Electrosynthesis at an industrial scale offers an opportunity to use renewable electricity in chemical manufacturing, accelerating the decarbonization of large-scale chemical processes. Organic electrosynthesis can improve product selectivity, reduce reaction steps, and minimize waste byproducts. Electrochemical synthesis of adiponitrile (ADN) via hydrodimerization of acrylonitrile (AN) is a prominent example of industrial organic electrochemical processes, with annual production reaching 0.3 MMT. It circumvents the drawbacks of thermochemical synthesis by reducing toxicity and leveraging clean electricity as an energy source. Despite its industrial importance, mechanistic understanding and experimental insights on the near-electrode molecular processes of AN electrohydrodimerization remain insufficient. Here we show, using in situ ATR-FTIR spectroscopy, that tetraalkylammonium ions populate the electrical double layer (EDL), creating a microenvironment that favors interactions with organic molecules and enhances AN concentration while expelling water molecules. Our results provide experimental evidence supporting long-standing mechanistic hypotheses. Kinetic isotope effect studies reveal that propionitrile (PN) formation is rate-limited by proton transfer, while ADN formation likely is not. Electron paramagnetic resonance spectroscopy confirms the presence of free radicals during AN electroreduction, suggesting that coupling of PN radicals occurs primarily in the electrolyte. These insights highlight the importance of carefully controlling the EDL composition for selective organic electrosynthesis and provide fundamental engineering guidance for designing high-performing electro-organic reactions. We anticipate these findings will guide the optimization of electrolyte formulations and electrode interfaces for ADN synthesis and other emerging electro-organic processes.

Electrochemistry can enable sustainable chemical manufacturing but is limited by the reactions possible with conventional metal electrodes. Plasma electrochemistry, which replaces a conventional solid electrode with plasma in electrochemical cells, opens new avenues for chemical synthesis by combining Faradaic and non-Faradaic processes at the plasma-liquid interface. To understand how plasma electrochemistry differs from conventional electrochemistry, we investigated plasma reactions with acrylonitrile, an industrially relevant molecule used as the precursor in the well-characterized electrosynthesis of adiponitrile. We demonstrate that non-Faradaic processes dominate plasma-driven chemistry through systematic variation of plasma polarity, current, and reactant concentration, combined with comprehensive quantitative analysis of solid, liquid, and gas products. Most notably, we observed no adiponitrile formation (the desired electrochemical product), while total product yields exceeded the theoretical charge-transfer maximum by up to 32-fold. Substantial polyacrylonitrile formation occurred under all conditions, a product not typically seen in conventional electrochemistry. The plasma anode produced consistently higher yields than the plasma cathode, generating hydrogen and propionitrile at 21 and 2 times the charge-transfer maximum, respectively. Electron scavenger experiments confirmed these transformations occurred primarily through non-Faradaic processes rather than charge transfer. These results demonstrate that plasma electrochemistry with acrylonitrile is primarily driven by non-Faradaic processes at plasma-electrolyte interfaces, providing fundamental insights for harnessing these interactions in chemical synthesis.

Electrosynthesis at an industrial scale offers an opportunity to use renewable electricity in chemical manufacturing, accelerating the decarbonization of large-scale chemical processes. Organic electrosynthesis can improve product selectivity, reduce reaction steps, and minimize waste byproducts. Electrochemical synthesis of adiponitrile (ADN) via hydrodimerization of acrylonitrile (AN) is a prominent example of industrial organic electrochemical processes. It circumvents the drawbacks of thermochemical synthesis by reducing toxicity and leveraging clean electricity as an energy source. Despite its industrial importance, mechanistic understanding and experimental insights on the near-electrode molecular processes of AN electrohydrodimerization remain insufficient. Here we show, using in-situ ATR-FTIR spectroscopy, that tetraalkylammonium ions populate the electrical double layer (EDL), creating a microenvironment that favors interactions with organic molecules and enhances AN concentration while expelling water molecules. Our results provide experimental evidence supporting long-standing mechanistic hypotheses. Kinetic isotope effect studies reveal that propionitrile (PN) formation is rate-limited by proton transfer, while ADN formation likely is not. Electron paramagnetic resonance spectroscopy confirms the presence of free radicals during AN electroreduction, suggesting that coupling of PN radicals occurs primarily in the electrolyte. These insights highlight the importance of carefully controlling the EDL composition for selective organic electrosynthesis and provide fundamental engineering guidance for designing high-performing electro-organic reactions. We anticipate these findings will guide the optimization of electrolyte formulations and electrode interfaces for ADN synthesis and other emerging electro-organic processes.

