Infrared Absorption Spectroscopy Research Articles

Reevaluating infrared spectroscopic signatures of polaron trapping in a chemically doped conducting polymer.

Charge conductivity in conducting polymers is typically improved by increasing carrier density via chemical oxidation. However, the resulting electrostatic stabilization of the carriers by the dopant ions, combined with their nanostructural environment, are both known to crucially affect charge trapping. Although the effects of charge-ion electrostatic interactions on carrier trapping have been well-characterized using conventional infrared (IR) spectroscopy, the impacts of the polymer chain ordering and energetic environment are difficult to disentangle. In this study, we examine the limitations of conventional IR absorption spectroscopy and introduce a complementary spectroscopic approach capable of discerning polaron trapping more generally. To do so, we investigated films of poly(3-hexylthiophene-2,5-diyl) (P3HT) chemically doped using four different oxidants, of which each preferentially dopes the amorphous and crystalline (lamellar) phases to varying extents. Using this model system, we observed counterintuitive shifts in the polaron IR absorption band, indicating that IR spectroscopy is a clear reporter of trapping only when the carriers exclusively reside in the lamellar phase and in the absence of bipolarons or coupled polarons. Alternatively, we found that polaron excited state dynamics, probed using ultrafast near-infrared transient absorption spectroscopy, more clearly report on charge trapping. This study demonstrates near-infrared transient absorption spectroscopy as a complementary tool for probing charge trapping in conducting polymers when doping induces carriers in different nanostructural environments.

Synergistic Catalysis in Fe─In Diatomic Sites Anchored on Nitrogen-Doped Carbon for Enhanced CO2 Electroreduction.

Diatomic catalysts are promising for the electrochemical CO2 reduction reaction (CO2RR) due to their maximum atom utilization and the presence of multiple active sites. However, the atomic-scale design of diatomic catalysts and the elucidation of synergistic catalytic mechanisms between multiple active centers remain challenging. In this study, heteronuclear Fe─In diatomic sites anchored on nitrogen-doped carbon (FeIn DA/NC) are constructed. The FeIn DA/NC electrocatalyst achieves a CO Faradaic efficiency exceeding 90% across a wide range of applied potentials from -0.4 to -0.7V, with a peak efficiency of 99.1% at -0.5V versus the reversible hydrogen electrode. In situ, attenuated total reflection surface-enhanced infrared absorption spectroscopy and density functional theory calculations reveal that the synergistic interaction between Fe and In diatomic sites induce an asymmetric charge distribution, which promote the adsorption of CO2 at the Fe site and lowered the energy barrier for the formation of *COOH. Moreover, the unique Fe─In diatomic site structure increase the adsorption energy of *OH through a bridging interaction, which decrease the energy barrier for water dissociation and further promoted CO2RR activity.

Ultrasensitive and Fast Gas Detection Based on Room‐Temperature Indium Arsenide Mid‐Wavelength Infrared Photodetectors

AbstractCombustible hydrocarbon gases, typified by methane, are invisible, odorless, and imperceptible, yet they pose significant hazards to human safety and the environment. Therefore, monitoring these gases is crucial in managing and mitigating potential hazards. Here, a gas sensing system is proposed based on the non‐dispersive infrared absorption spectroscopy (NDIR) technique. Its core component is a home‐built indium arsenide (InAs) semiconductor mid‐wavelength infrared photodetector. By material growth and device structure optimization (a peculiar potential barrier layer is designed to form a heterojunction and suppress diffusion carriers), the InAs‐based photodetectors show a low‐noise performance of 1.62 × 10−12 A·Hz−1/2 and a record high room‐temperature detectivity of 2.1 × 1010 cm·Hz1/2·W−1 with superior response speed of <40 ns. The sensing system, therefore, gains an ultra‐sensitive (<1 ppm) and fast (≈350 ms) gas detection capability of methane compared to current NDIR equipment. The method used in this study paves an avenue for designing ultrasensitive NDIR systems based on photovoltaic devices and provides a new paradigm for highly integrated gas sensing hardware.

