Continuous Electrochemical Reduction of CO2 to Formate: Comparative Study of the Influence of the Electrode Configuration with Sn and Bi-Based Electrocatalysts

Abstract

Climate change has become one of the most important challenges in the 21st century, and the electroreduction of CO2 to value-added products has gained increasing importance in recent years. In this context, formic acid or formate are interesting products because they could be used as raw materials in several industries as well as promising fuels in fuel cells. Despite the great number of studies published in the field of the electrocatalytic reduction of CO2 to formic acid/formate working with electrocatalysts of different nature and electrode configurations, few of them are focused on the comparison of different electrocatalyst materials and electrode configurations. Therefore, this work aims at presenting a rigorous and comprehensive comparative assessment of different experimental data previously published after many years of research in different working electrode configurations and electrocatalysts in a continuous mode with a single pass of the inputs through the reactor. Thus, the behavior of the CO2 electroreduction to formate is compared operating with Sn and Bi-based materials under Gas Diffusion Electrodes (GDEs) and Catalyst Coated Membrane Electrodes (CCMEs) configurations. Considering the same electrocatalyst, the use of CCMEs improves the performance in terms of formate concentration and energy consumption. Nevertheless, higher formate rates can be achieved with GDEs because they allow operation at higher current densities of up to 300 mA·cm−2. Bi-based-GDEs outperformed Sn-GDEs in all the figures of merit considered. The comparison also highlights that in CCME configuration, the employ of Bi-based-electrodes enhanced the behavior of the process, increasing the formate concentration by 35% and the Faradaic efficiency by 11%.

Continuous electroconversion of CO2 into formate using 2 nm tin oxide nanoparticles

“…), since those two operational variables were previously identified as key parameters in the production of formate from CO 2 RR [22,63,68]. Figure 7 shows that the production of formate, which is a key figure of merit to evaluate the CO 2 RR performance, is strongly dependent on both parameters:…”

“…This is the highest formate concentration value reported on Sn based electrocatalysts using a flow electrolyzer and a catholyte solution in equivalent conditions. Only catholyte-free electrolyzers have been able to produce significantly higher formate concentrations [68,70]. The catholyte flow per geometric electrode area (F/A) and the applied current density were the two parameters evaluated on the results reported in Table 1.…”

Towards the Electrochemical Conversion of CO2 to Formic Acid at an Applicative Scale: Technical and Economic Analysis of Most Promising Routes

“…Five CSs, all based on ERCO 2 to FA/formate using Sn-based electrodes in aqueous electrolyte, reported in the literature and characterised by particularly good performances and by usage of relatively cheap materials and simple cell designs were selected. [15,17,18,20,30] Indeed, most of the investigated technologies in the literature were based on the usage of more expensive cathodes (including core-shell structured Cu 2 O/Cu@C immobilized on nitrogen-doped graphene sheets (Cu2O/Cu@C/ NG), [31] Bi 2 O 2 CO 3 nanosheets, [32] Sn(S)/Au nanoparticles, [33] BiÀ SnO/Cu foam, [34] SnCu alloys, [35] Ag x Sn y alloys, [36][37] In x Sn y alloys, [38,39] Sn x Pb y alloys, [40] Sn x Pb y Bi z alloys, [41] Cu x In y alloys, [42][43][44][45] Pd-, [46] PdPt- [47] or Bi-based catalyst, [48][49][50] etc.) or more complex reactor designs, which are more difficult to scale-up.…”

“…or more complex reactor designs, which are more difficult to scale-up. As an example, Diaz-Sainz et al [48,49] achieved higher [FA] and FE than that obtained with Sn-based cathodes using Bi-based catalysts fitted in coated membrane electrodes complex reactors, but drastically increasing the energy consumption and, consequently, the energetic costs, and reducing the economic viability.…”

Recent Advances in the Electroreduction of CO2 over Heteroatom-Doped Carbon Materials

“…The utilization of gas-diffusion electrodes also minimized ohmic losses, thereby allowing current densities relevant for industrial purposes (e.g., 300 mA cm −2 ) to be reached. Diaz-Sainz et al [39] stressed the importance of the electrode configuration in this reaction by comparing the performance of a large number of electrode configurations and electrocatalysts in this reaction. Gas diffusion and catalyst-coated membrane Bi and Sn electrode configurations provided different results.…”