Interfacial Electron Engineering of PdSn-NbN/C for Highly Efficient Cleavage of the C-C Bonds in Alkaline Ethanol Electrooxidation.

The splitting of the C-C bonds of ethanol remains a key issue to be addressed, despite tremendous efforts made over the past several decades. This study highlights the enhancement mechanism of inexpensive NbN-modified Pd1 Sn3 -NbN/C towards the C-C bonds cleavage for alkaline ethanol oxidation reaction (EOR). The optimal Pd1 Sn3 -NbN/C delivers a catalytic activity up to 43.5 times higher than that of commercial Pd/C and high carbonate selectivity (20.5%) toward alkaline EOR. Most impressively, the Pd1 Sn3 -NbN/C presents good durability even after 25 200 s of chronoamperometric testing. The enhanced catalytic performance is mainly due to the interfacial interaction between PdSn and NbN, demonstrated by multiple structural characterization results. In addition, in situ ATR-SEIRAS (Attenuated total reflection-surface enhanced infrared absorption spectroscopy) results suggest that NbN facilitates the C-C bonds cleavage towards the alkaline EOR, followed by the enhanced OH adsorption to promote the subsequent oxidation of C1 intermediates after doping Sn. DFT (density functional theory) calculations indicate that the activation barriers of the C-H bond cleavage in CH3 CH2 OH, CH3 CHOH, CH3 CHO, CH3 CO, CH2 CO, and the C-C bond cleavage in CH3 CO, CH2 CO, CHCO are evidently reduced and the removal of adsorbed CH3 CO and CO becomes easier on the PdSn-NbN/C catalyst surface.

Electrochemical Synthesis of Urea: Co-Reduction of Nitrite and Carbon Dioxide on Binuclear Cobalt Phthalocyanine.

Exploration of molecular catalysts with the atomic-level tunability of molecular structures offers promising avenues for developing high-performance catalysts for the electrochemical co-reduction reaction of carbon dioxide (CO2) and nitrite (NO2 -) into value-added urea. In this work, a binuclear cobalt phthalocyanine (biCoPc) catalyst is prepared through chemical synthesis and applied as a C─N coupling catalyst toward urea. Achieving a remarkable Faradaic efficiency of 47.4% for urea production at -0.5 V versus reversible hydrogen electrode (RHE), this biCoPc outperforms many known molecular catalysts in this specific application. Its unique planar macromolecular structure and the increased valence state of cobalt promote the adsorption of nitrogenous and carbonaceous species, a critical factor in facilitating the multi-electron C─N coupling. Combining highly sensitive in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) with density functional theory (DFT) calculations, the linear adsorbed CO (COL) and bridge adsorbed CO (COB) is captured on biCoPc catalyst during the co-reduction reaction. COB, a pivotal intermediate in the co-reduction from CO2 and nitrite to urea, is evidenced to be labile and may be attacked by nitrite, promoting urea production. This work demonstrates the importance of designing molecular catalysts for efficient co-reduction of CO2 and nitrite to urea.

Uncovering Photoelectronic and Photothermal Effects in Plasmon-Mediated Electrocatalytic CO2 Reduction.

Plasmon-mediated electrocatalysis that rests on the ability of coupling localized surface plasmon resonance (LSPR) and electrochemical activation, emerges as an intriguing and booming area. However, its development seriously suffers from the entanglement between the photoelectronic and photothermal effects induced by the decay of plasmons, especially under the influence of applied potential. Herein, using LSPR-mediated CO2 reduction on Ag electrocatalyst as a model system, we quantitatively uncover the dominant photoelectronic effect on CO2 reduction reaction over a wide potential window, in contrast to the leading photothermal effect on H2 evolution reaction at relatively negative potentials. The excitation of LSPR selectively enhances the CO faradaic efficiency (17-fold at -0.6 VRHE ) and partial current density (100-fold at -0.6 VRHE ), suppressing the undesired H2 faradaic efficiency. Furthermore, in situ attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) reveals a plasmon-promoted formation of the bridge-bonded CO on Ag surface via a carbonyl-containing C1 intermediate. The present work demonstrates a deep mechanistic understanding of selective regulation of interfacial reactions by coupling plasmons and electrochemistry.

Irrelevance of Carbon Monoxide Poisoning in the Methanol Oxidation Reaction on a PtRu Electrocatalyst.

