Scanning electrochemical microscopy determination of hydrogen flux at liquid|liquid interface with potentiometric probe

Scanning electrochemical microscopy potentiometric determination of local hydrogen concentration and its flux next to the liquid|liquid interface was demonstrated. This method is based on the shift of open circuit potential of Pt-based reversible hydrogen electrode. The detection system was verified with a system generating hydrogen under galvanostatic conditions. Then, it was applied to aqueous|1,2-dichloroethane interface where hydrogen is produced with decamethylferrocene as electron donor

SECM study of hydrogen photogeneration in a 1,2-dichloroethane | water biphasic system with decamethylruthenocene electron donor regeneration

This paper reports light driven hydrogen evolution reaction (HER) at 1,2-dichloroethane | water (DCE | W) interface using photoexcited decamethylruthenocene (DMRc) as electron donor. DMRc is in situ regenerated by electroreduction of its oxidized form (DMRc+) formed during HER as a by-product. This enables continuous HER using small amount of DMRc. Proton transfer from the acidic aqueous phase to the DCE phase is ensured by negative chemical polarization of the liquid | liquid interface. The reduction of protons in DCE occurs only after excitation of DMRc by light. Voltammetry performed with the organic droplet-modified glassy carbon electrode immersed in the aqueous electrolyte solution of various anions, indicated that oxidation of DMRc is followed by an anion insertion from water into the organic phase. We demonstrate that DMRc can be electrochemically regenerated at the microelectrode positioned close to the interface between two immiscible electrolyte solutions (ITIES) by the scanning electrochemical microscopy. Regeneration of the electron donor allows further development of biphasic system towards continuous hydrogen generation platform

H2O2 generation at carbon paste electrode with decamethylferrocene solution in 2-nitrophenyloctyl ether as a binder. The catalytic effect of MoS2 particles

Here, we report hydrogen peroxide generation at 2-nitrophenyloctyl ether (NPOE)-water interface with decamethylferrocene as an electron donor. The progress of this reaction was detected by the observation of color change of the organic and aqueous phases in series of shake-flask experiments. The shape change of cyclic voltammograms recorded at carbon paste electrode with decamethylferrocene solution in NPOE also indicates (electro)catalytic reaction. Hydrogen peroxide was electrochemically detected at Pt microelectrode tip positioned in front of carbon paste electrode. For this purpose, scanning electrochemical microscopy (SECM) approach curves were recorded. Analogous experiments demonstrated the possibility of electrochemical regeneration of the electron donor. The (electro)catalytic effect of MoS2 on hydrogen peroxide generation was found by both shake-flask and SECM experiments

Hydrogen and Hydrogen Peroxide Formation in Trifluorotoluene-Water Biphasic Systems

Hydrogen or hydrogen peroxide can be generated in liquid-liquid biphasic systems, where the organic phase contains sufficiently strong electron donor (whose redox potential is lower than the potential of reversible hydrogen electrode). H2O2 generation with acidified aqueous phase occurs prior to H2 evolution when oxygen is present. No other organic solvent than highly toxic 1,2-dichloroethane (DCE) has been reported in biphasic system for H2 or H2O2 generation. In this work, we have used trifluorotoluene (TFT) instead of carcinogenic DCE, and studied these reactions in TFT-water biphasic system. To evaluate H2 flux, scanning electrochemical microscopy potentiometric approach curves to the TFT-water interface were recorded. H2O2 was detected voltametrically at a microelectrode located in the vicinity of the interface. H2 and H2O2 are formed and both reactions occur also in the absence of a hydrophobic salt in the organic phase. Their thermodynamics was discussed on the basis of Gibbs energies determined electrochemically with droplet-modified electrodes. The results show that DCE can be replaced by a noncarcinogenic solvent and the biphasic system for H2 and H2O2 generation can be simplified by elimination of the uncommon hydrophobic salt from the organic phase

Hydrogen Peroxide Generation at Liquid|Liquid Interface under Conditions Unfavorable for Proton Transfer from Aqueous to Organic Phase

