High Selectivity For Formation Research Articles

Lattice-dislocated bismuth nanowires formed by in-situ chemical etching on copper foam for enhanced electrocatalytic CO2 reduction

Electrochemical CO2 reduction reaction (CO2RR) to HCOOH is one of the most feasible and economical methods to achieve carbon neutrality. Bismuth (Bi), as a metal catalyst for CO2RR, is considered to have great potential for application and has been widely studied due to its high formate selectivity, low toxicity, cheapness, and abundance. Unfortunately, low current density and short electrode lifetime have hindered its progress towards practical applications. In this work, we present a method that enables the chemical etching of Bi on Cu, which is capable of spontaneously accomplishing the loading of Bi on Cu foam in the liquid phase at room temperature. Additionally, to provide more abundant catalytically active sites, twisted Bi nanowires (BiNWs) with lattice dislocations were successfully prepared on the surface of Cu foam using a three-step chemical method involving oxidation, reduction, and in-situ etching. The Cu Foam@BiNWs was found to be a highly active electrocatalyst for CO2 reduction to formate at a low applied potential, achieving a faradaic efficiency for formate (FEFormate) of 95 % and a formate partial current density of ∼ 12 mA cm−2 at −0.78 V vs. RHE (reversible hydrogen electrode). Even within such a wide potential window of −0.68 ∼ -1.08 V vs. RHE, the FEFormate is consistently above 90 %. Such exceptional CO2 reduction activity can be attributed to the distortions and lattice dislocations present in the surface BiNWs. Furthermore, the Cu Foam@BiNWs electrode demonstrated a total current density close to 100 mA cm−2 at −0.98 V in an alkaline flow cell, while maintaining excellent catalytic stability over a prolonged 30-hour period of high current density electrochemical activity, thus showing potential for advancing the industrialisation of formate production. This work emphasizes the crucial role of size-dependent catalysis and crystal defect engineering strategies in the field of electrocatalysis, elucidates the mechanism of the rate-determining step (RDS) in the electrocatalytic CO2 reduction process on the developed catalysts, which can provide valuable insights into the design and development of high performance electrocatalysts not only in CO2RR but also in other fields.

Solid Bi2O3-derived nanostructured metallic bismuth with high formate selectivity for the electrocatalytic reduction of CO2

Solid Bi2O3-derived nanostructured metallic bismuth with high formate selectivity for the electrocatalytic reduction of CO2

Synergistic Lewis and Brønsted Acid Sites Promote OH* Formation and Enhance Formate Selectivity: Towards High-efficiency Glycerol Valorization.

As a sustainable valorization route, electrochemical glycerol oxidation reaction (GOR) involves in formation of key OH* and selective adsorption/cleavage of C-C(O) intermediates with multi-step electron transfer, thus suffering from high potential and poor formate selectivity for most non-noble-metal-based electrocatalysts. So, it remains challenging to understand the structure-property relationship as well as construct synergistic sites to realize high-activity and high-selectivity GOR. Herein, we successfully achieve dual-high performance with low potentials and superior formate selectivity for GOR by forming synergistic Lewis and Brønsted acid sites in Ni-alloyed Co-based spinel. The optimized NiCo oxide solid-acid electrocatalyst exhibits low reaction potential (1.219 V@10 mA/cm2) and high formate selectivity (94.0 %) toward GOR. In situ electrochemical impedance spectroscopy and pH-dependence measurements show that the Lewis acid centers could accelerate OH* production, while the Brønsted acid centers are proved to facilitate high-selectivity formation of formate. Theoretical calculations reveal that NiCo alloyed oxide shows appropriate d-band center, thus balancing adsorption/desorption of C-O intermediates. This study provides new insights into rationally designing solid-acid electrocatalysts for biomass electro-upcycling.

