Mechanism Of Electrochemical Reduction Research Articles

A Comparative Study of Electrochemical Reduction of Levulinic Acid on Various Electrodes in Organic Solvents.

Studies on the electrochemical hydrogenation (ECH) of levulinic acid (LA) to valeric acid (VA) or γ-valerolactone (GVL) have mainly focused on the electrochemical reduction of LA in acidic aqueous solutions. However, the narrow range of applied potentials has hindered understanding of some mechanistic aspects of LA electrochemical conversion. Earlier, we discovered that employing proton-deficient non-aqueous reaction media provides more comprehensive insights into the mechanism of LA electrochemical reduction. Here, we conducted further investigations into the LA electroreduction process using cyclic voltammetry in various organic solvents on a Pt electrode and on various electrode materials in acetonitrile, both with and without the addition of proton donors. The products of the ECH processes were identified using HPLC. The solvent nature, the presence of proton donors, the electrode material, and the applied potential strongly influence the LA electroreduction process. This study reveals that LA, in the presence proton donors, can undergo electrochemical reduction through different pathways, depending on the difference (ΔE1/2) between the reduction half-wave potential of protons and LA on a certain electrode. When the difference is large, the LA reduction is incomplete and the formation of GVL is observed. Under the close reduction potentials of protons and LA, LA can be completely reduced to VA.

A First-Principles Study on the Reaction Mechanisms of Electrochemical CO2 Reduction to C1 and C2 Products on Cu(110)

The mechanism of the electrochemical CO2 reduction reaction on a Cu(110) surface has yet to be fully revealed. In this work, based on first-principles calculations, we investigate the mechanisms of the CO2 reduction reaction to produce C1 (including one C atom) and C2 (including two C atoms) products on a Cu(110) surface. The results show that CH4 and C2H5OH are the main C1 and C2 products on the Cu(110) surface, respectively. CH4 is produced along the pathway CO2 → COOH* → CO* → CHO* → CH2O* → CH3O* → CH4. C2H5OH is produced via the C-C coupling pathway between CO* and CH2O* intermediates, which is the key reaction step. This is because CO* and CH2O* coupling to CO-CH2O* has the lowest barrier among the CHxO* (x = 0–2) coupling pathways. Therefore, it is the most likely C-C coupling pathway. Further, CO-CH2O* is gradually hydrogenated to C2H5OH along the following pathway: CO-CH2O* → CHO-CH2O* → CHOH-CH2* → CH2OH-CH2* → CH2OH-CH3* → C2H5OH.

Electrochemical Preparation of Ti2CrV Alloy in CaCl2 Melt

Ti2CrV alloy shows good hydrogen storage characteristics at room temperature and ambient pressure. The present study investigated the feasibility of direct electrochemical reduction of TiO2-Cr2O3-V3O5 to Ti2CrV in CaCl2 melt at 900 °C by the FFC Cambridge process. The electrolysis was conducted in a two-electrode assembly with the sintered mixed oxide cathode and HD graphite anode at a constant cell voltage of 3.1 V for different time intervals to elucidate the reduction mechanism of the metal oxide mixture. The obtained products were characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy techniques. Cyclic voltammetry studies using metallic cavity electrode containing mixed metal oxide powder were also carried out to determine the electrochemical reduction behavior in CaCl2 melt at 900 °C. It was observed that the presence of pre-formed Cr and V metal in the vicinity of titanium oxide helped in its faster reduction. The complete metallization of the sintered mixed oxide pellet occurred after 15 h of electrolysis. The electrochemical reduction mechanism was observed to proceed through various intermediates such as chromium-rich Cr-V, vanadium-rich V-Cr, CaTiO3, TiO, Ti6O, Ti-V, and C15-TiCr2.

