Electrochemical Reduction of CO2 to Formate on Easily Prepared Carbon-Supported Bi Nanoparticles

Abstract

Herein, the electrochemical reduction of CO₂ to formate on carbon-supported bismuth nanoparticles is reported. Carbon-supported Bi nanoparticles (about 10 nm in size) were synthesized using a simple, fast and scalable approach performed under room conditions. The so-prepared Bi electrocatalyst was characterized by different physicochemical techniques, including transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction and subsequently air-brushed on a carbon paper to prepare electrodes. These electrodes were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and also by cyclic voltammetry. Finally, CO₂ electroreduction electrolyses were performed at different electrode potentials for 3 h. At the optimal electrode potential (-1.6 V vs AgCl/Ag), the concentration of formate was about 77 mM with a faradaic efficiency of 93 ± 2.5%. A 100% faradaic efficiency was found at a lower potential (-1.5 V vs AgCl/Ag) with a formate concentration of about 55 mM. In terms of stability, we observed that after about 70 h (in 3 h electrolysis experiments at different potentials), the electrode deactivates due to the gradual loss of metal as shown by SEM/EDX analyses of the deactivated electrodes.

Keywords: Bi electrodes; CO2 reduction; electrocatalysis; formate.

Figure 1

(a,b) TEM images and (c) particle size histogram corresponding to Bi/C prepared with a PVP to Bi ratio of 1.

Figure 2

Field emission SEM images of the Bi/C electrode with Bi loading of 0.1 mg cm⁻²: (a) magnification ×130, and (b) magnification ×100.00 K. Micrographs (c–e) correspond to SEM-EDX mapping: d and e highlight, in red, the distribution of BiNPs on the carbon substrate.

Figure 3

Cyclic voltammetry response of Bi/C electrode with Bi loading of 0.1 mg cm⁻² in Ar (black line) and CO₂ (red line) saturated 0.5 M KHCO₃. Scan rate 50 mV s⁻¹.

Figure 4

(a) Faradaic efficiency for formate production at different controlled potential from −1.5 to −1.8 V. Electrolysis time: 3 h. (b) Formate concentration produced after 3 h of electrochemical reduction of CO₂ at different controlled potentials as a function of Faradaic efficiency.

Figure 5

Back-scattered electrons field emission SEM images of the Bi-based electrodes with Bi loading of 0.1 mg cm⁻²: (a) as-prepared, and (b) after aprox. 70 h in 3-h CO₂ reduction experiments at different potentials.

Figure 6

Faradaic efficiency and formate concentration vs time during 24 h CO₂ electroreduction electrolysis at −1.6 V.