Synergistic Lewis and Brønsted Acid Sites Promote OH* Formation and Enhance Formate Selectivity: Towards High‐efficiency Glycerol Valorization

AbstractAs a sustainable valorization route, electrochemical glycerol oxidation reaction (GOR) involves in formation of key OH* and selective adsorption/cleavage of C−C(O) intermediates with multi‐step electron transfer, thus suffering from high potential and poor formate selectivity for most non‐noble‐metal‐based electrocatalysts. So, it remains challenging to understand the structure–property relationship as well as construct synergistic sites to realize high‐activity and high‐selectivity GOR. Herein, we successfully achieve dual‐high performance with low potentials and superior formate selectivity for GOR by forming synergistic Lewis and Brønsted acid sites in Ni‐alloyed Co‐based spinel. The optimized NiCo oxide solid‐acid electrocatalyst exhibits low reaction potential (1.219 V@10 mA/cm2) and high formate selectivity (94.0 %) toward GOR. In situ electrochemical impedance spectroscopy and pH‐dependence measurements show that the Lewis acid centers could accelerate OH* production, while the Brønsted acid centers are proved to facilitate high‐selectivity formation of formate. Theoretical calculations reveal that NiCo alloyed oxide shows appropriate d‐band center, thus balancing adsorption/desorption of C−O intermediates. This study provides new insights into rationally designing solid‐acid electrocatalysts for biomass electro‐upcycling.

Halide precursor reduction strategy to modulate bismuthene with high selectivity and wide potential window for electrochemical CO2 reduction

AbstractDeveloping high‐performance electrocatalysts for CO2 reduction reaction (CO2RR) is vital in achieving a carbon‐neutral society by converting CO2 into valuable chemicals. CO2RR electrocatalyst with lower overpotential, higher selectivity and wider working potential range is urgently desired, but it is still challenging to realize these factors simultaneously. Here, high‐performance bismuthene‐based electrocatalysts were synthesized by reducing bismuth precursors like BiCl3, BiBr3, and BiI3 in liquid phases. Especially, bismuthene‐I derived from BiI3 showed a nanosheet morphology (around four‐layer) with significantly enhanced (110) surfaces. It enabled an ultrawide potential window (0.7 V) for high formate selectivity (>90%) in a H‐type cell and achieved an ultralow potential (−0.46 V vs. reversible hydrogen electrode) to attain a current density of 200 mA cm−2 in a gas‐diffusion flow cell. The prominent long‐term operational capability of bismuthene‐I was demonstrated in both H‐type and gas‐diffusion cells. Density functional theory calculations revealed that bismuthene‐I possessed abundant topological Bi(110) surfaces states that can reduce the CO2RR overpotential, suppress the competitive hydrogen evolution reaction, and facilitate electron donation during CO2 electrocatalysis. The bismuthene‐I realized low overpotential, high selectivity and wide working potential range simultaneously for electrochemical CO2RR. This work unfolds the broader plausibility of facilely reducing precursors for the scalable fabrication of high‐performing CO2RR electrocatalysts.

Three-Dimensional Porous Indium Single-Atom Catalysts with Improved Accessibility for CO2 Reduction to Formate.

Single-atom catalysts (SACs) present substantial potential in electrocatalytic CO2 reduction reactions; however, inferior accessibility of single-atom sites to CO2 limits the overall CO2RR performances. Herein, we propose to improve the accessibility between In sites and CO2 through the construction of a three-dimensional (3D) porous indium single-atom catalyst (In1/NC-3D). The NaCl template-mediated synthesis strategy generates the unique 3D porous nanostructure of In1/NC-3D. Multiple characterizations validate that In1/NC-3D exhibits increased exposure of active sites and enhanced CO2 transport/adsorption capacity compared to the bulk In1/NC, thus improving accessibility of active sites to CO2. As a result, the In1/NC-3D presents superior CO2RR performance to the bulk In1/NC, with a partial current density of formate of 67.24 mA cm-2 at -1.41 V, relative to a reversible hydrogen electrode (vs RHE). The CO2RR performances with high formate selectivity at a large current density also outperform most reported In-based SACs. Importantly, the In1/NC-3D is demonstrated to maintain an FEformate of >82% at -66.83 mA·cm-2 over 21 h. This work highlights the design of a 3D porous single-atom catalyst for efficient CO2RR, promoting the development of advanced catalysts toward advanced energy conversion.