Reaction mechanism of metal-free borophene catalyst electrochemical reduction of CO2

The utilization of electricity generated from renewable energy sources for carbon dioxide reduction reaction (CO2RR) to produce high-value chemical resources is of significant importance for reducing CO2 emissions and for energy storage. However, the search for environmentally friendly and efficient metal-free catalysts to facilitate CO2 conversion continues to present numerous challenges. This study employs density functional theory (DFT) calculation to explore the potential of two-dimensional metal-free borophene catalysts in the activation and conversion of CO2. Through molecular dynamics simulations, energy band and density of states analysis, the stability and electronic properties of metal-free borophene were thoroughly examined. The calculations demonstrated that two specific sites on electron-deficient zigzag borophene possess strong adsorption capabilities for CO2, enabling effective activation of CO2. Further investigation revealed that the reduction of CO2 at site 1 on zigzag borophene efficiently produces CO, HCOOH, CH3OH, and CH4, with the potential determining steps (PDS) requiring overpotentials of 0.11V, 0.20V, 0.38V, and 0.52V, respectively. In summary, this research provides theoretical foundation for the use of metal-free borophene as an efficient catalyst for CO2RR.

Efficient removal of U(VI) by graphene-based electrode modified with amidoxime: Performance and mechanism

The burgeoning interest in nuclear energy as a sustainable power source brings to the fore significant environmental and human health concerns associated with wastewater from uranium mining. This study presented the successful synthesis of amidoxime modified graphene-based electrode materials (PAO-N-rGO/CF) designed for treating uranium containing wastewater. The influencing factors of PAO-N-rGO/CF during the electrokinetic restoration process were systematically investigated, exploring the mechanisms of adsorption and electrochemical reduction from the perspectives of establishing adsorption theoretical models, evaluating electrochemical performance, and characterizing reduction products. According to the results, the optimal removal efficiency for U(VI) by PAO-N-rGO/CF reached 99.93 % under conditions of an applied voltage of 5 V, an electrification duration of 20 min, and a pH of 7. Compared to Ca2+, K+, and Mg2+, PAO-N-rGO/CF exhibited strong selectivity for UO22+. Whether dissolved oxygen was present or not, PAO-N-rGO/CF maintained its excellent electrochemical performance. After undergoing 10 cycles of reuse, the removal efficiency for U(VI) only decreased by 8.75 %. The establishment of the adsorption model demonstrated the presence of a chemical bond between uranium and amidoxime groups. The electrochemical performance tests evidenced that PAO-N-rGO/CF exhibited superior electron transfer capability. The reduction of (UO2)3(OH+)5 to UO2 in wastewater at a pH = 7 was verified by analysis of the reduction products. The successful development and mechanistic study of the novel and efficient electrode material provide theoretical support for the control of radioactive nuclide pollution and possess practical value for engineering applications in treating uranium containing wastewater.

Electrochemical behavior of aluminum in 1-ethyl-3-methylimidazolium chloroaluminate ionic liquids

The mechanism of electrochemical oxidation and reduction of aluminum in 1-ethyl-3-methylimidazolium-based (EMImCl) chloroaluminate ionic liquids is studied across the concentration range of N = 1.1–2.0 (N the molar ratio of AlCl3 to EMImCl) at temperatures between 303 K and 418 К. Anodic stationary polarization curves (SPCs) indicate that the process of anodic dissolution of aluminum is complicated by passivation. The current density in the passive region and the passivation potential decrease with a higher concentration of Al2Cl7– ion in the melt. To elucidate the processes taking place at the aluminum electrode, the relationship between the concentration of the ions in the vicinity of the electrode and the potential applied in the cathodic and anodic region was analyzed by in-situ Raman spectroscopy for the concentrations of N = 1.1 and 2.0. The resulting dependences of relative peak intensity vs. potential correlate with the cathodic and anodic polarization curves. In the anodic region the content of Al2Cl7– grows with the potential, while the concentration of AlCl4– ion decreases. In the cathodic region the opposite process is observed: the concentration of Al2Cl7– decreases and that of AlCl4–increases with growing potential. It is shown that a precipitate of AlCl3 forms on the electrode surface in the region of passive aluminum dissolution, which is responsible for the electrode passivation. Based on the results obtained, we propose a model for the process of aluminum oxidation/reduction preceded and followed by a chemical reaction of aluminum chloride formation for the cathodic and anodic process, respectively. Temperature dependences of diffusion coefficients are studied by chronopotentiometry. The results indicate that diffusion coefficients are not affected by the concentration across the temperature range studied. The activation energy for diffusion was found to be 13.65 kJ∙mol−1. Impedance spectroscopy was used to investigate the concentration and temperature dependences of exchange current density. The exchange currents increase with increasing aluminum chloride content in the melt. The transfer coefficient and electrochemical reaction rate constant were found to be α = 0.17 ± 0.04, ks = (1.7 ± 0.4)∙10−6 cm∙s−1, respectively. The activation energy for the electrochemical reaction rate constant does not depend on the concentration and was found to be 33.5 kJ∙mol−1.