Optimized machine learning approaches to combine surface-enhanced Raman scattering and infrared data for trace detection of xylazine in illicit opioids.

Infrared absorption spectroscopy and surface-enhanced Raman spectroscopy were integrated into three data fusion strategies-hybrid (concatenated spectra), mid-level (extracted features from both datasets) and high-level (fusion of predictions from both models)-to enhance the predictive accuracy for xylazine detection in illicit opioid samples. Three chemometric approaches-random forest, support vector machine, and k-nearest neighbor algorithms-were employed and optimized using a 5-fold cross-validation grid search for all fusion strategies. Validation results identified the random forest classifier as the optimal model for all fusion strategies, achieving high sensitivity (88% for hybrid, 92% for mid-level, and 96% for high-level) and specificity (88% for hybrid, mid-level, and high-level). The enhanced performance of the high-level fusion approach (F1 score of 92%) is demonstrated, effectively leveraging the surface-enhanced Raman data with a 90% voting weight, without compromising prediction accuracy (92%) when combined with infrared spectral data. This highlights the viability of a multi-instrument approach using data fusion and random forest classification to improve the detection of various components in complex opioid samples in a point-of-care setting.

Stabilizing Lattice Oxygen of Bi2O3 by Interstitial Insertion of Indium for Efficient Formic Acid Electrosynthesis

Bismuth oxide (Bi2O3) emerges as a potent catalyst for converting CO2 to formic acid (HCOOH), leveraging its abundant lattice oxygen and the high activity of its Bi‐O bonds. Yet, its durability is usually impeded by the loss of lattice oxygen causing structure alteration and destabilized active bonds. Herein, we report an innovative approach via the interstitial incorporation of indium (In) into the Bi2O3, significantly enhancing bond stability and preserving lattice oxygen. The optimized In‐Bi2O3‐100 catalyst achieves over 90% Faradaic efficiency for HCOOH production across a wide potential range, in both H‐cells and flow cells, maintaining robust stability after 100 hours of continuous operation. In‐situ surface‐enhanced infrared absorption spectroscopy and theoretical calculations reveal that the interstitial In doping precisely tunes the adsorption of CO2* and OCHO* intermediate, facilitating rapid conversion. Further in‐situ Raman spectroscopy confirms the role of In bolstering the oxidized structure's stability within Bi2O3, critical for sustaining lattice oxygen during electrochemical CO2 reduction.

Stabilizing Lattice Oxygen of Bi2O3 by Interstitial Insertion of Indium for Efficient Formic Acid Electrosynthesis.

Bismuth oxide (Bi2O3) emerges as a potent catalyst for converting CO2 to formic acid (HCOOH), leveraging its abundant lattice oxygen and the high activity of its Bi-O bonds. Yet, its durability is usually impeded by the loss of lattice oxygen causing structure alteration and destabilized active bonds. Herein, we report an innovative approach via the interstitial incorporation of indium (In) into the Bi2O3, significantly enhancing bond stability and preserving lattice oxygen. The optimized In-Bi2O3-100 catalyst achieves over 90% Faradaic efficiency for HCOOH production across a wide potential range, in both H-cells and flow cells, maintaining robust stability after 100 hours of continuous operation. In-situ surface-enhanced infrared absorption spectroscopy and theoretical calculations reveal that the interstitial In doping precisely tunes the adsorption of CO2* and OCHO* intermediate, facilitating rapid conversion. Further in-situ Raman spectroscopy confirms the role of In bolstering the oxidized structure's stability within Bi2O3, critical for sustaining lattice oxygen during electrochemical CO2 reduction.

Toward Hyphenated In Situ Infrared and Raman Spectroscopies in Interfacial Electrochemistry.

