Reflection Surface-enhanced Infrared Absorption Spectroscopy Research Articles

Constructing Nanocaged Enzymes for Synergistic Catalysis of CO2 Reduction.

Promoting the activity of biological enzymes under in vitro environment is a promising technique for bioelectrocatalytic reactions, such as the conversion of carbon dioxide (CO2 ) into valuable chemicals, which is a promising strategy to address the environmental issue of CO2 in the atmosphere; however, this technique remains challenging. Herein, a nanocage structure for enzyme confinement is synthesized to enable the in situ encapsulation of formate dehydrogenase (FDH) in a porous metal-organic framework, which acts as a coenzyme and boosts the hybrid synergistic catalysis using enzymes. This study reveals that the synthesized FDH@ZIF-8 nanocage-structured hybrid (CSH) catalyst exhibits an improved catalytic ability of the enzymes and increases the hydrophobicity of the electrode and its affinity to CO2 . Thus, CSH can trap CO2 and control its microenvironments. The CSH catalyst boosts the conversion rate of CO2 to formic acid (HCOOH) to 28 times higher than that when using pure FDH. The in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) spectra indicates that OCHO* is the key intermediate. Density functional theory (DFT) calculations show that CSH has extremely low overpotential and is particularly effective for producing formate. This protection architecture for enzymes considerably promotes their biological application under in vitro environments.

Promoting electrocatalytic CO2 reduction via anchoring quaternary piperidinium cations onto copper electrode

Cation identity in the electrolyte is known to have a critical influence on electrocatalytic CO2 reduction reaction (CO2RR). However, the impact of cation aggregation state at the electrode/electrolyte interface, particularly for organic cations, remains unclear for CO2RR. In this study, we investigated the effect of the organic cation aggregation state, by examining the CO2RR behaviors over a copper (Cu) electrode, before and after the surface modification of a polyelectrolyte (i.e., quaternary ammonia poly (N-methyl-piperidine-co-p-terphenyl) with grafted piperidinium cations), in an aqueous electrolyte with free-moving piperidinium (Pip+) cations. Immobilizing the Pip+ cations on Cu surface was found to effectively promote the CO2RR selectivity. The underlying cause was further explored by in-situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy and electrochemical double-layer capacitance measurements, illustrating that the enhanced CO2RR performance was due to the change in electrode/electrolyte interface properties. These findings would contribute to further optimization of the electrode/electrolyte interface for efficient CO2RR.

Guanine adsorption on gold electrodes studied by in situ surface-enhanced infrared reflection absorption spectroscopy

The adsorption of guanine on single-crystal and thin-film gold electrodes has been explored by combination of cyclic voltammetry and ATR-SEIRA ‘in situ’ spectroscopy at two pD values (8 and 11.6) employing D2O as a solvent. The experimental conditions are selected to study the adsorption / desorption of the two forms of guanine involved in the second acid-base equilibria and its tautomeric forms.The ATR-SEIRA spectra of adsorbed guanine were compared to the absorption FT-IR spectra in solution and interpreted in light of DFT calculations of the different acid-base and tautomeric forms with different solvation states of the CO group. Furthermore, the preponderance of each tautomeric form and the possible changes in orientation with the electric field have been determined by analyzing the two-dimensional correlation spectrum (2D COS) as well as the influence of the potential on the integrated intensities of the spectral signals in the 1800–1400 cm−1 region. It has been found that at pD 8 the adsorbed keto-amino tautomer of neutral guanine predominates in solution and in adsorbed state, and adsorbed guanine slightly rotate its molecular plane with the potential. At pD 11.6 the keto-amino tautomer of anionic guanine is the unique form detectable in the solution, while in adsorbed state the keto-imino tautomeric form is also present with its preponderance increasing with the electrode potential.

A Spectroscopic Study on Nitrogen Electrooxidation to Nitrate.

As a potential substitute technique for conventional nitrate production, electrocatalytic nitrogen oxidation reaction (NOR) is gaining more and more attention. But, the pathway of this reaction is still unknown owing to the lack of understanding on key reaction intermediates. Herein, electrochemical in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and isotope-labeled online differential electrochemical mass spectrometry (DEMS) are employed to study the NOR mechanism over a Rh catalyst. Based on the detected asymmetric NO2- bending, NO3- vibration, N=O stretching, and N-N stretching as well as isotope-labeled mass signals of N2O and NO, it can be deduced that the NOR undergoes an associative mechanism (distal approach) and the strong N≡N bond in N2 prefers to break concurrently with the hydroxyl addition in distal N.

