impurity effects and test mitigation strategies, as well as engineer the gaseous feed system for high reactor tolerance to lower CO₂ concentration. In the last half year of the project, the focus was planned to shift to integrating the advances in the catalysis, electrochemical conditions, reactor design, and flue gas compatibility into a fully functional device and improve it for maximum current density and faradaic efficiency for C2 – C4 species. Knowledge of the full system components, constraints, and maximum performance was then to be used as the basis for a thorough technoeconomic analysis (TEA) and life cycle analysis (LCA) at the end of the project.

Electrochemical CO2 reduction versus CO reduction over Au/Ti electrocatalyts in phosphate buffer condition

Tandem effect of Ag@C@Cu catalysts enhances ethanol selectivity for electrochemical CO2 reduction in flow reactors

Electrochemical reduction of carbon dioxide to ethylene at a copper electrode in methanol using potassium hydroxide and rubidium hydroxide supporting electrolytes

CO binding energy has been widely employed as a descriptor for effective catalysts in the electrochemical CO2and CO reduction reactions (CO(2)RR), however, it has yet to be determined experimentally at electrochemical interfaces due to the lack of suitable techniques. In this work, we developed a method to determine the standard adsorption enthalpy of CO on Cu surfaces with quantitative surface enhanced infrared absorption spectroscopy. On dendritic Cu at −0.75 V vs. SHE, the standard adsorption enthalpy, entropy and Gibbs free energy were determined to 1.5±0.5 kJ mol−1, ≈37.9±13.4 J/(mol K), and ≈−9.8±4.0 kJ mol−1, respectively. Comparison of the standard adsorption enthalpy of oxide‐derived Cu and dendritic Cu, as well as their CORR activities, suggests the presence of stronger binding sites on OD Cu, which could favor multicarbon products. The method developed in this work will help establish the correlation between the CO binding energy and the CO(2)RR activity.

HI-Light: A Glass-Waveguide-Based "Shell-and-Tube" Photothermal Reactor Platform for Converting CO2 to Fuels.

Homogeneous electrocatalytic CO2 reduction by hexacarbonyl diiron dithiolate complex bearing hydroquinone

Electrocatalytic reduction of CO under high pressure (< 60 atm) using a gas diffusion electrode containing Pt catalyst (Pt-GDE) has been investigated. Acetic acid was formed at a high faradaic efficiency of 32% as a predominant CO reduction product at a constant current density of 200 mA cm−2 under CO 40 atm. Moreover, methane, ethane, ethylene, formaldehyde, acetaldehyde, ethanol, 1-propanol, and allyl alcohol were produced as CO reduction products. The selectivity of the reduction products depends remarkably on electrolysis conditions such as the current density, pressure of CO, and temperature. C2-compounds such as ethylene, ethanol, and acetic acid were preferentially formed at small current densities and/or high CO pressure conditions, whereas methane was predominantly produced at large current densities and/or low CO pressure conditions.

Advances in electrochemical reduction of carbon dioxide to formate over bismuth‐based catalysts

Electrochemical CO2 reduction (CO2R) is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent progress in fundamental understanding, catalyst development, and in engineering and scale-up. We discuss the outstanding challenges towards commercialization of electrochemical CO2R technology: energy efficiencies, selectivities, low current densities, and stability. We highlight the opportunities in establishing rigorous standards for benchmarking performance, advances in in operando characterization, the discovery of new materials towards high value products, the investigation of phenomena across multiple-length scales and the application of data science towards doing so. We hope that this collective perspective sparks new research activities that ultimately bring us a step closer towards establishing a low- or zero-emission carbon cycle.

