Molten‐Salt‐Assisted Synthesis of Bismuth Nanosheets for Long‐term Continuous Electrocatalytic Conversion of CO 2 to Formate

Bicontinuous RuO2 nanoreactors for acidic water oxidation

Improving activity and stability of Ruthenium (Ru)-based catalysts in acidic environments is eager to replace more expensive Iridium (Ir)-based materials as practical anode catalyst for proton-exchange membrane water electrolyzers (PEMWEs). Here, a bicontinuous nanoreactor composed of multiscale defective RuO2 nanomonomers (MD-RuO2-BN) is conceived and confirmed by three-dimensional tomograph reconstruction technology. The unique bicontinuous nanoreactor structure provides abundant active sites and rapid mass transfer capability through a cavity confinement effect. Besides, existing vacancies and grain boundaries endow MD-RuO2-BN with generous low-coordination Ru atoms and weakened Ru-O interaction, inhibiting the oxidation of lattice oxygen and dissolution of high-valence Ru. Consequently, in acidic media, the electron- and micro-structure synchronously optimized MD-RuO2-BN achieves hyper water oxidation activity (196 mV @ 10 mA cm-2) and an ultralow degradation rate of 1.2 mV h-1. A homemade PEMWE using MD-RuO2-BN as anode also conveys high water splitting performance (1.64 V @ 1 A cm-2). Theoretical calculations and in-situ Raman spectra further unveil the electronic structure of MD-RuO2-BN and the mechanism of water oxidation processes, rationalizing the enhanced performance by the synergistic effect of multiscale defects and protected active Ru sites.

Bismuth-Based Electrocatalysts for Identical Value-Added Formic Acid Through Coupling CO2 Reduction and Methanol Oxidation

It is an effective way to reduce atmospheric CO2 via electrochemical CO2 reduction reaction (CO2RR), while the slow oxygen evolution reaction (OER) occurs at the anode with huge energy consumption. Herein, methanol oxidation reaction (MOR) is used to replace OER, coupling CO2RR to achieve co-production of formate. Through enhancing OCHO* adsorption by oxygen vacancies engineering and synergistic effect by heteroatom doping, Bi/Bi2O3 and Ni─Bi(OH)3 are synthesized for efficient production of formate via simultaneous CO2RR and methanol oxidation reaction (MOR), achieving that the coupling of CO2RR//MOR only required 7.26 kWh gformate -1 power input, much lower than that of CO2RR//OER (13.67 kWh gformate -1). Bi/Bi2O3 exhibits excellent electrocatalytic CO2RR performance, achieving FEformate >80% in a wide potential range from -0.7 to -1.2 V (vs RHE). For MOR, Ni─Bi(OH)3 exhibits efficient MOR catalytic performance with the FEformate >98% in the potential range of 1.35-1.6 V (vs RHE). Not only demonstrates the two-electrode systems exceptional stability, working continuously for over 250 h under a cell voltage of 3.0 V, but the cathode and anode can maintain a FE of over 80%. DFT calculation results reveal that the oxygen vacancies of Bi/Bi2O3 enhance the adsorption of OCHO* intermediate, and Ni─Bi(OH)3 reduce the energy barrier for the rate determining step, leading to high catalytic activity.

Concentrated Formic Acid from CO2 Electrolysis for Directly Driving Fuel Cell

The production of formic acid via electrochemical CO2 reduction may serve as a key link for the carbon cycle in the formic acid economy, yet its practical feasibility is largely limited by the quantity and concentration of the product. Here we demonstrate continuous electrochemical CO2 reduction for formic acid production at 2 M at an industrial-level current densities (i.e., 200 mA cm-2 ) for 300 h on membrane electrode assembly using scalable lattice-distorted bismuth catalysts. The optimized catalysts also enable a Faradaic efficiency for formate of 94.2 % and a highest partial formate current density of 1.16 A cm-2 , reaching a production rate of 21.7 mmol cm-2  h-1 . To assess the practicality of this system, we perform a comprehensive techno-economic analysis and life cycle assessment, showing that our approach can potentially substitute conventional methyl formate hydrolysis for industrial formic acid production. Furthermore, the resultant formic acid serves as direct fuel for air-breathing formic acid fuel cells, boasting a power density of 55 mW cm-2 and an exceptional thermal efficiency of 20.1 %.

Resolving the Origins of Superior Cycling Performance of Antimony Anode in Sodium-ion Batteries: A Comparison with Lithium-ion Batteries

Alloying-type antimony (Sb) with high theoretical capacity is a promising anode candidate for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Given the larger radius of Na+ (1.02 Å) than Li+ (0.76 Å), it was generally believed that the Sb anode would experience even worse capacity degradation in SIBs due to more substantial volumetric variations during cycling when compared to LIBs. However, the Sb anode in SIBs unexpectedly exhibited both better electrochemical and structural stability than in LIBs, and the mechanistic reasons that underlie this performance discrepancy remain undiscovered. Here, using substantial in situ transmission electron microscopy, X-ray diffraction, and Raman techniques complemented by theoretical simulations, we explicitly reveal that compared to the lithiation/delithiation process, sodiation/desodiation process of Sb anode displays a previously unexplored two-stage alloying/dealloying mechanism with polycrystalline and amorphous phases as the intermediates featuring improved resilience to mechanical damage, contributing to superior cycling stability in SIBs. Additionally, the better mechanical properties and weaker atomic interaction of Na-Sb alloys than Li-Sb alloys favor enabling mitigated mechanical stress, accounting for enhanced structural stability as unveiled by theoretical simulations. Our finding delineates the mechanistic origins of enhanced cycling stability of Sb anode in SIBs with potential implications for other large-volume-change electrode materials.