To address the pressing demand for hyphenated in situ characterization of the electrode-electrolyte interfaces at the molecular level, we report herein a technical note to demonstrate the hyphenation of in situ electrochemical surface-enhanced infrared absorption spectroscopy (SEIRAS) and shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS). The core setup incorporates a top-down configured Raman optic fiber head loaded on a 3-dimension positioning module and a bottom-up configured attenuated total reflection infrared spectroscopy (ATR-IR) spectroelectrochemical cell accommodated in a custom-designed optical accessory. The feasibility of this integrated design is initially validated by the simultaneous measurement of two model systems, namely, potential dependent adsorption of pyridine on a Au film electrode and the CO2 reduction reaction on a Cu film electrode by in situ SEIRAS and SHINERS, yielding distinct and complementary spectral information.

Study on the Aging Effects of Relative Humidity on the Primary Chemical Components of Palm Leaf Manuscripts.

Palm Leaf Manuscripts represent a significant component of the world's cultural heritage. Investigating their primary chemical components and understanding the transformations these materials undergo under environmental influences are crucial for elucidating their material characteristics and aging mechanisms and developing effective strategies for preventive conservation. This study utilized infrared absorption spectroscopy and X-ray diffraction analysis to examine changes in the primary chemical components of Palm Leaf Manuscripts under varying relative humidity conditions over extended periods. The findings reveal that dry environments lead to surface cracking, while humid environments promote mold growth, both of which contribute to the degradation of the primary chemical components. These degradative processes reduce cellulose crystallinity and thermal stability. The deterioration is particularly severe under high humidity, with hemicellulose degrading faster and more extensively than cellulose under the same conditions. After 200 days of aging at 10% RH and 90% RH, cellulose degradation reached 19.82% and 54.40%, respectively, while hemicellulose degradation was 34.78% and 64.28%. Correspondingly, the relative crystallinity of cellulose decreased by 8.01% and 13.11%. In contrast, samples maintained at 50% RH exhibited minimal deterioration, with cellulose and hemicellulose degrading by only 4.08% and 13.55%, respectively, and a 6.61% reduction in cellulose crystallinity. These results suggest that a relative humidity of 50% is optimal for the preservation of Palm Leaf Manuscripts. This study offers significant insights into the ageing mechanisms and preventive conservation of Palm Leaf Manuscripts, as well as other cellulose-based organic heritage materials.

Ultrasensitive infrared spectroscopy via vibrational modulation of plasmonic scattering from a nanocavity.

Most molecules and dielectric materials have characteristic bond vibrations or phonon modes in the mid-infrared regime. However, infrared absorption spectroscopy lacks the sensitivity for detecting trace analytes due to the low quantum efficiency of infrared sensors. Here, we report mid-infrared photothermal plasmonic scattering (MIP-PS) spectroscopy to push the infrared detection limit toward nearly a hundred molecules in a plasmonic nanocavity. The plasmon scattering from a nanoparticle-on-film cavity has extremely high sensitivity to the spacing defined by the analyte molecules inside the nanogap. Meanwhile, a 1000-fold infrared light intensity enhancement at the bond vibration frequency further boosts the interaction between mid-IR photons and analyte molecules. MIP-PS spectroscopic detection of nitrile or nitro group in ~130 molecules was demonstrated. This method heralds potential in ultrasensitive bond-selective biosensing and bioimaging.

Key Structure Parameters for Designing High-Performance Substrates of Surface-Enhanced Infrared Absorption Spectroelectrochemistry.

Attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) plays a crucial role in understanding the interfacial reaction mechanisms at the molecular level, achieving an enhancement factor (EF) of up to 103. However, when this technique is integrated with electrochemistry (EC-ATR-SEIRAS), the EF is significantly reduced by ten- to hundred-fold. Thus, understanding of the key parameters that contribute to the EF is of great importance in designing high-performance substrates and extending the application for EC-SEIRAS. In this study, we propose that the structure of the substrate for EC-ATR-SEIRAS consists of an enhancement unit (EU) supported on a conductivity unit (CU). The CU will screen the incident IR light reaching and interacting with the EU, resulting in a smaller EF as the CU thickness increases. Then, we introduce a strategy to optimize the performance of the EC-SEIRAS substrate by assembling a plasmonic antenna array as the EU that is supported on IR-transparent and conductive monolayer graphene as the CU. The established plasmon-enhanced EC-SEIRAS substrate demonstrates much higher IR enhancement, repeatability, and stability.