The charge transfer processes across the interface between two immiscible electrolyte solutions (ITIES) can be employed for energy storage and conversion, solvent extraction, or sensing or in life sciences. Among them are catalytic reactions, which have only been recently studied. Here H2O2 generation is studied with decamethylferrocene (DMFc) as electron donor at the interface between tetrahexylammonium perchlorate solution in 1,2- dichloroethane (1,2-DCE) and aqueous HClO4. These conditions are unfavorable for proton transfer across ITIES because of positive Galvani potential difference. Voltammetry with 1,2-DCE droplet modified electrode shows that DMFc oxidation is accompanied by ClO4− insertion into the organic phase. The reaction progress was followed by UV−vis spectroscopy, voltammetry, and scanning electrochemical microscopy (SECM). In the first and last method, horseradish peroxidase was used as catalyst. It is concluded that O2 is reduced to H2O2 at the liquid|liquid interface not only under conditions when proton transfer to organic phase is strongly favored, namely, when Galvani potential difference is negative (Angew. Chem., Int. Ed. 2008, 47, 4675−4678)

Towards the detection limit of electrochemistry: Studying anodic processes with a fluorogenic reporting reaction

Recently, shot noise has been shown to be an inherent part of all charge transfer processes, leading to a practical limit of quantification of 2100 electrons (~0.34 fC) (Curr. Opin. Electrochem. 2020, 22, 170177). Attainable limits of quantification are made much larger by greater background currents and insufficient instrumentation, which restricts progress in sensing and single-entity applications. This limitation can be overcome by converting electrochemical charges into photons, which can be detected with much greater sensitivity, even down to a single-photon level. In this work, we demonstrate the use of fluorescence, induced through a closed-bipolar set-up, to monitor charge transfer processes below the detection limit of electrochemical workstations. During this process, the oxidation of ferrocenemethanol (FcMeOH) in one cell is used to concurrently drive the oxidation of Amplex Red (AR), a fluorogenic redox molecule, in another cell. The spectroelectrochemistry of AR is investigated and new insights on the commonplace practise of using deprotonated glucose to limit AR photooxidation are presented. The closed-bipolar set-up was used to produce fluorescent signals corresponding to the steady-state voltammetry of FcMeOH on a microelectrode. Chronopotentiometry is then used to show a linear relationship between the charge passed through FcMeOH oxidation and the integrated AR fluorescence signal. The sensitivity of the measurements obtained at different timescales varies between 2200 - 500 electrons per detected photon. The electrochemical detection limit is approached using a diluted FcMeOH solution in which no current signal is observed. Nevertheless, a fluorescence signal corresponding to FcMeOH oxidation is still seen, and detection of charges down to 300 fC is demonstrated

The Solvent Effect on H2O2 Generation at Room Temperature Ionic Liquid|Water Interface

H2O2 is a versatile chemical and can be generated by the oxygen reduction reaction (ORR) in proton donor solution in molecular solvents or room temperature ionic liquids (IL). We investigated this reaction at interfaces formed by eleven hydrophobic ILs and acidic aqueous solution as a proton source with decamethylferrocene (DMFc) as an electron donor. H2O2 is generated in colorimetrically detectable amounts in biphasic systems formed by alkyl imidazolium hexafluorophosphate or tetraalkylammonium bis(trifluoromethylsulfonyl)imide ionic liquids. H2O2 fluxes were estimated close to liquid|liquid interface by scanning electrochemical microscopy (SECM). Contrary to the interfaces formed by hydrophobic electrolyte solution in a molecular solvent, H2O2 generation is followed by cation expulsion to the aqueous phase. Weak correlation between the H2O2 flux and the difference between DMFc/DMFc(+) redox potential and 2 electron ORR standard potential indicates kinetic control of the reaction

Toward the Detection Limit of Electrochemistry: Studying Anodic Processes with a Fluorogenic Reporting Reaction