Revealing the Intrinsic Restructuring of Bi2O3 Nanoparticles into Bi Nanosheets during Electrochemical CO2 Reduction

Bismuth is a catalyst material that selectively produces formate during the electrochemical reduction of CO2. While different synthesis strategies have been employed to create electrocatalysts with better performance, the restructuring of bismuth precatalysts during the reaction has also been previously reported. The mechanism behind the change has, however, remained unclear. Here, we show that Bi2O3 nanoparticles supported on Vulcan carbon intrinsically transform into stellated nanosheet aggregates upon exposure to an electrolyte. Liquid cell transmission electron microscopy observations first revealed the gradual restructuring of the nanoparticles into nanosheets in the presence of 0.1 M KHCO3 without an applied potential. Our experiments also associated the restructuring with solubility of bismuth in the electrolyte. While the consequent agglomerates were stable under moderate negative potentials (-0.3 VRHE), they dissolved over time at larger negative potentials (-0.4 and -0.5 VRHE). Operando Raman spectra collected during the reaction showed that under an applied potential, the oxide particles reduced to metallic bismuth, thereby confirming the metal as the working phase for producing formate. These results inform us about the working morphology of these electrocatalysts and their formation and degradation mechanisms.

Highly selective electrocatalytic reduction of CO2 to HCOOH over an in situ derived Ag-loaded Bi2O2CO3 electrocatalyst

The electrochemical reduction of CO2 to HCOOH is considered one of the most appealing routes to alleviate the energy crisis and close the anthropogenic CO2 cycle. However, it remains challenging to develop electrocatalysts with high activity and selectivity towards HCOOH in a wide potential window. In this regard, Ag/Bi2O2CO3 was prepared by an in situ electrochemical transformation from Ag/Bi2O3. The Ag/Bi2O2CO3 catalyst achieves a faradaic efficiency (FE) of over 90% for HCOOH in a wide potential window between -0.8 V and -1.3 V versus the reversible hydrogen electrode (RHE). Moreover, a maximum FE of 95.8% and a current density of 15.3 mA cm-2 were achieved at a low applied potential of -1.1 V. Density functional theory (DFT) calculations prove that the high catalytic activity of Ag/Bi2O2CO3 is ascribed to the fact that Ag can regulate the electronic structure of Bi, thus facilitating the adsorption of *OCHO and hindering the adsorption of *COOH. This work expands the in situ electrochemical derivatization strategy for the preparation of electrocatalysts.

Advances in the Stability of Catalysts for Electroreduction of CO2 to Formic Acid

The electroreduction of CO2 to high-value products is a promising approach for achieving carbon neutrality. Among these products, formic acid stands out as having the most potential for industrialization due to its optimal economic value in terms of consumption and output. In recent years, the Faraday efficiency of formic acid from CO2 electroreduction has reached 90~100 %. However, this high selectivity cannot be maintained for extended periods under high currents to meet industrial requirements. This paper reviews excellent work from the perspective of catalyst stability, summarizing and discussing the performance of typical catalysts. Strategies for preparing stable and highly active catalysts are also briefly described. This review may offer a useful data reference and valuable guidance for the future design of long-stability catalysts.

Crystalline-Amorphous Interfaces Engineering of CoO-InOx for Highly Efficient CO2 Electroreduction to CO

As a fundamental product of CO2 conversion through two-electron transfer, CO is used to produce numerous chemicals and fuels with high efficiency, which has broad application prospects. In this work, it has successfully optimized catalytic activity by fabricating an electrocatalyst featuring crystalline-amorphous CoO-InOx interfaces, thereby significantly expediting CO production. The 1.21%CoO-InOx consists of randomly dispersed CoO crystalline particles among amorphous InOx nanoribbons. In contrast to the same-phase structure, the unique CoO-InOx heterostructure provides plentiful reactive crystalline-amorphous interfacial sites. The Faradaic efficiency of CO (FECO ) can reach up to 95.67% with a current density of 61.72 mA cm-2 in a typical H-cell using MeCN containing 0.5 M 1-Butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6 ) as the electrolyte. Comprehensive experiments indicate that CoO-InOx interfaces with optimization of charge transfer enhance the double-layer capacitance and CO2 adsorption capacity. Theoretical calculations further reveal that the regulating of the electronic structure at interfacial sites not only optimizes the Gibbs free energy of *COOH intermediate formation but also inhibits HER, resulting in high selectivity toward CO.

Enhancing Electroreduction CO2 to Hydrocarbons via Tandem Electrocatalysis by Incorporation Cu NPs in Boron Imidazolate Frameworks

Due to the higher value of deeply-reduced products, electrocatalytic CO2 reduction reaction (CO2 RR) to multi-electron-transfer products has received more attention. One attractive strategy is to decouple individual steps within the complicated pathway via multi-component catalysts design in the concept of tandem catalysts. Here, a composite of Cu@BIF-144(Zn) (BIF = boron imidazolate framework) is synthesized by using an anion framework BIF-144(Zn) as host to impregnate Cu2+ ions that are further reduced to Cu nanoparticles (NPs) via in situ electrochemical transformation. Due to the microenvironment modulation by functional BH(im)3 - on the pore surfaces, the Cu@BIF-144(Zn) catalyst exhibits a perfect synergetic effect between the BIF-144(Zn) host and the Cu NP guest during CO2 RR. Electrochemistry results show that Cu@BIF-144(Zn) catalysts can effectively enhance the selectivity and activity for the CO2 reduction to multi-electron-transfer products, with the maximum FECH4 value of 41.8% at -1.6 V and FEC2H4 value of 12.9% at -1.5 V versus RHE. The Cu@BIF-144(Zn) tandem catalyst with CO-rich microenvironment generated by the Zn catalytic center in the BIF-144(Zn) skeleton enhanced deep reduction on the incorporated Cu NPs for the CO2 RR to multi-electron-transfer products.