Surface Passivation of Silicon Nanoparticles Monitored by In Situ FTIR

ABSTRACTA setup consisting of two atmospheric plasma sources is used for the combined synthesis and passivation of nanoparticles. The silicon nanoparticles synthesized in the first source are analyzed for their chemical composition, morphology, and photoluminescence. The particles are then treated with a second plasma to induce surface passivation. The passivation process of the particles is monitored in real time using in situ infrared absorption spectroscopy. The results indicate that this treatment induces methylation of the silicon nanocrystals, which is further supported by XPS analysis. This surface passivation shifts the maximum of the photoluminescent signal to blue in the visible spectral region. Further optimization of the reported nanoparticle passivation process can provide a flexible tool for tuning nanoparticle properties.

An Interstitial Boron Inserted Metastable Hexagonal Rh Nanocrystal for Efficient Hydrogen Oxidation Electrocatalysis

AbstractConstructing metastable phase structure plays an important role in changing the physicochemical properties and improving the catalytic performance of nanocrystals. Unfortunately, the synthesis of metastable phase metallic nanocrystals is highly challenging, mainly due to the thermodynamically unstable ground‐state. Here, we report a synthesis of unconventional metastable hexagonal rhodium nanocrystal (Bint−Rhhcp/C) via interstitial boron insertion. The insertion of boron atoms into the interstitial sites of cubic Rh lattice not only induces the atomic arrangements from face‐centered cubic (fcc) to hexagonal close‐packed (hcp), but also stabilizes the metastable hexagonal Rh structure. Benefiting from the phase transition and interstitial boron doping, the Bint−Rhhcp/C catalyst exhibits remarkable catalytic performance toward hydrogen oxidation reaction (HOR) under alkaline media, with a mass activity of 1.413 mA μgPGM−1. Experimental measurements including in situ surface‐enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) calculations indicate that the strengthened adsorption of hydroxyl species on the electrode surface of Bint−Rhhcp/C is responsible for the reconstruction of interfacial water structure and increased water proportions in the gap region in the electric double layers. As a result, the increased water connectivity and hydrogen bond network facilitate high‐efficiency hydrogen transfer across the interface, thereby boost the alkaline HOR performance.

Atomically precise (AgPd)27 nanoclusters for nitrate electroreduction to NH3: Modulating the metal core by a ligand induced strategy

Electrochemical nitrate reduction reaction (eNO3–RR) to synthesize NH3 is a sustainable method to convert environmental contaminants into valuables. Pd based bimetallic nanocatalysts have demonstrated great promise as efficient catalysts, yet modulating the composition and configuration to improve the catalytic performance and achieve comprehensive mechanistic understanding remains challenging. Herein, by employing two ligands with different electron functional groups, we successfully prepared two atomically precise (AgPd)27 bimetallic clusters of Ag18Pd9(C8H4F)24 (Ag18Pd9) and Ag22Pd5(C9H10O2)26 (Ag22Pd5). The two clusters possess markedly different metal core composition and configuration, where Ag18Pd9 has a sandwich metal core structure with 9 Pd atoms located in the middle layer and Ag22Pd5 has a rod-shaped metal core structure composed of the M13 configuration with 5 Pd atoms located at the center and vertices of the M13 configuration. Unexpectedly, Ag22Pd5 exhibited remarkably superior eNO−3RR performance than Ag18Pd9. Specifically, the highest Faradaic efficiency of NH3 (FENH3) and its yield rate can reach 94.42 ​% and 1.41 ​mmol ​h−1 ​mg−1 ​at −0.6 ​V vs. RHE for Ag22Pd5, but the largest FENH3 and NH3 yield rate is only 43.86 ​% and 0.41 ​mmol ​h−1 ​mg−1 ​at −0.5 ​V vs. RHE for Ag18Pd9. The in situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) test provides the experimental evidence of the reaction intermediates hence revealing the reaction pathway, also shows that Ag22Pd5 has stronger capability for NO−3 adsorption and NH3 desorption than that of Ag18Pd9. Theoretical calculations indicate that the de-ligated clusters can expose the available AgPd bimetallic sites, synergistically serving as effective active sites and the different configurations result in significantly different catalytic activities, where the active sites in Ag22Pd5 are more favorable for NO−3 adsorption and NH3 desorption to accelerate the catalytic process.

