Interfacial CO2 Research Articles

Efficient charge transfer at the donor-bridge-acceptor interface for excellent supercapacitors

The intrinsic electrochemical activity and active sites of the battery-like electrode in supercapacitors originate from efficient charge transfer at the interface. A seamless all-carbon graphdiyne layer on CoNi2S4 yolk-shell spheres (CoNi2S4/GDY YSSs) provides a unique structure of a flawless “donor–bridge–acceptor” interface, where Ni atoms and Co atoms serve as electron donors and acceptors, respectively, connected by the sp-C–Ni and sp-C–Co bonds as bridges. Importantly, this particular can facilitate effective electron transfer from the Ni atoms to the Co atoms, resulting in more interfacial Co2+ active sites and reversible redox coupling of Co-S/Co-S-OH and Co-S-OH/Co-S-O to increase the specific capacitance. Additionally, the seamless all-carbon graphdiyne layer greatly enhances the structural and interfacial stability of CoNi2S4 yolk-shell spheres, effectively avoiding structural deterioration to enhance cycling stability performance. Profiting from its structural merits, the CoNi2S4/GDY YSSs electrode delivers a considerable capacitance of 856C/g at 1 A/g, along with exceptional rate capability (61.9 % for 50-fold current density increase). Furthermore, an asymmetric supercapacitor with the CoNi2S4/GDY YSSs electrode cathode achieves a remarkable maximum energy density of 91.7 Wh/kg at a power density of 793 W/kg. Furthermore, the strategy proposed in this study has the potential to open up new pathways for the battery-like electrode design with realistic supercapacitor applications.

Electrochemical Flow Reactor Design Allows Tunable Mass Transport Conditions for Operando Surface Enhanced Infrared Absorption Spectroscopy

AbstractIn situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR‐SEIRAS) is often used to investigate the near‐surface electrocatalytic reaction environment. However, there is a gap in directly correlating the near‐surface reaction environment with electrocatalytic reaction rates. To that end, we designed an electrochemical flow reactor for operando electrochemical ATR‐SEIRAS and demonstrate its capability with the CO2 reduction reaction (CO2RR). Roughened gold catalyst thin films are prepared on ATR silicon crystals as a model system to probe local species under CO2RR conditions in 0.1 M KHCO3. We measured changes in the interfacial CO2 concentration as a function of applied potential and electrolyte flow rate in operando, allowing us to correlate the changes in reaction rates with the observed CO2 concentration. Including the choice of the catalyst and electrolyte, coupling hydrodynamic control with ATR‐SEIRAS in this platform enables investigations of how the local microenvironment affects the activity and selectivity of electrochemical reactions.

Nanoclay-Modulated Interfacial Chemical Bond and Internal Electric Field at the Co3 O4 /TiO2 p-n Junction for Efficient Charge Separation.

To achieve a high separation efficiency of photogenerated carriers in semiconductors, constructing high-quality heterogeneous interfaces as charge flow highways is critical and challenging. This study successfully demonstrates an interfacial chemical bond and internal electric field (IEF) simultaneously modulated 0D/0D/1D-Co3 O4 /TiO2 /sepiolite composite catalyst by exploiting sepiolite surface-interfacial interactions to adjust the Co2+ /Co3+ ratio at the Co3 O4 /TiO2 heterointerface. In situ irradiation X-ray photoelectron spectroscopy and density functional theory (DFT) calculations reveal that the interfacial Co2+ OTi bond (compared to the Co3+ OTi bond) plays a major role as an atomic-level charge transport channel at the p-n junction. Co2+ /Co3+ ratio increase also enhances the IEF intensity. Therefore, the enhanced IEF cooperates with the interfacial Co2+ OTi bond to enhance the photoelectron separation and migration efficiency. A coupled photocatalysis-peroxymonosulfate activation system is used to evaluate the catalytic activity of Co3 O4 /TiO2 /sepiolite. Furthermore, this work demonstrates how efficiently separated photoelectrons facilitate the synergy between photocatalysis and peroxymonosulfate activation to achieve deep pollutant degradation and reduce its ecotoxicity. This study presents a new strategy for constructing high-quality heterogeneous interfaces by consciously modulating interfacial chemical bonds and IEF, and the strategy is expected to extend to this class of spinel-structured semiconductors.