In recent years, atmospheric concentrations of carbon dioxide (CO2) have risen to alarming levels, exacerbating environmental crises such as ocean acidification and global warming (United Nations, n.d.). Plants, through photosynthesis, slow but do not halt the progression of these issues, absorbing roughly 30% of carbon emissions each year (Friedlingstein et al., 2022). However, it is theoretically possible to enhance plants’ CO2 uptake using some catalyst for photosynthesis (Department of Energy, n.d.). The photocatalyst titanium dioxide (TiO2) is a promising candidate because of studies demonstrating its ability to boost plant growth and to photocatalyze water splitting and CO2 reduction, both rate-determining steps in photosynthesis (Li et al., 2022; Tao et al., 2022, Rehman et al. 2022). To investigate the potential of TiO2 as a photosynthetic catalyst, 0, 0.352 and 0.652 g of TiO2 were sprinkled atop three pots of Ocimum basilicum (basil). Placed in sealable containers with CO2 meters, the plants’ consumption of CO2 was measured twice every day. Although previous literature has looked into The average consumption for the 0.652 g TiO2 group was 223.875 ppm, almost 15% times the average for the 0 g TiO2 control, which came out to be 151.625 ppm. Surprisingly, the 0.326 g TiO2 group was around 62% of the control, with an average consumption of 94.625 ppm.

A new scheme for ammonia and fertilizer generation by coal direct chemical looping hydrogen process: Concept design, parameter optimization, and performance analysis

Introduction: Climate change, due to the release of greenhouse gases such as carbon dioxide (CO2), is a global environmental issue. An effective energy transition relies on the substantial utilization of renewable energy sources and the development of CO2 reduction products, such as e-fuels and e-chemicals. In particular, the potential for large-scale CO2 reduction could contribute significantly to mitigating the greenhouse effect. Accordingly, promising CO2 recycling approaches include electrochemical as well as bio-electrochemical methods. Currently, both methods for CO2 reduction are limited by relatively low selectivity, high cost and low material stability, particularly with respect to cathode materials (Farooqi et al., 2023; Zhang et al., 2021).The approach presented in this study proposes using cathode materials based on synthesized non-noble bimetallic oxides for electrochemical and bioelectrochemical reduction of CO2. This is the first time a comparison of electrochemical and bioelectrochemical reduction of CO2 is carried out. Experimental: Bimetallic oxides FeCuO, MnCuO, and SnCuO, CoMnO and FeSnO were synthesized using sol-gel methods in three molar ratios (1/2, 1/1, and 2/1) and characterized by XRD and EDS methods. The electrocatalyst was fabricated by mixing their powder with Nafion solution to obtain a paste, which is deposited on carbon felt. CO2 reduction was performed in an electrolytic cell (EC) and a microbial electrosynthesis (MES) cell using sodium bicarbonate solution (pH 6.5, 0.5M) and enriched mixed acidogenic culture at pH 6.0, respectively. Batch activity tests were first carried out to evaluate the bimetallic oxides’ performances on CO2 reduction by methanogenic and acidogenic microorganisms using serological bottles containing microbial cultures capable of reducing CO2 and hydrogen to methane (CH4) and volatile fatty acids (VFAs). The bimetallic oxides were used either in powder form at concentrations of 1–2.5 g/L or deposited on carbon felt at an active loading of 10 mg cm-2. Among the five bimetallic oxides tested, three promising candidates were selecte. Stability tests were conducted with these oxides at three molar ratios at a current density of 156 A m-2 for 20 hours in an electrolytic cell. Electrochemical CO2 reduction was subsequently performed using the most stable oxides across various current densities (13–100 A m-2) under standard conditions, and Coulombic efficiency (CE) was calculated. Additionally, bioelectrochemical reduction tests were conducted at 3, 5, and 8 A m-2 in a MES cell, inoculated with enriched mixed acetogenic culture (table 1). Both uncoated carbon felt, and carbon felt coated with FeSnO (1/1) were used as cathode materials. Analysis of gases and VFAs was performed using gas chromatography, while liquid chromatography was employed for alcohol analysis. Preliminary Results: The crystalline structure and the stoichiometric composition of the bimetallic oxides were confirmed, respectively by XRD and EDS characterization of annealed samples. Based on Cyclic Voltammetry, current-voltage polarization and Tafel plot curves, the electrolytic currents of the CO2 electro-reduction were identified. Table 2 shows the CE of the electro-reduction of CO2 to methanol and tert-butanol for various current density on the best bimetallic oxides FeCuO (2/1), CoMnO (2/1) and FeSnO (1/1), respectively. For these electrodes, the CE of the water electrolysis to hydrogen is, of course, significantly higher (at least 75%) than those of the electro-reduction of CO2. The CE of the CO2 electro-reduction is less than 20%. The CE of the CO2 electro-reduction to methanol is lower than that of its electrochemical reduction to tert-butanol. The highest CE of the CO2 electro-reduction to e-fuels and e-chemicals is obtained on the FeCuO electrocatalyst. The optimum current density for CO2 electro-reduction is in the range of 30-75 A m-2. Table 3 shows the results of the bioelectrochemical reduction of CO2 in MES cell using FeSnO (1/1) electrode. Calculated CE ranged from 60% to 88% at various current densities. The CE of CO₂ reduction to VFAs ranged from 53% to 79%, with a CO₂ conversion efficiency reaching 96% under continuous operation with CO₂ flow rates of 200 and 300 mL/day to the cathode compartment. Production of butyrate and caproate increased by 4.6 and 3.9 times, respectively, in the MES cell with the FeSnO (1/1) cathode compared to a MES cell with an uncoated carbon felt cathode. Conclusion: The study shows that selecting specific bimetallic oxides can influence microbial CO2 reduction. Furthermore, converting an electrochemical cell to a microbial electrosynthesis cell by adding an enriched mixed acidogenic culture in the cathode compartment enhances CO2 reduction. The findings also indicate that the microbial chain elongation activity of the mixed culture improves with the presence of certain bimetallic oxides, such as FeSnO. Figure 1