In Situ Surface-Enhanced Infrared Absorption Spectroscopy to Explore the Stability of Electrolyte in Nonaqueous Lithium Oxygen Batteries

Tetraethylene glycol dimethyl ether (TEGDME) decomposition on the Au electrode surface is studied using in situ attenuated total reflectance surface enhanced infrared absorption spectroscopy (ATR-SEIRAS). Due to the weak solvation of TEGDME, the superoxide intermediate (LiO2/O2−) of the discharge process rapidly gains electrons on the electrode surface to generate Li2O2. Furthermore, alkyl radical, formed by LiO2/O2− extracting hydrogen from ether, undergoes oxidative decomposition reactions to form by-products. During the charge process, amorphous film-like Li2O2 obtained from surface-phase mechanism oxidizes in the low potential range of 3–3.4 V, while the oxidation potential of large-sized crystal Li2O2 particles obtained from solution-phase mechanism is above 3.4 V. Besides, TEGDME is intrinsically unstable and can decompose at 3.8 V even the solution is saturated with argon, indicating that the degradation of ether-based electrolyte is inevitable during the cycling process. This work confirms the feasibility of ATR-SEIRAS in probing the reaction mechanism and electrolyte stability of lithium oxygen batteries, and provides direct spectroscopic evidence for subsequent optimization of electrolyte components.

External Cavity Quantum Cascade Laser Vibrational Circular Dichroism Spectroscopy for Fast and Sensitive Analysis of Proteins at Low Concentrations.

Proteins are characterized by their complex levels of structures, which in turn define their function. Understanding and evaluating these structures is therefore crucial to illuminating biological processes. One of the possible analytical methods is vibrational circular dichroism (VCD), which expands the structural sensitivity of classical infrared (IR) absorbance spectroscopy by the chiral sensitivity of circular dichroism. While this technique is powerful, it is plagued by low signal intensities and long measurement times. Here we present an optical setup leveraging the high brilliance of a quantum cascade laser to measure proteins in D2O at a path length of 204 μm. It was compared to classical Fourier-transform infrared spectroscopy (FT-IR) in terms of noise levels and in its applicability to secondary structure elucidation of proteins. Protein concentrations as low as 2 mg/mL were accessible by the laser-based system at a measurement time of 1 h. Further increase of the time resolution was possible by adapting the emission to cover only the amide I' band. This allowed for the collection of spectral data at a measurement time of 5 min without a loss of performance. With this high time resolution, we are confident that dynamic processes of protein can now be monitored by VCD, increasing our understanding of these reactions.

Monitoring Surface-Enhanced Infrared Absorption Spectroscopy on a Graphitic Electrode for in-Situ Surface-Sensitive Electrochemistry: Designing Electrode Interfaces for Carbon Capture

