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The inhibition of the electrochemical oxygen reduction reaction (ORR) by zinc corrosion products plays an important role in the corrosion protection of galvanized steel. Hence, the electrocatalytic mechanism of the ORR on electrodeposited zinc hydroxide-based model corrosion products was investigated by in situ and operando attenuated total reflection infrared (ATR-IR) spectroscopy, supplemented by density functional theory (DFT) calculations. Model corrosion products containing flake-like crystalline Zn5(NO3)2(OH)8 were cathodically electrodeposited on germanium(100) electrodes from a zinc nitrate precursor electrolyte. Substantial amounts of the films are non-crystalline, and their surfaces predominantly consist of zinc oxide and hydroxide species, as evidenced by x-ray photoelectron spectroscopy. ATR-IR spectra show a peak at 1180 cm−1 during cathodic currents in O2-saturated NaClO4 solution. This peak is assigned to a surface-bound superoxide, the only ORR intermediate detected. Absorbance from the intermediate increases with increasing cathodic current, indicating an increase in surface concentration of superoxide intermediates at larger ORR current densities. The zinc hydroxide ages in the experiments, most likely by a transformation into zinc oxide, consistent with the observed decrease in absorbance over time of the OH bending mode of zinc hydroxide at 1380 cm−1. This aging is a time-dependent chemical process, implying that pure chemical aging is important in actual corrosion products as well. DFT calculations of adsorbed superoxide yield a Zn–O bond length similar to the bond length in Zn–O, thus enhancing superoxide interaction with undercoordinated tetrahedral Zn2+ sites on the surface. Thus, such active sites catalyze the first reduction step in the ORR. [ABSTRACT FROM AUTHOR]

Abstract: The sluggish kinetics of oxygen reduction to water remains a significant limitation in the viability of proton‐exchange‐membrane fuel cells, yet details of the four‐electron oxygen reduction reaction remain elusive. Herein, we apply in situ infrared spectroscopy to probe the surface chemistry of a commercial carbon‐supported Pt nanoparticle catalyst during oxygen reduction. The IR spectra show potential‐dependent appearance of adsorbed superoxide and hydroperoxide intermediates on Pt. This strongly supports an associative pathway for oxygen reduction. Analysis of the adsorbates alongside the catalytic current suggests that another pathway must also be in operation, consistent with a parallel dissociative pathway. [ABSTRACT FROM AUTHOR]

The sluggish kinetics of oxygen reduction to water remains a significant limitation in the viability of proton‐exchange‐membrane fuel cells, yet details of the four‐electron oxygen reduction reaction remain elusive. Herein, we apply in situ infrared spectroscopy to probe the surface chemistry of a commercial carbon‐supported Pt nanoparticle catalyst during oxygen reduction. The IR spectra show potential‐dependent appearance of adsorbed superoxide and hydroperoxide intermediates on Pt. This strongly supports an associative pathway for oxygen reduction. Analysis of the adsorbates alongside the catalytic current suggests that another pathway must also be in operation, consistent with a parallel dissociative pathway. [ABSTRACT FROM AUTHOR]

The fabrication of sub-nanoliter fluidic channels is demonstrated, with merely 10 nm depth on germanium, using conventional semiconductor device fabrication methods and a polymer assisted room-temperature sealing method. As a first application, an ultralow volume (650 pL) was studied by ATR-IR spectroscopy. A detection limit of ∼7.9 × 1010 molecules of human serum albumin (HSA) (∼0.2 mM) in D2O was achieved with highly specific ATR-IR spectroscopy. [ABSTRACT FROM AUTHOR]

It is reported that metals on polyaniline (PANI) prepared by a simple method can exhibit excellent activity in the electro-reduction of CO2 to HCOOH or CH3OH due to tunable properties: N atoms on PANI capture CO2 through a strong Lewis acid–base interaction while Pd atoms, amongst Pd, Pt, and Cu studied, facilitate the fastest proton and electron transfers along PANI to the CO2 trapped sites to give rise to the best HCOOH yield in a highly cooperative manner. [ABSTRACT FROM AUTHOR]