Electrochemically decoupled reduction of CO2 to formate over a dispersed heterogeneous bismuth catalyst enabled via redox mediators.

Electrochemical CO2 reduction is a topic of major interest in contemporary research as an approach to use renewably-derived electricity to synthesise useful hydrocarbons from waste CO2. Various strategies have been developed to optimise this challenging reaction at electrode interfaces, but to-date, decoupled electrolysis has not been demonstrated for the reduction of CO2. Decoupled electrolysis aims to use electrochemically-derived charged redox mediators - electrical charge and potential vectors - to separate catalytic product formation from the electrode surface. Utilising an electrochemically generated highly reducing redox mediator; chromium propanediamine tetraacetate, we report the first successful application of decoupled electrolysis to electrochemical CO2 reduction. A study of metals and metal composites found formate to be the most accessible product, with bismuth metal giving the highest selectivity. Copper, tin, gold, nickel and molybdenum carbide heterogeneous catalysts were also investigated, in which cases H2 was found to be the major product, with minor yields of two-electron CO2 reduction products. Subsequent optimisation of the bismuth catalyst achieved a high formate selectivity of 85%. This method represents a radical new approach to CO2 electrolysis, which may be coupled directly with renewable energy storage technology and green electricity.

Molecular‐level insight on CO2 electroreduction to formate facilitated by triazole ionic liquid interfacial microhabitat

AbstractThe interfacial microhabitat induced by functionalized ionic liquid (IL) electrolyte can effectively improve product selectivity for CO2 electroreduction. The multiple interactions in IL electrolytes affect the ions, CO2, proton distribution, and the protonation reaction, which are relevant to product selectivity. However, the specific effects are still unclear. Herein, molecular dynamics simulation and density functional theory were combined to reveal the regulatory mechanisms. The results showed that the dipolar interaction between CO2 and [124Triz]− cooperating the hydrogen bonds between [124Triz]− and H2O facilitates the accumulation of H atoms around C atoms of CO2. Moreover, the strong polar [124Triz]− induces protons to attack the C atoms of CO2, which results in lower free energy (−0.10 eV) for the formation of *HCOO intermediate and promotes the formation of formate, compared with the free energy of 0.43 eV for [NTf2]−. This work reveals the [124Triz]− regulatory mechanism for high formate selectivity.

High Formate Selectivity and Deactivation Mechanism of CuS Nanoparticles in CO2 Electrocatalytic Reduction Reaction.

CO2 electroreduction into liquid fuels is of broad interest and benefits reducing the energy crisis and environment burdens. CuS has been reported to be a desirable candidate for CO2 electroreduction into formate; however, its formate selectivity and stability are still far from the demands of practical application. Herein, we report CuS nanoparticles exhibiting good Faradaic efficiency of formate (about 98 %) in CO2 electroreduction and its deactivation mechanism during the reaction. The deactivation of CuS was found to be associated with the reconstruction and S loss of CuS, which deteriorates the Faradaic efficiency of formate. Combined with ionic and gas analyses, the S atom in CuS was lost in the form of H2 S, SO2 , and SO4 2- , followed by the reconstruction of CuS into copper oxides. Such a catalyst reconstruction facilitates electroreductions of CO2 and H2 O, respectively, into CO and H2 , etc., resulting in the degradation of catalytical performance of CO2 electroreduction into formate. This work reveals the important role of S loss and reconstruction of metal sulfide catalysts during the electroreduction reaction, which may benefit the further development of CuS-based electro-catalyst for CO2 electroreduction.

