Metal–Organic Framework-Derived Carbon Nanorods Encapsulating Bismuth Oxides for Rapid and Selective CO2 Electroreduction to Formate

Carbon dioxide (CO₂) conversion is promising in alleviating the excessive CO₂ level and simultaneously producing valuables. This work reports the preparation of carbon nanorods encapsulated bismuth oxides for the efficient CO₂ electroconversion toward formate production. This resultant catalyst exhibits a small onset potential of −0.28 V vs. RHE and partial current density of over 200 mA cm⁻² with a stable and high Faradaic efficiency of 93 % for formate generation in a flow cell configuration. Electrochemical results demonstrate the synergistic effect in the Bi₂O₃@C promotes the rapid and selective CO₂ reduction in which the Bi₂O₃ is beneficial for improving the reaction kinetics and formate selectivity, while the carbon matrix would be helpful for enhancing the activity and current density of formate production. This work provides effective bismuth-based MOF derivatives for efficient formate production and offers insights in promoting practical CO₂ conversion technology.     

In-Situ Hydrogen-Bond Tailoring To Construct Ultrathin Bi2O2O/Bi2O2(OH)(NO3) Nanosheets: Interactive CO2RR Promotion and Bismuth-Oxygen Moiety Preservation

Bismuth–oxygen moieties are beneficial for high-efficiency electrochemical CO₂ reduction (CO₂RR) to produce formate; however, preserving bismuth-oxygen moieties while applying a cathodic potential is challenging. This work reports the preparation of ultrathin Bi₂O₂O/Bi₂O₂(OH)(NO₃) nanosheets (BiON-uts) by in-situ tailoring of hydrogen bonds in a Bi₂O₂(OH)(NO₃) precursor. The BiON-uts exhibits a formate faradaic efficiency of 98 % with higher partial current density than that of most reported bismuth-based catalysts. Mechanistic studies demonstrate that the ultrathin nanosheet morphology facilitates ion-exchange between BiON-uts and the electrolyte to produce Bi₂O₂CO₃ as intermediate, and adsorption of CO₂ with surface Bi₂O₂O. DFT calculations reveal that the rate-limiting first electron transfer is effectively improved by the high electron affinity of Bi₂O₂CO₃. More importantly, high-efficiency CO₂RR in turn protects the bismuth–oxygen moieties from being reduced and thus helps to maintain the excellent CO₂RR activity. This work offers an interactive mechanism of CO₂RR promotion and bismuth–oxygen moiety preservation, opening up new opportunities for developing high-performance catalysts.     

A Nanocomposite of Bismuth Clusters and Bi2O2CO3 Sheets for Highly Efficient Electrocatalytic Reduction of CO2 to Formate

The renewable-electricity-driven CO₂ reduction to formic acid would contribute to establishing a carbon-neutral society. The current catalyst suffers from limited activity and stability under high selectivity and the ambiguous nature of active sites. Herein, we report a powerful Bi₂S₃-derived catalyst that demonstrates a current density of 2.0 A cm⁻² with a formate Faradaic efficiency of 93 % at −0.95 V versus the reversible hydrogen electrode. The energy conversion efficiency and single-pass yield of formate reach 80 % and 67 %, respectively, and the durability reaches 100 h at an industrial-relevant current density. Pure formic acid with a concentration of 3.5 mol L⁻¹ has been produced continuously. Our operando spectroscopic and theoretical studies reveal the dynamic evolution of the catalyst into a nanocomposite composed of Bi⁰ clusters and Bi₂O₂CO₃ nanosheets and the pivotal role of Bi⁰−Bi₂O₂CO₃ interface in CO₂ activation and conversion.     