Interfacial assembled porous bismuthene/Ti3C2Tx MXene heterostructure for highly efficient capacitive deionization

Capacitive deionization (CDI) is perceived as a promising technology for freshwater production owing to its environmentally friendly nature and low energy consumption. To date, the development of high-performance electrode materials represents the foremost challenge for CDI technology. In this work, the porous bismuthene/MXene (P-Bi-ene/MXene) heterostructure was synthesized using a simple interfacial self-assembly method with two-dimensional (2D) bismuthene and Ti3C2Tx MXene. Within the P-Bi-ene/MXene heterostructure, the porous structure can increase the active site and facilitate ion transport. Simultaneously, MXene effectively enhances the conductivity of the heterostructure, resulting in accelerating electron transport. Due to these attributes, the P-Bi-ene/MXene heterostructure demonstrates high desalination capacity (90.0 mg/g), fast desalination rate, and good cycling performance. The simple self-assembly strategy between 2D/2D materials described herein may offer inspirations for the synthesis of innovative electrode materials with high performance.

A Bismuth-Based Zeolitic Organic Framework with Coordination-Linked Metal Cages for Efficient Electrocatalytic CO2 Reduction to HCOOH

Zeolitic metal-organic frameworks (ZMOFs) have emerged as one of the most promsing catalysts for energy conversion, but they suffer from either weak bonding between metal-organic cubes (MOCs) that decrease their stability during catalysis processes or low activity due to inadequate active sites. In this work, through ligand-directing strategy, we successfully obtain an unprecedented bismuth-based ZMOF (Bi-ZMOF) featuring a ACO topological crystal structure with strong coordination bonding between the Bi-based cages. As a result, it enables efficient reduction of CO2 to formic acid (HCOOH) with Faradaic efficiency as high as 91 %. A combination of in situ surface-enhanced infrared absorption spectroscopy and density functional theory calculation reveals that the Bi-N coordination contributes to facilitating charge transfer from N to Bi atoms, which stabilize the intermediate to boost the reduction efficiency of CO2 to HCOOH. This finding highlights the importance of the coordination environment of metal active sites on electrocatalytic CO2 reduction. We believe that this work will offer a new clue to rationally design zeolitic MOFs for catalytic reaction.

Molten salt-assisted synthesis of bismuth nanosheets with long-term cyclability at high rates for sodium-ion batteries

Bismuth is a promising anode material for sodium-ion batteries (SIBs) due to its high capacity and suitable working potential. However, the large volume change during alloying/dealloying would lead to poor cycling performance. Herein, we have constructed a 3D hierarchical structure assembled by bismuth nanosheets, addressing the challenges of fast kinetics, and providing efficient stress and strain relief room. The uniform bismuth nanosheets are prepared via a molten salt-assisted aluminum thermal reduction method. Compared with the commercial bismuth powder, the bismuth nanosheets present a larger specific surface area and interlayer spacing, which is beneficial for sodium ion insertion and release. As a result, the bismuth nanosheet anode presents excellent sodium storage properties with an ultralong cycle life of 6500 cycles at a high current density of 10 A g-1, and an excellent capacity retention of 87% at an ultrahigh current rate of 30 A g-1. Moreover, the full SIBs that paired with the Na3V2(PO4)3/rGO cathode exhibited excellent performance. This work not only presents a novel strategy for preparing bismuth nanosheets with significantly increased interlayer spacing but also offers a straightforward synthesis method utilizing low-cost precursors. Furthermore, the outstanding performance demonstrated by these nanosheets indicates their potential for various practical applications.

Controllable Crystallization of Two-Dimensional Bi Nanocrystals with Morphology-Boosted CO2 Electroreduction in Wide pH Environments

Two-dimensional low-melting-point (LMP) metal nanocrystals are attracting increasing attention with broad and irreplaceable applications due to their unique surface and topological structures. However, the chemical synthesis, especially the fine control over the nucleation (reduction) and growth (crystallization), of such LMP metal nanocrystals remains elusive as limited by the challenges of low standard redox potential, low melting point, poor crystalline symmetry, etc. Here, a controllable reduction-melting-crystallization (RMC) protocol to synthesize free-standing and surfactant-free bismuth nanocrystals with tunable dimensions, morphologies, and surface structures is presented. Especially, ultrathin bismuth nanosheets with flat or jagged surfaces/edges can be prepared with high selectivity. The jagged bismuth nanosheets, with abundant surface steps and defects, exhibit boosted electrocatalytic CO2 reduction performances in acidic, neutral, and alkaline aqueous solutions, achieving the maximum selectivity of near unity at the current density of 210 mA cm-2 for formate evolution under ambient conditions. This work creates the RMC pathway for the synthesis of free-standing two-dimensional LMP metal nanomaterials and may find broader applicability in more interdisciplinary applications.

Size Effects of Highly Dispersed Bismuth Nanoparticles on Electrocatalytic Reduction of Carbon Dioxide to Formic Acid

Electrocatalytic reduction of carbon dioxide into value-added chemical fuels is a promising way to achieve carbon neutrality. Bismuth-based materials have been considered as favorable electrocatalysts for converting carbon dioxide to formic acid. Moreover, size-dependent catalysis offers significant advantages in catalyzed heterogeneous chemical processes. However, the size effects of bismuth nanoparticles on formic acid production have not been fully explored. Here, we prepared Bi nanoparticles uniformly supported on porous TiO₂ substrate electrocatalytic materials by in situ segregation of the Bi element from Bi₄Ti₃O₁₂. The Bi-TiO₂ electrocatalyst with Bi nanoparticles of 2.83 nm displays a Faradaic efficiency of greater than 90% over a wide potential range of 400 mV. Theoretical calculations have also demonstrated subtle electronic structural evolutions induced by the size variations of Bi nanoparticles, where the 2.83 nm Bi nanoparticles display the most active p-band and d-band centers to guarantee high electroactivity toward CO₂RR.