Enhancing Selective Electrochemical CO2 Reduction by In Situ Constructing Tensile-Strained Cu Catalysts

Heteroatom-doped Cu-based catalysts have been found to show not only enhanced activity of electrochemical CO2 reduction reaction (CO2RR) but also the possibility to tune the selectivity of CO2RR. However, the complex and variable nature of Cu-based materials renders it difficult to elucidate the origin of the improved performance, which further hinders the rational design of catalysts. Here, we demonstrate that the activity and selectivity of CO2RR can be tuned by manipulating the lattice strain of Cu-based catalysts. The combined operando and ex situ spectroscopic characterizations reveal that the initial compressively strained Sn-doped CuO catalysts could be converted to tensile-strained Sn/Cu alloy catalysts under reaction conditions. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEITAS) and theoretical calculations further show that the tensile-strained Sn/Cu alloy catalysts favor CO formation due to the preponderant adsorption of *CO and much lower adsorption free energies of *COOH, thus effectively suppressing the dimerization process and the production of HCOOH and H2. This work provides a strategy to tune the CO2RR performance of Cu-based catalysts by manipulating the lattice strain.

Operando Spectroscopic Analysis of Axial Oxygen-Coordinated Single-Sn-Atom Sites for Electrochemical CO2 Reduction

Sn-based materials have been demonstrated as promising catalysts for the selective electrochemical CO2 reduction reaction (CO2RR). However, the detailed structures of catalytic intermediates and the key surface species remain to be identified. In this work, a series of single-Sn-atom catalysts with well-defined structures is developed as model systems to explore their electrochemical reactivity toward CO2RR. The selectivity and activity of CO2 reduction to formic acid on Sn-single-atom sites are shown to be correlated with Sn(IV)-N4 moieties axially coordinated with oxygen (O-Sn-N4), reaching an optimal HCOOH Faradaic efficiency of 89.4% with a partial current density (jHCOOH) of 74.8 mA·cm-2 at -1.0 V vs reversible hydrogen electrode (RHE). Employing a combination of operando X-ray absorption spectroscopy, attenuated total reflectance surface-enhanced infrared absorption spectroscopy, Raman spectroscopy, and 119Sn Mössbauer spectroscopy, surface-bound bidentate tin carbonate species are captured during CO2RR. Moreover, the electronic and coordination structures of the single-Sn-atom species under reaction conditions are determined. Density functional theory (DFT) calculations further support the preferred formation of Sn-O-CO2 species over the O-Sn-N4 sites, which effectively modulates the adsorption configuration of the reactive intermediates and lowers the energy barrier for the hydrogenation of *OCHO species, as compared to the preferred formation of *COOH species over the Sn-N4 sites, thereby greatly facilitating CO2-to-HCOOH conversion.

