Understanding CO2 electro-reduction in porous materials

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Imidazolium and picolinium-based electrolytes for electrochemical reduction of CO2 at high pressure

Publication . Messias, Sofia; Paz, Vitória; Cruz, Hugo; Rangel, C. M.; Branco, Luis C; Machado, Ana

ABSTRACT: Ionic liquids (ILs) have been considered among one of the most promising materials under investigation for integration of CO2 capture and electrochemical reduction (ECR). In the design of an IL-based electrolyte that can be employed industrially, the understanding of the influence of IL structure on ECR was considered essential. In this context, electrolytes with trifluoromethanosulfonate (OTf) anion were investigated as aqueous electrolytes for electrochemical reduction of CO2 at high pressure and near room temperature with zinc electrodes. The effect of replacing the 1-ethyl-3-methyl-imidazolium cation [EMIM] by 1-ethyl-3-picolinium [C2(3)pic] and by 1-ethyl-4-picolinium [C2(4)pic] cations was studied. The use of picolinium-based electrolytes in ECR is for the first time reported. A high-pressure single compartment test bed was used for electrolyte screening. Carbon monoxide productivities and selectivities were determined for the several electrolytes with different water contents. The electrolytes were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Electrolyte conductivities and diffusion coefficients were estimated. The effect of the cations is complex as it affects conductivity, double layer structure, reaction reversibility and even the ionic liquid physical state. Notwithstanding, it is possible to tune these properties to achieve similar CO productions with reduced IL amounts, considering the nature of the cation and the water content, leading to the design of more cost effective electrolytes for efficient ECR process.

2022-03Journal article

Open access

Study of the degradation of Nafion modified membranes

Publication . Teixeira, Fatima; Teixeira, António P. S.; Rangel, C. M.

ABSTRACT: The development of new proton exchange membranes for PEM technology in fuel cells and electrolysers with increased durability is paramount to system´s lifetime and scalability. In this work, new modified Nafion membranes are proposed with increased resilience to chemical degradation by H2O2 /Fe2+, mimicking ex-situ radical attack to membrane structure.

2022-07Conference object

Open access

Chemical stability of new nafion membranes doped with bisphosphonic acids under Fenton oxidative conditions

Publication . Teixeira, Fatima; Teixeira, António P. S.; Rangel, C. M.

ABSTRACT: The development of new proton exchange membranes for PEM technology in fuel cells and electrolysers with increased durability is paramount to system's lifetime and scalability. In this work, new modified Nafion membranes doped with bisphosphonic acids are proposed with increased resilience to chemical degradation by H2O2/Fe2+, mimicking ex-situ radical attack to membrane structure. Relevant properties were evaluated throughout Fenton's test using fluoride ion release and gravimetry determinations, and by ATR-FTIR spectros-copy and SEM before and after the chemical degradation. The new membranes showed a very good chemical stability after oxidative degradation under Fenton's test conditions at 80 degrees C, with more durability than Nafion 115 commercial membrane. After chemical degradation, the proton conduction of the membranes was assessed through EIS which reveals a decrease in the proton conductivity of all membranes, with the new modified membranes showing a smaller decrease of their proton conduction properties than Nafion 115 membrane. Fluoride ion release, weight loss measurements and ATR-FTIR spectros-copy data analysis suggest degradation of the side chain of the ionomer.

2023-12Journal article

Open access

Protic ionic liquids as electrolyte for electrochemical CO2 reduction [Resumo]

Publication . Messias, Sofia; Paninho, A. B.; Rangel, C. M.; Branco, Luis C; Machado, Ana

ABSTRACT: Ionic liquids have been considered a promising material under investigation for integration of CO2 capture and electrochemical reduction, due to their recognized sustainability and tunable properties. During previous works, the development of an electrochemical process to produce syngas (CO+H2) using electrolytes based on 1-ethyl-3-methyl-imidazolium trifluoromethanosulfate [EMIM][OTf] was reported [1-2]. A more recent work reported the effect of replacing the 1-ethyl-3-methyl-imidazolium cation [EMIM] by 1-ethyl-3-picolinium [C2-3-pic] and 1-ethyl-4-picolinium [C2-4-pic] cations as electrolyte for electrochemical reduction of CO2 at pressures higher than atmospheric [3]. The objective of this work is to study the influence of protic ionic liquids-based electrolytes in electrochemical CO2 reduction. In this context, protic ionic liquids prepared by direct protonation of different imidazolium compounds using suitable organic acids have been investigated. All electrolytes are characterized by cyclic voltammetry and electrochemical impedance spectroscopy to evaluate their electrochemistry behavior for CO2 electroreduction processes. Productivities of gaseous products resulting from the co-electrolysis of CO2 and water together with their faradaic efficiencies have been also determined.

2023-03Conference object

Open access

Advances in electrochemical reduction of CO2 in ionic liquid-based electrolytes [Resumo]

Publication . Machado, Ana; Messias, Sofia; Paninho, A. B.; Nunes, A. V. M.; Rangel, C. M.; Branco, Luis C

ABSTRACT: Electrochemical reduction of CO2 was for the first time reported in 1870 [1], but it was only after 2010 that this field was the subject of intense research efforts. The use of renewable electricity to convert CO2 into products that are currently derived from fossil products and have high carbon footprint will certainly make this technology one pillar of a sustainable chemical industry. The scepticism towards the availability of cost effective products derived from CO2 electro-reduction that customers will be willing to buy has shifted to the belief that they can be commercially viable. Turning electrochemical CO2 reduction into a commercial technology will depend on economics, on the price of electricity, efficiency of the process and the value of the products. One way to improve the economics and improve the efficiency of the process is to integrate CO2 capture with conversion [2,3]. In this way the energy intensive regeneration step of the capture media can be eliminated and also CO2 transportation and storage. Ionic liquids are ideal media to achieve this integration, due to high CO2 adsorption capacity, high selectivity, wide electrochemical windows and nearly zero vapour pressure. The present work reports the progress of electrochemical reduction of CO2 in ionic liquids and the work of the authors in this field. It has been recognized that ionic liquids promote CO2 electro-reduction through lowering the reduction potential, the suppression of the competing hydrogen evolution reaction and by increasing the selectivity towards the target products. However, the understanding of the interactions between ionic liquids, CO2 and catalyst is still quite limited, but fundamental for synthetizing more efficient electrolytes for CO2 electro-reduction [4]. Thus, current cation and anion effects will be analysed and an overview of the current performance of heterogeneous electro-catalysts in ionic liquid- based electrolytes for CO2 electro-reduction will be provided.

2023-06Conference object

Open access