Simply and effectively electrodepositing Bi-MWCNT-COOH composite on Cu electrode for efficient electrocatalytic CO2 reduction to produce HCOOH

Spherical Bi2O3/ATO catalyst with N2 pre-reduction electrocatalytic reduction of CO2 to formic acid

Bi2O3 catalyst with Bi-O bond crystal structure has more active sites, which shows better CO2 catalytic performance than pure Bi catalysts in many catalytic reactions. How to strengthen the Bi-O bond in Bi2O3 to obtain higher selectivity and catalytic activity is a problem worthy of consideration. Here, we develop a N2 pre-reduced spherical Bi2O3/ATO catalyst that has a high formate Faradaic efficiency of 92.7%, which is superior to the existing tin oxide catalyst. Detailed electrocatalytic analysis shows that N2 pre-reduction and spherical structure are helpful for Sn to stabilize the oxidation state of Bi, thus retaining part of the Bi-O structure. The existence of the Bi-O structure can reduce the energy barrier of the CO2 production *OCHO reaction and promote the reaction rate of the CO2-*OCHO-HCOOH path, thus promoting the formation of formate.

In-modified Sn-MOFs with high catalytic performance in formate electrosynthesis from aqueous carbon dioxide

Electrochemical reduction of carbon dioxide (CO2ER) has become an effective solution to relieve the energy crisis and tackle climate change. In this study, a series of tin-based organic frameworks modified by In (Sn-MOF/Inx) were successfully synthesized via a simple hydrothermal method and explored for high formate-selective CO2ER. The pure Sn-MOF exhibits maximum formate selectivity with a faradaic efficiency (FEformate) of approximately 85.0% and a current density of 15 mA cm-2 at -1.16 VRHE, while the In (6%)-modified Sn-MOF (Sn-MOF/In6) delivers a much higher maximum FEformate (around 97.5%) and a current density of 16 mA cm-2 at -0.96 VRHE. Remarkably, the Sn-MOF/In6 exhibits a significantly larger specific surface area (183.3 m2 g-1) compared to the Sn-MOF (65.2 m2 g-1). These findings indicate that introducing In, an alien element with a slightly different outer orbital electron number from that of Sn, can significantly boost the selectivity and activity for CO2ER to formate. This study presents an efficient way to modify MOF catalysts through a well-designed introducing process.

Alloying strategies for tuning product selectivity during electrochemical CO2 reduction over Cu

Excessive reliance on fossil fuels has led to the release and accumulation of large quantities of CO₂ into the atmosphere which has raised serious concerns related to environmental pollution and global warming. One way to mitigate this problem is to electrochemically recycle CO₂ to value-added chemicals or fuels using electricity from renewable energy sources. Cu is the only metallic electrocatalyst that has been shown to produce a wide range of industrially important chemicals at appreciable rates. However, low product selectivity is a fundamental issue limiting commercial applications of electrochemical CO₂ reduction over Cu catalysts. Combining copper with other metals that actively contribute to the electrochemical CO₂ reduction reaction process can selectively facilitate generation of desirable products. Alloying Cu can alter surface binding strength through electronic and geometric effects, enhancing the availability of surface confined carbon species, and stabilising key reduction intermediates. As a result, significant research has been undertaken to design and fabricate copper-based alloy catalysts with structures that can enhance the selectivity of targeted products. In this article, progress with use of alloying strategies for development of Cu-alloy catalysts are reviewed. Challenges in achieving high selectivity and possible future directions for development of new copper-based alloy catalysts are considered.

Enhanced electrocatalytic reduction of CO2 to formate via doping Ce in Bi2O3 nanosheets

Formate is considered as the most economically viable product of the prevalent electrochemical CO₂ reduction (ECR) products. However, most of the catalysts for ECR to formate in aqueous solution often suffer from low activity and limited selectivity. Herein, we report a novel Ce-doped Bi₂O₃ nanosheet (NS) electrocatalyst by a facile solvothermal method for highly efficient ECR to formate. The 5.04% Ce-doped Bi₂O₃ NSs exhibited a current density of 37.4 mA cm^-2 for the production of formate with a high formate faradaic efficiency (FE) of 95.8% at -1.12 V. The formate FE was stably maintained at about 90% in a wide potential range from -0.82 to -1.22 V. More importantly, density functional theory (DFT) calculations revealed that Ce doping can lead to a significant synergistic effect, which promotes the formation and the adsorption of the OCHO* intermediate for ECR, while significantly inhibiting the hydrogen evolution reaction via depressing the formation of *H, thus helping achieve high current density and FE. This work provides an effective and promising strategy to develop efficient electrocatalysts with heteroatom doping and new insights for boosting ECR into formate.