Mechanism of electrochemical carbon dioxide reduction to formate on tin electrode

Carbon dioxide can be electrochemically reduced to formate on tin electrodes. Formate is one of the most economically viable products of CO2 reduction reaction (CO2RR). While CO2 is reduced to formate, hydrogen evolution reaction (HER) occurs concomitantly. The kinetics of CO2RR and HER on the tin electrode was investigated. Potentiodynamic polarization studies were conducted in CO2 saturated and N2 saturated 0.1 M KHCO3 solutions, in the potential range from −0.014 V to −1.59 V vs. RHE. A faradaic efficiency of 93.95 % towards formate production was obtained at −1.09 V vs. RHE. The mass transfer effects and bicarbonate dissociation equilibrium were used to estimate the concentration of the reactants at the electrode surface. Density functional theory calculations indicate that –OCHO intermediate species is thermodynamically favoured, and a four-step reaction with two intermediates is proposed. The proposed mechanism captures the major features of the polarization data. CO2 reduction occurs via two intermediate species, viz. adsorbed H and OCHO species, while HER occurs via Volmer-Heyrovsky steps. The model predicts that in N2 saturated solutions, the fractional surface coverage of adsorbed H reaches a maximum of ∼0.48 at a potential of −0.82 V vs. RHE while in CO2 saturated solutions, the corresponding value is ∼0.29. In addition, the maximum fractional surface coverage of adsorbed OCHO is predicted to be ∼0.12 in CO2 saturated solutions.

Revisiting the Electrochemical Reduction Mechanism of Nitrosobenzene in Acetonitrile. Concomitant Reactions and Voltammetric Simulation

AbstractThe electrochemical reduction mechanism of nitrosobenzene in acetonitrile was reconsidered in this work. The commonly accepted mechanism assumes that the nitrosobenzene radical anion dimerize to yield a dianion, which decompose into azoxybenzene as the reduction product. Even though this proposal is consistent with preparative experiments, it does not reproduce fully the experimental voltammetric behaviour when it is simulated. Also, It does not explain why the apparent electron number is different in the time scale of cyclic voltammetry and preparative electrolysis. To understand these discrepancies, it was proposed the intervention of reactions consuming part of the starting nitrosobenzene, which allowed to reconsider the role of alternative chemical reactions like that occurring between the anion of phenylhydroxylamine with nitrosobenzene and the hydroxyl ion with nitrosobenzene. In this framework, these concomitant reactions were additionally included in the mechanism to simulate the voltammetric behaviour at different scan rates. Thermodynamic and kinetic parameters of the extended mechanism are reported. Since in the hydroxyl ion is either product or reactive in some reaction steps, the global mechanism was deemed to occurs as a kind of loop.

Coverage-sensitive mechanism of electrochemical NO reduction on the SrTiO3(001) surface: a DFT investigation.

Due to its adverse environmental and human health hazards, addressing the elimination of nitric oxide (NO) has become a pressing concern for modern society. Currently, electrochemical NO reduction provides a new alternative to traditional selective catalytic reduction technology under mild reaction conditions. However, the complexity and variability of products make the coverage of NO an influencing factor that needs to be investigated. Hence, this study delves into the coverage-sensitive mechanism of electrochemical NO reduction on cost-effective perovskite catalysts, using SrTiO3 as an example, through density functional theory calculations. Phase diagrams analysis reveals that the coverage range from 0.25 to 1.00 monolayer (ML) coverage is favorable for NO adsorption. Gibbs free energy results indicate that the selectivity is significantly influenced by NO coverage. NH3 is likely to be generated at low coverage, while N2O and N2 are more likely to be produced at high coverage through a dimer mechanism. Charge analysis suggests that the charge transfer and Ti-O bond strength between reactants and catalysts are crucial factors. This work not only provides deep insights into coverage-sensitive reaction mechanisms but also is a guideline towards further rational design of high-performance perovskite catalysts.

