Electro-reduction of carbon dioxide to formate on lead electrode in aqueous medium

Facile synthesis of lead-tin nanoparticles for electrocatalyzing carbon dioxide reduction to formate

A series of Pb-Sn catalysts were synthesized via facile chemical reduction for electrocatalytic CO₂ reduction (ECR). The optimized sample (Pb₇Sn₁) achieved 90.53% formate faradaic efficiency (FE) at a potential of -1.9 V vs. Ag/AgCl. Electrochemical and material evaluation reveals that its high performance can be attributed to the rich active sites exposed by the high specific surface area of the electrode. In addition, the synergy between Pb and Sn is also a strong contributor to the high selectivity of formate. This work provides some insights into the preparation of simple and efficient ECR catalysts.

Can microbes be harnessed to reduce atmospheric loads of greenhouse gases?

Reducing atmospheric loads of greenhouse gases (GHGs), especially CO₂ and CH₄ , has been considered the key to alleviating global crises we are facing, such as climate change, sea level elevation and ocean acidification. To this end, development of strategies and technologies for carbon capture, sequestration and utilization (CCSU) is urgently needed. Although physicochemical methods have been the most actively studied in the early stages of developing CCSU technologies, there have recently been growing interests in developing microbe-based CCSU processes. In this article, we discuss advantages of microbe-based CCSU technologies over physicochemical approaches and even plant-based approaches. Next, various parts of the global carbon cycle where microorganisms can contribute, such as sequestering atmospheric GHGs, facilitating the carbon cycle, and slowing down the depletion of carbon reservoirs are described, emphasizing the impacts of microbes on the carbon cycle. Strategies to upgrade microbes and increase their performance in assimilating GHGs or converting GHGs to value-added chemicals are also provided. Moreover, several examples of exploiting microbes to address environmental crises are discussed. Finally, we discuss things to overcome in microbe-based CCSU technologies and provide future perspectives.

Waste-Derived Copper-Lead Electrocatalysts for CO2 Reduction

It remains a real challenge to control the selectivity of the electrocatalytic CO₂ reduction (eCO₂R) reaction to valuable chemicals and fuels. Most of the electrocatalysts are made of non-renewable metal resources, which hampers their large-scale implementation. Here, we report the preparation of bimetallic copper-lead (CuPb) electrocatalysts from industrial metallurgical waste. The metal ions were extracted from the metallurgical waste through simple chemical treatment with ammonium chloride, and Cu_xPb_y electrocatalysts with tunable compositions were fabricated through electrodeposition at varying cathodic potentials. X-ray spectroscopy techniques showed that the pristine electrocatalysts consist of Cu⁰, Cu¹⁺ and Pb²⁺ domains, and no evidence for alloy formation was found. We found a volcano-shape relationship between eCO₂R selectivity toward two electron products, such as CO, and the elemental ratio of Cu and Pb. A maximum Faradaic efficiency towards CO was found for Cu_9.00Pb_1.00, which was four times higher than that of pure Cu, under the same electrocatalytic conditions. In situ Raman spectroscopy revealed that the optimal amount of Pb effectively improved the reducibility of the pristine Cu¹⁺ and Pb²⁺ domains to metallic Cu and Pb, which boosted the selectivity towards CO by synergistic effects. This work provides a framework of thinking to design and tune the selectivity of bimetallic electrocatalysts for CO₂ reduction through valorization of metallurgical waste.

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.

Catalytic potential of post-transition metal doped graphene-based single-atom catalysts for the CO2 electroreduction reaction

Catalysts are required to ensure electrochemical reduction of CO₂ to fuels proceeds at industrially acceptable rates and yields. As such, highly active and selective catalysts must be developed. Herein, a density functional theory study of p‐block element and noble metal doped graphene‐based single‐atom catalysts in two defect sites for the electrochemical reduction of CO₂ to CO and HCOOH is systematically undertaken. It is found that on all of the systems considered, the thermodynamic product is HCOOH. Pb/C₃, Pb/N₄ and Sn/C₃ are identified as having the lowest overpotential for HCOOH production while Al/C₃, Al/N₄, Au/C₃ and Ga/C₃ are identified as having the potential to form higher order products due to the strength of binding of adsorbed HCOOH.

