National Research Infrastructure in Solar Energy Concentration

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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

Thermochemical performance of ceria coated-macroporous 3D-printed black zirconia structures for solar CO/H2 fuels production

Publication . Oliveira, Fernando; Barreiros, Maria Alexandra; Sardinha, Manuel; Leite, Marco; Fernandes, Jorge; Abanades, Stéphane

ABSTRACT: The use of macroporous structured ceria for the solar thermochemical splitting of CO2 and H2O to produce clean fuels through two-step redox cycles was investigated. The research aimed to assess the reactivity of 3D-printed black zirconia gyroid structures coated with a microporous layer of pure CeO2 for producing CO and H2. Such porous designs are intended to increase both the absorption of solar radiation and the available surface area for the solid-gas reaction. It was observed that the structure degraded more at the top of the reactor cavity, where the formation of CexZr1-xO2 solid solutions occurred at the coating/substrate interface. Besides, the porous ceria structure remained after redox cycles in the samples not directly exposed to solar radiation. Consequently, the solar reactor achieved CO and H2 production rates of up to 5.4 and 1.9 mL min-1 g-1 with fuel yield over 0.2 mmol g-1, and the material maintained its performance over several consecutive cycles without any loss of reactivity. This indicates a strong potential for producing solar fuels at a large facility using custom 3D-printed ceria-coated structures.

2025-01Journal article

Open access