Strong interface coupling boosting hierarchical bismuth embedded carbon hybrid for high-performance capacitive deionization

Capacitive deionization (CDI) is regarded as a promising desalination technology owing to its low cost and environmental friendliness. However, the lack of high-performance electrode materials remains a challenge in CDI. Herein, the hierarchical bismuth-embedded carbon (Bi@C) hybrid with strong interface coupling was prepared through facile solvothermal and annealing strategy. The hierarchical structure with strong interface coupling between the bismuth and carbon matrix afforded abundant active sites for chloridion (Cl^-) capture, improved electrons/ions transfer and the stability of the Bi@C hybrid. As a result of these advantages, the Bi@C hybrid showed a high salt adsorption capacity (75.3 mg/g under 1.2 V), salt adsorption rate and good stability, making it a promising electrode material for CDI. Furthermore, the desalination mechanism of the Bi@C hybrid was elucidated through various characterizations. Therefore, this work provides valuable insights for the design of high-performance bismuth-based electrode materials for CDI.

Nanosecond Laser Confined Bismuth Moiety with Tunable Structures on Graphene for Carbon Dioxide Reduction

Substrate-supported catalysts with atomically dispersed metal centers are promising for driving the carbon dioxide reduction reaction (CO₂RR) to produce value-added chemicals; however, regulating the size of exposed catalysts and optimizing their coordination chemistry remain challenging. In this study, we have devised a simple and versatile high-energy pulsed laser method for the enrichment of a Bi "single atom" (SA) with a controlled first coordination sphere on a time scale of nanoseconds. We identify the mechanistic bifurcation routes over a Bi SA that selectively produce either formate or syngas when bound to C or N atoms, respectively. In particular, C-stabilized Bi (Bi-C) exhibits a maximum formate partial current density of -29.3 mA cm^-2 alongside a TOF value of 2.64 s^-1 at -1.05 V vs RHE, representing one of the best SA-based candidates for CO₂-to-formate conversion. Our results demonstrate that the switchable selectivity arises from the different coupling states and metal-support interactions between the central Bi atom and adjacent atoms, which modify the hybridizations between the Bi center and *OCHO/*COOH intermediates, alter the energy barriers of the rate-determining steps, and ultimately trigger the branched reaction pathways after CO₂ adsorption. This work demonstrates a practical and universal ultrafast laser approach to a wide range of metal-substrate materials for tailoring the fine structures and catalytic properties of the supported catalysts and provides atomic-level insights into the mechanisms of the CO₂RR on ligand-modified Bi SAs, with potential applications in various fields.

Bismuth-Decorated Honeycomb-like Carbon Nanofibers: An Active Electrocatalyst for the Construction of a Sensitive Nitrite Sensor

The existence of carcinogenic nitrites in food and the natural environment has attracted much attention. Therefore, it is still urgent and necessary to develop nitrite sensors with higher sensitivity and selectivity and expand their applications in daily life to protect human health and environmental safety. Herein, one-dimensional honeycomb-like carbon nanofibers (HCNFs) were synthesized with electrospun technology, and their specific structure enabled controlled growth and highly dispersed bismuth nanoparticles (Bi NPs) on their surface, which endowed the obtained Bi/HCNFs with excellent electrocatalytic activity towards nitrite oxidation. By modifying Bi/HCNFs on the screen-printed electrode, the constructed Bi/HCNFs electrode (Bi/HCNFs-SPE) can be used for nitrite detection in one drop of solution, and exhibits higher sensitivity (1269.9 μA mM^-1 cm^-2) in a wide range of 0.1~800 μM with a lower detection limit (19 nM). Impressively, the Bi/HCNFs-SPE has been successfully used for nitrite detection in food and environment samples, and the satisfactory properties and recovery indicate its feasibility for further practical applications.

Two-Dimensional Metal Coordination Polymer Derived Indium Nanosheet for Efficient Carbon Dioxide Reduction to Formate

Main group indium materials have been known as promising electrocatalysts for two-electron-involved carbon dioxide reduction to produce formate, which is a key energy vector in many industrial reactions. However, the synthesis of two-dimensional (2D) monometallic nonlayered indium remains a great challenge. Here, we present a facile electrochemical reduction strategy to transform 2D indium coordination polymer into elemental indium nanosheets. In a customized flow cell, the reconstructed metallic indium exhibits a high Faradaic efficiency (FE) of 96.3% for formate with a maximum partial current density exceeding 360 mA cm^-2 and negligible degradation after 140 h operation in 1 M KOH solution, outperforming the state-of-the-art indium-based electrocatalysts. Moreover, in and ex situ electrochemical analysis and characterizations demonstrate that the enhanced exposure of active sites and mass/charge transport at the CO₂ gas-catalyst-electrolyte triple-phase interface and the restrained electrolyte flooding are contributing to producing and stabilizing carbon dioxide radical anion intermediates, thus leading to superior catalytic performance.

Boosting CO2 Electroreduction on Bismuth Nanoplates with a Three-Dimensional Nitrogen-Doped Graphene Aerogel Matrix

Electrochemical CO₂ reduction reaction (CO₂RR), which uses renewable electricity to produce high-value-added chemicals, offers an alternative clean path to the carbon cycle. However, bismuth-based catalysts show great potential for the conversion of CO₂ and water to formate, but their overall efficiency is still hampered by the weak CO₂ adsorption, low electrical conductivity, and slow mass transfer of CO₂ molecules. Herein, we report that a rationally modulated nitrogen-doped graphene aerogel matrix (NGA) can significantly enhance the CO₂RR performance of bismuth nanoplates (BiNPs) by both modulating the electronic structure of bismuth and regulating the interface for chemical reaction and mass transfer environments. In particular, the NGA prepared by reducing graphene oxide (GO) with hydrazine hydrate (denoted as NGA_hdrz) exhibits significantly enhanced strong metal-support interaction (SMSI), increased specific surface area, strengthened CO₂ adsorption, and modulated wettability. As a result, the Bi/NGA_hdrz exhibits significantly boosted CO₂RR properties, with a Faradaic efficiency (FE) of 96.4% at a current density of 51.4 mA cm^-2 for formate evolution at a potential of -1.0 V versus reversible hydrogen electrode (vs RHE) in aqueous solution under ambient conditions.