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

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

Mechanism of CO2 Capture and Release on Redox-Active Organic Electrodes

The mechanism of faradaic electro-swing for CO2 capture/release on a redox-active organic electrode is studied from the point of view of realizing a reversible process for CO2 separation. First, the cyclic voltammograms (CVs) of two redox-active organic monomers, anthraquinone (AQ) and 2,1,3-benzothiadiazole (BTZ), were measured under a CO2 atmosphere. The waveforms of CVs of the two redox-active organic monomers are altered under a CO2 atmosphere relative to a N2 atmosphere. There is a change in the number of redox waves from two to one for AQ and a change from reversible to irreversible waves for BTZ. To further understand the mechanisms of CO2 capture/release on redox-active organic compounds, redox-active polymer electrodes coated with polyanthraquinone (PAQ) and polybenzothiadiazole (PBTZ) were investigated using a spectroscopic analysis known as in situ attenuated total reflectance–surface-enhanced infrared absorption spectroscopy (ATR–SEIRAS) as well as density functional theory (DFT) calculations. The CVs measured with two redox-active polymer electrodes have more positive shifts of reduction potentials for PAQ and PBTZ under a CO2 atmosphere than under an N2 atmosphere, as measured versus Ag/AgNO3: −1.8 and −1.4 V → −1.4 and −0.9 V for PAQ and −2.5 V → −2.1 and −1.9 V for PBTZ. In addition, the oxidation current on the PBTZ electrode disappears only under a CO2 atmosphere. DFT calculations indicate that the positive shifts of reduction potentials in the two electrodes under CO2 conditions are due to an exergonic adsorption reaction of CO2 onto the redox-active organic compounds. To clarify the reaction behavior between CO2 and the redox-active organic electrode, an ATR–SEIRAS spectroscopic analysis was performed. Infrared peaks are observed at 2200 and 2100 cm–1 for PAQ and PBTZ electrodes, respectively, under a CO2 atmosphere, which have been confirmed by measurements under a 13CO2 atmosphere to have adsorbed CO2. The wavenumbers corresponding to the CO2 molecules adsorbed on the two electrodes are different. These findings indicate that one electron reduction and CO2 adsorption for each redox-active organic compound are occurring simultaneously. The calculated adsorption energy of CO2 for two redox-active organic electrodes indicates that the adsorption energies of two CO2 molecules for AQ and BTZ are −7.3 and −36.3 kJ/mol. The larger adsorption energy in BTZ than that in AQ is clearly related to the disappearance of the oxidation current. However, both adsorption energies indicating adsorption of CO2 onto organic units are less than the covalent bond energies of common organic compounds, indicating that such weak adsorptions are suitable for the faradaic electro-swing of CO2 capture/release on the redox-active organic units.

Why surface hydrophobicity promotes CO2 electroreduction: a case study of hydrophobic polymer N-heterocyclic carbenes.

We report the use of polymer N-heterocyclic carbenes (NHCs) to control the microenvironment surrounding metal nanocatalysts, thereby enhancing their catalytic performance in CO2 electroreduction. Three polymer NHC ligands were designed with different hydrophobicity: hydrophilic poly(ethylene oxide) (PEO-NHC), hydrophobic polystyrene (PS-NHC), and amphiphilic block copolymer (BCP) (PEO-b-PS-NHC). All three polymer NHCs exhibited enhanced reactivity of gold nanoparticles (AuNPs) during CO2 electroreduction by suppressing proton reduction. Notably, the incorporation of hydrophobic PS segments in both PS-NHC and PEO-b-PS-NHC led to a twofold increase in the partial current density for CO formation, as compared to the hydrophilic PEO-NHC. While polymer ligands did not hinder ion diffusion, their hydrophobicity altered the localized hydrogen bonding structures of water. This was confirmed experimentally and theoretically through attenuated total reflectance surface-enhanced infrared absorption spectroscopy and molecular dynamics simulation, demonstrating improved CO2 diffusion and subsequent reduction in the presence of hydrophobic polymers. Furthermore, NHCs exhibited reasonable stability under reductive conditions, preserving the structural integrity of AuNPs, unlike thiol-ended polymers. The combination of NHC binding motifs with hydrophobic polymers provides valuable insights into controlling the microenvironment of metal nanocatalysts, offering a bioinspired strategy for the design of artificial metalloenzymes.

Adsorption of croconic acid anions at silver electrodes in sodium fluoride solutions. Interplay of DFT calculations and in situ ATR-SEIRAS measurements for the interpretation of experimental spectra of adsorbed species

The adsorption of species coming from the disodium salt of croconic acid (4,5-dihydroxy-4-cyclopentene-1,2,3-trione, H2C5O5) at chemically deposited silver electrodes was studied in aqueous sodium fluoride solutions by combining in situ ATR-SEIRAS (Surface-Enhanced Infrared Reflection Absorption Spectroscopy experiments under Attenuated Total Reflection conditions) and Density Functional Theory (DFT) calculations. Voltammetric experiments suggest the existence of reversible adsorption processes in the potential range between −0.55 and −0.20 V vs Ag/AgCl (KCl 1 M), whereas irreversible reduction is observed for potentials below-0.55 V. ATR-SEIRA spectra show potential-dependent adsorbate bands in the potential range for reversible adsorption, that were assigned according to DFT calculations. Calculated optimized geometry of adsorbed croconate and bicroconate correspond to bonding to the silver surface in a bidentate configuration through two oxygen atoms with the molecular plane perpendicular to the metal surface. The broadening and splitting at high electrode potentials of the CO stretching bands for adsorbates coming from croconic acid can be explained by invoking the existence of collective vibrational modes appearing at high coverage. In overall, the ATR-SEIRA spectra obtained with Ag thin layer electrodes resembles that reported for Au thin layers. As a difference, higher adsorbate coverage seems to be obtained in the case of silver. Moreover, a strong feature at ca. 1580 cm−1 is experimentally observed, that was much weaker on gold samples. The calculated frequencies for adsorbed croconate and bicroconate do not change significantly with the adsorption bonding sites for the optimized geometries. Taking into account the calculated frequencies of both types of species, a better agreement with the experimental behavior (including the splitting/shifting caused by dipole–dipole coupling in high-coverage collective modes) is obtained in the case of bicroconate. The coexistence with some adsorbed croconate species cannot be ruled out.

