Electrochemical reduction of CO2 to formate on nanoparticulated Bi-Sn-Sb electrodes

Human activities during the last century have increased the concentration of greenhouse gases in Earth's atmosphere, mainly carbon dioxide (CO2), and the impacts of climate change around the world are becoming more damaging. Therefore, scientific research is needed to mitigate the consequences of atmospheric CO2, and, among others, the electrochemical CO2 conversion to useful chemicals is one of the most interesting alternatives. Herein, different Bi, Sn and Sb systems were synthesised as nanoparticles, supported on carbon (Vulcan XC-72R) and finally used to manufacture electrodes. The Bi-Sn-Sb nanoparticulated systems and their corresponding electrodes were characterised by TEM, XPS, ICP-OES and SEM. Electrochemical reduction of CO2 to formate was performed in an electrochemical H-type cell in a CO2-saturated KHCO3 and KCl solution. The Bi-Sn-Sb electrodes exhibited good activity and selectivity for the CO2 reduction towards formate. Particularly, Bi95Sb05/C and Bi80Sn10Sb10/C electrodes showed improved stability compared to previous works, keeping values of formate efficiency over 50 % after 24 h.This research was funded by the MICINN Spanish Ministry, through the projects CTQ2016-76231-C2-2-R (AEI/FEDER, UE) and PID2019-108136RB-C32

Revealing the Intrinsic Restructuring of Bi2O3 Nanoparticles into Bi Nanosheets during Electrochemical CO2 Reduction

Bismuth is a catalyst material that selectively produces formate during the electrochemical reduction of CO2. While different synthesis strategies have been employed to create electrocatalysts with better performance, the restructuring of bismuth precatalysts during the reaction has also been previously reported. The mechanism behind the change has, however, remained unclear. Here, we show that Bi2O3 nanoparticles supported on Vulcan carbon intrinsically transform into stellated nanosheet aggregates upon exposure to an electrolyte. Liquid cell transmission electron microscopy observations first revealed the gradual restructuring of the nanoparticles into nanosheets in the presence of 0.1 M KHCO3 without an applied potential. Our experiments also associated the restructuring with solubility of bismuth in the electrolyte. While the consequent agglomerates were stable under moderate negative potentials (−0.3 VRHE), they dissolved over time at larger negative potentials (−0.4 and −0.5 VRHE). Operando Raman spectra collected during the reaction showed that under an applied potential, the oxide particles reduced to metallic bismuth, thereby confirming the metal as the working phase for producing formate. These results inform us about the working morphology of these electrocatalysts and their formation and degradation mechanisms.B.Á.-B. is grateful to the MICINN Spanish Ministry for the predoctoral grant (reference CTQ2016-76231-C2-2-R). B.Á.-B., V.M., and J.S.-G. acknowledge financial support by the MICINN Spanish Ministry, (Project PID2019-108136RB-C32) and Generalitat Valenciana (Project PROMETEO/2020/063). F.Y. acknowledges funding from the Chinese Scholars Council, A.Y. from the Humboldt Foundation (Germany), and M.L.L from the National Council of Science and Technology of Mexico (CONACyT, Grant No. 708585)

On the activity and stability of Sb2O3/Sb nanoparticles for the electroreduction of CO2 toward formate

The development of new electrocatalysts with improved properties for the electrochemical reduction of CO2 is being the objective of innumerable contributions. In this contribution, the electrochemical reduction of CO2 to formate on novel carbon-supported antimony nanoparticles (Sb/C NPs) is studied. The carbon-supported Sb2O3/Sb nanoparticles were synthesised using a simple methodology at room temperature and characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The Sb2O3/Sb/C electrodes were prepared by air-brushed onto a carbon paper and were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The Sb2O3/Sb/C electrodes were also electrochemically characterized by cyclic voltammetry and displayed a clear activity for CO2 electroreduction. To evaluate the properties of the electrodes for the reduction of CO2, electrolyses at different potentials were systematically conducted. Hydrogen and formate were the only products found. The faradic efficiency towards formate was found to be about 20%. This FE was in good agreement with previous finding obtained with comparable system. Interestingly, 24-hour tests were carried out to analyse the stability of the material under working conditions. The results indicate that Sb2O3/Sb-based electrodes display a remarkably better stability than other nanostructured electrocatalysts such as Sn or Bi.This work was supported by the MINECO, through the projects CTQ2016-76231-C2-2-R (AEI/FEDER, UE) and PID2019-108136RB-C32. Also, the invitation by the E3TECH Spanish Network of Excellence (CTQ2017-90659-REDT (MEIC/AEI)) is kindly acknowledged

Cathodic reduction of CO2 to formic acid: Effect of the nature of the cathode for pressurized systems

Electrochemical conversion of CO2 into formic acid (FA) in an aqueous electrolyte is considered a promising strategy to valorise waste-CO2. Some studies, mainly performed using Sn cathodes, have shown that the performance of the process can be strongly improved using pressurized systems. On the other hand, other studies, usually carried out in non-pressurized systems, have indicated that the nature of the cathode can strongly affect the process. Hence, in this work, we have investigated the coupled effect of nature of the cathode and CO2 pressure (PCO2 ) on the electrochemical conversion of CO2 to FA. Four electrodes (Sn, Sn/C-NP, Bi, Bi/C-NP) have been used as model cathodes. The results obtained have shown that the increase of PCO2 enhances the production of FA and the faradic efficiency of the process (FEFA) for all tested cathodes. Moreover, it has been observed that nanoparticle-based cathodes provided better results for electrolyses carried out at 1 bar and high current density. Conversely, at relatively high PCO2 , the effect of the nature of the cathode becomes less important and bulk Sn and Bi electrodes display very interesting results in terms of production of FA, FEFA and stability

CO2 reduction to formate on an affordable bismuth metal-organic framework based catalyst

Electrochemical reduction of carbon dioxide (CO2) into green fuels and valuable chemicals is an up-and-coming method of CO2 valorization. Formate/formic acid is one the most desirable product among the many other possible chemicals that can be generated from CO2. Herein, we report on a simple and tunable method to prepare Bi-based electrocatalyst. An affordable metal-organic framework (MOF) precursor TAL-33 has been utilized upon carbonization. This MOF was fabricated from a novel modular carbon-rich ligand 1H-benzo[d]imidazole-5,6-diol and bismuth chloride. Cyclic voltammetry and chronoamperometric measurements were performed to investigate the electrocatalytic activity and selectivity towards the formate. The most promising samples have shown high Faradaic efficiency and stability. The in-depth physical characterization of catalyst structure (XPS, XRD, SEM, and TEM) was performed to investigate the structure-activity relationships. Theoretical studies have been performed to confirm that the enhanced CO2 electroreduction to formate is linked to the presence of metallic bismuth sites.This research was supported by Estonian Research Council grant PSG250; EU through the European Regional Development Fund, Estonia (TK141, “Advanced materials and high-technology devices for energy recuperation systems” and TK143, “Molecular Cell Engineering”); Environmental Investment Center circular economy program (KIK18070). A.B, V. M. and J.S.G. acknowledge the financial support of the Ministerio de Ciencia e Innovación-FEDER (Spain) through the project PID2019-108136RB-C32 and Generalitat Valenciana (Project PROMETEO/2020/063). S.V. acknowledges the financial support of ERA Chair MATTER from the European Union’s Horizon 2020, Estonia research and innovation programme under grant agreement No 856705