Nitrogen‐Doped Graphene Quantum Dots Enhance the Activity of Bi2O3 Nanosheets for Electrochemical Reduction of CO2 in a Wide Negative Potential Region

Large numbers of catalysts have been developed for the electrochemical reduction of CO₂ to value‐added liquid fuels. However, it remains a challenge to maintain a high current efficiency in a wide negative potential range for achieving a high production rate of the target products. Herein, we report a 2D/0D composite catalyst composed of bismuth oxide nanosheets and nitrogen‐doped graphene quantum dots (Bi₂O₃‐NGQDs) for highly efficient electrochemical reduction of CO₂ to formate. Bi₂O₃‐NGQDs demonstrates a nearly 100 % formate Faraday efficiency (FE) at a moderate overpotential of 0.7 V with a good stability. Strikingly, Bi₂O₃‐NGQDs exhibit a high activity (average formate FE of 95.6 %) from ?0.9 V to ?1.2 V vs. RHE. Additionally, DFT calculations reveal that the origin of enhanced activity in this wide negative potential range can be attributed to the increased adsorption energy of CO₂(ads) and OCHO* intermediate after combination with NGQDs.     

Template‐Free Fabrication of Bi2O3 and (BiO)2CO3 Nanotubes and Their Application in Water Treatment

Uniform bismuth oxide (Bi₂O₃) and bismuth subcarbonate ((BiO)₂CO₃) nanotubes were successfully synthesized by a facile solvothermal method without the need for any surfactants or templates. The synergistic effect of ethylene glycol (EG) and urea played a critical role in the formation of the tubular nanostructures. These Bi₂O₃ and (BiO)₂CO₃ nanotubes exhibited excellent Cr^VI‐removal capacity. Bi₂O₃ nanotubes, with a maximum Cr^VI‐removal capacity of 79 mg g^?1, possessed high removal ability in a wide range of pH values (3–11). Moreover, Bi₂O₃ and (BiO)₂CO₃ nanotubes also displayed highly efficient photocatalytic activity for the degradation of RhB under visible‐light irradiation. This work not only demonstrates a new and facile route for the fabrication of Bi₂O₃ and (BiO)₂CO₃ nanotubes, but also provides new promising adsorbents for the removal of heavy‐metal ions and potential photocatalysts for environmental remediation.     

Controllable Synthesis of Few‐Layer Bismuth Subcarbonate by Electrochemical Exfoliation for Enhanced CO2 Reduction Performance

Two‐dimensional (2D) engineering of materials has been recently explored to enhance the performance of electrocatalysts by reducing their dimensionality and introducing more catalytically active ones. In this work, controllable synthesis of few‐layer bismuth subcarbonate nanosheets has been achieved via an electrochemical exfoliation method. These nanosheets catalyse CO₂ reduction to formate with high faradaic efficiency and high current density at a low overpotential owing to the 2D structure and co‐existence of bismuth subcarbonate and bismuth metal under catalytic turnover conditions. Two underlying fast electron transfer processes revealed by Fourier‐transformed alternating current voltammetry (FTacV) are attributed to CO₂ reduction at bismuth subcarbonate and bismuth metal. FTacV results also suggest that protonation of CO₂^.? is the rate determining step for bismuth catalysed CO₂ reduction.     

Boosting Electrochemical Reduction of CO2 at a Low Overpotential by Amorphous Ag‐Bi‐S‐O Decorated Bi0 Nanocrystals

Bimetal‐S‐O composites have been rarely researched in electrochemical reduction of CO₂. Now, an amorphous Ag‐Bi‐S‐O decorated Bi⁰ catalyst derived from Ag_0.95BiS_0.75O_3.1 nanorods by electrochemical pre‐treatment was used for catalyzing eCO₂RR, which exhibited a formate FE of 94.3 % with a formate partial current density of 12.52 mA cm^?2 at an overpotential of only 450 mV. This superior performance was attributed to the attached amorphous Ag‐Bi‐S‐O substance. S could be retained in the amorphous region after electrochemical pre‐treatment only in samples derived from metal‐S‐O composites, and it would greatly enhance the formate selectivity by accelerating the dissociation of H₂O. The existence of Ag would increase the current density, resulting in a higher local pH, which made the role of S in activating H₂O more significantly and suppressed H₂ evolution more effectively, thus endowing the catalyst with a higher formate FE at low overpotentials.     

