Layered Double Hydroxide-based materials: efficient catalysts for the electroreduction of CO2,
Résumé
The emission of CO2 by industrial action seriously impacts our environment which requires us to consider strategies to reduce the emitted CO2 to the atmosphere. The electrochemical reduction of CO2 (CO2ER) into molecules such as CO, HCOOH, CH3COOH, and CH4 is one of the many ways to valorize CO2 as fuels or chemicals1. Amongst the different catalysts investigated, Layered Double Hydroxides (LDH) appeared to be particularly interesting. In the one hand, these two-dimensional matrices can be used to immobilize molecular catalysts such as iron (III) tetraphenyl porphyrins, showed an efficient electro-transformation of CO2 to CO in both organic and aqueous media. On the other hand, since various types of Cu-based materials have revealed unique advantages as electro-catalysts for CO2ER, including hydrocarbon production and product selectivity2, Cu-based LDH ([M(II)1-xAl(III)x(OH)2]x+[An-]x/n·yH2O, 0.20 ≤ x ≤ 0.33), with M(II) = Cu and M(III) = Al have also been investigated for CO2ER3. The CuAl-LDH matrices appeared as promising electrocatalyst promoting the electrochemical conversion, in galvanostatic conditions, of CO2 to CO and HCOOH. A morphology control allowed to improve the catalytic activity by tailoring the structure of active sites and increasing the surface area/number of active sites.
Herein, the electrochemical efficiencies towards CO2ER of a series of LDH matrices will be discussed. Firstly, to improve the catalytic durability and enhance the catalytic efficiency, heterogeneous electro-catalysts were prepared by the intercalation of (4-sulfonatophenyl)-porphyrin-Fe(III) chloride (FeTSPP) in LDH. The structural and morphological characteristics and the electroactivity in different electrolytes under inert atmosphere Ar or in the presence of CO2, of LDH-FeTSPP LDH were investigated. Based on these results, a preparative scale electrolysis was performed to determine the selectivity and the faradic efficiency of the transformation of CO2 to CO and the efficiency of these approach. Secondly, CuAl- LDH materials were also synthesized by both the coprecipitation and the polyol method and characterized by solid-state techniques. Electrochemical characterization of the Cu-LDH modified electrodes was carried out following a specific protocol by linear sweep voltammetry and cyclic voltammetry showing that an electrochemical activation of the Cu-LDH occurred at Eapp >-1.4 V, leading to an enhancement of the electrochemical signal of the copper redox couples, addressing to more accessible catalytic sites and to an increase in current under CO2 and hence CO2 activation. The influence of the LDH composition that is the Cu amount into the layer, the presence of Mg or Zn in a ternary layer composition, and the nature of the interlayer anions were investigated to identify the best electrocatalyst.
1- Zhu, D. D.; Liu, J. L.; Qiao, S. Z. Recent Advances in Inorganic Heterogeneous Electrocatalysts for Reduction of Carbon Dioxide. Advanced Materials 2016, 28 (18), 3423.
2- Zhao, J.; Xue, S.; Barber, J.; Zhou, Y.; Meng, J.; Ke, X. An overview of Cu-based heterogeneous electrocatalysts for CO2 reduction. Journal of Materials Chemistry A 2020, 8 (9), 4700
3- Iwase, K.; Hirano, T.; Honma, I. Copper Aluminum Layered Double Hydroxides with Different Compositions and Morphologies as Electrocatalysts for the Carbon Dioxide Reduction Reaction. ChemSusChem 2022, 15 (2), e202102340