Molten Salts Approach of Poly(vinyl alcohol)-Derived Bimetallic Nickel-Iron Sheets Supported on Porous Carbon Nanosheet as an Effective and Durable Electrocatalyst for Methanol Oxidation

The preparation of metallic nanostructures supported on porous carbon materials that are facile, green, efficient, and low-cost is desirable to reduce the cost of electrocatalysts, as well as reduce environmental pollutants. In this study, a series of bimetallic nickel-iron sheets supported on porous carbon nanosheet (NiFe@PCNs) electrocatalysts were synthesized by molten salt synthesis without using any organic solvent or surfactant through controlled metal precursors. The as-prepared NiFe@PCNs were characterized by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction, and photoelectron spectroscopy (XRD and XPS). The TEM results indicated the growth of NiFe sheets on porous carbon nanosheets. The XRD analysis confirmed that the Ni_1-xFe_x alloy had a face-centered polycrystalline (fcc) structure with particle sizes ranging from 15.5 to 30.6 nm. The electrochemical tests showed that the catalytic activity and stability were highly dependent on the iron content. The electrocatalytic activity of catalysts for methanol oxidation demonstrated a nonlinear relationship with the iron ratio. The catalyst doped with 10% iron showed a higher activity compared to the pure nickel catalyst. The maximum current density of Ni_0.9Fe_0.1@PCNs (Ni/Fe ratio 9:1) was 190 mA/cm² at 1.0 M of methanol. In addition to the high electroactivity, the Ni_0.9Fe_0.1@PCNs showed great improvement in stability over 1000 s at 0.5 V with a retained activity of 97%. This method can be used to prepare various bimetallic sheets supported on porous carbon nanosheet electrocatalysts.

Vertically Aligned Bismuthene Nanosheets on MXene for High-Performance Capacitive Deionization

Capacitive deionization has been considered as a promising solution to the challenge of freshwater shortage due to its high efficiency, low environmental footprint, and low energy consumption. However, developing advanced electrode materials to improve capacitive deionization performance remains a challenge. Herein, the hierarchical bismuthene nanosheets (Bi-ene NSs)@MXene heterostructure was successfully prepared by combining the Lewis acidic molten salt etching and the galvanic replacement reaction, which achieves the effective utilization of the molten salt etching byproducts (residual copper). The vertically aligned bismuthene nanosheets array evenly in situ grown on the surface of MXene, which not only facilitate ion and electron transport as well as offer abundant active sites but also provide strong interfacial interaction between bismuthene and MXene. Benefiting from the above advantages, the Bi-ene NSs@MXene heterostructure as a promising capacitive deionization electrode material exhibits high desalination capacity (88.2 mg/g at 1.2 V), fast desalination rate, and good long-term cycling performance. Moreover, the mechanisms involved were elaborated by systematical characterizations and density functional theory calculations. This work provides inspirations for the preparation of MXene-based heterostructures and their application for capacitive deionization.

Two-Dimensional Metal Nanostructures: From Theoretical Understanding to Experiment

This paper reviews recent studies on the preparation of two-dimensional (2D) metal nanostructures, particularly nanosheets. As metal often exists in the high-symmetry crystal phase, such as face centered cubic structures, reducing the symmetry is often needed for the formation of low-dimensional nanostructures. Recent advances in characterization and theory allow for a deeper understanding of the formation of 2D nanostructures. This Review firstly describes the relevant theoretical framework to help the experimentalists understand chemical driving forces for the synthesis of 2D metal nanostructures, followed by examples on the shape control of different metals. Recent applications of 2D metal nanostructures, including catalysis, bioimaging, plasmonics, and sensing, are discussed. We end the Review with a summary and outlook of the challenges and opportunities in the design, synthesis, and application of 2D metal nanostructures.

Nitrogen-Doped Bismuth Nanosheet as an Efficient Electrocatalyst to CO2 Reduction for Production of Formate

Electrochemical CO₂ reduction (CO₂RR) to produce high value-added chemicals or fuels is a promising technology to address the greenhouse effect and energy challenges. Formate is a desirable product of CO₂RR with great economic value. Here, nitrogen-doped bismuth nanosheets (N-BiNSs) were prepared by a facile one-step method. The N-BiNSs were used as efficient electrocatalysts for CO₂RR with selective formate production. The N-BiNSs exhibited a high formate Faradic efficiency (FE_formate) of 95.25% at -0.95 V (vs. RHE) with a stable current density of 33.63 mA cm^-2 in 0.5 M KHCO₃. Moreover, the N-BiNSs for CO₂RR yielded a large current density (300 mA cm^-2) for formate production in a flow-cell measurement, achieving the commercial requirement. The FE_formate of 90% can maintain stability for 14 h of electrolysis. Nitrogen doping could induce charge transfer from the N atom to the Bi atom, thus modulating the electronic structure of N-Bi nanosheets. DFT results demonstrated the N-BiNSs reduced the adsorption energy of the *OCHO intermediate and promoted the mass transfer of charges, thereby improving the CO₂RR with high FE_formate. This study provides a valuable strategy to enhance the catalytic performance of bismuth-based catalysts for CO₂RR by using a nitrogen-doping strategy.