(Invited) Plasma-Synthesized Coupled Nanoplasmonic Gold for DNA Sersing

The facilitated electrochemical properties of plasma play a critical role in enhancing the synthesis and design of functional nanomaterials for the development of novel sensors. The targeted challenge is to customize and tailor functionality at multiple scales to improve detection device performance. In the realm of optoelectronics, plasmonic sensing is considered an efficient tool for investigating molecular properties, often accompanied by Raman, FTIR or Fluorescent spectroscopy. Specifically, Raman scattering, also known as SERS (surface-enhanced Raman scattering), is commonly used to probe analytes at a reduced scale using plasmonic enhancers. This technique is especially useful for rapidly and accurately investigating biologically relevant samples, such as DNA and RNA. DNA/RNA-related investigations are crucial in modern nanomedicine due to the progress made in bionanotechnology, DNA vaccines, and functional gene engineering. DNA, in particular, is highly valued by microbiologists because it contains information about the nature of bio-species. Currently, PCR-related methods dominate the field for molecular-sensitive DNA-level studies, but it is challenging to investigate using optical techniques like SERS. Despite its promise, SERS still requires technological and analytical improvements. A sophisticated plasmonic nanomaterial provides considerably improved photon scattering due to the strongly localized field confinement effect, resulting in better performance. In this report, a nanoplasmonic sensor was designed using a plasma-driven electrochemical reduction mechanism, achieved through an atmospheric pressure He-plasma jet setup operating at kHz frequency. The reactive oxidative species donated electrons via liquid-gas electrochemistry towards the Ar-delivered Au(3+)-containing microdroplets, resulting in microscaled aggregates composed of AuNPs obtained from the nebulized ionic gold liquid precursor. Due to the strong coupling between nanoparticles, a high analytical enhancement factor of about 107 was achieved, and the substrate enabled obtaining Raman fingerprints of bacterial DNA fragments (M. luteus and S. aureus, E. coli, J. lividum) at nanovolume sample quantities. Additionally, the main DNA molecular vibrational signatures associated with nucleobase motions were extracted from the collected spectra and used to reliably classify bacterial strains using statistical principal component analysis.[1] References[1] Shvalya, V., Vasudevan, A., Modic, M., Abutoama, M., Skubic, C., Nadižar, N., ... & Cvelbar, U. (2022). Bacterial DNA Recognition by SERS Active Plasma-Coupled Nanogold. Nano Letters.

Electrochemical behavior and separation of Ce(III) in LiCl-KCl molten salt

In order to improve the utilization of spent fuel, molten salt electrolysis is used to separate lanthanides from spent fuel. The electrochemical reduction mechanism of Ce(III) ions and dynamic properties of Ce(III)/Ce(0) were provided in the LiCl-KCl molten salt by diversified electrochemical techniques. The diffusion coefficient of Ce(III) and the exchange current densities of Ce(III)/Ce(0) on the W electrode were calculated by cyclic voltammetry and linear polarization, and the reaction activation energy was calculated to be 30.8 kJ∙mol−1. The electrochemical behaviors were measured in the LiCl-KCl-CeCl3-K2ZrF6 molten salt on the W electrode and LiCl-KCl-CeCl3 molten salt on the Zr electrode at 753 K. The redox mechanism of Ce(III) ions was studied on the Zr electrode. Compared the reaction at different electrodes, the reduction potential of cerium on the Zr electrode is more correct than that on the W electrode, the underpotential displacement of cerium and zirconium due to the formation of alloy is 0.26 V, which was detecteted using cyclic voltammetry, square wave voltammetry and chronopotentiometry. In addition, the feasibility of extracting Ce on the Zr electrode by potentiostatic electrolysis at −1.9 V and −2.2 V in the LiCl-KCl molten salt. The cathodic deposition output was characterized by XRD and SEM-EDS, Ce-Zr solid solution was derived under the different conditions. Simultaneously, the Ce metal was discovered when the deposition potential at −2.2 V. The ICP-OES results showed that the extraction ratio of was about 94.02 % for Ce(III) after potentiostatic electrolysis at −2.2 V for 5 h.

