Direct Electrochemical Synthesis Research Articles

Electrochemical methods for synthesis and in situ generation of organometallic compounds

• Electrochemical methods have been used for the preparation of organometallic compounds. • Main electrochemical synthetic and analytical methods and types of the electrochemical cells are described. • The electrochemically generated high-reactive organometallic species have been used in situ as the reagents for the synthesis of organic and organoelement compounds. • The application of in situ spectroelectrochemical methods for elucidating of the nature of organometallic intermediates formed in the electrochemical process and their application for the activation of organometallics for catalytical purposes are discussed. The electrochemical methods have a huge synthetic potential in both academia and industry. However, the implementation of electrochemistry for the synthesis of organometallic compounds is presented limitedly, while the sustainability and greenness of the electrochemical protocols allow considering them as a very promising and intriguing approach. This review summarizes the most important and practically useful advances in the electrochemistry of organometallics with the emphases on the direct electrochemical synthesis of organometallic derivatives by the formation of a carbon–metal bond, electrosynthesis of organic compounds mediated by in situ generated organometallics as well as cyclic voltammetry and related techniques, applied for analysis and preparation of organometallic compounds.

Direct electrochemical synthesis of the copper based metal-organic framework on/in the heteroatoms doped graphene/pencil graphite electrode: Highly sensitive and selective electrochemical sensor for sertraline hydrochloride

Abstract In this study, a simple and innovative electrochemical method was utilized for the synthesis of the copper based metal-organic framework (Cu-MOF)/sulfur and nitrogen co-doped graphene (SNDGr) nanocomposite on the pencil graphite electrode (PGE) and developing of an electrochemical sensor for determination of sertraline hydrochloride (STLHC); an antidepressant drug. Firstly, the SNDGr was simply synthesized through the electrochemical exfoliation of PGE by using potentiostatic procedure in the mixture solution of melamine and ammonium sulfate. Thereafter, the Cu-MOF was also electrochemically deposited on/in SNDGr/PGE using chronoamperometry technique. The as-fabricated modified electrode (Cu-MOF/SNDGr/PGE) was characterized through relevant instrumental methods (scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray powder diffraction, and electrochemical techniques). The designed modified electrode exhibited excellent electrocatalytic activity for the oxidation of STLHC compared with bare PGE, SNDGr/PGE and Cu-MOF/PGE due to its high specific surface area, high conductivity and fast charge transfer ability of the nanocomposite. The experimental results demonstrated that the present modified electrode has a promising potential as a stable and efficient electrochemical sensor for determination of STLHC. Under the optimized experimental condition, the designed sensor responds efficiently to STLHC over the concentration range of 0.05 to 2.67 µM with a low detection limit (0.038 μM), high selectivity, good sensitivity (0.4557 μA/μM cm2) and repeatability. Further, the suggested sensor was successfully employed for the determination of STLHC in real samples with suitable recovery values.

Roles of Interface and Surface of Electrode Catalysts in Ammonia Electrochemical Synthesis with Proton-Conducting Ceramic Fuel Cells