Molecularly Distorted Local Structure in Bi2 CuO4 Oxide to Stabilize Lattice Oxygen for Efficient Formate Electrosynthesis

The electrochemical CO₂ reduction reaction (CO₂ RR) provides an economically feasible way for converting green energy into valuable chemical feedstocks and fuels. Great progress has been achieved in the understanding and synthesis of oxidized-based precatalysts; however, their dynamical changes of local structure under operando conditions still hinder their further applications. Here a molecularly distorted Bi₂ CuO₄ precatalyst for efficient CO₂ -to-formate conversion is reported. X-ray absorption fine structure (XAFS) results and theoretical calculations suggest that the distorted structure with molecularly like [CuO₄ ]^6- unit rotation is more conducive to the structural stability of the sample. Operando XAFS and scanning transmission electron microscopy (STEM) results prove that quite a bit of lattice oxygen can remain in the distorted sample after CO₂ RR. Electrochemical measurements of the distorted sample show an excellent activity and selectivity with a high formate partial current density of 194.6 mA cm^-2 at an extremely low overpotential of -400 mV. Further in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) calculations illustrate that the retained oxygen can optimize the adsorption of *OCHO intermediate for the enhanced CO₂ RR performance.

Cage Bismuth Metal-Organic Framework Materials Based on a Flexible Triazine-Polycarboxylic Acid: Subgram Synthesis, Application for Sensing, and White Light Tuning

Bismuth-based metal-organic frameworks (MOFs) have always attracted the attention of many researchers. Here, we first report a crystalline Bi-MOF (Bi-TDPAT) based on a flexible triazine-polycarboxylic linker 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine (H₆TDPAT) and bismuth nitrate; its crystallite quality is adequately good and the diffraction data can be collected directly by single crystal X-ray diffraction rather than 3D electron diffraction. The structure of Bi-TDPAT belongs to a novel topology type btt. Notably, the synthesis scale of Bi-TDPAT can be expanded, and sub-gram synthesis can be realized. At the same time, we synthesized a microcrystalline material Bi-TATAB utilizing 2,4,6-tris(4-carboxylphenylamino)-1,3,5-triazine (H₃TATAB). The structures of the two materials were characterized by several microanalysis tools. Considering that Bi-TDPAT is a blue light-emitting material with a broad emission peak, we prepared a white light emitting composite material Eu/Tb@Bi-TDPAT by encapsulating Eu(III)/Tb(III) in Bi-TDPAT. In addition, the fluorescence sensing functions of Bi-TDPAT and Bi-TATAB were explored. The results showed that they could detect and recognize various nitrophenols, and the optimal limit of detection is as low as 0.21 μM, which can be reused even after five cycles. Energy competitive absorption (CA) and photo-induced electron transfer are the main sensing mechanisms. By comparing and analyzing the properties of these two bismuth-based crystalline materials, we believe that this work also provides inspiration for the synthesis and development of bismuth-based MOF in the future.

MOF-Transformed In2O3-x@C Nanocorn Electrocatalyst for Efficient CO2 Reduction to HCOOH

For electrochemical CO₂ reduction to HCOOH, an ongoing challenge is to design energy efficient electrocatalysts that can deliver a high HCOOH current density (J_HCOOH) at a low overpotential. Indium oxide is good HCOOH production catalyst but with low conductivity. In this work, we report a unique corn design of In₂O_3-x@C nanocatalyst, wherein In₂O_3-x nanocube as the fine grains dispersed uniformly on the carbon nanorod cob, resulting in the enhanced conductivity. Excellent performance is achieved with 84% Faradaic efficiency (FE) and 11 mA cm^-2 J_HCOOH at a low potential of - 0.4 V versus RHE. At the current density of 100 mA cm^-2, the applied potential remained stable for more than 120 h with the FE above 90%. Density functional theory calculations reveal that the abundant oxygen vacancy in In₂O_3-x has exposed more In³⁺ sites with activated electroactivity, which facilitates the formation of HCOO* intermediate. Operando X-ray absorption spectroscopy also confirms In³⁺ as the active site and the key intermediate of HCOO* during the process of CO₂ reduction to HCOOH.

1D α-Fe2O3/ZnO Junction Arrays Modified by Bi as Photocathode: High Efficiency in Photoelectrochemical Reduction of CO2 to HCOOH

Photoelectrocatalytic (PEC) CO₂ reduction to value-added chemicals is a promising solution to address the energy and environmental issues we face currently. Herein, a unique photocathode Bi@ZFO NTs (Bi and α-Fe₂O₃ co-modified ZnO nanorod arrays) with high utilization of visible light and sharp-tips effect are successfully prepared using a facile method. Impressively, the performance of Bi@ZFO NTs for PEC CO₂ reduction to HCOOH included small onset potential (-0.53 V vs RHE), Tafel slope (101.2 mV dec^-1), and a high faraday efficiency of 61.2% at -0.65 V vs RHE as well as favorable stability over 4 h in an aqueous system under visible light illumination. Also, a series of experiments were performed to investigate the origin of its high activity, indicating that the metallic Bi and α-Fe₂O₃/ZnO nanojunction should be responsible for the favorable CO₂ adsorption/activation and charge transition/carrier separation, respectively. Density functional theory calculations reveal that the Bi@ZFO NTs could lower the intermediates' energy barrier of HCOO* and HCOOH* to form HCOOH due to the strong interaction of Bi and α-Fe₂O₃/ZnO.

Aligned InS Nanorods for Efficient Electrocatalytic Carbon Dioxide Reduction

Electrochemical CO₂ reduction technology can combine renewable energy sources with carbon capture and storage to convert CO₂ into industrial chemicals. However, the catalytic activity under high current density and long-term electrocatalysis process may deteriorate due to agglomeration, catalytic polymerization, element dissolution, and phase change of active substances. Here, we report a scalable and facile method to fabricate aligned InS nanorods by chemical dealloying. The resulting aligned InS nanorods exhibit a remarkable CO₂RR activity for selective formate production at a wide potential window, achieving over 90% faradic efficiencies from -0.5 to -1.0 V vs reversible hydrogen electrode (RHE) under gas diffusion cell, as well as continuously long-term operation without deterioration. In situ electrochemical Raman spectroscopy measurements reveal that the *OCHO* species (Bidentate adsorption) are the intermediates that occurred in the reaction of CO₂ reduction to formate. Meanwhile, the presence of sulfur can accelerate the activation of H₂O to react with CO₂, promoting the formation of *OCHO* intermediates on the catalyst surface. Significantly, through additional coupling anodic methanol oxidation reaction (MOR), the unusual two-electrode electrolytic system allows highly energy-efficient and value-added formate manufacturing, thereby reducing energy consumption.