Local Proton Source Enhanced Nitrogen Reduction on a Combined Cobalt-Molybdenum Catalyst for Electrochemical Ammonia Synthesis.

Electrochemical nitrogen reduction reaction (NRR) under ambient conditions has attracted considerable scientific and engineering interest as a green alternative route for NH3 production. Molybdenum is a promising candidate as an electrocatalyst for NRR as it has a suitable binding strength with N species. However, the design of an efficient Mo-based catalyst remains elusive. To enhance the selectivity of NRR toward NH3 , we have developed a carbon nanofiber catalyst embedded with molybdenum and cobalt (Co-Mo-CNF). Co with a strong ability to dissociate water enhances local proton source near Mo, where the hydrogenation step of the NRR occurs. A NH3 formation rate of 72.72 μg h-1 mg-1 and a Faradaic efficiency of 34.5 % were obtained at -0.5 V vs. RHE. We also attempted to provide a mechanistic understanding of the NRR via in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and isotopic labeling experiments using 15 N2 and D2 O.

Unraveling the electrocatalytic reduction mechanism of enols on copper in aqueous media

Deoxygenation of aldehydes and their tautomers to alkenes and alkanes has implications in refining biomass-derived fuels for use as transportation fuel. Electrochemical deoxygenation in ambient, aqueous solution is also a potential green synthesis strategy for terminal olefins. In this manuscript, direct electrochemical conversion of vinyl alcohol and acetaldehyde on polycrystalline Cu to ethanol, ethylene and ethane; and propenol and propionaldehyde to propanol, propene and propane is reported. Sensitive detection was achieved using a rotating disk electrode coupled with gas chromatography-mass spectrometry. In-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy, and in-situ Raman spectroscopy confirmed the adsorption of the vinyl alcohol. Calculations using canonical and grand-canonical density functional theory and experimental findings suggest that the rate-determining step for ethylene and ethane formation is an electron transfer step to the adsorbed vinyl alcohol. Finally, we extend our conclusions to the enol reaction from higher-order soluble aldehyde and ketone. The products observed from the reduction reaction also sheds insights into plausible reaction pathways of CO2 to C2 and C3 products.

In Situ Wide-Frequency Surface-Enhanced Infrared Absorption Spectroscopy Enables One to Decipher the Interfacial Structure of a Cu Plating Additive.

In situ spectroscopic characterization of the interfacial structure of an organic additive at a Cu electrode is essential for a mechanistic understanding of Cu superfilling at the molecular level. In this work, we demonstrate wide-frequency attenuated total reflection surface-enhanced infrared absorption spectroscopy (wf-ATR-SEIRAS) to elucidate the dissociative adsorption of bis(sodium sulfopropyl)-disulfide (a typical accelerator) on a Cu electrode in conjunction with the electrochemical quartz crystal microbalance measurement and modeling calculations. The wf-ATR-SEIRAS clearly identifies the peaks featuring the sulfonate and methylene groups as well as the C-Ssulfonate and C-Sthiol vibrations of the adsorbate. Analysis of relative peak intensities from 1100 to 650 cm-1 reveals a more tilted alkyl chain axis for the thiolate on Cu than that on Au, which is supported by comparative density functional theory calculations. This work opens a new avenue for the wf-ATR-SEIRAS to study interfacial structures of electroplating additives related to advanced microelectronics manufacture.

Electrochemical Upgrading of Formic Acid to Formamide via Coupling Nitrite Co-Reduction.