Combining spectroscopy with electrochemistry enables the monitoring of changes in bonding, molecular orientation, and chemical composition during electrochemical processes at the electrode/electrolyte interface. Surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) allows a direct in situ monitoring of electrochemical processes occurring at the electrode interface due plasmonic enhancement by surface plasmon polaritons (SPP).1 Electrochemical ATR-SEIRAS has been used extensively for investigating electrocatalysis2,3, characterizing adsorbed species4, and detecting reaction intermediates5. However, SEIRAS literature has focused on plasmonic metals while the small number of SEIRAS studies reported on graphene surfaces are incompatible with electrochemical experimentation or not considered. Nonetheless, carbon electrodes are ubiquitous in electrocatalysis, sensing, and energy storage6, thus probing their surface chemistries are of particular interest. Thus, there is still a need for a convenient substrate for probing graphitic interfaces using electrochemical SEIRAS.In our first study1, we expanded the scope of SEIRAS by introducing a robust hybrid graphene on gold (graphene-gold) substrate where we monitored electrografting processes occurring on the graphene/electrolyte interface. The graphene-gold substrate successfully monitored the electrografting of 2,2,6,6-tetremethyl-1-pipperridine N-oxyl (4-amino-TEMPO) and 4-nitrobenzene diazonium (4-NBD) in real-time using SEIRAS and cyclic voltammetry. The graphene-gold substrate is proficient at resolving the spectral responses of the electrografting and redox transformations of the grafted moieties occurring at the graphene interface spectroscopically and electrochemically. We clearly demonstrate highly sensitive SEIRAS in real-time at a graphene interface.This substrate opens a plethora of possibilities for real-time electrochemical ATR-SEIRAS investigations on graphitic interfaces such as catalysis, battery research, and CO2 capture and conversion, the latter of which our laboratory is exploring using modified electrodes. Electrochemical carbon capture and concentration (eCCC) methods have emerged as a prosing alternative to the current state-of-the-art temperature-pressure swing systems.7 Redox-active organic (RAO) molecules such as quinones have been reported to reversibly capture and release CO2. 7 However, they suffer from low solubility in solution. New approaches have explored immobilizing these molecules on electrode interfaces for increased CO2 adsorption capacities.11 Our graphene-gold allows a unique opportunity for an in situ mechanistic investigation of the immobilization and carbonization of RAOs. Our current work investigating immobilized aminoanthraquinone and a riboflavin derivative will be presented.

(Invited) Operando Spectroscopy-Inspired Design of Electrolyte-Electrode Interface

There has been a growing recognition that not only electrocatalysts but electrolytes influence the activity of surface electrocatalytic reactions. Therefore, understanding the electrolyte-electrode interface under realistic operating conditions is critical to designing active and stable electrochemical devices. The past few decades of research have focused on developing a range of spectroscopic and imagining tools to enable the study of the chemical and structural changes at the electrolyte-electrode interface. Here, we introduce operando surface-enhanced infrared absorption spectroscopy (SEIRAS), a promising lab-based tool for gaining a molecular-level understanding of interfacial electrochemical processes. This talk will bring the most recent understanding of the electrochemical interface during the operation of electrolysis applications, including electrochemical CO2 reduction reaction and water splitting, using operando SEIRAS. Furthermore, we demonstrate that the holistic information about the complex interaction in the electrochemical interface can alter the reaction energetics/kinetics in a way incapable of electrode-centered design strategy. We will highlight the significance of advanced operando techniques to accelerate the design of electrochemical interfaces by providing additional knobs to tune the reaction energetics/kinetics, leading further improvements in electrocatalytic activity for energy conversion and storage reactions.

(Invited) Protein Film Electrochemistry and Surface-Enhanced Infrared Absorption Spectroscopy of Transmembrane Metalloenzymes

Transmembrane metalloenzymes encapsulating transition metal complexes are involved in electron transfer and in material transformation in living organisms. Understanding their operating principles is not only important for identifying the origin of highly efficient enzymatic reactions but also for developing sensors and catalysts inspired by metalloenzymes [1]. Protein film electrochemistry (PFE) is a powerful technique to investigate the redox behavior and enzymatic activity of transmembrane metalloenzymes even with a submonolayer amount of the target protein (~10 pmol cm–2). The challenge of PFE of metalloenzymes is the interpretation of the results obtained in PFE: PFE provides current–potential curves like cyclic voltammograms and relatively large transmembrane metalloenzymes tend to have multiple redox active cofactors inside the protein, which makes the interpretation of cyclic voltammograms difficult.We are using PFE coupled with surface-enhanced infrared absorption (SEIRA) spectroscopy, which is a surface-sensitive vibrational spectroscopy, to understand enzymatic mechanisms and protein–lipid or protein–protein interactions of transmembrane metalloenzymes at the electrode surface. In this talk, we will discuss PFE–SEIRA spectroscopy results about the determination of redox potential using a vibrational probe of carbon monoxide for heme proteins [2], the mechanistic insights into nitric oxide reduction to nitrous oxide at cytochrome c-dependent nitric oxide reductase (cNOR) using in situ PFE-SEIRA spectroscopy, and protein–lipid and protein–protein interactions with cNOR [3] and cytochrome c oxidase (CcO) [4].References.[1] M. Kato, N. Fujibayashi, D. Abe, N. Matsubara, S. Yasuda, I. Yagi, ACS Catal., 11, 2356–2365 (2021).[2] M. Kato, S. Nakagawa, T. Tosha, Y. Shiro, Y. Masuda, K. Nakata, I. Yagi, J. Phys. Chem. Lett., 9, 5196 (2018).[3] M. Kato, Y. Masuda, N. Yoshida, T. Tosha, Y. Shiro, I. Yagi, Electrochim. Acta, 373, 137888 (2021).[4] M. Kato, R. Sano, N. Yoshida, M. Iwafuji, Y. Nishiyama, S. Oka, K. Shinzawa-Itoh, Y. Nishida, Y. Shintani, I. Yagi, J. Phys. Chem. Lett., 13, 9165-9170 (2022).