Galvanic-Cell Deposition Enables the Exposure of Bismuth Grain Boundary for Efficient Electroreduction of Carbon Dioxide

Metallic bismuth (Bi) holds great promise in efficient conversion of carbon dioxide (CO₂ ) into formate, yet the complicated synthetic routes and unobtrusive performance hinder the practical application. Herein, a facile galvanic-cell deposition method is proposed for the rapid and one-step synthesis of Bi nanodendrites. Compared to the traditional deposition method, it is found that the special galvanic-cell configuration can promote the exposure of low-angle grain boundaries. X-ray absorption spectroscopy, in situ characterizations and theoretical calculations indicate the electronical structures can be greatly tailored by the grain boundaries, which can facilitate the CO₂ adsorption and intermediate formation. Consequently, the grain boundary-enriched Bi nanodendrites exhibit a high selectivity toward formate with an impressively high production rate of 557.2 µmol h^-1 cm^-2 at -0.94 V versus reversible hydrogen electrode, which outperforms most of the state-of-the-art Bi-based electrocatalysts with longer synthesis time. This work provides a straightforward method for rapidly fabricating active Bi electrocatalysts, and explicitly reveals the critical effect of grain boundary in Bi nanostructures on CO₂ reduction.

Active and conductive layer stacked superlattices for highly selective CO2 electroreduction

Metal oxides are archetypal CO₂ reduction reaction electrocatalysts, yet inevitable self-reduction will enhance competitive hydrogen evolution and lower the CO₂ electroreduction selectivity. Herein, we propose a tangible superlattice model of alternating metal oxides and selenide sublayers in which electrons are rapidly exported through the conductive metal selenide layer to protect the active oxide layer from self-reduction. Taking BiCuSeO superlattices as a proof-of-concept, a comprehensive characterization reveals that the active [Bi₂O₂]²⁺ sublayers retain oxidation states rather than their self-reduced Bi metal during CO₂ electroreduction because of the rapid electron transfer through the conductive [Cu₂Se₂]^2- sublayer. Theoretical calculations uncover the high activity over [Bi₂O₂]²⁺ sublayers due to the overlaps between the Bi p orbitals and O p orbitals in the OCHO* intermediate, thus achieving over 90% formate selectivity in a wide potential range from −0.4 to −1.1 V. This work broadens the studying and improving of the CO₂ electroreduction properties of metal oxide systems.

It is important yet challenging to improve the interface contact between commonly used carbon conductive layer and metal oxide catalysts. Here the authors propose BiCuSeO with alternant active [Bi₂O₂]²⁺ sublayers and conductive [Cu₂Se₂]^2- sublayer within its superlattice as efficient catalyst for CO₂ electroreduction to formate.

Simple Bottom-Up Synthesis of Bismuthene Nanostructures with a Suitable Morphology for Competitive Performance in the Electrocatalytic Nitrogen Reduction Reaction

Nitrogen reduction to ammonia under ambient conditions has received important attention, in which high-performing catalysts are sought. A new, facile, and seedless solvothermal method based on a high-temperature reduction route has been developed in this work for the production of bismuthene nanostructures with excellent performance in the electrocatalytic nitrogen reduction reaction (NRR). Different reaction conditions were tested, such as the type of solvent, surfactant, reducing agent, reaction temperature, and time, as well as bismuth precursor source, resulting in distinct particle morphologies. Two-dimensional sheet-like structures and small particles displayed very high electrocatalytic activity, attributed to the abundance of tips, edges, and high surface area. NRR experiments resulted in an ammonia yield of 571 ± 0.1 μg h^-1 cm^-2 with a respective Faradaic efficiency of 7.94 ± 0.2% vs Ag/AgCl. The easy implementation of the synthetic reaction to produce Bi nanostructures facilitates its potential scale up to larger production yields.

Bismuth with abundant defects for electrocatalytic CO2 reduction and Zn-CO2 batteries

To regulate the electronic structure of Bi sites and enhance their intrinsic activity, metal Bi with abundant defects was constructed. The optimized sample displayed a higher selectivity (93.9% at -0.9 V) and a larger current density (-10 mA cm^-2 at -1.0 V) towards electrocatalytic CO₂ reduction to formate, which can be mainly attributed to abundant defect sites and the optimized electronic structure. The assembled Zn-CO₂ batteries displayed a power density of 1.16 mW cm^-2 and a cycling stability up to 22 h. This work deepens the research of Bi-based catalysts towards CO₂ transformation and related energy devices.

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.

A gradient Sn4+@Sn2+ core@shell structure induced by a strong metal oxide–support interaction for enhanced CO2 electroreduction

A gradient Sn4+@Sn2+ core@shell structure induced by a strong tin oxide–g-C3N4 support interaction enhanced the adsorption and stabilization of CO2˙−, and hence the CO2RR performances.

Two-dimensional materials for electrochemical CO2 reduction: materials, in situ/operando characterizations, and perspective

Electrochemical CO₂ reduction (CO₂ ECR) is an efficient approach to achieving eco-friendly energy generation and environmental sustainability. This approach is capable of lowering the CO₂ greenhouse gas concentration in the atmosphere while producing various valuable fuels and products. For catalytic CO₂ ECR, two-dimensional (2D) materials stand as promising catalyst candidates due to their superior electrical conductivity, abundant dangling bonds, and tremendous amounts of surface active sites. On the other hand, the investigations on fundamental reaction mechanisms in CO₂ ECR are highly demanded but usually require advanced in situ and operando multimodal characterizations. This review summarizes recent advances in the development, engineering, and structure-activity relationships of 2D materials for CO₂ ECR. Furthermore, we overview state-of-the-art in situ and operando characterization techniques, which are used to investigate the catalytic reaction mechanisms with the spatial resolution from the micron-scale to the atomic scale, and with the temporal resolution from femtoseconds to seconds. Finally, we conclude this review by outlining challenges and opportunities for future development in this field.

