Reflection Surface-enhanced Infrared Absorption Spectroscopy Research Articles

Boosting protonation kinetics for ammonia electrosynthesis on Ru sites embedded in nanoporous ReSe2

Electrocatalytic N2 reduction reaction (NRR) is a promising approach for renewable NH3 production but is constrained by poor activity and selectivity, owing to the sluggish hydrogenation kinetics. Herein, we prepare a nanoporous Ru-doped ReSe2 (NP Ru-ReSe2) with controllable selenium vacancies by regulating the amount of Ru dopants. The catalyst exhibits excellent the NRR performance, which affords a high Faradaic efficiency of 22.7% and NH3 yield rate of 19.41 μg h−1 mg−1 at –0.4 V versus a reversible hydrogen electrode(RHE). In situ attenuated total reflectance–surface-enhanced infrared absorption spectroscopy studies combined with theoretical calculations unravel that a clear synergistic effect of Ru dopants and selenium vacancies onregulating the proton (H*) coverage on the ReSe2 surface to accelerate the proton-coupled processes as NN → NNH. while N2 dissociation becomes exothermic over the Ru active sites via Ru-to-N2 π back-donation, lowering energy barriers of the rate-determining step, ultimately enhancing the overall NRR catalytic performance.

In situ surface-enhanced infrared absorption analysis of the excited carrier transfer from n-type Si photoelectrode to Pt oxygen evolution cocatalyst by probing adsorbed CO molecules

BackgroundThe development of efficient photoelectrode material for water-splitting reactions has received considerable attention as it produces hydrogen gas from water using solar energy. Photoexcited holes migrate to the surface of an n-type photoelectrode oxidizing water to oxygen, and excited electrons migrate to the counter electrode reducing protons to hydrogen. However, there is limited knowledge of excited carrier transfer. MethodsTherefore, in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) has been used to investigate the excited hole migration from n-type Si photoelectrode to Pt oxygen evolution cocatalysts by monitoring the frequency of CO adsorbed on the Pt cocatalysts. Significant findingsAt the positive potential of Si photoelectrode under UV irradiation, the SEIRA spectrum of the CO adsorbed on the Pt cocatalyst shifted to higher wavenumbers owing to the excited hole transfer from n-type Si photoelectrode to the Pt cocatalyst attributed to band bending at the interface between the Si photoelectrode and Pt cocatalysts. It was successfully demonstrated that the regulation of photoexcited carriers was crucial for enhancing the photoelectrochemical activity of water splitting.

Role of Electrolyte-Adsorbates Interaction in Determining CO2 Reduction Reaction Pathways

Electrochemical CO2 reduction reaction (CO2RR) is a promising strategy to convert atmospheric CO2 into valuable fuels and chemicals. Although the optimization of the catalyst-adsorbates interaction via tuning the binding energies of electrocatalysts has been extensively studied, activity and product selectivity remain a challenge. Recently, there has been a growing recognition that cations in electrolytes influence the activity of surface electrocatalytic reactions.1 A recent density functional theory study suggested that partially desolvated metal cations stabilize CO2RR intermediates via electrostatic interactions.2 Therefore, an experimental understanding of how the cations (and surrounding water molecules) control the intermediates present on the surface and govern the reaction pathway is critical to establish further insights into the design of electrolytes for CO2RR.In this talk, the role of alkali metal cations and water molecules on the CO2RR is revealed by tracking the surface-bound intermediates using operando attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). We will also integrate the operando surface analysis with final product selectivity, further strengthening the understanding of the reaction mechanism. It will also be demonstrated that the holistic information about the electrolyte-adsorbates interaction can provide additional knobs to tune the energetics of key reaction intermediates, leading to further improvements in electrocatalytic activity for the CO2RR.[Reference]1 Ringe, S. et al., Energy Environ. Sci. 2019, 12, 3001–3014.2 Monteiro, MCO. et al., Nat. Catal. 2021, 4, 654–662.