Application of liquid Ga-Pb cathode for selective separation of samarium fission products from molten alkali metal chlorides

The efficient separation of the rare earth element Sm from spent nuclear fuel is of strategic importance for the nuclear industries. This study explored the feasibility of a novel liquid Ga-Pb hybrid electrode for electrochemical extraction of samarium compounds, and the electrochemical reduction mechanism and dynamic properties of Sm(III) ions were provided in NaCl-2CsCl molten salt. It was established that the reduction mechanisms of Sm(III) to Sm(II) and Pb(II) to Pb(0) on the Mo cathode were a one-step reaction processes, respectively, while Ga(III) to Ga(0) was a two-step reaction process. The co-deposition mechanisms of Sm(III), Ga(III) and Pb(II) ions on the Mo cathode were identified, and the types of intermetallic compounds, formation potentials and reaction processes were analyzed. The deposition potential of Sm on Ga-Pb mixed cathode is determined, and the value of its depolarization was greater than on the liquid Pb electrode. Simultaneously, Sm ions have higher exchange current densities and lower activation energies for electrode reactions on the liquid Ga-Pb mixed electrodes than on the liquid Pb electrodes. Furthermore, the electro-separation of NaCl-2CsCl-SmCl3 molten salt was executed via potentiostatic electrolysis technique, and the separation efficiency and the effect of cathode product type were analyzed and compared in Ga-Pb hybrid electrode and Pb electrode. It was obtained that the maximum extraction efficiency on the Ga-Pb hybrid electrode and the separation efficiency of Sm could reach 91.3 % after 8 h of electrolysis.

Electrochemical Behavior and Reduction of in LiCl-KCl Molten Salt

In this work, we explored the electrochemical behavior and reduction process of uranyl ions in molten LiCl-KCl eutectic at 773 K. Cyclic voltammetry (CV) and square wave voltammetry (SWV) results showed that the reduction of ions on the inert W electrode was a three-step process: (1) (2) and (3) Electrolysis experiments further confirmed this reduction mechanism that ions were reduced to UO2 on the molybdenum electrode by applying a constant potential of −1.00 V vs Ag/AgCl and subsequently to uranium metal at a more negative potential of −2.35 V vs Ag/AgCl. In addition, ions could be thoroughly reduced to uranium metal through a 4-h constant current electrolysis at −18 mA cm−2. Electronic absorption spectroscopy (EAS) and inductively coupled plasma optical emission spectroscopy (ICP-OES) respectively illustrated that the oxidation state of uranium was unchanged and uranium concentration gradually decreased during the electrolysis. Finally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the phase composition and microstructure of deposited products. Nano-sized UO2 and U metal particles were successfully obtained by constant potential and current electrolysis. The results of this work further reveal the electrochemical behavior and reduction mechanism of ions in molten LiCl-KCl, providing a guiding ideology for the pyrochemical reprocessing of oxide spent fuels.

Plasma-Made Nanogold for DNA Sensing with SERS

Facilitated electrochemical properties of plasma are crucial for improving functional nanomaterials synthesis and design for novel sensor development. Controlled customization and functionality tailoring at multiscale is the targeted challenge for better detection devices performance. In the modern era of optoelectronics, among various probing approaches, plasmonic sensing accompanied by Raman, FTIR or Fluorescent spectroscopy is considered a tool for the efficient investigation of molecular properties. In particular, Raman scattering is often called SERS (surface-enhanced Raman scattering) due to plasmonic enhancers, which are used to improve the probing of analytes at a reduced scale. This feature is extremely useful for biologically relevant analytical tasks when samples alike DNA and similar need to be investigated fast and accurately. DNA/RNA-related investigations are highly important in modern nanomedicine due to the solid progress of bionanotechnology, DNA vaccines, and functional gene engineering. DNA is the most valued substance for microbiologists because it contains information about bio-species' nature.[1] Currently, the number of molecular-sensitive methods for DNA-level study is quite limited, among which PCR (polymer chain reaction) related methods dominate the field. However, it is challenging to investigate it with optical techniques like SERS. Despite being promising, SERS is still under technological and analytical improvement. Better performance comes with sophisticated plasmonic nanomaterials, which provide considerably improved photon scattering due to the strongly localized field confinement effect.[2] In the current report, a well-performing nanoplasmonic sensor was designed using a plasma-driven electrochemical reduction mechanism. Exploiting atmospheric pressure He-plasma jet setup operating kHz frequency, the reactive oxidative species donated electrons via liquid-gas electrochemistry towards the Ar-delivered Au(3+)-containing microdroplets. Through this method, microscaled aggregates composed of AuNPs were obtained from the nebulized ionic gold liquid precursor. Due to the strong coupling between nanoparticles, a high analytical enhancement factor of about 107 was achieved and the substrate allowed to obtain Raman fingerprints of bacterial DNA fragments (M. luteus and S. aureus, E. coli, J. lividum) at nanovolume sample quantities. In addition, main DNA molecular vibrational signatures associated with nucleobase motions were extracted from spectra collected and used to classify the bacterial strains reliably by employing statistical principal component analysis.