Investigation of energy carriers is of critical importance for chemical energy storage and transport technologies in combination with the large-scale utilization of renewable energy. Ammonia is a promising energy carrier in terms of carbon-free fuel, high energy density, and easy liquefaction (1).Electrochemical approaches can provide a more efficient reaction process and allow more flexible operations for ammonia production, compared with the industrial Haber–Bosch process. In this study, we investigated direct electrochemical synthesis of ammonia using proton-conducting ceramic fuel cells (PCFCs) operating at high temperatures around 773 K. A ceramic proton conductor, BaCe1-xYxO3 (BCY), was used for an electrolyte membrane.In our previous studies, metal catalysts of Ru and Fe were investigated with a variety of electrode structures such as metal nanoparticle (2, 3) and cermet electrode (4). In terms of metal nanoparticle catalyst, Ru-doped BCY (BCYR) was examined (2,3). The ammonia formation rate was not so high with BCYR (ca. 10-11 mol/s cm2). To improve the ammonia formation rate, Ru-BCY and Fe-BCY (or K-Al-Fe-BCY) cermet electrodes were investigated. When pure N2 was supplied to the cathode, low ammonia formation rate was observed (ca. 10-11 mol/s cm2). When a N2/H2 gaseous mixture was supplied to the cathode, higher ammonia formation rate was observed; ammonia formation rate with Fe-BCY electrode was increased up to ca. 10-10 mol/s cm2 with an increase in cathodic polarization. In addition, our recent study showed a significant improvement of ammonia formation rate with pure Fe electrode (ca. 10-8 mol/s cm2) (5). Considering the above, the roles of interface and surface of electrode catalysts on ammonia electrochemical synthesis should be investigated for clarifying the reaction mechanism and developing effective cell design. In this study, we conducted the deuterium isotope analysis for ammonia electrochemical synthesis to investigate the contributions of interface between electrode and electrolyte, i.e., triple-phase boundary, and electrode surface for ammonia formation processes as well as relevant kinetic measurements of ammonia formation on Fe catalyst (Fig. 1a).The cell configuration was Pt|BCY|Fe-BCY for a cermet electrode. Also, Pt|BCY|Fe cell with pure iron electrode was fabricated to investigate the ammonia formation mechanism. Ammonia formation rate was measured with the configuration of Pt, H2 H2O-Ar |BCY|Fe, H2-N2. Ammonia formed in the cathode was trapped in an H2SO4 solution. Then, the obtained solution was analyzed by ion chromatography. The ammonia formation was also observed using an FTIR spectrometer with a multiple refraction cell to perform the deuterium isotope analysis.Significantly high ammonia formation rate was observed using the Pt|BCY|Fe cell: 1~6x10-8 mol/s cm2 at -1.5 V and 623 K with changing a flow rate in the cathode, which is the best performance for ammonia electrochemical formation under the H2 flow condition. This suggests that Fe surface may play a dominant role in ammonia formation rather than the triple-phase boundary between Fe and BCY. Deuterium isotope analysis was carried out with Pt, D2-H2O-Ar|BCY|Fe, H2-N2. Observed FTIR spectra showed the formation of NH3 and NH2D under the condition (Fig. 1b). The absorbance of NH2D was very weak, which suggested that most of hydrogen atoms in the ammonia molecule originated from H2 in the cathode. In the case of Pt, H2-H2O-Ar|BCY|Fe, D2-N2, ND3 was observed as a main product under the D2 flow condition in the cathode. Considering the above, the electrochemical promotion of catalyst (EPOC) for ammonia formation will be induced via promotion of N2 dissociation on Fe. N2 dissociation is the rate determining step in the ammonia formation reaction. Possible mechanism for the promotion of N2 dissociation is electron back donation with an increase in cathodic polarization. This mechanism gives a hint for designing an electrochemical reactor to promote efficient ammonia formation. Acknowledgements This work was supported by CREST, Japan Science and Technology Agency (JPMJCR1441). References D. Miura, T. Tezuka, Energy, 68(15), 428-436 (2014).J. Otomo, N. Noda, F. Kosaka ECS Trans., 68, 2663-2670 (2015).F. Kosaka, T. Nakamura, J. Otomo, J. Electrochem. Soc., 164, F1323-F1330 (2017).F. Kosaka, T. Nakamura, A. Oikawa, J. Otomo. ACS Sustainable Chem. Eng., 5(11), 10439–10446 (2017).J. Otomo, et al., 435c, 2019 AIChE Annual Meeting, Orlando, USA. Figure 1

Electrochemical Ring Expansion to Synthesize Medium-Sized Lactams Through C–C Bond Cleavage

Medium-sized nitrogen heterocycles are prevalent motifs in many kinds of bioactive molecules and natural products. Owing to the unfavorable enthalpic and entropic barriers during the transition sta...

Imaging electrochemically synthesized Cu2O cubes and their morphological evolution under conditions relevant to CO2 electroreduction

Copper is a widely studied catalyst material for the electrochemical conversion of carbon dioxide to valuable hydrocarbons. In particular, copper-based nanostructures expressing predominantly {100} facets have shown high selectivity toward ethylene formation, a desired reaction product. However, the stability of such tailored nanostructures under reaction conditions remains poorly understood. Here, using liquid cell transmission electron microscopy, we show the formation of cubic copper oxide particles from copper sulfate solutions during direct electrochemical synthesis and their subsequent morphological evolution in a carbon dioxide-saturated 0.1 M potassium bicarbonate solution under a reductive potential. Shape-selected synthesis of copper oxide cubes was achieved through: (1) the addition of chloride ions and (2) alternating the potentials within a narrow window where the deposited non-cubic particles dissolve, but cubic ones do not. Our results indicate that copper oxide cubes change their morphology rapidly under carbon dioxide electroreduction-relevant conditions, leading to an extensive re-structuring of the working electrode surface.