Based on detailed in situ attenuated total-reflection-surface-enhanced IR reflection absorption spectroscopy (ATR-SEIRAS) studies of the methanol oxidation reaction (MOR) on Ru/Pt thin film and commercial Johnson-Matthey PtRu/C, a revised MOR enhancement mechanism is proposed in which CO on Pt sites is irrelevant but instead Pt-Ru boundary sites catalyze the oxygen insertion reaction that leads to the formation of formate and enhances the direct reaction pathway.

Layered Sn-Au Thin Films for Increased Electrochemical ATR-SEIRAS Enhancement.

Operando electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (EC ATR-SEIRAS) is a valuable method for a fundamental understanding of electrochemical interfaces under real operating conditions. The applicability of this method depends on the ability to tune the optical and catalytic properties of an electrode film, and it thus requires unique optimization for any given material. Motivated by the growing interest in Sn-based electrocatalysts for selective reduction of CO2 to formate species, we investigate several Sn thin-film synthesis routes for the resulting SEIRA signal response. We compare the SEIRA performance of thermally evaporated metallic Sn to a series of Sn-based films on top of a SEIRA-active Au substrate (metallic Sn, oxide-derived metallic Sn, and metal oxide SnOx). Using alkanethiol self-assembled monolayers as a probe, we find that electrodepositing metallic catalyst films on top of SEIRA-active Au substrates yield higher signal relative to thermal evaporation as well as higher signal than the independent SEIRA-active Au underlayer. These observations come despite the fact that thermally evaporated Sn has a significantly higher surface roughness (and thus higher adsorbate population), suggesting specific SEIRA-magnifying effects for the stacked films. Finally, we applied these films to observe the electrochemical conversion of CO2. Differences are observed in spectral features based on the composition of the electrode being either metallic or oxide-derived metallic Sn, implying differences in their respective reaction pathways.

Nano-Plasticity of an Electrified Ionic Liquid/Electrode Interface: Uncovering Hard-Soft Structuring via Controlled Metal Fill Factor.

Ionic liquids (ILs) nanostructuring at electrified interfaces is of both fundamental and practical interest as these materials are increasingly gaining prominence in energy storage and conversion processes. However, much remains unresolved about IL potential-controlled (re)organization under highly polarized interfaces, mostly due to the difficulty of selectively probing both the distal and proximal surface layers of adsorbed ions. In this work, the structural dynamics of the innermost layer (<10 nm from the surface) were independently interrogated from that of the ionic layers in the sub-surface region (>100 nm from the surface), using an infrared (IR) spectroscopy approach. By tuning the metal fill factor of gold films deposited on conductive metal oxide-modified IR internal reflection elements, the charge-driven (re)structuring of the inner and distal layers of 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate is unveiled. Within a relatively wide potential region (∼±1 V) bounding the potential of zero charges, the ionic liquid is shown to undergo a reversible (i.e., soft) reorganization whereby the innermost layer of anions (cations) is exchanged by a layer of cations (anions). Kinetically unhindered changes in the number density of constituent cations and anions largely follow electrostatic expectations in the subsurface region, whereas the innermost layer exhibits a pronounced hysteresis and very slow relaxation. Under larger negative potential bias, IL restructuring is characterized by a highly irreversible (i.e., hard) and intense interfacial densification of the BMPy+ cations, consistent with the formation of nanoscale segregated liquids. The outcomes of this work reveal a plastic IL nanostructuring under a strong electric field.

Time-resolved in situ vibrational spectroscopy for electrocatalysis: challenge and opportunity.

Understanding the structure-activity relationship of catalysts and the reaction pathway is crucial for designing efficient, selective, and stable electrocatalytic systems. In situ vibrational spectroscopy provides a unique tool for decoding molecular-level factors involved in electrocatalytic reactions. Typically, spectra are recorded when the system reaches steady states under set potentials, known as steady-state measurements, providing static pictures of electrode properties at specific potentials. However, transient information that is crucial for understanding the dynamic of electrocatalytic reactions remains elusive. Thus, time-resolved in situ vibrational spectroscopies are developed. This mini review summarizes time-resolved in situ infrared and Raman techniques and discusses their application in electrocatalytic research. With different time resolutions, these time-resolved techniques can capture unique dynamic processes of electrocatalytic reactions, short-lived intermediates, and the surface structure revolution that would be missed in steady-state measurements alone. Therefore, they are essential for understanding complex reaction mechanisms and can help unravel important molecular-level information hidden in steady states. Additionally, improving spectral time resolution, exploring low/ultralow frequency detection, and developing operando time-resolved devices are proposed as areas for advancing time-resolved techniques and their further applications in electrocatalytic research.

