In Situ Spectroelectrochemical Study of Acetate Formation by CO2 Reduction Using Bi Catalyst in Amine-Based Capture Solution.

Carbon capture and utilization (CCU) are technologies sought to reduce the level of CO2 in the atmosphere. Industrial carbon capture is associated with energetic penalty, thus there is an opportunity to research alternatives. In this work, spectroelectrochemistry was used to analyze the electrochemical CO2 reduction (eCO2R) in CO2 saturated monoethanolamine (MEA)-based capture solutions, in a novel CCU process. The in situ Fourier transform infrared (FTIR) spectroscopy experiments show that at the Bi catalyst, the active species involved in the eCO2R is the dissolved CO2 in solution, and not carbamate. In addition, the products of eCO2R were evaluated under flow, using commercial Bi2O3 NP as catalyst. Formate and acetate were detected, with normalized FE for acetate up to 14.5 %, a remarkable result, considering the catalyst used. Acetate is formed either in the presence of cetrimonium bromide (CTAB) as surfactant or at higher current density (>-100 mA cm-2) and the results enabled the proposition of a pathway for its production. This work sheds light on the complex reaction environment of a capture medium electrolyte and is thus relevant for an improved understanding of the conversion of CO2 into value-added products and to evaluate the feasibility of a combined CCU approach.

Improving Stability of CO2 Electroreduction by Incorporating Ag NPs in N-Doped Ordered Mesoporous Carbon Structures.

The electroreduction of carbon dioxide (eCO2RR) to CO using Ag nanoparticles as an electrocatalyst is promising as an industrial carbon capture and utilization (CCU) technique to mitigate CO2 emissions. Nevertheless, the long-term stability of these Ag nanoparticles has been insufficient despite initial high Faradaic efficiencies and/or partial current densities. To improve the stability, we evaluated an up-scalable and easily tunable synthesis route to deposit low-weight percentages of Ag nanoparticles (NPs) on and into the framework of a nitrogen-doped ordered mesoporous carbon (NOMC) structure. By exploiting this so-called nanoparticle confinement strategy, the nanoparticle mobility under operation is strongly reduced. As a result, particle detachment and agglomeration, two of the most pronounced electrocatalytic degradation mechanisms, are (partially) blocked and catalyst durability is improved. Several synthesis parameters, such as the anchoring agent, the weight percentage of Ag NPs, and the type of carbonaceous support material, were modified in a controlled manner to evaluate their respective impact on the overall electrochemical performance, with a strong emphasis on operational stability. The resulting powders were evaluated through electrochemical and physicochemical characterization methods, including X-ray diffraction (XRD), N2-physisorption, Inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), SEM-energy-dispersive X-ray spectroscopy (SEM-EDS), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), STEM-EDS, electron tomography, and X-ray photoelectron spectroscopy (XPS). The optimized Ag/soft-NOMC catalysts showed both a promising selectivity (∼80%) and stability compared with commercial Ag NPs while decreasing the loading of the transition metal by more than 50%. The stability of both the 5 and 10 wt % Ag/soft-NOMC catalysts showed considerable improvements by anchoring the Ag NPs on and into a NOMC framework, resulting in a 267% improvement in CO selectivity after 72 h (despite initial losses) compared to commercial Ag NPs. These results demonstrate the promising strategy of anchoring Ag NPs to improve the CO selectivity during prolonged experiments due to the reduced mobility of the Ag NPs and thus enhanced stability.

Steering Hydrocarbon Selectivity in CO2 Electroreduction over Soft-Landed CuOx Nanoparticle-Functionalized Gas Diffusion Electrodes.

The use of physical vapor deposition methods in the fabrication of catalyst layers holds promise for enhancing the efficiency of future carbon capture and utilization processes such as the CO2 reduction reaction (CO2RR). Following that line of research, we report in this work the application of a sputter gas aggregation source (SGAS) and a multiple ion cluster source type apparatus, for the controlled synthesis of CuOx nanoparticles (NPs) atop gas diffusion electrodes. By varying the mass loading, we achieve control over the balance between methanation and multicarbon formation in a gas-fed CO2 electrolyzer and obtain peak CH4 partial current densities of -143 mA cm-2 (mass activity of 7.2 kA/g) with a Faradaic efficiency (FE) of 48% and multicarbon partial current densities of -231 mA cm-2 at 76% FE (FEC2H4 = 56%). Using atomic force microscopy, electron microscopy, and quasi in situ X-ray photoelectron spectroscopy, we trace back the divergence in hydrocarbon selectivity to differences in NP film morphology and rule out the influence of both the NP size (3-15 nm, >20 µg cm-2) and in situ oxidation state. We show that the combination of the O2 flow rate to the aggregation zone during NP growth and deposition time, which affect the NP production rate and mass loading, respectively, gives rise to the formation of either densely packed CuOx NPs or rough three-dimensional networks made from CuOx NP building blocks, which in turn affects the governing CO2RR mechanism. This study highlights the potential held by SGAS-generated NP films for future CO2RR catalyst layer optimization and upscaling, where the NPs' tunable properties, homogeneity, and the complete absence of organic capping agents may prove invaluable.

Effects of Benzyl-Functionalized Cationic Surfactants on the Inhibition of the Hydrogen Evolution Reaction in CO2 Reduction Systems.

Cationic surfactants, mainly hexadecyl cetrimonium bromide (CTAB), are widely used in electrocatalysis to affect the selectivity of the reaction, specifically to inhibit the hydrogen evolution reaction (HER) in CO2 reduction (CO2R) systems. However, little research has been done on the modification of the functional groups present in such surfactants in order to promote this HER-inhibiting effect. In this work, the effectiveness of CTAB was promoted by substituting a methyl group of the quaternary amine for a benzyl group. This cationic surfactant, cetalkonium chloride (CKC), increased the hydrophobicity of the surface of the electrode, promoting the HER inhibition and the CO2R when HCO3- is used as a carbon source, which allows combining capture and conversion in one and the same medium, making it industrially highly attractive. By performing a detailed electrochemical characterization, we proved that the benzyl group formed an enhanced hydrophobic layer on the surface of the electrode in addition to the alkyl chain of the surfactant, showing higher effectiveness compared to CTAB. In fact, the Faradaic efficiency of the CO2R increased from 39 to 66% in saturated HCO3- electrolytes by using CKC instead of CTAB as the HER inhibitor. This opens up a wide range of avenues for research on the application of surfactants in the field of electrocatalysis, because, as proven, a selective modification of it can tune the selectivity of the reaction, adding a new variable in the design of an efficient carbon capture and utilization system.

High-performance membranes with full pH-stability.

Following current strong demands from, among others, paper, food and mining industries, a novel type of nanofiltration membrane was developed, which displays excellent performance in terms of selectivity/flux with a unique combination of chemical stability over the full (0-14) pH-range and thermal stability up to 120 °C. The membrane consists of polyvinylidene fluoride grafted with polystyrene sulfonic acid. The optimum membrane showed water permeances of 2.4 L h-1 m-2 bar-1 while retaining NaCl, MgSO4 and Rhodamine B (479 Da) for respectively ≈60%, ≈80% and >96%.