Potential Economic Feasibility of Direct Electrochemical Nitrogen Reduction as a Route to Ammonia

The Haber–Bosch process produces ammonia from hydrogen and nitrogen gases in a globally important energy-intensive process that uses coal or natural gas as a fuel and hydrogen source. Direct electrochemical ammonia synthesis from nitrogen and water using renewable energy sources presents an alternative to the Haber–Bosch process that would be more sustainable. Additionally, the different production structure of direct electrochemical nitrogen reduction technology suggests a supply chain alternative to the ammonia industry and a method for load leveling of the electrical grid. This alternative route to ammonia from dinitrogen would require smaller capital investments than the Haber–Bosch process and would not require a fossil fuel supply. The impact of dynamic electrical power pricing is analyzed for a system that could take advantage of pricing volatility. We show that, under certain scenarios, at achievable levels of energy efficiency with a future electrocatalyst, direct nitrogen reduction would be economically competitive or advantageous compared with Haber–Bosch-based ammonia production.

Direct Electrochemical Ammonia Synthesis from Nitric Oxide.

NO removal from exhausted gas is necessary owing to its damage to environment. Meanwhile, the electrochemical ammonia synthesis (EAS) from N2 suffers from low reaction rate and Faradaic efficiency (FE). Now, an alternative route for ammonia synthesis is proposed from exhaust NO via electrocatalysis. DFT calculations indicate electrochemical NO reduction (NORR) is more active than N2 reduction (NRR). Via a descriptor-based approach, Cu was screened out to be the most active transition metal catalyst for NORR to NH3 owing to its moderate reactivity. Kinetic barrier calculations reveal NH3 is the most preferred product relative to H2 , N2 O, and N2 on Cu. Experimentally, a record-high EAS rate of 517.1 μmol cm-2 h-1 and FE of 93.5 % were achieved at -0.9 V vs. RHE using a Cu foam electrode, exhibiting stable electrocatalytic performances with a 100 h run. This work provides an alternative strategy to EAS from exhaust NO, coupled with NO removal.

Direct Electrochemical Ammonia Synthesis from Nitric Oxide

AbstractNO removal from exhausted gas is necessary owing to its damage to environment. Meanwhile, the electrochemical ammonia synthesis (EAS) from N2 suffers from low reaction rate and Faradaic efficiency (FE). Now, an alternative route for ammonia synthesis is proposed from exhaust NO via electrocatalysis. DFT calculations indicate electrochemical NO reduction (NORR) is more active than N2 reduction (NRR). Via a descriptor‐based approach, Cu was screened out to be the most active transition metal catalyst for NORR to NH3 owing to its moderate reactivity. Kinetic barrier calculations reveal NH3 is the most preferred product relative to H2, N2O, and N2 on Cu. Experimentally, a record‐high EAS rate of 517.1 μmol cm−2 h−1 and FE of 93.5 % were achieved at −0.9 V vs. RHE using a Cu foam electrode, exhibiting stable electrocatalytic performances with a 100 h run. This work provides an alternative strategy to EAS from exhaust NO, coupled with NO removal.

Direct electrochemical synthesis of oxygenates from ethane using phosphate-based electrolysis cells.

Ethane was converted directly to acetaldehyde and ethanol by partial oxidation at 220 °C and ambient pressure using an electrolysis cell with a proton-conducting electrolyte, CsH2PO4/SiP2O7, and Pt/C electrodes. The ethane conversion and the selectivity to the products increased with the voltage applied to the cell. It was found that O species generated by water electrolysis functioned as a favorable oxidant for partial oxidation of ethane on the Pt/C anode at intermediate temperatures. The production rates of acetaldehyde and ethanol recorded in this study were significantly higher than those in preceding reports.

Catalyst-free, direct electrochemical synthesis of annulated medium-sized lactams through C–C bond cleavage

Expanding ring under green electricity: The electrosynthetic approach enabled atom-economical synthesis of challenging medium-sized lactams through a unique remote amidyl migration under exceedingly mild, transition metal- and oxidant-free conditions.