Mechanistic study of lodenafil carbonate electrochemical reduction in acid medium

The electrochemical reduction mechanism of lodenafil carbonate in acidic medium was studied using cyclic voltammetry, square wave voltammetry and chronoamperometry (sulfuric acid 0.1 mol L-1, potential controlled at -1.2 V). The formed product characterization was carried out by FT-IR spectroscopy combined with quantum calculations of the lodenafil molecular orbitals. Over the products IR spectrum, it was possible to note the presence of absorption bands corresponding to the aldehyde, amine and ethanol groups. These results, together with those obtained by electrochemical techniques and quantum calculations, allowed us to propose that the process of reducing lodenafil is dependent on protons and occurs in four irreversible steps, the first being the amide group reduction to an aldehyde and a primary amine. Then, the aldehyde is reduced to an alcohol, with the consumption of two electrons and two protons in each of these steps. Then, there is a reduction in two processes of one electron and one proton each, one of which by a radical way. In this last process, there are two possibilities: one is the sulfone group reduction and the other is the azomethine reduction adjacent to the amine group formed in the previous step.

Effect of Reaction Temperature on the Molten Salt Electrodeposition of Silicide Coating on Molybdenum Substrate and its Oxidation Behavior

In this study, silicide coatings were successfully prepared on Mo substrates using NaCl-KCl-NaF molten salt as the reaction medium and K2SiF6 as the silicon source. The electrochemical reduction mechanism of Si(IV) was studied by cyclic voltammetry and chronoamperometry technology. The effect of reaction temperature on the phase composition, microstructure, and growth kinetics of the electrodeposited coatings were investigated in detail. The long-term oxidation behaviors of Mo and MoSi2-coated Mo samples at 873 K were also compared. The results revealed that the electrodeposition of silicide coatings was closely related to the reaction temperature. Dense and coherent single-layer MoSi2 coatings could be obtained at 1023 K and 1073 K, while double-layer coatings with inner MoSi2 layer and outer Si layer could be obtained at 1123 K. Under the same electrodeposition time, the overall thickness of the silicide coatings increased with the reaction temperature. Moreover, long-term oxidation tests at 873 K proved that MoSi2 coatings could effectively prevent the Mo substrate from oxidation. The mass gain of the MoSi2-coated Mo sample was only 0.46 wt% after 500 h of oxidation, which could be attributed to the formation of the continuous SiO2 protective layer.

Improved performance of electrochemical reduction of CO2 to HCOOH by Cu incorporation into the supported Au monolayer on tungsten carbide: A DFT study

Electrochemical reduction of CO2 into useful chemicals and fuels is a promising strategy to achieve carbon neutrality and storage of renewable electricity. But the realization of industrial application of this technology is hindered by the high energy consumption and low product selectivity. Using the first-principles methods, we explored the mechanism of electrochemical reduction of CO2 on Cu1Au8/WC(0001), in comparison with that on AuML/WC(0001) and CuML/WC(0001). The calculated results showed that incorporating of Cu into Au monolayer significantly enhanced the electrochemical adsorption of CO2, promoting the generation of HCOOH on the alloy surface. Electronic properties such as charge density differences (CDD), Bader charges and density of states (DOS) were investigated to reveal the intrinsic physical origin of the enhanced interaction between OCHO and the catalyst, which results in the improvement in the selectivity and reactivity of CO2 reduction to formic acid (HCOOH) on Cu1Au8/WC(0001). Cu1Au8/WC(0001) was confirmed to be a promising bifunctional catalyst for the efficient conversion of toxic CO to CO2 and selectively reduction of CO2 to useful value-added chemical HCOOH. This work provides a clue to design supported alloy catalysts with high product selectivity and catalytic activity for CO2RR.