Formic acid (HCOOH) can be exclusively prepared through CO2 electroreduction at an industrial current density (0.5 A cm-2). However, the global annual demand for formic acid is only ∼1 million tons, far less than the current CO2 emission scale. The exploration of an economical and green approach to upgrading CO2-derived formic acid is significant. Here, we report an electrochemical process to convert formic acid and nitrite into high-valued formamide over a copper catalyst under ambient conditions, which offers the selectivity from formic acid to formamide up to 90.0%. Isotope-labeled in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy and quasi in situ electron paramagnetic resonance results reveal the key C-N bond formation through coupling *CHO and *NH2 intermediates. This work offers an electrochemical strategy to upgrade CO2-derived formic acid into high-value formamide.

Characterization of Interfacial Properties in Electrochemical Nitrate Reduction to Optimize Ammonia Production

Nitrate pollution of wastewater from agricultural runoff and industrial waste streams is common around the globe. Nitrate negatively impacts the environment through harmful algal blooms and can be dangerous for human consumption. Rather than treat nitrate as a waste, we electrochemically reduce nitrate (NO3RR) to ammonia (NO3 - + 9H+ + 8e- → NH3 + 3H2O), a commonly used fertilizer and clean fuel. Electrochemical treatment can enable on-site, modular treatment powered by renewable energy. As an inner-sphere reaction involving multiple hydrogenation and electron-transfer steps, the activity and selectivity of electrochemical NO3RR to NH3 are strongly influenced by properties at the electrode–electrolyte interface. When potential is applied, the electric double layer (EDL) forms that comprises ordered molecular layers extending up to 10 Å from the surface. This EDL is the primary environment where the heterogeneous NO3RR occurs and can impact the reaction in several ways, including blocking catalytic sites and stabilizing reactants and reaction intermediates. To understand the molecular mechanisms of these impacts, the EDL structure is studied with x-ray reflectivity (XRR), which provides atomic-level resolution of the near-surface electron density profile and reveals the number of ordered layers, the distance of each layer from the surface, the ion surface coverage, and the degree of hydration of ions in each layer. We complement these investigations with operando attenuated total reflectance–surface-enhanced infrared absorption spectroscopy (ATR–SEIRAS) under similar reaction conditions to investigate the adsorbed reactants, intermediates, and local pH. Furthermore, composition and structure of the EDL can change with varying bulk electrolyte compositions and mass transport regimes, which also provide levers to control reaction activity and selectivity. We use a continuum model (generalized modified Poisson–Nernst–Planck, GMPNP) to develop the spatial profiles of the electric field, reactant nitrate concentration, cation concentrations, and pH outside the EDL and how they change as functions of applied potential, bulk electrolyte composition, and flow rate. Taken together, our results relate 1) bulk electrolyte properties with interfacial EDL properties and 2) interfacial properties with reaction activity and selectivity, informing the choice of operating parameters such as electrolyte composition and flow rate to optimize ammonia production in electrochemical NO3RR.

Rhombohedral Pd–Sb Nanoplates with Pd‐Terminated Surface: An Efficient Bifunctional Fuel‐Cell Catalyst

Developing high-performance electrocatalysts for both ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR) is essential for the commercialization of direct ethanol fuel cells (DEFCs), but it is still formidable challenging. Herein, for the first time we have successfully prepared a novel Pd-Sb hexagonal nanoplate for boosting both cathodic and anodic fuel cell reactions. Detailed structural characterizations reveal that the nanoplates have ordered rhombohedral phase of Pd8 Sb3 (denoted as Pd8 Sb3 HPs) with Pd-terminated surface. Significantly, the unique Pd8 Sb3 HPs can exhibit much enhanced activity towards the oxidation of various alcohols in alkaline media. In particular, Pd8 Sb3 HPs/C displays superior specific and mass activities of 29.3mA cm-2 and 4.5 A mgPd -1 towards EOR, which are 7.0 and 11.3 times higher than those of commercial Pd/C, and 9.8 and 3.8 times higher than those of commercial Pt/C, respectively, representing one of the best EOR catalysts reported to date. In-situ electrochemical ATR-SEIRAS measurements reveal that Pd8 Sb3 HPs/C can effectively promote the C2 pathway of EOR, which is the key to the improved activity. As further disclosed by the density functional theory calculations, the higher EOR intrinsic catalytic activity of Pd8 Sb3 HPs can be ascribed to the reduced energy barrier of ethanol dehydrogenation. In addition, Pd8 Sb3 HPs/C can also show superior performance to both commercial Pd/C and Pt/C in cathodic ORR. This work advances the controllable synthesis of Pd-Sb nanostructure, which give huge impetus to the design of high-efficiency bifunctional electrocatalysts for energy conversion and beyond. This article is protected by copyright. All rights reserved.