Temperature Effects on the Surface Dynamics of the CO2 Reduction Reaction over Copper

The electrochemical reduction of CO2 (CO2RR) has stood out as a pathway to mitigate carbon emissions and supply multi-carbon feedstocks to the chemical industry. While most CO2RR studies over copper are carried out at room temperature, heat transfer limitations in the electrolyte will result in temperature buildup near the electrode in industrial CO2 electrolyzers. Reaction temperature plays a key role in the reaction activity and product selectivity by controlling the distribution of species on the copper surface. In this study, we use surface enhanced infrared absorption spectroscopy (SEIRAS) and surface enhanced Raman spectroscopy (SERS) to investigate the effect of temperature on the dynamics of reactive intermediates in the reaction microenvironment (Fig. A).Using SEIRAS, we showed site-specific CO coverage is dependent on temperature, and how CO migration seems to directly impact product distribution at higher temperatures. We found that increasing temperature leads to decreased CO and increased alkyl groups coverage for a given potential (Fig. B). This suggests that temperature has a direct effect on the selection of mechanistic pathways in the conversion of CO to C1 and C2 products, beyond just controlling mass transport and local CO2 availability. Using SERS, we showed that the local pH is considerably higher than their bulk values, and that higher temperatures consistently led to higher local pH values (Fig. C). The significant depletion of local hydrogen with increasing temperature indicates that local pH plays a key role in driving reaction selectivity dependence on temperature. Understanding the effect of temperature on the CO2RR surface dynamics through surface sensitive techniques is a key step to rationalize product distribution and to design solutions for enhanced C2+ production in industrial CO2 electrolyzers. Figure 1

Multi-Shell Copper Catalysts for Selective Electroreduction of CO2 to Multicarbon Chemicals

Electrocatalytic CO2 reduction (CO2R) coupled with renewable electricity has been considered as a promising route for the sustainability transition of energy and chemical industries. However, the unsatisfactory yield of desired products, particularly multicarbon (C2+) products, has hindered the implementation of this technology. This work describes a strategy to enhance the yield of C2+ products formation in CO2R by utilizing spatial confinement effects. Our finite element simulation results suggest that increasing the number of shells in the catalyst will lead to a high local concentration of *CO and promote the formation of C2+ products. Inspired by this, we synthesize Cu nanoparticles with desired hollow multi-shell structures. The CO2 reduction results confirmed that as the number of shells increased, the hollow multi-shelled copper catalysts exhibited improved selectivity towards C2+ products. Specifically, Cu catalyst with 4.4-shell achieved a high selectivity of over 80% towards C2+ at a current density of 900 mA cm−2. Evidence from in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy unveils that multi-shelled Cu catalyst exhibits an enhanced *COatop coverage and the stronger interaction with *COatop compared to commercial Cu, confirming our simulation results. Overall, our work promises an effective approach for boosting CO2R selectivity towards value-added chemicals.