Highly selective NH3 synthesis from N2 on electron-rich Bi0 in a pressurized electrolyzer

Electrochemical conversion of N2 into ammonia presents a sustainable pathway to produce hydrogen storage carrier but yet requires further advancement in electrocatalyst design and electrolyzer integration. This technology suffers from low selectivity and yield owing to the extremely strong N≡N bond and the exceptionally low solubility of N2 in aqueous systems. A high NH3 synthesis performance is restricted by the high activation energy of N≡N bond and the supply insufficiency of N2 to active sites. This paper describes the introduction of electron-rich Bi0 sites into Ag catalysts with a high-pressure electrolyzer that enables a dramatically enhanced Faradaic efficiency of 44.0% and yield of 28.43 μg cm-2 h-1 at 4.0 MPa. Combined with density functional theory results, in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy demonstrates that N2 reduction reaction follows an associative mechanism, in which a high coverage of N-N bond and -NH2 intermediates suggest electron-rich Bi0 boosts sound activation of N2 molecules and low hydrogenation barrier. The proposed strategy of engineering electrochemical catalysts and devices provides powerful guidelines for achieving industrial-level green ammonia production.

Achieving Efficient CO2 Electrolysis to CO by Local Coordination Manipulation of Nickel Single-Atom Catalysts.

Selective electroreduction of CO2 to C1 feed gas provides an attractive avenue to store intermittent renewable energy. However, most of the CO2-to-CO catalysts are designed from the perspective of structural reconstruction, and it is challenging to precisely design a meaningful confining microenvironment for active sites on the support. Herein, we report a local sulfur doping method to precisely tune the electronic structure of an isolated asymmetric nickel-nitrogen-sulfur motif (Ni1-NSC). Our Ni1-NSC catalyst presents >99% faradaic efficiency for CO2-to-CO under a high current density of -320 mA cm-2. In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy and differential electrochemical mass spectrometry indicated that the asymmetric sites show a significantly weaker binding strength of *CO and a lower kinetic overpotential for CO2-to-CO. Further theoretical analysis revealed that the enhanced CO2 reduction reaction performance of Ni1-NSC was mainly due to the effectively decreased intermediate activation energy.

Reaction-induced iodine adsorption on Cu surfaces facilitates electrocatalytic CO2 reduction.

The electrolyte effect has been key to the electrochemical CO2 reduction reaction (CO2RR) and has received extensive attention in recent years. Here we combined atomic force microscopy, quasi-in situ X-ray photoelectron spectroscopy, and in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) to study the effect of iodine anions on Cu-catalyzed CO2RR in the absence or presence of KI in the KHCO3 solution. Our results suggested that iodine adsorption caused coarsening of the Cu surface and altered its intrinsic activity for CO2RR. As the potential of the Cu catalyst became more negative, there was an increase in surface iodine anion concentration ([I-]), which could be connected to the reaction-enhanced adsorption of I- ions accompanying the increase in CO2RR activity. A linear relationship was observed between [I-] and current density. SEIRAS results further suggested that the presence of KI in the electrolyte strengthened the Cu-CO bond and facilitated the hydrogenation process, enhancing the production of CH4. Our results have thus provided insight into the role of halogen anions and aided in the design of an efficient CO2RR process.

Circumventing CO2 Reduction Scaling Relations Over the Heteronuclear Diatomic Catalytic Pair.

In the electrochemical CO2 reduction reaction (CO2RR), CO2 activation is always the first step, followed by the subsequent hydrogenation. The catalytic performance of CO2RR is intrinsically restricted by the competition between molecular CO2 activation and CO2 reduction product release. Here, we design a heteronuclear Fe1-Mo1 dual-metal catalytic pair on ordered porous carbon that features a high catalytic performance for driving electrochemical CO2 reduction to CO. Combining real-time near-ambient pressure X-ray photoelectron spectroscopy, operando 57Fe Mössbauer spectroscopy, and in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy measurements with density functional theory calculations, chemical adsorption of CO2 is observed on the Fe1-Mo1 catalytic pair through a bridge configuration, which prompts the bending of the CO2 molecule for CO2 activation and then facilitates the subsequent hydrogeneration reaction. More importantly, the dynamic adsorption configuration transition from the bridge configuration of CO2 on Fe1-Mo1 to the linear configuration of CO on the Fe1 center results in breaking the scaling relationship in CO2RR, simultaneously promoting the CO2 activation and the CO release.

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.