The availability of inexpensive industrial CO gas streams motivates efficient electrocatalytic upgrading of CO to higher-value feedstocks such as ethylene. However, the electrosynthesis of ethylene by the CO reduction reaction (CORR) has suffered from low selectivity and energy efficiency. Here we find that the recent strategy of increasing performance through use of highly alkaline electrolyte—which is very effective in CO2RR—fails in CORR and drives the reaction to acetate. We then observe that ethylene selectivity increases when we constrain (decrease) CO availability. Using density functional theory, we show how CO coverage on copper influences the reaction pathways of ethylene versus oxygenate: lower CO coverage stabilizes the ethylene-relevant intermediates whereas higher CO coverage favours oxygenate formation. We then control local CO availability experimentally by tuning the CO concentration and reaction rate; we achieve ethylene Faradaic efficiencies of 72% and a partial current density of >800 mA cm−2. The overall system provides a half-cell energy efficiency of 44% for ethylene production. The electrocatalytic upgrading of CO to higher-value feedstocks provides a promising route to multicarbon products. Here, the authors show that high ethylene selectivity can be achieved by constraining CO availability on copper, with an ethylene Faradaic efficiency of 72% and a partial current density of >800 mA cm−2.

The electrochemical CO2 or CO reduction to chemicals and fuels using renewable energy is a promising way to reduce anthropogenic carbon emissions. The gas diffusion electrode (GDE) design enables low-carbon manufacturing of target products at a current density (e.g., 500 mA cm−2) relevant to industrial requirements. However, the long-term stability of the GDE is restricted by poor water management and flooding, resulting in a significant hydrogen evolution reaction (HER) within almost an hour. The optimization of water management in the GDE demands a thorough understanding of the role of the gas diffusion layer (GDL) and the catalyst layer (CL) distinctively. Herein, the hydrophobicity of the GDL and CL is independently adjusted to investigate their influence on gas transport efficiency and water management. The gas transport efficiency is more enhanced with the increase in hydrophobicity of the GDL than the CL. Direct visualization of water distribution by optical microscope and micro-computed tomography demonstrates that the water flow pattern transfers from the stable displacement to capillary fingering as GDL hydrophobicity increases. Unfortunately, only increasing the hydrophobicity is not sufficient to prevent flooding. A revolutionary change in the design of the GDE structure is essential to maintain the long-term stability of CO2/CO reduction.