Applications of Carbon Dots for the Photocatalytic and Electrocatalytic Reduction of CO2

The photocatalytic and electrocatalytic conversion of CO2 has the potential to provide valuable products, such as chemicals or fuels of interest, at low cost while maintaining a circular carbon cycle. In this context, carbon dots possess optical and electrochemical properties that make them suitable candidates to participate in the reaction, either as a single component or forming part of more elaborate catalytic systems. In this review, we describe several strategies where the carbon dots participate, both with amorphous and graphitic structures, in the photocatalysis or electrochemical catalysis of CO2 to provide different carbon-containing products of interest. The role of the carbon dots is analyzed as a function of their redox and light absorption characteristics and their complementarity with other known catalytic systems. Moreover, detailed information about synthetic procedures is also reviewed.

The challenges of using NAD+-dependent formate dehydrogenases for CO2 conversion

In recent years, CO₂ reduction and utilization have been proposed as an innovative solution for global warming and the ever-growing energy and raw material demands. In contrast to various classical methods, including chemical, electrochemical, and photochemical methods, enzymatic methods offer a green and sustainable option for CO₂ conversion. In addition, enzymatic hydrogenation of CO₂ into platform chemicals could be used to produce economically useful hydrogen storage materials, making it a win-win strategy. The thermodynamic and kinetic stability of the CO₂ molecule makes its utilization a challenging task. However, Nicotine adenine dinucleotide (NAD⁺)-dependent formate dehydrogenases (FDHs), which have high selectivity and specificity, are attractive catalysts to overcome this issue and convert CO₂ into fuels and renewable chemicals. It is necessary to improve the stability, cofactor necessity, and CO₂ conversion efficiency of these enzymes, such as by combining them with appropriate hybrid systems. However, metal-independent, NAD⁺-dependent FDHs, and their CO₂ reduction activity have received limited attention to date. This review outlines the CO₂ reduction ability of these enzymes as well as their properties, reaction mechanisms, immobilization strategies, and integration with electrochemical and photochemical systems for the production of formic acid or formate. The biotechnological applications of FDH, future perspectives, barriers to CO₂ reduction with FDH, and aspects that must be further developed are briefly summarized. We propose that constructing hybrid systems that include NAD⁺-dependent FDHs is a promising approach to convert CO₂ and strengthen the sustainable carbon bio-economy.

Reconstructed Bismuth-Based Metal-Organic Framework Nanofibers for Selective CO2 -to-Formate Conversion: Morphology Engineering

Electrochemical reduction of carbon dioxide (ERCO₂ ) is an attractive and sustainable approach to close the carbon loop. Formic acid is a high-value and readily collectible liquid product. However, the current reaction selectivity remains unsatisfactory. In this study, the bismuth-containing metal-organic framework CAU-17, with morphological variants of hexagonal prisms (CAU-17-hp) and nanofibers (CAU-17-fiber), is prepared at room temperature through a wet-chemical approach and employed as the electrocatalyst for highly selective CO₂ -to-formate conversion. An H₃ BTC-mediated morphology reconstruction is systematically investigated and further used to build a CAU-17-fiber hierarchical structure. The as-prepared CAU-17-fiber_400 electrodes give the best electrocatalytic performance in selective and efficient formate production with FE_HCOO- of 96.4 % and j_COOH- of 20.4 mA cm^-2 at -0.9 V_RHE . This work provides a new mild approach for synthesis and morphology engineering of CAU-17 and demonstrates the efficacy of morphology engineering in regulating the accessible surface area and promoting the activity of MOF-based materials for ERCO₂ .

Electrocatalysis for CO2 conversion: from fundamentals to value-added products

This timely and comprehensive review mainly summarizes advances in heterogeneous electroreduction of CO₂: from fundamentals to value-added products.

Graphene oxide/reduced graphene oxide films as protective barriers on lead against differential aeration corrosion induced by water drops

Graphene-based materials have demonstrated high chemical stability and are very promising for protection against the corrosion of metal surfaces. For this reason, in this work, protective layers composed of graphene oxide, reduced graphene oxide and their mixtures were investigated, respectively, against the corrosion of the surface of lead induced by water drops. The materials were deposited on a Pb surface from their suspensions using a Meyer rod. The surface chemical composition, morphology and structure of the coatings were studied by X-ray photoemission spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and stylus profilometry. Moreover, a specific methodology based on the evolution of the water contact angle with time was used to evaluate the reactivity of the lead surface. The results show that the graphene-based materials can form an efficient barrier layer against the degradation of the Pb surface and that the degradation process induced by water is reduced by more than 70%. Moreover, unexpectedly, the best protective performance was obtained using graphene oxide as the coating.