Hydrophobic Ni@N‐Doped TiO2 Nanosheet Arrays‐Carbon Paper Photocatalyst for CO2 Photoreduction at Tri‐Phase Interfaces

AbstractRational interphase reaction provides a feasible method to overcome the matters of insufficient adsorption of CO2 molecules at the catalytic sites and competitive hydrogen evolution reaction (HER), which can increase the formation rate and selectivity of carbon derivatives in photocatalytic CO2 reduction. Herein, a hydrophobic photocatalyst with TiO2 nanosheet arrays grown on hydrophobic carbon paper (TiO2‐HCP) is fabricated using a combination of magnetron sputtering and hydrothermal method, and its unique structure not only endows it excellent light absorption and effective carrier spatial separation but also avoids the hydrophobic reagent covering reactive sites. When the interphase reaction shifts from solid–liquid diphase to gas‐liquid‐solid tri‐phase, the photocatalytic CO2 reduction over TiO2‐HCP mainly generates CO molecules and effectively suppresses HER due to the HCP suppressing the mass transfer of H2O molecules to active sites. Notably, amounts of H2 byproduct can further react with CO2/CO to produce high value‐added CH4 resultant by modifying the N‐doped TiO2‐HCP with nickel/nickel oxide species. In the tri‐phase interfacial CO2 photoreduction system, the CH4 formation rate of Ni@N‐doped TiO2‐HCP reaches 134.17 µmol m−2 h−1 (about 74.6% selectivity) and total carbon derivatives selectivity is about 93%.

Efficient CO2 photoreduction triggered by oxygen vacancies in ultrafine Bi5O7Br nanowires

Sluggish charge kinetics, poor photoabsorption and low CO2 affinity have been regarded as the main obstacles inhibiting the efficiency of CO2 photoreduction. Herein, freestanding ultrafine Bi5O7Br nanowires with abundant oxygen vacancies were initially fabricated to synchronously optimize these critical processes. The 1D ultrafine configuration and abundant oxygen vacancies endow the Bi5O7Br nanowires with extended photoadsorption, boosted charge separation and enhanced interfacial CO2 adsorption and activation. Density functional calculations reveal that the presence of oxygen vacancies on the Bi5O7Br surface can not only afford abundant localized electrons and lower the CO2 reaction energy barriers, but also have a stronger covalent interaction and more efficient electron exchange and transfer between CO2 and oxygen vacancies. Without any co-catalyst or sacrifice reagent, OV-rich Bi5O7Br nanowires show a 27.76-fold enhancement of CO2 photoreduction activity relative to bulk Bi5O7Br in the gas-solid system. This work may inspire the future design of ultrafine catalysts for artificial photosynthesis.

Triphase Photocatalytic CO2 Reduction over Silver‐Decorated Titanium Oxide at a Gas–Water Boundary

AbstractPhotocatalytic CO2 reduction reaction (CO2RR) is an attractive process to convert CO2 into valuable chemicals. But this reaction is often restricted by the poor mass transfer of CO2 in the liquid phase. Here, we have developed a triphase photocatalytic CO2RR system by supporting Ag‐decorated TiO2 nanoparticles at a gas–water boundary with hydrophobic–hydrophilic abrupt interfacial wettability. Such a triphase system allows the rapid delivery of gas‐phase CO2 to the surface of photocatalysts while maintaining an efficient water supply and uncovered active sites. Ag‐TiO2 supported at the gas–water boundary showed a CO2 reduction rate of 305.7 μmol g−1 h−1, without hole scavengers, approximately 8 times higher than the nanoparticles dispersed in the liquid phase. Even using diluted CO2 (10 %) as the reactant, the CO2RR activity was superior to most reported Ag‐TiO2 based photocatalysts using pure CO2. The findings provide a general strategy to promote the interfacial CO2 mass transfer to improve photoactivity and selectivity.

Triphase Photocatalytic CO2 Reduction over Silver-Decorated Titanium Oxide at a Gas-Water Boundary.