Synergetic effect of nitrogen-doped carbon catalysts for high-efficiency electrochemical CO2 reduction

The use of carbon-based materials is an appealing strategy to solve the issue of excessive CO2 emissions. In particular, metal-free nitrogen-doped carbon materials (mf-NCs) have the advantages of convenient synthesis, cost-effectiveness, and high conductivity and are ideal electrocatalysts for the CO2 reduction reaction (CO2RR). However, the unclear identification of the active N sites and the low intrinsic activity of mf-NCs hinder the further development of high-performance CO2RR electrocatalysts. Achieving precise control over the synthesis of mf-NC catalysts with well-defined active N-species sites is still challenging. To this end, we adopted a facile synthesis method to construct a set of mf-NCs as robust catalysts for CO2RR. The resulting best-performing catalyst obtained a Faradaic efficiency of CO of approximately 90% at −0.55 V (vs. reversible hydrogen electrode) and good stability. The electrocatalytic performance and in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy measurements collectively revealed that graphitic and pyridinic N can synergistically adsorb CO2 and H2O and thus promote CO2 activation and protonation.

Engineering ordered vacancies and atomic arrangement over the intermetallic PdM/CNT (M = Pb, Sn, In) nanocatalysts for synergistically promoting electrocatalysis N2 fixation

The synthesis of intermetallic compounds with small size and defective structures is rigorous challenge. In this work, the small size (< 10 nm) of intermetallic PdM (M = Pb, Sn, In) with ordered vacancies (OVs) are successfully prepared by ultrafast and solvent-free microwave method for the first time. With the optimized vacancies, atomic arrangement and components, the intermetallic OVs-Pd3Pb-2 shows the best nitrogen reduction (NRR) performance among intermetallic OVs-PdM (M = Sn, In), intermetallic OVs-Pd3Pb with various degrees of vacancies, intermetallic Pd3Pb with vacancies-free, Pd3Pb/CNT and Pd/CNT in Li2SO4 solution. In situ Raman spectroscopy, in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) technique and density functional theory (DFT) further demonstrate the synergy mechanism of good NRR activity at low overpotentials on OVs-Pd3Pb-2 catalysts.

Adjusting Local CO Confinement in Porous-Shell Ag@Cu Catalysts for Enhancing C-C Coupling toward CO2 Eletroreduction.

Tuning the local confinement of reaction intermediates is of pivotal significance to promote C-C coupling for enhancing the selectivity for multicarbon (C2+) products toward CO2 electroreduction. Herein, we have gained insights into the confinement effect of local CO concentration for enhanced C-C coupling over core-shell Ag@Cu catalysts by tuning the pore diameters within porous Cu shells. During CO2 electroreduction, the core-shell Ag@Cu catalysts with an average pore diameter of 4.9 nm within the Cu shells (Ag@Cu-p4.9) exhibited the highest Faradaic efficiency of 73.7% for C2+ products at 300 mA cm-2 among the three Ag@Cu catalysts. Finite-element-method simulations revealed that the pores with a diameter of 4.9 nm in Cu conspicuously enhanced the local CO concentration. On the basis of in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy measurements, Ag@Cu-p4.9 exhibited the highest surface coverage of adsorbed CO intermediates with a linear adsorption configuration due to the confinement effect, thus facilitating C-C coupling.

Observation of Electric-Field-Induced Liberation of Guest Molecules from Clathrate Hydrate.

Clathrate hydrates can store a high density of guest molecules in cages. However, as a gas-storage material, the controllable release of guests therefrom is still challenging. Here we report on the utilization of an electric field as a control agent. Attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) is used to investigate the release of tetrahydrofuran (THF) from the clathrate in the electrochemical double layer (EDL). When voltage is applied, the ATR-SEIRA signal from encaged THF rapidly decreases, and the water characteristic O-H absorption peak exhibits an appreciable blue-shift. Our measurements indicate a transformation of the hydrate lattice to a less H-bonded configuration at the electrode surface. In combination with previous experimental results on the orientation of water molecules in the EDL, we propose that the strong electric field in the EDL aligns the water molecules of the clathrate and distorts the hydrate lattice structure enough to release the trapped guest molecules.