Controllable synthesis of diazocine - investigation on electroreduction mechanism for intramolecular cyclization of 2,2′- dinitrodibenzyl in the presence of CO2

11,12-dihydrodibenzo[c,g][1,2]diazocine (Diazocine, 12), a molecular switch capable of reversible interconversion between (at least) two states by light, has been widely used in pharmacology and biochemistry. However, most of the synthetic methods so far have been limited by tedious steps, complicated derivatives, and long reaction times, resulting in poor synthetic yields of 12. Here, we propose a green, effective, and controllable strategy for synthesizing 12. The intramolecular cyclization (8-membered ring) of 2,2′-dinitrodibenzyl (1) was achieved by electrochemical reduction in the presence of CO2, and 12 and its derivatives 11,12-dihydrodibenzo[c,g][1,2]diazocine-N-oxide (DDCG-N, 11) were synthesized. The electrochemical reduction mechanism of 1 in the presence of CO2 was investigated by cyclic voltammetry (CV) and in situ FT-IR spectroelectrochemistry. The molecular structures of the electrolytic product (12) and intermediate (11) were confirmed by single-crystal X-ray diffraction, NMR, and MS. The results show that the electrochemical behavior of 1 in acetonitrile (AN) changes from a reversible two-step 1-electron transfer process (in the absence of CO2) to an irreversible 8-electron transfer process (in the presence of CO2). The 12 and 11 can be obtained by controlling the electrolytic potential and time. Under the optimum conditions, the yields of 12 and 11 were 84% and 71%, respectively.

An interactive study of catalyst and mechanism for electrochemical CO2 reduction to formate on Pd surfaces

Electrochemical CO2 reduction reaction to formate (CO2RRTF) on Pd-based surfaces merits very low overpotentials, yet is challenged with identification of a high-performance catalyst and validation of the reaction pathway. In this work, an interactive study of catalyst and mechanism is presented to address the above bottleneck. On one hand, inspired by preliminary mechanistic understanding of HCOOH ↔ CO2 interconversion at Pd surfaces, a Bi-modified Pd/C with the known high performance towards formic acid dehydrogenation (FAD) is elected as the prototype candidate catalyst for CO2RRTF, exhibiting indeed significantly higher activity, selectivity, durability and extended working potentials. On the other hand, the CO2 chemical hydrogenation mechanism is clarified with monodentate formate being the key intermediate for CO2RRTF on Pd surfaces, by applying isotope labeled ATR-SEIRAS measurement and kinetic analysis in conjunction with DFT calculations. The research paradigm facilitates locating efficient catalysts and advancing mechanistic study for CO2RRTF on Pd surfaces and beyond.

Study on electrochemical reduction mechanism of p-nitrophenylacetic acid prepared by electrocarboxylation

The direct carboxylation of organic halides under CO2 atmosphere by electrochemical reduction is an effective way to realize the value utilization of waste (CO2), and has great potential in green organic synthesis. P-nitrophenylacetic acid is a chemical raw material in great demand, which can be used not only in medicine and other organic synthesis intermediates but also in biochemical research. In this paper, the electrochemical reduction mechanism of p-nitrobenzyl bromide (PNBB) in N2 and CO2 atmosphere was investigated by cyclic voltammetry (CV), in-situ FT-IR spectroelectrochemistry, and bulk electrolysis experiments. Under N2 conditions, the electrochemical behavior of PNBB in aprotic acetonitrile solvent is a 1-electron irreversible transfer process. However, in the presence of CO2, it is a completely irreversible 2-electron transfer process. The electrolytic products were analyzed by 1H NMR, 13C NMR and MS. The results showed that the electrolytic products were 1,2-bis(4-nitrophenyl) ethane and p-nitrophenylacetic acid under N2 and CO2 conditions, respectively. The successful preparation of p-nitrophenylacetic acid provides more possibilities for the “green” synthesis of helpful chemical products from organic halides.