Unveiling hydrocerussite as an electrochemically stable active phase for efficient carbon dioxide electroreduction to formate

For most metal-containing CO2 reduction reaction (CO2RR) electrocatalysts, the unavoidable self-reduction to zero-valence metal will promote hydrogen evolution, hence lowering the CO2RR selectivity. Thus it is challenging to design a stable phase with resistance to electrochemical self-reduction as well as high CO2RR activity. Herein, we report a scenario to develop hydrocerussite as a stable and active electrocatalyst via in situ conversion of a complex precursor, tannin-lead(II) (TA-Pb) complex. A comprehensive characterization reveals the in situ transformation of TA-Pb to cerussite (PbCO3), and sequentially to hydrocerussite (Pb3(CO3)2(OH)2), which finally serves as a stable and active phase under CO2RR condition. Both experiments and theoretical calculations confirm the high activity and selectivity over hydrocerussite. This work not only offers a new approach of enhancing the selectivity in CO2RR by suppressing the self-reduction of electrode materials, but also provides a strategy for studying the reaction mechanism and active phases of electrocatalysts.

Conversion of Escherichia coli to Generate All Biomass Carbon from CO2

The living world is largely divided into autotrophs that convert CO₂ into biomass and heterotrophs that consume organic compounds. In spite of widespread interest in renewable energy storage and more sustainable food production, the engineering of industrially relevant heterotrophic model organisms to use CO₂ as their sole carbon source has so far remained an outstanding challenge. Here, we report the achievement of this transformation on laboratory timescales. We constructed and evolved Escherichia coli to produce all its biomass carbon from CO₂. Reducing power and energy, but not carbon, are supplied via the one-carbon molecule formate, which can be produced electrochemically. Rubisco and phosphoribulokinase were co-expressed with formate dehydrogenase to enable CO₂ fixation and reduction via the Calvin-Benson-Bassham cycle. Autotrophic growth was achieved following several months of continuous laboratory evolution in a chemostat under intensifying organic carbon limitation and confirmed via isotopic labeling.

Development of self-supported 3D microporous solder alloy electrodes for scalable CO2 electroreduction to formate

The overpotential decreased by 0.1 V for self-supported 3D micro-porous electrodes as compared to the flat surface electrodes for the CO₂RR to formate.

Multivariate calibration method for mass spectrometry of interfering gases such as mixtures of CO, N2 , and CO2

A multivariate calibration method for mass spectrometry is presented that enables a quantitative analysis of gas mixtures containing interfering gases that contribute to the same mass-to-charge ratios at nominal resolution. Multiple calibration gas mixtures with linearly independent compositions are used in order to obtain the calibration constants for the contribution of each gas to each of the mass-to-charge ratio peaks. The method was successfully applied to the quantitative detection of CO in a mixture with CO₂ and N₂ , which represents a difficulty commonly encountered in heterogeneous catalysis and electrocatalysis research.

Assimilation of formic acid and CO2 by engineered Escherichia coli equipped with reconstructed one-carbon assimilation pathways

Gaseous one-carbon (C1) compounds or formic acid (FA) converted from CO2 can be an attractive raw material for bio-based chemicals. Here, we report the development of Escherichia coli strains assimilating FA and CO2 through the reconstructed tetrahydrofolate (THF) cycle and reverse glycine cleavage (gcv) pathway. The Methylobacterium extorquens formate-THF ligase, methenyl-THF cyclohydrolase, and methylene-THF dehydrogenase genes were expressed to allow FA assimilation. The gcv reaction was reversed by knocking out the repressor gene (gcvR) and overexpressing the gcvTHP genes. This engineered strain synthesized 96% and 86% of proteinogenic glycine and serine, respectively, from FA and CO2 in a glucose-containing medium. Native serine deaminase converted serine to pyruvate, showing 4.5% of pyruvate-forming flux comes from FA and CO2 The pyruvate-forming flux from FA and CO2 could be increased to 14.9% by knocking out gcvR, pflB, and serA, chromosomally expressing gcvTHP under trc, and overexpressing the reconstructed THF cycle, gcvTHP, and lpd genes in one vector. To reduce glucose usage required for energy and redox generation, the Candida boidinii formate dehydrogenase (Fdh) gene was expressed. The resulting strain showed specific glucose, FA, and CO2 consumption rates of 370.2, 145.6, and 14.9 mg⋅g dry cell weight (DCW)-1⋅h-1, respectively. The C1 assimilation pathway consumed 21.3 wt% of FA. Furthermore, cells sustained slight growth using only FA and CO2 after glucose depletion, suggesting that combined use of the C1 assimilation pathway and C. boidinii Fdh will be useful for eventually developing a strain capable of utilizing FA and CO2 without an additional carbon source such as glucose.