Recently, shot noise has been shown to be an inherent part of all charge-transfer processes, leading to a practical limit of quantification of 2100 electrons (≈0.34 fC) [Curr. Opin. Electrochem. 2020, 22, 170−177]. Attainable limits of quantification are made much larger by greater background currents and insufficient instrumentation, which restricts progress in sensing and single-entity applications. This limitation can be overcome by converting electrochemical charges into photons, which can be detected with much greater sensitivity, even down to a single-photon level. In this work, we demonstrate the use of fluorescence, induced through a closed bipolar setup, to monitor charge-transfer processes below the detection limit of electrochemical workstations. During this process, the oxidation of ferrocenemethanol (FcMeOH) in one cell is used to concurrently drive the oxidation of Amplex Red (AR), a fluorogenic redox molecule, in another cell. The spectroelectrochemistry of AR is investigated and new insights on the commonplace practice of using deprotonated glucose to limit AR photooxidation are presented. The closed bipolar setup is used to produce fluorescence signals corresponding to the steady-state voltammetry of FcMeOH on a microelectrode. Chronopotentiometry is then used to show a linear relationship between the charge passed through FcMeOH oxidation and the integrated AR fluorescence signal. The sensitivity of the measurements obtained at different timescales varies between 2200 and 500 electrons per detected photon. The electrochemical detection limit is approached using a diluted FcMeOH solution in which no faradaic current signal is observed. Nevertheless, a fluorescence signal corresponding to FcMeOH oxidation is still seen, and the detection of charges down to 300 fC is demonstrated

Toward the Detection Limit of Electrochemistry: Studying Anodic Processes with a Fluorogenic Reporting Reaction

Recently, shot noise has been shown to be an inherent part of all charge-transfer processes, leading to a practical limit of quantification of 2100 electrons (≈0.34 fC) [Curr. Opin. Electrochem. 2020, 22, 170−177]. Attainable limits of quantification are made much larger by greater background currents and insufficient instrumentation, which restricts progress in sensing and single-entity applications. This limitation can be overcome by converting electrochemical charges into photons, which can be detected with much greater sensitivity, even down to a single-photon level. In this work, we demonstrate the use of fluorescence, induced through a closed bipolar setup, to monitor charge-transfer processes below the detection limit of electrochemical workstations. During this process, the oxidation of ferrocenemethanol (FcMeOH) in one cell is used to concurrently drive the oxidation of Amplex Red (AR), a fluorogenic redox molecule, in another cell. The spectroelectrochemistry of AR is investigated and new insights on the commonplace practice of using deprotonated glucose to limit AR photooxidation are presented. The closed bipolar setup is used to produce fluorescence signals corresponding to the steady-state voltammetry of FcMeOH on a microelectrode. Chronopotentiometry is then used to show a linear relationship between the charge passed through FcMeOH oxidation and the integrated AR fluorescence signal. The sensitivity of the measurements obtained at different timescales varies between 2200 and 500 electrons per detected photon. The electrochemical detection limit is approached using a diluted FcMeOH solution in which no faradaic current signal is observed. Nevertheless, a fluorescence signal corresponding to FcMeOH oxidation is still seen, and the detection of charges down to 300 fC is demonstrated

Toward the Detection Limit of Electrochemistry: Studying Anodic Processes with a Fluorogenic Reporting Reaction

Recently, shot noise has been shown to be an inherent part of all charge-transfer processes, leading to a practical limit of quantification of 2100 electrons (≈0.34 fC) [Curr. Opin. Electrochem. 2020, 22, 170−177]. Attainable limits of quantification are made much larger by greater background currents and insufficient instrumentation, which restricts progress in sensing and single-entity applications. This limitation can be overcome by converting electrochemical charges into photons, which can be detected with much greater sensitivity, even down to a single-photon level. In this work, we demonstrate the use of fluorescence, induced through a closed bipolar setup, to monitor charge-transfer processes below the detection limit of electrochemical workstations. During this process, the oxidation of ferrocenemethanol (FcMeOH) in one cell is used to concurrently drive the oxidation of Amplex Red (AR), a fluorogenic redox molecule, in another cell. The spectroelectrochemistry of AR is investigated and new insights on the commonplace practice of using deprotonated glucose to limit AR photooxidation are presented. The closed bipolar setup is used to produce fluorescence signals corresponding to the steady-state voltammetry of FcMeOH on a microelectrode. Chronopotentiometry is then used to show a linear relationship between the charge passed through FcMeOH oxidation and the integrated AR fluorescence signal. The sensitivity of the measurements obtained at different timescales varies between 2200 and 500 electrons per detected photon. The electrochemical detection limit is approached using a diluted FcMeOH solution in which no faradaic current signal is observed. Nevertheless, a fluorescence signal corresponding to FcMeOH oxidation is still seen, and the detection of charges down to 300 fC is demonstrated