High-efficient carbon dioxide-to-formic acid conversion on bimetallic PbIn alloy catalysts with tuned composition and morphology

CO₂ electroreduction to value-added chemicals and fuels has gained increasing attention; however, there are only a few catalysts with high performance under mild conditions that can be used in this technique. In this study, single metal Pb, In and bimetallic PbIn catalysts for aqueous CO₂ electroreduction were prepared using a facile 3-step process including PbIn granulation by reducing Pb(NO₃)₂/In(NO₃)₃ aqueous solution with NaBH₄, calcination in air, and in situ electroreduction. The bimetallic PbIn catalysts had better catalytic performance on CO₂ electroreduction than single metal catalysts. The bimetallic Pb₇In₃ catalyst (atomic ratios of Pb and In is 7:3) presented the highest formic acid faradaic efficiency of 91.6% at -1.26 V vs reversible hydrogen electrode in a 0.5 M CO₂-saturated KHCO₃ aqueous solution, which was 13% and 9.7% higher than that of single Pb and In catalysts, respectively. Moreover, the catalyst remained active after 10 h of continuous CO₂ electrolysis with a stale current density of -17 mA cm^-2. The experimental results showed that the excellent catalytic performance of Pb₇In₃ catalyst may stem from its higher electrochemical active surface area, lower charge-transfer resistance and the synergistic effect of Pb and In in the catalyst. The presented bimetallic PbIn catalysts may have a wide of application prospect, and they may be synthesized from heavy metals in industrial wastewaters.

CuBi electrocatalysts modulated to grow on derived copper foam for efficient CO2-to-formate conversion

Electrochemical reduction of CO₂ to fuels and chemicals is an effective way to reduce greenhouse gas emissions and alleviate the energy crisis, but the highly active catalysts necessary for this reaction under mild conditions are still rare. In this work, we grew CuBi bimetallic catalysts on derived copper foam substrates by co-electrodeposition, and then investigated the correlation between co-electrodeposition potential and electrochemical performance in CO₂-to-formate conversion. Results showed that the bimetallic catalyst formed at a low potential of - 0.6 V vs. AgCl/Ag electrode achieved the highest formate Faradaic efficiency (FE_formate) of 94.4% and a current density of 38.5 mA/cm² at a low potential of - 0.97 V vs. reversible hydrogen electrode (RHE). Moreover, a continuous-flow membrane electrode assembly reactor also enabled the catalyst to show better performance (a FE_formate of 98.3% at 56.6 mA/cm²) than a traditional H-type reaction cell. This work highlights the vital impact of co-electrodeposition potential on catalyst performance and provides a basis for the modulated growth of bimetallic catalysts on substrates. It also shows the possibility of preparing Bi-based catalysts with no obvious decrease in catalytic activity that have been partially replaced with more economic copper.

Nanoporous bismuth for the electrocatalytic reduction of CO2 to formate

Bi is an attractive catalyst towards the electrochemical reduction of CO₂ to formate. In this work, nanoporous bismuth was prepared by dealloying Mg₃Bi₂ with tartaric acid (TA) solution, and the size of the primary Bi nanoparticles was adjusted according to the concentration of TA. When the concentration of TA increased from 2 wt% to 20 wt%, the particle size of Bi increased from about 70 nm to 400 nm. The synthesized nanoporous Bi samples were investigated as electrocatalysts for the reduction of CO₂ in KHCO₃ electrolyte, and it was found that the smaller the particle size, the higher the catalytic activity. However, nanoporous Bi comprising 70 nm particles suffered from mass transfer difficulty and sintering during the reaction, whereas the 100 nm nanoporous Bi delivered both a high formate formation current and faradaic efficiency (FE) (16 mA cm^-2, FE > 90% at -0.88 V vs. RHE) and showed excellent durability.

Towards the Large-Scale Electrochemical Reduction of Carbon Dioxide

The severe increase in the CO2 concentration is a causative factor of global warming, which accelerates the destruction of ecosystems. The massive utilization of CO2 for value-added chemical production is a key to commercialization to guarantee both economic feasibility and negative carbon emission. Although the electrochemical reduction of CO2 is one of the most promising technologies, there are remaining challenges for large-scale production. Herein, an overview of these limitations is provided in terms of devices, processes, and catalysts. Further, the economic feasibility of the technology is described in terms of individual processes such as reactions and separation. Additionally, for the practical implementation of the electrochemical CO2 conversion technology, stable electrocatalytic performances need to be addressed in terms of current density, Faradaic efficiency, and overpotential. Hence, the present review also covers the known degradation behaviors and mechanisms of electrocatalysts and electrodes during electrolysis. Furthermore, strategic approaches for overcoming the stability issues are introduced based on recent reports from various research areas involved in the electrocatalytic conversion.