Bi2O3 Nanosheets Grown on Multi‐Channel Carbon Matrix to Catalyze Efficient CO2 Electroreduction to HCOOH

Bi₂O₃ nanosheets were grown on a conductive multiple channel carbon matrix (MCCM) for CO₂RR. The obtained electrocatalyst shows a desirable partial current density of ca. 17.7 mA cm^?2 at a moderate overpotential, and it is highly selective towards HCOOH formation with Faradaic efficiency approaching 90 % in a wide potential window and its maximum value of 93.8 % at ?1.256 V. It also exhibits a maximum energy efficiency of 55.3 % at an overpotential of 0.846 V and long‐term stability of 12 h with negligible degradation. The superior performance is attributed to the synergistic contribution of the interwoven MCCM and the hierarchical Bi₂O₃ nanosheets, where the MCCM provides an accelerated electron transfer, increased CO₂ adsorption, and a high ratio of pyrrolic‐N and pyridinic‐N, while ultrathin Bi₂O₃ nanosheets offer abundant active sites, lowered contact resistance and work function as well as a shortened diffusion pathway for electrolyte.     

Metal–Organic Layers Leading to Atomically Thin Bismuthene for Efficient Carbon Dioxide Electroreduction to Liquid Fuel

Electrochemical reduction of CO₂ to valuable fuels is appealing for CO₂ fixation and energy storage. However, the development of electrocatalysts with high activity and selectivity in a wide potential window is challenging. Herein, atomically thin bismuthene (Bi‐ene) is pioneeringly obtained by an in situ electrochemical transformation from ultrathin bismuth‐based metal–organic layers. The few‐layer Bi‐ene, which possesses a great mass of exposed active sites with high intrinsic activity, has a high selectivity (ca. 100 %), large partial current density, and quite good stability in a potential window exceeding 0.35 V toward formate production. It even deliver current densities that exceed 300.0 mA cm^?2 without compromising selectivity in a flow‐cell reactor. Using in situ ATR‐IR spectra and DFT analysis, a reaction mechanism involving HCO₃^? for formate generation was unveiled, which brings new fundamental understanding of CO₂ reduction.     

Bismuth-Oxide-Decorated Graphene Oxide Hybrids for Catalytic and Electrocatalytic Reduction of CO2

Global warming challenges are fueling the demand to develop an efficient catalytic system for the reduction of CO₂, which would contribute significantly to the control of climate change. Herein, as-synthesized bismuthoxide-decorated graphene oxide (Bi₂O₃@GO) was used as an electro/thermal catalyst for CO₂ reduction. Bi₂O₃@GO is found to be distributed uniformly, as confirmed by scanning electron and transmission electron microscopic analysis. The X-ray diffraction (XRD) pattern shows that the Bi₂O₃ has a β-phase with 23.4 m² g⁻¹ BET surface area. Significantly, the D and G bands from Raman spectroscopic analysis and their intensity ratio (I_D/I_G) reveal the increment in defective sites on GO after surface decoration. X-ray photoelectron spectroscopic (XPS) analysis shows clear signals for Bi, C, and O, along with their oxidation states. An ultra-low onset potential (−0.534 V vs. RHE) for the reduction of CO₂ on Bi₂O₃@GO is achieved. Furthermore, potential-dependent (−0.534, −0.734, and −0.934 vs. RHE) bulk electrolysis of CO₂ to formate provides Faradaic efficiencies (FE) of approximately 39.72, 61.48, and 83.00 %, respectively. Additionally, in time-dependent electrolysis at a potential of −0.934 versus RHE for 3 and 5 h, the observed FEs are around 84.20 % and 87.17 % respectively. This catalyst is also used for the thermal reduction of CO₂ to formate. It is shown that the thermal reduction provides a path for industrial applications, as this catalyst converts a large amount of CO₂ to formate (10 mm ).     