Co‐generation of Ammonia and H2 from H2O Vapor and N2 Using a Membrane Electrode Assembly

AbstractThe direct electrochemical synthesis of NH3 from nitrogen and water vapor without the use of a fossil carbon source is highly desired. This synthesis is a viable option to store energy and produce fertilizer precursors. Here, a new Pt‐free membrane electrode assembly is presented. An electrochemical membrane reactor demonstrates the feasibility of co‐generating NH3 and H2 directly from nitrogen and water vapor at ambient conditions. An unprecedented high NH3‐specific current efficiency of up to 27.5% using Ti as cathodic catalyst is reported. The co‐generation can be tuned by the balance of process parameters.

Electrochemical promotion of ammonia synthesis with proton-conducting solid oxide fuel cells

Direct electrochemical synthesis of ammonia was performed using proton-conducting solid oxide fuel cells. In this study, we investigated the effect of electrode potential on the reaction kinetics of ammonia formation with Fe- and Ru-based catalysts in detail. The cell configuration was Pt|BaCe0.9Y0.1O3 (BCY)|K-modified Fe or Ru-BCY. The ammonia formation rate of K-Ru was higher than that of K-Fe at the rest potential. However, the ammonia formation rate significantly increased by cathodic polarization for the Fe catalyst, and it showed a linear increase for the Ru catalyst, i.e., the ammonia formation rate for K-Fe significantly increased from the rest potential by several hundred times to -1.2V at 700 o C, but K-Ru showed only a five times increase. The results suggest that the addition of K into Fe-BCY and cathodic polarization can improve the ammonia formation rate because of the promotion of bond dissociation of the N molecule on the Fe catalyst. The present work provides a hint for efficient ammonia formation and contribute to further development of ammonia electrochemical synthesis with proton-conducting solid oxide fuel cells. Copyright © VBRI Press.

Direct Electrochemical Synthesis of Graphene Oxide/Cobalt Oxide Nanocomposite on Pencil Graphite Electrode for Highly Sensitive and Selective Detection of Insulin in Pharmaceutical Samples

In the present study, wholly of electrochemical methodology was used to acquire an inexpensive and stable graphene oxide/cobalt oxide nanocomposite on a pencil graphite electrode (PGE). At first, the graphene oxide (GO) nanosheets were directly synthesized at pencil graphite electrode as a carbon source via a potentiostatic method in sulfuric acid solution. Then, cobalt oxide nanoparticles (CoOxNPs) was loaded by cyclic voltammetry on the GO-coated PGE. The morphology of unmodified PGE, GO/PGE and CoOxNP/GO/PGE were characterized by scanning electron microscopy (SEM). The catalytic properties of the quickly designed sensor were used to appraise the electrochemical behavior of insulin. The electroactivity of insulin was significantly enhanced on the CoOxNPs/GO nanocomposite compared with unmodified electrode. A linear dynamic range between 0.46 to 100 nmol dm−3 were obtained with a detection limit of 0.12 nmol dm−3 and a superior detection sensitivity 0.687 μA/nmol dm−3. Also, the sensor response was not damaged by the presence of common biological intruders such as ascorbic acid, uric acid, citric acid, and glucose. Eventually, three pharmaceutical insulin samples from three different brands (Regular, Isophane, and Lansolin) were selected and analyzed. The recovery percentage suggests that the proposed sensor could be utilized in routine analysis of pharmaceutical preparations.

Materials for electrochemical ammonia synthesis.

Direct electrochemical synthesis of ammonia is proposed as a means of reducing the carbon footprint of the fertiliser industry, as well as providing new opportunities for carbon-free liquid energy storage. We review the current status of research into materials for electrochemical ammonia synthesis and evaluate the reported rates and efficiencies in terms of recent US Department of Energy targets. Surprisingly, development of electrocatalysts has only recently received much attention, and despite a number of promising rates, the target values remain distant. A number of theoretical studies suggest a range of candidate materials yet to be explored.

Understanding the high activity of mildly reduced graphene oxide electrocatalysts in oxygen reduction to hydrogen peroxide

The direct electrochemical synthesis of hydrogen peroxide (H2O2) would provide an attractive alternative to the traditional anthraquinone oxidation process for continuous on-site applications.