Photocatalytic CO2 reduction reaction (CO2 RR) is an attractive process to convert CO2 into valuable chemicals. But this reaction is often restricted by the poor mass transfer of CO2 in the liquid phase. Here, we have developed a triphase photocatalytic CO2 RR system by supporting Ag-decorated TiO2 nanoparticles at a gas-water boundary with hydrophobic-hydrophilic abrupt interfacial wettability. Such a triphase system allows the rapid delivery of gas-phase CO2 to the surface of photocatalysts while maintaining an efficient water supply and uncovered active sites. Ag-TiO2 supported at the gas-water boundary showed a CO2 reduction rate of 305.7 μmol g-1 h-1 , without hole scavengers, approximately 8 times higher than the nanoparticles dispersed in the liquid phase. Even using diluted CO2 (10 %) as the reactant, the CO2 RR activity was superior to most reported Ag-TiO2 based photocatalysts using pure CO2 . The findings provide a general strategy to promote the interfacial CO2 mass transfer to improve photoactivity and selectivity.

Spatio-temporal 1D gas–liquid model for biological methanation in lab scale and industrial bubble column

Numerical simulation of biological methanation in bubble column reactors is challenging due to strong coupling between hydrodynamics, mass transfer and bioreaction. A satisfactory prediction of the mass transfer coefficient and the gas solubility is crucial to couple hydrodynamics and biokinetics. A comprehensive 1D multispecies multiple-way coupled gas–liquid model is developed. The hydrodynamics of the model is validated using experimental gas loading data at very low gas holdup. The local mass transfer is validated using literature data on CO2 mass transfer in the large-scale. The local gas holdup and interfacial CO2 mass transfer flux are correctly described thanks to a two-way coupling between hydrodynamics and mass transfer, including changes in bubble diameter and pressure effects. When a mixture of H2, CO2 and CH4 is used, highly non-linear mass transfer profiles due to differences in solubilities are observed. An original flux-based metabolic model is proposed to simulate an industrial biological methanation process. This allows smooth transition between biologically and physically controlled regimes as the culture reaches a steady-state. The comprehensive model enlightens that the biological methanation performances are governed by the H2 mass transfer limitation balanced by growth in the transient state and biological maintenance in the steady-state.

The Role of Surface Hydrophobicity on the Structure and Dynamics of CO2 and CH4 Confined in Silica Nanopores

Advancing a portfolio of technologies that range from the storage of excess renewable natural gas for distributed use to the capture and storage of CO2 in geological formation are essential for meeting our energy needs while responding to challenges associated with climate change. Delineating the surface interactions and the organization of these gases in nanoporous environments is one of the less explored approaches to ground advances in novel materials for gas storage or predict the fate of stored gases in subsurface environments. To this end, the molecular scale interactions underlying the organization and transport behavior of CO2 and CH4 molecules in silica nanopores need to be investigated. To probe the influence of hydrophobic surfaces, a series of classical molecular dynamics (MD) simulations are performed to investigate the structure and dynamics of CO2 and CH4 confined in OH-terminated and CH3-terminated silica pores with diameters of 2, 4, 6, 8, and 10 nm at 298 K and 10 MPa. Higher adsorption extents of CO2 compared to CH4 are noted on OH-terminated and CH3-terminated pores. The adsorbed extents increase with the pore diameter. Further, the interfacial CO2 and CH4 molecules reside closer to the surface of OH-terminated pores compared to CH3-terminated pores. The lower adsorption extents of CH4 on OH-terminated and CH3-terminated pores result in higher diffusion coefficients compared to CO2 molecules. The diffusivities of both gases in OH-terminated and CH3-terminated pores increase systematically with the pore diameter. The higher adsorption extents of CO2 on OH-terminated and CH3-terminated pores are driven by higher van der Waals and electrostatic interactions with the pore surfaces, while CH4 adsorption is mainly due to van der Waals interactions with the pore walls. These findings provide the interfacial chemical basis underlying the organization and transport behavior of pressurized CO2 and CH4 gases in confinement.

Efficient Electrocatalytic CO2 Reduction to C2+ Alcohols at Defect-Site-Rich Cu Surface

Summary Electrochemical CO2 reduction is a promising approach for upgrading excessive CO2 into value-added chemicals, while the exquisite control of the catalyst atomic structures to obtain high C2+ alcohol selectivity has remained challenging due to the intrinsically favored ethylene pathways at Cu surface. Herein, we demonstrate a rational strategy to achieve ∼70% faradaic efficiency toward C2+ alcohols. We utilized a CO-rich environment to construct Cu catalysts with stepped sites that enabled high surface coverages of ∗CO intermediates and the bridge-bound ∗CO adsorption, which allowed to trigger CO2 reduction pathways toward the formation alcohols. Using this defect-site-rich Cu catalyst, we achieved C2+ alcohols with partial current densities of > 100 mA·cm−2 in both a flow-cell electrolyzer and a membrane electrode assembly (MEA) electrolyzer. A stable alcohol faradaic efficiency of ∼60% was also obtained, with ∼500 mg C2+ alcohol production per cm2 catalyst during a continuous 30-h operation.