Constructing Heterogeneous Structure in Metal-Organic Framework-Derived Hierarchical Sulfur Hosts for Capturing Polysulfides and Promoting Conversion Kinetics

Lithium-sulfur batteries (LSBs) are still severely blocked by the shuttle of polysulfides (LiPSs), resulting in low sulfur utilization and decreased lifetime. The optimal design of hosts with tailored porous structures and catalytic sites is expected to address this issue. Herein, a Bi/Bi₂O₃ heterostructure within the metal-organic framework (MOF)-derived sulfur host with a hierarchical structure was elaborated for both serving as sulfur hosts and promoting the redox reaction kinetics of LiPSs. The shuttle effects of LiPSs can be mitigated by the dual functional Bi/Bi₂O₃ heterostructure enriched in the outer layer of CAU-17-derived carbonic rods, i.e., the effective redox conversion of LiPSs can be realized at the Bi/Bi₂O₃ heterointerface by the adsorption of LiPSs over Bi₂O₃ and subsequently catalytic conversion over Bi. Benefiting from these merits, the fabricated LSBs realized a significantly optimized performance, including a high discharge capacity of 740.8 mAh g^-1 after 1000 cycles with an ultralow decay rate of 0.022% per cycle at 1 C, a high areal capacity of 6.6 mAh cm^-2 after 100 cycles with a sulfur loading of 8.1 mg cm^-2, and good performance in pouch cells as well.

Oxygen vacancy-rich N-doped carbon encapsulated BiOCl-CNTs heterostructures as robust electrocatalyst synergistically promote oxygen reduction and Zn-air batteries

The development of non-precious metal catalysts for oxygen reduction reactions (ORR) is vital for promising clean energy technologies such as fuel cells, and zinc-air batteries. Herein, we present a stepwise synthesis of N-doped and carbon encapsulated BiOCl-CNTs heterostructures. Electrocatalytic ORR studies show that the optimized catalyst has a high half-wave potential (E_1/2) of 0.85 V (vs. RHE), large limiting current density (-5.34 mA cm^-2@0.6 V) in alkaline medium, and nearly perfect 4e^- reduction characteristics, even surpassing commercial Pt/C. Meanwhile, the catalyst has exceptional durability (above 97.5 % after 40000 s) and strong resistance towards methanol poisoning. The good ORR activity also results in high-performance zinc-air batteries with a specific capacity (724 mAh g^-1@10 mA cm^-2), a high open-circuit potential of 1.51 V and a peak power density of 170.7 mW cm^-2, as well as an ultra-long charge-discharge cycle stability (155 h), comparable with the Pt/C catalyst. The catalytic mechanism reveals that the excellent electrocatalytic performance originates from the synergistic effect of N doping, oxygen vacancies, and BiOCl sites.

Anion Modulation of Pt-Group Metals and Electrocatalysis Applications

Pt-group metal (PGM) electrocatalysts with unique electronic structures and irreplaceable comprehensive properties play crucial roles in electrocatalysis. Anion engineering can create a series of PGM compounds (such as RuP₂ , IrP₂ , PtP₂ , RuB₂ , Ru₂ B₃ , RuS₂ , etc.) that provide a promising prospect for improving the electrocatalytic performance and use of Pt-group noble metals. This review seeks the electrochemical activity origin of anion-modulated PGM compounds, and systematically analyzes and summarizes their synthetic strategies and energy-relevant applications in electrocatalysis. Orientation towards the sustainable development of nonfossil resources has stimulated a blossoming interest in the design of advanced electrocatalysts for clean energy conversion. The anion-modulated strategy for Pt-group metals (PGMs) by means of anion engineering possesses high flexibility to regulate the electronic structure, providing a promising prospect for constructing electrocatalysts with superior activity and stability to satisfy a future green electrochemical energy conversion system. Based on the previous work of our group and others, this review summarizes the up-to-date progress on anion-modulated PGM compounds (such as RuP₂ , IrP₂ , PtP₂ , RuB₂ , Ru₂ B₃ , RuS₂ , etc.) in energy-related electrocatalysis from the origin of their activity and synthetic strategies to electrochemical applications including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), N₂ reduction reaction (NRR), and CO₂ reduction reaction (CO₂ RR). At the end, the key problems, countermeasures and future development orientations of anion-modulated PGM compounds toward electrocatalytic applications are proposed.

Spontaneously Sn-Doped Bi/BiOx Core-Shell Nanowires Toward High-Performance CO2 Electroreduction to Liquid Fuel

Electrochemical CO₂ reduction provides a promising strategy to product value-added fuels and chemical feedstocks. However, it remains a grand challenge to further reduce the overpotentials and increase current density for large-scale applications. Here, spontaneously Sn doped Bi/BiOx nanowires (denoted as Bi/Bi(Sn)O_x NWs) with a core-shell structure were synthesized by an electrochemical dealloying strategy. The Bi/Bi(Sn)O_x NWs exhibit impressive formate selectivity over 92% from -0.5 to -0.9 V versus reversible hydrogen electrode (RHE) and achieve a current density of 301.4 mA cm^-2 at -1.0 V vs RHE. In-situ Raman spectroscopy and theoretical calculations reveal that the introduction of Sn atoms into BiO_x species can promote the stabilization of the *OCHO intermediate on the Bi(Sn)O_x surface and suppress the competitive H₂/CO production. This work provides effective in situ construction of the metal/metal oxide hybrid composites with heteroatom doping and new insights in promoting electrochemical CO₂ conversion into formate for practical applications.

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.