Direct Electrochemical Synthesis of Organocadmium Halide Complexes at Sacrificial Anode

Direct Electrochemical Synthesis of Organocadmium Halide Complexes at Sacrificial Anode

Surface Modifications of Materials by Electrochemical Methods to Improve the Properties for Industrial and Medical Applications

There are two applied electrochemical methods in our group in order to obtain advanced functional surfaces on materials: (i) direct electrochemical synthesis by electro-codeposition process and (ii) anodization of materials to form nanoporous oxide layers followed by electrodeposition of hydroxyapatite or other bioactive molecules and compounds into porous film. Electrodeposition is a process of low energy consumption, and therefore very convenient for the surface modification of various types of materials. Electrodeposition is a powerful method compared with other methods, which led her to be adopted and spread rapidly in nanotechnology to obtain nanostructured layers and films. Nanoporous thin oxide layers on titanum alloys as support for hydroxyapatite or other biomolecules electrodeposition in view of biomedical applications could be obtained by electrochemical methods. For surface modification of titanium or titanium alloys to improve the biocompatibility or osseointegration, the two steps must be fulfilled; the first is controlled growth of oxide layer followed by second being biomolecule electrodeposition into nanoporous formed titanium oxide layer.

Transition-Metal-Free and Base-Free Electrosynthesis of 1H-Substituted Benzimidazoles

A direct electrochemical synthesis of 1H-substituted benzimidazoles is described. Benzimidazole is a commonly used nitrogen heterocycle in U.S. FDA approved drugs; therefore, a direct and sustainable approach that limits chemical waste for the synthesis of substituted benzimidazoles is appealing. The electrosynthetic approach described within is able to synthesize a variety of 1H-substitubed benzimidazoles while concurrently producing H2, without a transition-metal catalyst or added bases. Furthermore, the procedure works efficiently with only simple carbon electrodes, thus avoiding commonly employed platinum and gold electrodes. This electrochemical procedure also exhibited good functional group tolerance. Desired products were achieved with up to 88% yield, illustrating the range and possible sustainability of this approach.

(Invited) Role of Ion-Conducting Membranes in Synthesis and Use of Sustainable Fuels

Replacement of conventional catalytic technologies for synthesis of sustainable, carbon-neutral fuels with direct electrochemical synthesis has a potential for big energy savings due to reduction of number of process steps and pressure/temperature. In addition, electrochemical technologies are easily scaled down to allow for low capital, modular plants that match the scale of renewable energy production. The use of these fuels in electrochemical devices opens a path to cost-effective long-term energy storage and distributed energy generation. Development of low cost, ion-selective membranes with low area specific resistance is, along with electrocatalyst development, critical for the success of such technologies. Not less important is development of membrane manufacturing methods at a practical scale. This presentation will review prospective technologies using ion-selective membranes for synthesis of carbon-neutral fuels for chemical energy storage and their use for generation of electricity (using fuel cells) and hydrogen. Advantages of electrochemical synthesis of ammonia from nitrogen and hydrogen or water compared to the conventional Haber-Bosch process will be discussed. Other processes include direct electrochemical synthesis of alcohols from CO2. The requirements to ion-selective membranes for these processes and fuel cells will be presented. The Advanced Research Projects Agency (ARPA-E) funds high risk, high reward transformational research to reduce energy related emissions, reduce imports of energy from foreign sources, improve energy efficiency across all economic sectors, and ensure US technological lead in advanced energy technologies, including electrochemical energy storage and transformation for grid scale and automotive applications. The Renewable Electricity to Fuels through Utilization of Energy-dense Liquids (REFUEL) program funds the development of transformational technologies to reduce the barriers to widespread adoption of intermittent renewable energy sources by enabling the conversion of energy from these sources, water and air to energy-dense zero-carbon liquid fuels and their use for electricity or hydrogen generation. REFUEL projects targeting various ion conducting membranes as well as related projects supported by ARPA-E through OPEN program will be highlighted.

Direct Electrochemical Synthesis of Bismuth (III) Thiolates/Dithiolates and Their Coordination Compounds

Direct Electrochemical Synthesis of Bismuth (III) Thiolates/Dithiolates and Their Coordination Compounds