High dispersion dendritic fibrous morphology nanospheres for electrochemical CO2 reduction to C2H4.

The electrochemical CO2 reduction to specific multi-carbon product on copper-based catalysts is subjected to low activity and poor selectivity. Herein, catalyst structure, morphology, and chemical component are systematically studied for bolstering the activity and selectivity of as-prepared catalyzers in this study. Dendritic fibrous nano-silica spheres favor the loading of active species and the transport of reactant from the central radial channel. Cu/DFNS with high dispersion active sites are fabricated through urea-assisted precipitation way. The coexistence of Cu(I)/Cu(II) induces a close combination of Cu active sites and CO2 on the Cu/DFNS interface, promoting the CO2 activation and CC coupling. The Cu-O-Si interface (Cu phyllosilicate) can improve CO2 and CO attachment. Cu/DFNS show the utmost Faradaic efficiency of C2H4 with a value of 53.04% at -1.2 V vs. RHE. And more importantly, in-situ ATR-SEIRAS reveals that the CC coupling is boosted for effectively producing C2H4 as a consequence of the existence of *COL, *COOH, and *COH intermediates. The mechanism reaction path of Cu/DFNS is inferred to be *CO2 â†’ *COOH â†’ *CO â†’ *CO*COH â†’ C2H4. Our findings will be helpful to gain insight into the links between morphology, texture, chemical component of catalyzers, and electrochemical reduction of CO2, providing valuable guidance in the design of more efficient catalysts.

Preanodized Cu Surface for Selective CO2 Electroreduction to C1 or C2+ Products.

The electrochemical CO2 reduction over Cu catalysts has shown great potential in producing a wide range of valuable chemicals, but it is still plagued by a poor controllability on product distribution. Herein, we demonstrate an effective regulation of CO2 reduction paths through a preanodization treatment of Cu foil electrodes in different electrolytes. The Cu electrode exhibits a superior C1 and C2+ product selectivity after being preanodized in NaClO4 (Cu-NaClO4) and Na2HPO4 electrolyte (Cu-Na2HPO4), respectively. Combined with in situ electrochemical Raman, ATR-SEIRAS, and SEM characterizations, the preferential C1 path is due to the deposition of many Cu nanocrystals with dominant Cu(111) facets on the Cu-NaClO4 electrode. In contrast, the preferential C2+ path over the Cu-Na2HPO4 is attributed to formation of a unique Cu nanodendritic morphology, which strengthens the *CO intermediate adsorption and induces an environment of low local H2O/CO2 stoichiometric ratio, thus facilitating C-C coupling for C2+ production. Our findings may shed light on the rational control of the CO2 reduction path through engineering of the Cu surface structure.

Enhanced Electrochemical CO2 Reduction to Formate on Poly(4-vinylpyridine)-Modified Copper and Gold Electrodes.

Developing active and selective catalysts that convert CO2 into valuable products remains a critical challenge for further application of the electrochemical CO2 reduction reaction (CO2RR). Catalytic tuning with organic additives/films has emerged as a promising strategy to tune CO2RR activity and selectivity. Herein, we report a facile method to significantly change CO2RR selectivity and activity of copper and gold electrodes. We found improved selectivity toward HCOOH at low overpotentials on both polycrystalline Cu and Au electrodes after chemical modification with a poly(4-vinylpyridine) (P4VP) layer. In situ attenuated total reflection surface-enhanced infrared reflection-adsorption spectroscopy and contact angle measurements indicate that the hydrophobic nature of the P4VP layer limits mass transport of HCO3- and H2O, whereas it has little influence on CO2 mass transport. Moreover, the early onset of HCOOH formation and the enhanced formation of HCOOH over CO suggest that P4VP modification promotes a surface hydride mechanism for HCOOH formation on both electrodes.

In situ monitoring of the selective adsorption mechanism of small environmental pollutant molecules on aptasensor interface by attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS).

In situ monitoring of the interactions and properties of pollutant molecules at the aptasensor interface is being a very hot and interesting topic in environmental analysis since its charming molecule level understanding of the mechanism of environmental biosensors. Attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) provides a unique and convenient technique for the in situ analysis, but is not easy for small molecules. Herein, an ATR-SEIRAS platform has been successfully developed to in situ monitor the selective adsorption mechanism of small pollutant molecule atrazine (ATZ) on the aptasensor interface by characteristic N‒H peak of ATZ for the first time. Based on the constructed ATR-SEIRAS platform, a thermodynamics model is established for the selective adsorption of ATZ on the aptasensor interface, described with Langmuir adsorption with a dissociation constant of 1.1 nM. The adsorption kinetics parameters are further obtained with a binding rate constant of 8.08×105 M-1 s-1. A promising and feasible platform has therefore successfully provided for the study of the selective sensing mechanism of small pollutant molecules on biosensors interfaces, further broadening the application of ATR-SEIRAS technology in the field of small pollutant molecules.