(Invited) Cascading Catalytic Microenvironments for (photo)Electroreduction of CO2

Although copper is a useful electrocatalyst for generation of a variety of chemical products from CO2 and H2O, it has become widely recognized that the catalyst by itself is not capable of high selectivity for formation of pure streams of specific products. By controlling the local environment around the catalytic reaction center, and providing multiple types of catalysts that can perform a sequence of specific reactions, improved control over selectivity can be envisioned. The mesoscale design rules for such cascades are unknown, however. In this talk I will describe computational studies that begin to examine the molecular-level factors that control coupled reaction-diffusion processes involved in CO2 reduction via cascaded catalytic reactions, including interfacial reactivity and catalyst placement. Key design considerations and gaps in understanding that emerge from these calculations will be discussed.

Interface engineering of a GaN/In2O3 heterostructure for highly efficient electrocatalytic CO2 reduction to formate

Electrocatalytic CO2 reduction reaction (eCO2RR) to obtain formate is a promising method to consume CO2 and alleviate the energy crisis. Indium-based electrocatalysts have demonstrated considerable potential to produce formate. However, their unsatisfactory long-term stability and selectivity restrict their widespread application. In this study, a heterostructure of GaN- and In2O3-encapsulated porous carbon nanofibers was constructed via electrospinning and the phase transition of eutectic gallium-indium during calcination. The GaN and In2O3 nanoparticle-encapsulated porous carbon nanofibers, when used as electrocatalysts for eCO2RR, displayed high formate selectivity with a faradaic efficiency of 87% and maximum partial current density of 29.7 mA cm−2 in a 0.5 mol L−1 KHCO3 aqueous solution. The existence of the interface can cause a positive shift in the In 3d binding energy, leading to electronic redistribution. Moreover, the GaN component induced a higher proportion of O-vacancy sites in the In2O3 phase, resulting in improved selectivity for CO2-to-formate. In-situ Raman experiments and density functional theory calculations revealed that the interface between GaN and In2O3 could lower the adsorption energy of the key intermediates for formate production, thus providing superior eCO2RR performance. In addition, the framework of the porous carbon nanofibers exhibited a large electrochemically active surface area, which enabled the full exposure of the active sites. This study highlights the cooperation between GaN and In2O3 components and provides new insights into the rational design of catalysts with high CO2-to-formate conversion efficiencies.

Ligand-Controlled Electroreduction of CO2 to Formate over Facet-Defined Bimetallic Sulfide Nanoplates

CO2 reduction (CO2R) catalyzed by an efficient, stable, and earth-abundant electrocatalyst offers an attractive means to store energy derived from renewable sources. Here, we describe the synthesis of facet-defined Cu2SnS3 nanoplates and the ligand-controlled CO2R property. We show that thiocyanate-capped Cu2SnS3 nanoplates possess excellent selectivity toward formate over a wide range of potentials and current densities, attaining a maximum formate Faradaic efficiency of 92% and partial current densities as high as 181 mA cm–2 when tested using a flow cell with gas-diffusion electrode. In situ spectroscopic measurements and theoretical calculations reveal that the high formate selectivity originates from favorable adsorption of HCOO* intermediates on cationic Sn sites that are electronically modulated by thiocyanates bound to adjacent Cu sites. Our work illustrates that well-defined multimetallic sulfide nanocrystals with tailored surface chemistries could provide a new avenue for future CO2R electrocatalyst design.

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Pressure dependence in aqueous-based electrochemical CO2 reduction

Electrochemical CO2 reduction (CO2R) is an approach to closing the carbon cycle for chemical synthesis. To date, the field has focused on the electrolysis of ambient pressure CO2. However, industrial CO2 is pressurized—in capture, transport and storage—and is often in dissolved form. Here, we find that pressurization to 50 bar steers CO2R pathways toward formate, something seen across widely-employed CO2R catalysts. By developing operando methods compatible with high pressures, including quantitative operando Raman spectroscopy, we link the high formate selectivity to increased CO2 coverage on the cathode surface. The interplay of theory and experiments validates the mechanism, and guides us to functionalize the surface of a Cu cathode with a proton-resistant layer to further the pressure-mediated selectivity effect. This work illustrates the value of industrial CO2 sources as the starting feedstock for sustainable chemical synthesis.