Predictable interfacial mass transfer intensification of Sn–N doped multichannel hollow carbon nanofibers for the CO2 electro-reduction reaction

Construction of controllable multichannel and mesoporous structures on Sn and N co-doped carbon nanofibers enables intensified interfacial CO2 transfer and stabilized high-loading CO2,ads, enhancing CO2 electro-reduction performance.

Cation Effect on Interfacial CO2 Concentration in the Electrochemical CO2 Reduction Reaction

The capacity of larger alkali metal cations to maintain the interfacial CO2 concentration by buffering the interfacial pH has been proposed to enhance the electrochemical CO2 reduction reaction (CO...

Efficient wettability-controlled electroreduction of CO2 to CO at Au/C interfaces

The electrochemical CO2 reduction reaction (CO2RR) represents a very promising future strategy for synthesizing carbon-containing chemicals in a more sustainable way. In spite of great progress in electrocatalyst design over the last decade, the critical role of wettability-controlled interfacial structures for CO2RR remains largely unexplored. Here, we systematically modify the structure of gas-liquid-solid interfaces over a typical Au/C gas diffusion electrode through wettability modification to reveal its contribution to interfacial CO2 transportation and electroreduction. Based on confocal laser scanning microscopy measurements, the Cassie-Wenzel coexistence state is demonstrated to be the ideal three phase structure for continuous CO2 supply from gas phase to Au active sites at high current densities. The pivotal role of interfacial structure for the stabilization of the interfacial CO2 concentration during CO2RR is quantitatively analysed through a newly-developed in-situ fluorescence electrochemical spectroscopic method, pinpointing the necessary CO2 mass transfer conditions for CO2RR operation at high current densities.

3D-Printed interfacial devices for biocatalytic CO2 conversion at gas-liquid interface

Carbonic anhydrases (CAs) are enzymes that can function at physiologic interfaces and catalyze the interfacial conversion of carbon dioxide (CO2) into bicarbonate (HCO3−) with an extraordinarily high catalytic efficiency. Even though CAs have potential to be used for CO2 sequestration, significant mass transfer resistance and poor enzyme stability at gas-liquid interface often limit the effectiveness of the enzyme. Here, we report a density-adjustable 3D-printed platform, which can accommodate electrospun polymer fibers with immobilized CA and enable the positioning of immobilized CA in an air-water biphasic system. By using 3D printing, we fabricate interfacial devices consisting of two floating units and different number of biocatalytic units. Two mesh structures of each biocatalytic unit are used to sandwich immobilized CA while two floating units, connected on either side of the biocatalytic units, have an internal hollow volume that enables controlling the position of the enzyme-loaded interfacial device at or near the air-water interface. The positioning of interfacial device directly at the biphasic interface accelerated CO2 conversion by 1.8- and 3.4-fold when compared to reactions performed with immobilized CA within the aqueous solution and a control interfacial device without immobilized CA, respectively. The CA-loaded interfacial device retained 99.3 % and 88.2 % of its initial CO2 conversion rate after ten recycles and after subsequent storage in an aqueous buffer at 4 °C for 459 days, respectively. Facile combination of interfacial devices and immobilized enzymes on polymer fibers has paved the way to practical uses of biocatalysts for interfacial CO2 sequestration.

Theoretical Insights into the Role of Metal–Support Interactions of an Al2O3-Supported Ru4 Cluster in CO2 Dissociation

First-principles calculations were conducted to determine the effect of metal–support interactions on CO2 dissociation by using Ru4/Al2O3(110), Ru4/Al2O3(100), and Ru4/hydroxylated-Al2O3(110) catalysts. The results indicate that CO2 adsorption and decomposition are sensitive to the support surface structure and hydroxylation, which control the metal–support interaction. Interfacial CO2 is prone to direct decomposition on Ru4/Al2O3(110), whereas bidentate CO2 on Ru4/Al2O3(100) prefers a direct dissociation pathway at low temperatures and HCOO*-mediated association at high temperatures. The irregular (110) surface helps separate products and raises the d-band center of involved Ru, causing the direct decomposition to be more favorable than H-assisted routes. The less reactant charge makes HCOO*-mediated routes thermodynamically favorable; however, the lower d-band energy of the participated Ru in Ru4/Al2O3(100) elevates the overall barrier to be 0.71 eV higher than that of the direct dissociation pathway. S...