Probing Heterogeneity in Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS) Response with Synchrotron Infrared Microspectroscopy.

The heterogeneity of metal island films electrodeposited on conductive metal oxide modified internal reflection elements is shown to provide a variable attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) response. A self-assembled monolayer of a ferrocene-terminated thiol monolayer (FcC11SH) was formed on the gold islands covering a single substrate, which was measured using both a conventional spectrometer and a custom-built horizontal microscope. Cyclic voltammetry and ATR-SEIRAS results reveal that the FcC11SH-modified substrate undergoes a reversible electron transfer and an associated re-orientation of both the ferrocene/ferrocenium headgroup and the hydrocarbon backbone. The magnitude of the absorption signal arising from the redox changes in the monolayer, as well as the IR signature arising from the ingress/egress of the perchlorate counterions, is shown to depend significantly on the size of the infrared beam spot when using a conventional Fourier transform infrared spectrometer. By performing equivalent measurements on a horizontal microscope, the primary cause of the differences in the signal level is found to be the heterogeneity in the density of gold islands on the conductive metal oxide.

Origin of the Drastic Current Decay during Potentiostatic Alkaline Methanol Oxidation.

The current production from the alkaline methanol electro-oxidation reaction does not reach a steady state on a smooth platinum catalyst under potentiostatic conditions. We investigated two possible explanations for this phenomenon: changes on the catalyst surface and changes in the solution near the electrode. In situ Fourier transform infrared spectroscopy experiments were conducted to evaluate the adsorbed species on the catalyst surface and a simulation model was set up to describe the changes of concentrations inside the solution. Linear- and bridge-bonded carbon monoxide are the only organic compounds which can be detected by in situ spectroscopy at fixed potentials, but their amount does not increase over time. The simulation shows that the consumption of hydroxide ions and production of carbonaceous species during alkaline oxidation causes a local pH shift near the catalyst surface. Assuming a one-electron transfer as the limiting step, this pH shift was found to contribute to the observed current loss at a potential of 0.77 V.

Optimization of a Commercial Variable Angle Accessory for Entry Level Users of Electrochemical Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS).

An evaluation of several experimental aspects that can optimize electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) performance using a commercially available, specular reflection accessory is provided. A comparison of different silicon single-bounce internal reflection elements (IREs) is made with emphasis on different face-angled crystal (FAC) options. Selection of optimal angle of incidence for maximizing signal and minimizing noise is shown to require consideration of the optical throughput of the accessory, reflection losses at the crystal surfaces, and polarization effects. The benefits of wire-grid polarizers and antireflective (AR) coatings on the IREs is discussed. High signal-to-noise ratios can be achieved by omitting polarizers, using an AR-coated FAC with a larger face angle, and working at angles of incidence close to the maximum throughput angle of the accessory.

Spectroscopic Evidence of Size-Dependent Buffering of Interfacial pH by Cation Hydrolysis during CO2 Electroreduction.

The nature of the electrolyte cation is known to affect the Faradaic efficiency and selectivity of CO2 electroreduction. Singh et al. (J. Am. Chem. Soc. 2016, 138, 13006-13012) recently attributed this effect to the buffering ability of cation hydrolysis at the electrical double layer. According to them, the pKa of hydrolysis decreases close to the cathode due to the polarization of the solvation water molecules sandwiched between the cation's positive charge and the negative charge on the electrode surface. We have tested this hypothesis experimentally, by probing the pH at the gold-electrolyte interface in situ using ATR-SEIRAS. The ratio between the integrated intensity of the CO2 and HCO3- bands, which has to be inversely proportional to the concentration of H+, provided a means to determining the pH change at the electrode-electrolyte interface in situ during the electroreduction of CO2. Our results confirm that the magnitude of the pH increase at the interface follows the trend Li+ > Na+ > K+ > Cs+, adding strong experimental support to Singh's et al.'s hypothesis. We show, however, that the pH buffering effect was overestimated by Singh et al., their overestimation being larger the larger the cation. Moreover, our results show that the activity trend of the alkali-metal cations can be inverted in the presence of impurities that alter the buffering effect of the electrolyte, although the electrolyte with maximum activity is always that for which the increase in the interfacial pH is smaller.