Interfacial engineering of bismuth sulfide/oxychloride heterostructure for boosting the conversion from CO2 to formate at large current densities

Electrochemical reduction of CO2 into green fuels is considered as a promising strategy to achieve carbon neutrality and has received increasing attentions. Herein, bismuth sulfide-bismuth oxychloride heterojunctions (Bi2S3-BiOCl) with abundant hetero-interface are rational synthesized and used as electrocatalysts for CO2 reduction reaction. The high formate selectivity of 97.2% at large current density of 300 mA cm−2 can be easily achieved. The in situ Raman spectroscopy and ex situ characterizations indicate that BiOCl converts to metallic Bi at negative potential to form a Bi2S3-Bi heterojunction. Based on the theoretical calculations, Bi2S3-Bi shows increasing density of states around the Fermi level and decreased energy barrier for CO2 conversion, and eventually promots electrocatalytic CO2 reduction reaction. This work not only provides an in-depth study of the application of Bi-involved heterojunctions for CO2 conversion, but also proposes a new strategy for the development of efficient catalysts for industrial-level CO2 conversion.

Photoreactive Carbon Dioxide Capture by a Zirconium–Nanographene Metal–Organic Framework

The mechanism of photochemical CO2 reduction to formate by PCN-136, a Zr-based metal-organic framework (MOF) that incorporates light-harvesting nanographene ligands, has been investigated using steady-state and time-resolved spectroscopy and density functional theory (DFT) calculations. The catalysis was found to proceed via a "photoreactive capture" mechanism, where Zr-based nodes serve to capture CO2 in the form of Zr-bicarbonates, while the nanographene ligands have a dual role of absorbing light and storing one-electron equivalents for catalysis. We also find that the process occurs via a "two-for-one" route, where a single photon initiates a cascade of electron/hydrogen atom transfers from the sacrificial donor to the CO2-bound MOF. The mechanistic findings obtained here illustrate several advantages of MOF-based architectures in molecular photocatalyst engineering and provide insights on ways to achieve high formate selectivity.

Upgrading CO2 into acetate on Bi2O3@carbon felt integrated electrode via coupling electrocatalysis with microbial synthesis

AbstractUpgrading of atmospheric CO2 into high‐value‐added acetate using renewable electricity via electrocatalysis solely remains a great challenge. Here, inspired by microbial synthesis via biocatalysts, we present a coupled system to produce acetate from CO2 by bridging inorganic electrocatalysis with microbial synthesis through formate intermediates. A 3D Bi2O3@CF integrated electrode with an ice‐sugar gourd shape was fabricated via a straightforward hydrothermal synthesis strategy, wherein Bi2O3 microspheres were decorated on carbon fibers. This ice‐sugar gourd‐shaped architecture endows electrodes with multiple structural advantages, including synergistic contribution, high mass transport capability, high structural stability, and large surface area. Consequently, the resultant Bi2O3@CF exhibited a maximum Faradic efficiency of 92.4% at −1.23 V versus Ag/AgCl for formate generation in 0.5 M KHCO3, exceeding that of Bi2O3/CF prepared using a conventional electrode preparation strategy. Benefiting from the high formate selectivity, unique architecture, and good biocompatibility, the Bi2O3@CF electrode attached with enriched CO2‐fixing electroautotrophs served as a biocathode. As a result, a considerable acetate yield rate of 0.269 ± 0.009 g L−1 day−1 (a total acetate yield of 3.77 ± 0.12 g L−1 during 14‐day operation) was achieved in the electrochemical–microbial system equipped with Bi2O3@CF.

Self-Supporting Bi-Sb Bimetallic Nanoleaf for Electrochemical Synthesis of Formate by Highly Selective CO2 Reduction.