Simultaneous Generation of H2O2 and Formate by Co-Electrolysis of Water and CO2 over Bifunctional Zn/SnO2 Nanodots

Hydrogen peroxide (H₂O₂) and formate are important chemicals used in various chemical manufacturing industries. One promising approach for the simultaneous production of these chemicals is coupling anodic two-electron water oxidation with cathodic CO₂ reduction in an electrolyzer using nonprecious bifunctional electrocatalysts. Herein, we report an innovative hybrid electrosynthesis strategy using Zn-doped SnO₂ (Zn/SnO₂) nanodots as bifunctional redox electrocatalysts to achieve Faradaic efficiencies of 80.6 % and 92.2 % for H₂O₂ and formate coproduction, respectively, along with excellent stability for at least 60 h at a current density of ≈150 mA cm⁻². Through a combination of physicochemical characterizations, including operando attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), isotope labeling mass spectrometry (MS)/¹H NMR and quasi-in situ electron paramagnetic resonance (EPR), with density functional theory (DFT) calculations, we discovered that the Zn dopant facilitates the coupling of *OH intermediates to promote H₂O₂ production and optimizes the adsorption of *OCHO intermediates to accelerate formate formation. Our findings offer new insights into designing more efficient bifunctional electrocatalyst-based pair-electrosynthesis system for the coproduction of H₂O₂ and formate feedstocks.     

Selective and Efficient CO2 Electroreduction to Formate on Copper Electrodes Modified by Cationic Gemini Surfactants

Electroreduction of CO₂ into valuable chemicals and fuels is a promising strategy to mitigate energy and environmental problems. However, it usually suffers from unsatisfactory selectivity for a single product and inadequate electrochemical stability. Herein, we report the first work to use cationic Gemini surfactants as modifiers to boost CO₂ electroreduction to formate. The selectivity, activity and stability of the catalysts can be all significantly enhanced by Gemini surfactant modification. The Faradaic efficiency (FE) of formate could reach up to 96 %, and the energy efficiency (EE) could achieve 71 % over the Gemini surfactants modified Cu electrode. In addition, the Gemini surfactants modified commercial Bi₂O₃ nanosheets also showed an excellent catalytic performance, and the FE of formate reached 91 % with a current density of 510 mA cm⁻² using the flow cell. Detailed studies demonstrated that the double quaternary ammonium cations and alkyl chains of the Gemini surfactants played a crucial role in boosting electroreduction CO₂, which can not only stabilize the key intermediate HCOO* but also provide an easy access for CO₂. These observations could shine light on the rational design of organic modifiers for promoted CO₂ electroreduction.     

Acid–Base Interaction Enhancing Oxygen Tolerance in Electrocatalytic Carbon Dioxide Reduction

Hybrid electrodes with improved O₂ tolerance and capability of CO₂ conversion into liquid products in the presence of O₂ are presented. Aniline molecules are introduced into the pore structure of a polymer of intrinsic microporosity to expand its gas separation functionality beyond pure physical sieving. The chemical interaction between the acidic CO₂ molecule and the basic amino group of aniline renders enhanced CO₂ separation from O₂. Loaded with a cobalt phthalocyanine‐based cathode catalyst, the hybrid electrode achieves a CO Faradaic efficiency of 71 % with 10 % O₂ in the CO₂ feed gas. The electrode can still produce CO at an O₂/CO₂ ratio as high as 9:1. Switching to a Sn‐based catalyst, for the first time O₂‐tolerant CO₂ electroreduction to liquid products is realized, generating formate with nearly 100 % selectivity and a current density of 56.7 mA cm^?2 in the presence of 5 % O₂.     