In Situ Monitoring Using ATR-SEIRAS of the Electrocatalytic Reduction of CO2 on Au in an Ionic Liquid/Water Mixture

The electrochemical reduction of CO2 to CO in ionic liquids and ionic-liquid/water mixtures has received considerable attention due to recent claims of extraordinarily high energy efficiencies. We report here a study of CO2 electroreduction on Au in an [EMIM]BF4/H2O mixture (18% mol/mol) combining cyclic voltammetry and surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode (ATR-SEIRAS). The onset of the reduction current in the CV coincides with a decrease of the interfacial CO2 concentration, but the appearance of adsorbed CO (COad) is slightly delayed, as CO must probably first reach a minimum concentration at the interface. Comparisons with spectra collected in the absence of CO2 and in CO-saturated electrolyte reveal that the structure of the double layer at negative potentials is different when CO2 is present (probably due to the formation of COad) and allow us to assign the main band in the spectra to CO adsorbed linearly on Au (COL), with a smaller band correspon...

A computational study of dicationic ionic liquids/CO₂ interfaces.

Recent studies on CO2 capture using dicationic ionic liquids (DILs) demonstrated that DILs are promising absorbents for CO2 uptake especially compared with monocationic ionic liquids (MILs) analogues, in which each cation carries single positive charge in contrast to two unit charges of a dication. However, DILs/CO2 interfacial properties at the molecular level are still unknown. This work investigated the CO2 absorption properties of representative DILs, 1-alkyl-3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, [Cn(mim)2](Tf2N)2 (n = 3, 6, 12), using molecular dynamics (MD) simulations. The higher interfacial CO2 density at DIL than that at MIL interfaces suggests the increased CO2 interaction sites in DILs. The interfacial CO2 density also exhibits an alkyl chain length dependence which decreases with the elongation of alkyl chain and proportionally correlates with the content of fluorine atoms at interfaces. Different alkyl chain orientations in DILs were illustrated in contrast to those of MILs; both DILs and CO2 inside DILs exhibit lower diffusivity than MILs, in agreement with the stronger cation-anion binding energy of DILs. Moreover, DILs show a lower H2O and N2 uptake from flue gas compared with MILs, implicating the higher CO2/H2O and CO2/N2 selectivity.

Direct‐contact steam condensation with simultaneous noncondensable gas absorption

AbstractExperimental results are reported on simulataneous heat transfer and gas dissolution during the direct‐contact condensation of steam on water in the presence of CO2. A column filled with structured packing is used as condenser with the water in counterflow with the steam/CO2 mixture. The region along the column where the bulk of condensation takes place is controllable by suitable choice of the steam/water ratio. Measured local heat‐transfer coefficients change by roughly an order of magnitude from the bottom to the top of the column. The extent of CO2 dissolution in the water/condensate under most conditions is unexpectedly high and depends strongly on the exit liquid temperature. A driving force based on the interfacial CO2 concentration, not the overall concentration difference used in conventional absorption operations, is suggested as more appropriate to describe the phenomenon. The data are complemented with preliminary results from a computational model based on the integration along the column of local heat‐ and mass‐transfer rates.

Reactive deposition of ultrafine cobalt powders

The particle size distributions of cobalt powders prepared by reactive deposition were examined and correlated with the deposition condition. In reactive deposition, a Co(OH)2 colloid layer was formed at the electrode surface upon reduction of dissolved oxygen. The colloid layer accelerated the decrease in interfacial Co2+ concentration and inhibited crystal growth of the metal, and was therefore instrumental in the formation of fine cobalt particles. The powders from reactive deposition were statistically a factor of two finer and of more uniform size distribution than those from normal electrodeposition. It was found that both the reactive deposition of cobalt powders and the reactive deposition of porous cobalt structures were driven by the same kinetic factors, namely the requirement of maintaining an effective presence of the Co(OH)2 colloid layer at the electrode surface. Hence a similar dependence on deposition conditions for both processes was obtained.