Electrocatalytic reduction of CO2 into valuable fuels and chemical feedstocks in a sustainable and environmentally friendly manner is an ideal way to mitigate climate change and environmental problems. Here, we fabricated a series of self-supporting Bi-Sb bimetallic nanoleaves on carbon paper (CP) by a facile electrodeposition method. The synergistic effect of Bi and Sb components and the change of the electronic structure lead to high formate selectivity and excellent stability in the electrochemical CO2 reduction reaction (CO2RR). Specifically, the Bi-Sb/CP bimetallic electrode achieved a high Faradic efficiency (FEformate, 88.30%) at -0.9 V (vs RHE). The FE of formate remained above 80% in a broad potential range of -0.9 to -1.3 V (vs RHE), while FECO was suppressed below 6%. Density functional theory calculations showed that Bi(012)-Sb reduced the adsorption energy of the *OCHO intermediate and promoted the mass transfer of charges. The optimally adsorbed *OCHO intermediate promoted formate production while inhibiting the CO product pathway, thereby enhancing the selectivity to formate synthesis. Moreover, the CO2RR performance was also investigated in a flow-cell system to evaluate its potential for industrial applications. The bimetallic Bi-Sb catalyst can maintain a steady current density of 160 mA/cm2 at -1.2 V (vs RHE) for 25 h continuous electrolysis. Such excellent stability for formate generation in flow cells has rarely been reported in previous studies. This work offers new insights into the development of bimetallic self-supporting electrodes for CO2 reduction.

Charge-acquired Pb2+ boosts actively and selectively electrochemical carbon dioxide reduction reaction to formate

For lead carbonate-based (PbCO3) carbon dioxide reduction reaction (CO2RR) electrocatalysts, the electron-deficiency of Pb2+ active sites adverse to activate *CO2 and generate HCOO* intermediates hinder the active and selective CO2RR to formate. In this work, the Co modified (heterojunction and doping) PbCO3 electrocatalyst is constructed with prominent catalytic activity and high formate selectivity (Faradaic efficiency about 98.15% at −0.70 V vs. RHE). The in-depth experimental and theoretical analyses reveal that the Co-PbCO3 interaction can enable the electron of Co transfer to Pb2+, leading to the charge-acquired Pb2+ (CA-Pb2+). Its highly catalytic activity and selectivity of formate is attributed to the reduced formation energy barrier and enhanced adsorption behavior of HCOO* intermediate. The in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy demonstrates HCOO* intermediate is more likely to generate and adsorb on CA-Pb2+ than Pb2+, verifying the charge acquisition of Pb2+ enhances the activity and selectivity of formate product.

Cu-THQ-EFG Composite for Highly Selective Electrochemical CO2 Reduction to Formate at Low Overpotentials

Metal organic framework (MOFs) are promising materials for electrocatalysis. However, the active sites of bulk MOFs crystal normally cannot be fully utilized because of the slow reagent penetration of pores and blockage of active sites. Herein, we report a facile way to deposit copper-benzoquinoid (Cu-THQ) on the edge-functionalized graphene (EFG) which prevented material's aggregation. EFG used as a substrate provides higher electrical conductivity and stability in water than previously utilized graphene oxide (GO). Besides, the plate-like morphology of EFG proved to be more beneficial to support the MOF, because of the functional groups on its edge regions and much lower resistance compared to the sheet GO. Therefore, EFG can boost the resultant material's catalytic activity for CO2 electroreduction (CO2RR). Furthermore, Cu-THQ exhibits high selectivity for formate formation in CO2RR. Representing as the only CO2 reduced liquid product, formate can be separated from gaseous products and further extracted from the electrolyte for practical use. The electrocatalytic results of Cu-THQ-EFG indicate the composite exhibits a higher current density of -3 mA/cm2 and faradaic efficiency of -0.25 V vs. RHE, corresponding to 50 mV of overpotential. Moreover, it features a less negative on-set potential of -0.22 V vs. RHE, which is close to the equilibrium potential of CO2RR (-0.2 V vs. RHE) and is 0.16 V more positive than the on-set potential of Cu-THQ-GO (-0.38 V vs. RHE).