Synthesis and properties of bismuth oxide nanoshell coated polyaniline nanoparticles for promising photovoltaic properties

A novel heterostructure made of polyaniline (PANI) nanoparticles coated by nanolayer of bismuth oxide Bi₂O₃ was synthesized. The structure was characterized by scanning electron microscopy, X‐ray diffraction, and transmission electron microscopy. These characterizations showed that the bismuth oxide nanoshell was pure and crystalline, and has thickness in the range of 10 nm. The experiment on photoluminescence (PL) of Bi₂O₃ nanoshell coated polyaniline nanoparticle, at room temperature, shows an emission band peaked at around 385 nm. When compared with the PL spectrum of Bi₂O₃ nanoparticles, about 100 times PL enhancement was found in the PL spectrum of Bi₂O₃ nanoshell coated polyaniline nanoparticle. The current density versus voltage (J–V) measurements in dark and illumination showed that this heterojunction has 4 orders of magnitude rectification in the dark and 3 orders of magnitude rectification under illumination. The obtained power conversion efficiency of polyaniline nanoparticles coated by nanoshell of bismuth oxide (η = 7.453%) was much enhanced compared with polyaniline alone (η = 8.33 × 10^?4%) this indicates that the prepared heterostructure represents a promising photovoltaic solar cell. Copyright © 2009 John Wiley & Sons, Ltd.     

Plasmonic Ag/AgCl‐modified bismuth subcarbonate with enhanced visible light photocatalytic activity

Plasmonic Ag/AgCl‐modified bismuth subcarbonate (Bi₂O₂CO₃) composites were prepared by a multistep process with hydrothermal, deposition, and photoreduction in the absence of organic capping agents. The properties of the obtained Ag/AgCl/Bi₂O₂CO₃ samples were characterized using X‐ray diffraction, field emission scanning electron microscopy and X‐ray photoelectron, UV–visible diffuse reflectance, and photoluminescence spectroscopies. The results reveal that Ag/AgCl nanoparticles are dispersed on the Bi₂O₂CO₃ surface to achieve plasmonic Ag/AgCl/Bi₂O₂CO₃. The Ag/AgCl/Bi₂O₂CO₃ nanocomposites show improved rhodamine B (RhB) adsorption capacity and photocatalytic activity compared with pure Bi₂O₂CO₃ and Ag/AgCl. In addition, the Ag/AgCl/Bi₂O₂CO₃ composite with 20 wt% Ag/AgCl exhibits the highest photocatalytic activity and remains stable for the photodegradation of RhB under visible light. The enhanced photocatalytic activity of Ag/AgCl/Bi₂O₂CO₃ may be attributed to the surface plasmon resonance effect of in situ generated Ag nanoparticles and synergistic effect of Ag/AgCl and Bi₂O₂CO₃, which increase the separation efficiency of photogenerated electron–hole pairs under visible light irradiation.     

Bioinspired Photocatalytic NADH Regeneration by Covalently Metalated Carbon Nitride for Enhanced CO2 Reduction

Natural photosynthesis is a highly unified biocatalytic system, which coupled cofactor (NAD(P)H) regeneration and enzymatic CO₂ reduction efficiently for solar energy conversion. Mimicking nature, a novel system with Rh complex covalently grafted onto NH₂-functionalized polymeric carbon nitride (NH₂-PCN) was constructed. The integrated connection of the light-harvesting and electron mediation modules as Rh_m3-N-PCN could promote the efficient NAD⁺ reduction to NADH. As a result, the integrated system exhibited a conversion of ∼66 % within 20 minutes. By further coupling in situ generated NADH with formate dehydrogenase (FDH), a photoenzymatic production of formic acid (HCOOH) from CO₂ was accomplished. Moreover, by immobilizing FDH onto a hydrophobic membrane, an enhanced HCOOH production of ∼5.0 mM can be obtained due to the concentrated CO₂ on the gas-liquid-solid three-phase interface. Our work herein provides an integrated strategy for coupling the anchored electron mediator with immobilized enzyme for enhanced artificial photosynthesis.     