Corrosion of iron infrastructure in anoxic environments is commonly ascribed to the metabolic activity of sulfate-reducing bacteria (SRB), which can influence electrochemical processes on the metallic surface. The present study characterizes electron transfer processes at the electrode/microorganism interface of the specialized lithoautotrophic SRB Desulfopila corrodens strain IS4 that is capable of taking up electrons directly from elemental iron, thereby leading to severe corrosion. Electrochemical analysis of the highly corrosive SRB is performed in bio-electrochemical cells operated with artificial seawater under anoxic conditions, complemented by infrared spectroelectrochemical analysis and environmental SEM observations. In order to provide clear insights into electron transfer processes, sterile controls and a non-corrosive hydrogenotrophic control strain are analyzed in parallel. Remarkably, the electron uptake from electrodes by D. corrodens strain IS4 is not restricted to iron serving as the sole electron donor for the microbial metabolism, but instead proceeds also on graphite and doped germanium cathodes. Consequently, a well-defined electrochemical analysis of the electron uptake mechanism is possible, since corrosion precipitates typically observed on iron electrodes are absent on both of the other cathode materials. Direct electron transfer in the absence of artificial electron mediators is achieved at a potential of −0.4 V vs. SHE under neutral conditions. Electrochemical and infrared spectroelectrochemical analysis indicated c-type cytochromes as the redox active components associated with the outer membrane to be involved in the direct electron uptake from reduced surfaces by D. corrodens strain IS4. [ABSTRACT FROM AUTHOR]

Highlights: [•] Superoxide and peroxide with upright orientation are ORR intermediates at alkaline pH. [•] Vibrational frequency of superoxide intermediate changes with electrolyte. [•] Relation between absorbance and current is discussed in a simple kinetic scheme. [•] A way is shown to obtain rate constants of individual steps in multistep reactions. [•] Reaction from superoxide to peroxide is faster in chloride than in perchlorate. [Copyright &y& Elsevier]

The charge-dependent structure of interfacial water at the n-Ge(100)-aqueous perchlorate interface was studied by controlling the electrode potential. Specifically, a joint attenuated total reflection infrared spectroscopy and electrochemical experiment was used in 0.1M NaClO4 at pH ≈ 1–10. The germanium surface transformation to an H-terminated surface followed the thermodynamic Nernstian pH dependence and was observed throughout the entire pH range. A singular value decomposition-based spectra deconvolution technique coupled to a sigmoidal transition model for the potential dependence of the main components in the spectra shows the surface transformation to be a two-stage process. The first stage was observed together with the first appearance of Ge–H stretching modes in the spectra and is attributed to the formation of a mixed surface termination. This transition was reversible. The second stage occurs at potentials ≈0.1–0.3 V negative of the first one, shows a hysteresis in potential, and is attributed to the formation of a surface with maximum Ge–H coverage. During the surface transformation, the surface becomes hydrophobic, and an effective desolvation layer, a “hydrophobic gap,” developed with a thickness ≈1–3 Å. The largest thickness was observed near neutral pH. Interfacial water IR spectra show a loss of strongly hydrogen-bound water molecules compared to bulk water after the surface transformation, and the appearance of “free,” non-hydrogen bound OH groups, throughout the entire pH range. Near neutral pH at negative electrode potentials, large changes at wavenumbers below 1000 cm−1 were observed. Librational modes of water contribute to the observed changes, indicating large changes in the water structure. [ABSTRACT FROM AUTHOR]

We describe a method for addressing redox enzymes adsorbed on a carbon electrode using synchrotron infrared microspectroscopy combined with protein film electrochemistry. Redox enzymes have high turnover frequencies, typically 10-1000 s-1, and therefore, fast experimental triggers are needed in order to study subturnover kinetics and identify the involvement of transient species important to their catalytic mechanism. In an electrochemical experiment, this equates to the use of microelectrodes to lower the electrochemical cell constant and enable changes in potential to be applied very rapidly. We use a biological cofactor, flavin mononucleotide, to demonstrate the power of synchrotron infrared microspectroscopy relative to conventional infrared methods and show that vibrational spectra with good signal-to-noise ratios can be collected for adsorbed species with low surface coverages on microelectrodes with a geometric area of 25 ? 25 μm². We then demonstrate the applicability of synchrotron infrared microspectroscopy to adsorbed proteins by reporting potential-induced changes in the flavin mononucleotide active site of a flavoenzyme. The method we describe will allow time-resolved spectroscopic studies of chemical and structural changes at redox sites within a variety of proteins under precise electrochemical control. [ABSTRACT FROM AUTHOR]