Liquid Hydrocarbon Production from CO2 : Recent Development in Metal-Based Electrocatalysis

Rising levels of CO₂ accumulation in the atmosphere have attracted considerable interest in technologies capable of CO₂ capture, storage and conversion. The electrochemical reduction of CO₂ into high-value liquid organic products could be of vital importance to mitigate this issue. The conversion of CO₂ into liquid fuels by using photovoltaic cells, which can readily be integrated in the current infrastructure, will help realize the creation of a sustainable cycle of carbon-based fuel that will promote zero net CO₂ emissions. Despite promising findings, significant challenges still persist that must be circumvented to make the technology profitable for large-scale utilization. With such possibilities, this Minireview presents the current high-performing catalysts for the electrochemical reduction of CO₂ to liquid hydrocarbons, address the limitations and unify the current understanding of the different reaction mechanisms. The Minireview also explores current research directions to improve process efficiencies and production rate and discusses the scope of using photo-assisted electrochemical reduction systems to find stable, highly efficient catalysts that can harvest solar energy directly to convert CO₂ into liquid hydrocarbons.

Tuning the Composition of Electrodeposited Bimetallic Tin-Lead Catalysts for Enhanced Activity and Durability in Carbon Dioxide Electroreduction to Formate

Bimetallic Sn-Pb catalysts with five different Sn/Pb atomic ratios were electrodeposited on Teflonated carbon paper and non-Teflonated carbon cloth using both fluoroborate- and oxide-containing deposition media to produce catalysts for the electrochemical reduction of CO₂ (ERC) to formate (HCOO^- ). The interaction between catalyst composition, morphology, substrate, and deposition media was investigated by using cyclic voltammetry and constant potential electrolysis at -2.0 V versus Ag/AgCl for 2 h in 0.5 m KHCO₃ . The catalysts were analyzed before and after electrolysis by using SEM and XRD to determine the mechanisms of Faradaic efficiency loss and degradation. Catalysts that are mainly Sn with 15-35 at % Pb generated Faradaic efficiencies up to 95 % with a stable performance. However, pure Sn catalysts showed high initial stage formate production rates but experienced an extensive (up to 30 %) decrease of the Faradaic efficiency. The XRD results demonstrated the presence of polycrystalline SnO₂ after electrolysis using Sn-Pb catalysts with 35 at % Pb and its absence in the case of pure Sn. It is proposed that the presence of Pb (15-35 at %) in mainly Sn catalysts stabilized SnO₂ , which is responsible for the enhanced Faradaic efficiency and catalytic durability in the ERC.

Study of Electrochemical Reduction of CO2 for Future Use in Secondary Microbial Electrochemical Technologies

The fluctuation and decentralization of renewable energy have triggered the search for respective energy storage and utilization. At the same time, a sustainable bioeconomy calls for the exploitation of CO₂ as feedstock. Secondary microbial electrochemical technologies (METs) allow both challenges to be tackled because the electrochemical reduction of CO₂ can be coupled with microbial synthesis. Because this combination creates special challenges, the electrochemical reduction of CO₂ was investigated under conditions allowing microbial conversions, that is, for their future use in secondary METs. A reproducible electrodeposition procedure of In on a graphite backbone allowed a systematic study of formate production from CO₂ with a high number of replicates. Coulomb efficiencies and formate production rates of up to 64.6±6.8 % and 0.013±0.002 mmol_formate  h^-1  cm^-2 , respectively, were achieved. Electrode redeposition, reusability, and long-term performance were investigated. Furthermore, the effect of components used in microbial media, that is, yeast extract, trace elements, and phosphate salts, on the electrode performance was addressed. The results demonstrate that the integration of electrochemical reduction of CO₂ in secondary METs can become technologically relevant.

Theoretical insight into effect of doping of transition metal M (M = Ni, Pd and Pt) on CO2 reduction pathways on Cu(111) and understanding of origin of electrocatalytic activity

The doped Pt can simultaneously reduce overpotential for CO formation and further reduction and most easily remove OH, thus suggesting the best electrocatalytic activity.