MoP Nanoparticles Supported on Indium‐Doped Porous Carbon: Outstanding Catalysts for Highly Efficient CO2 Electroreduction

Electrochemical reduction of CO₂ into value‐added product is an interesting area. MoP nanoparticles supported on porous carbon were synthesized using metal–organic frameworks as the carbon precursor, and initial work on CO₂ electroreduction using the MoP‐based catalyst were carried out. It was discovered that MoP nanoparticles supported on In‐doped porous carbon had outstanding performance for CO₂ reduction to formic acid. The Faradaic efficiency and current density could reach 96.5 % and 43.8 mA cm^?2, respectively, when using ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate as the supporting electrolyte. The current density is higher than those reported up to date with very high Faradaic efficiency. The MoP nanoparticles and the doped In₂O₃ cooperated very well in catalyzing the CO₂ electroreduction.     

Catholyte‐Free Electrocatalytic CO2 Reduction to Formate

Electrochemical reduction of carbon dioxide (CO₂) into value‐added chemicals is a promising strategy to reduce CO₂ emission and mitigate climate change. One of the most serious problems in electrocatalytic CO₂ reduction (CO₂R) is the low solubility of CO₂ in an aqueous electrolyte, which significantly limits the cathodic reaction rate. This paper proposes a facile method of catholyte‐free electrocatalytic CO₂ reduction to avoid the solubility limitation using commercial tin nanoparticles as a cathode catalyst. Interestingly, as the reaction temperature rises from 303 K to 363 K, the partial current density (PCD) of formate improves more than two times with 52.9 mA cm^?2, despite the decrease in CO₂ solubility. Furthermore, a significantly high formate concentration of 41.5 g L^?1 is obtained as a one‐path product at 343 K with high PCD (51.7 mA cm^?2) and high Faradaic efficiency (93.3 %) via continuous operation in a full flow cell at a low cell voltage of 2.2 V.     

Non‐natural Cofactor and Formate‐Driven Reductive Carboxylation of Pyruvate

A non‐natural cofactor and formate driven system for reductive carboxylation of pyruvate is presented. A formate dehydrogenase (FDH) mutant, FDH*, that favors a non‐natural redox cofactor, nicotinamide cytosine dinucleotide (NCD), for generation of a dedicated reducing equivalent at the expense of formate were acquired. By coupling FDH* and NCD‐dependent malic enzyme (ME*), the successful utilization of formate is demonstrated as both CO₂ source and electron donor for reductive carboxylation of pyruvate with a perfect stoichiometry between formate and malate. When ¹³C‐isotope‐labeled formate was used in in vitro trials, up to 53 % of malate had labeled carbon atom. Upon expression of FDH* and ME* in the model host E. coli, the engineered strain produced more malate in the presence of formate and NCD. This work provides an alternative and atom‐economic strategy for CO₂ fixation where formate is used in lieu of CO₂ and offers dedicated reducing power.     

Acid–Base Interaction Enhancing Oxygen Tolerance in Electrocatalytic Carbon Dioxide Reduction

Hybrid electrodes with improved O₂ tolerance and capability of CO₂ conversion into liquid products in the presence of O₂ are presented. Aniline molecules are introduced into the pore structure of a polymer of intrinsic microporosity to expand its gas separation functionality beyond pure physical sieving. The chemical interaction between the acidic CO₂ molecule and the basic amino group of aniline renders enhanced CO₂ separation from O₂. Loaded with a cobalt phthalocyanine-based cathode catalyst, the hybrid electrode achieves a CO Faradaic efficiency of 71 % with 10 % O₂ in the CO₂ feed gas. The electrode can still produce CO at an O₂/CO₂ ratio as high as 9:1. Switching to a Sn-based catalyst, for the first time O₂-tolerant CO₂ electroreduction to liquid products is realized, generating formate with nearly 100 % selectivity and a current density of 56.7 mA cm⁻² in the presence of 5 % O₂.