Electrosynthesis is a popular, green alternative to traditional organic methods. Understanding the mechanisms is not trivial yet is necessary to optimize reaction processes. To this end, a multitude of analytical tools is available to identify and quantitate reaction products and intermediates. The first portion of this review serves as a guide that underscores electrosynthesis fundamentals, including instrumentation, electrode selection, impacts of electrolyte and solvent, cell configuration, and methods of electrosynthesis. Next, the broad base of analytical techniques that aid in mechanism elucidation are covered in detail. These methods are divided into electrochemical, spectroscopic, chromatographic, microscopic, and computational. Technique selection is dependent on predicted reaction pathways and electrogenerated intermediates. Often, a combination of techniques must be utilized to ensure accuracy of the proposed model. To conclude, future prospects that aim to enhance the field are discussed.

Electrochemical dehalogenation of polyhalogenated compound is an inefficient process as the working electrode is passivated by the deposition of short-chain polymers that form during early stages of electrolysis. Herein, we report use of 1,1,1,3,3,3-hexaflouroisopropanol (HFIP) as an efficient reagent to control C–H formation over radical association. Debromination of 1,6-dibromohexane was examined in the presence of Ni(II) salen and HFIP as the electrocatalyst and hydrogen atom source, respectively. Electrolysis of 10 mM 1,6-dibromohexane and 2 mM Ni(II) salen in the absence of HFIP yields 50% unreacted 1,6-dibromohexane and ~40% unaccounted for starting material whereas electrolysis with 50 mM HFIP affords 65% n-hexane. The mechanism of hydrogen atom incorporation was examined via deuterium incorporation coupled with high-resolution mass spectrometry, and density functional theory (DFT) calculations. Deuterium incorporation analysis revealed that the hydrogen atom originated from the secondary carbon of HFIP. DFT calculations showed that the deprotonation of hydroxyl moiety of HFIP, prior to the hydrogen atom transfer, is a key step for C-H formation. The scope of electrochemical dehalogenation was examined by electrolysis of 10 halogenated compounds. Our results indicate that through the use of HFIP, formation of short-chain polymers is no longer observed and monomer formation is the dominant product.

Metrics & MoreArticle Recommendations CONSPECTUS:The enhanced catalytic properties of alloy nanostructures have made them a focus of extensive research in the field of catalysis. Alloy nanostructures can be classified into two types: disordered alloys (also known as solid solutions) and ordered intermetallics. The latter are of particular interest as they possess long-range atomic scale ordering, which leads to well-defined active sites that can be used to accurately assess structure−property relationships and their impact on (electro)catalytic performance. While many ordered intermetallics (OICs) have been synthesized and evaluated as electrocatalysts, there is still a lack of understanding on how the local structure of atoms controls their catalytic performance. Ordered intermetallics are difficult to synthesize and often require high-temperature annealing for the atoms to equilibrate into ordered structures. High temperature processing results in aggregated structures (usually >30 nm) and/or contamination from the support, which can decrease their performance and preclude these materials from being used as model systems for elucidating insight into structure and electrochemical properties. Therefore, alternative methods are required to enable more efficient atomic ordering while maintaining some level of morphological control.This Account delves into the potential of electrochemical methods as a practical alternative for synthesizing ordered intermetallics at lower temperatures. Specifically, it explores the viability of electrochemical dealloying and electrochemical deposition to synthesize Pd−Bi and Cu−Zn intermetallics at room temperature and atmospheric pressure. These methods have proven useful in synthesizing phases that are typically inaccessible under ambient conditions. The high homologous temperatures at which these materials are synthesized provide the necessary atomic mobility required for equilibration and formation of ordered phases, thus making the direct synthesis of ordered intermetallic materials at room temperature by electrochemical means a reality. Beyond synthesis, the electrocatalytic performance of these intermetallics was assessed for the oxygen reduction reaction (ORR), which is an important process employed in fuel cells. The OICs displayed increased performance with respect to commercial Pd/C and Pt/C benchmarks because of lower coverages of spectator species. Furthermore, these materials exhibited improved methanol tolerance.This Account provides valuable insights into the electrochemical synthesis of ordered intermetallics and their potential use as highly effective catalysts for electrocatalytic reactions. By using electrochemical methods, it is possible to obtain ordered intermetallics with unique atomic arrangements and tailored properties, which can be optimized for specific catalytic applications. With further research, electrochemical synthesis methods may enable the development of new and improved ordered intermetallics with even higher catalytic activity and selectivity, m...

No abstract

In recent decades, nanoparticles have become a prominent research topic due to their increased catalytic activity, which is attributed to their high surface areas. Although typical synthesis methods yield highly ordered monodispersed particles, they often require harsh synthesis conditions, such as high pressure or temperatures, and the use of high-purity reagents. Moreover, these syntheses are conducted on a microliter basis and are not easily scaled-up.1 Electrochemistry offers an alternative approach for the synthesis of nanoparticles under mild conditions, since most metal reduction potentials occur at less than 2 V. One of the earliest attempts at the electrosynthesis of nanoparticles was conducted by Reetz et al.2 In their work, a palladium sheet was stripped and then reduced ions at a platinum sheet to form nanoparticles. However, these nanoparticles were not monodispersed, and therefore not ideal for catalysis. In the present work, copper nanoparticles have been synthesized in bulk via oxidation of a copper wire into a 99.7:2.3 nitromethane-water solution in the presence of an acid. A copper wire was stripped into solution and monitored via chronocoulometry. Once oxidized, copper ions were stabilized with polyethylene glycol and diffused to the cathode where they underwent electrochemical reduction with the aid of a sonic probe, which dispersed uniform-sized nanoparticles into solution. The size of these nanospheres can be controlled to range from approximately 2 nm to 250 nm due to different amounts of surfactant and copper in solution. In addition, other nanoparticle shapes, namely nanospheres and nanocubes, were obtained when the acid was changed from perchloric acid to hydrochloric acid. These changes in composition of the electrolyte allow for control over the shape and size of nanoparticles. This new method for electrosynthesis of nanoparticles allows for their shape and size control, which can be useful for large-scale, industrial purposes. References Gawande, M.B., Goswami, A., Felpin, F., Asefa, T., Huang, X., Silva, R., Zou, X., Zboril, R., Varma, R. S., Cu and Cu-Based Nanoparticles: Synthesis and Applications in Catalysis. Rev. 2016, 116, 3722–3811. Reetz, M.T. , Helbig W., Size-Selective Synthesis of Nanostructured Transition Metal Clusters. Am. Chem. Soc. 1994, 116, 7401–7402.