Electrochemistry can enable sustainable chemical manufacturing but is limited by the reactions possible with conventional metal electrodes. Plasma electrochemistry, which replaces a conventional solid electrode with plasma in electrochemical cells, offers new avenues for chemical synthesis by combining charge transfer with alternative energy transfer processes at the plasma-liquid interface. To understand how plasma electrochemistry differs from conventional electrochemistry, we investigated plasma reactions with acrylonitrile, an industrially relevant molecule used as the precursor in the well-characterized electrosynthesis of adiponitrile. We demonstrate that non-charge transfer processes dominate plasma-driven chemistry through systematic variation of plasma polarity, current, and reactant concentration, combined with comprehensive quantitative analysis of solid, liquid, and gas products. Most notably, we observed no adiponitrile formation (the desired electrochemical product) while total product yields exceeded the theoretical charge-transfer maximum by up to 32-fold. Substantial polyacrylonitrile formation occurred under all conditions, a product not typically seen in conventional electrochemistry. The plasma anode yielded consistently higher products than the plasma cathode, producing hydrogen and propionitrile at 21 and 2 times the charge-transfer maximum, respectively. Electron scavenger experiments confirmed these transformations occurred primarily through non-Faradaic processes rather than charge transfer. These results demonstrate that plasma electrochemistry is primarily driven by energy transfer at plasma-electrolyte interfaces, providing fundamental insights for harnessing these interactions in chemical synthesis.

The industrial sector, particularly chemical manufacturing, is a significant contributor to global greenhouse gas emissions, with traditional processes primarily fueled by fossil fuels and operating under high temperatures and pressures. Introducing electrosynthesis at an industrial scale offers a promising avenue for integrating renewable electricity in chemical manufacturing, thus accelerating the decarbonization of large-scale chemical processes. This is especially pertinent in the production of Nylon 6,6, a key polymer reliant on adiponitrile (ADN) as a crucial intermediate. The dominant thermochemical production of ADN is not only energy-intensive but also employs hazardous reagents, such as HCN, highlighting the need for more sustainable production methods such as the electrochemical hydrodimerization of acrylonitrile (AN). Our research focuses on improving the performance and fundamentally understanding the electrochemical production of ADN from AN, one of the largest electro-organic reaction practiced in industry. In this reaction, the addition of tetraalkylammonium (TAA) salts as supporting electrolytes in moderate concentrations can enhance the solubility of organic reactants. By manipulating the molecular size and concentration of TAA ions, we observed an improvement in ADN selectivity and production efficiency, primarily influenced by the mass transport of organic reactants to the electrical double layer (EDL). 1,2 To better understand the local effects of TAA ions at the electrode/electrolyte interface, we combined an electrochemical flow cell with attenuated total reflection Fourier-transform infrared (FTIR) spectroscopy. This approach revealed that TAA ions significantly increase the local concentration of AN near the electrode, which is influenced by the applied cathodic potentials and correlates with improved ADN selectivity. Additionally, we investigated the reaction mechanism of ADN synthesis using kinetic isotope effect (KIE) studies and electron paramagnetic resonance (EPR) spectroscopy. Results from KIE studies suggest that hydrogen transfer to AN is a rate-determining step in ADN production. EPR spectroscopy further revealed the presence of alkyl radicals in the solution, suggesting that ADN production partially occurs through the coupling of free AN radicals in solution. These insights can help in the design of electrolytes and the understanding of molecular processes that govern the selectivity and efficiency of ADN production via AN electrohydrodimerization and can inform the development and optimization of other electro-organic manufacturing processes. References 1. Blanco, D. E., Dookhith, A. Z. & Modestino, M. A. Enhancing selectivity and efficiency in the electrochemical synthesis of adiponitrile. Reaction Chemistry & Engineering 4 , 8-16, doi:10.1039/c8re00262b (2019). 2. Blanco, D. E., Lee, B. & Modestino, M. A. Optimizing organic electrosynthesis through controlled voltage dosing and artificial intelligence. Proc Natl Acad Sci U S A 116 , 17683-17689, doi:10.1073/pnas.1909985116 (2019). Figure 1

Environmental and societal pressures are demanding a transition from fossil-based resources to renewable and sustainable feedstocks for the production of materials. In this context, biomass streams emerge as scalable candidates for creating sustainable chemicals. Electrocatalytic transformation of biomass can facilitate the production of chemicals under mild conditions and can be easily integrated with renewable energy sources. These transformations could lead to the production of sustainable monomers and polymers from biomass, significantly enhancing the sustainability of plastics production. Amongst a large number of plastics manufactured by the chemical industry, Nylon 6,6 is one of the most important fossil-derived polymers for the production of high-performance textiles and structural materials. Central to Nylon 6,6 production is adiponitrile (ADN), predominantly synthesized via energy-intensive thermochemical processes. An alternative route, electrochemical hydrodimerization of acrylonitrile (AN), although successful, still depends on fossil feedstocks. A promising sustainable source for ADN is renewable glutamic acid, derived from hydrolysis of waste proteins. 1,2 This process involves transforming glutamic acid to 3-cyanopropanoic acid (CPA) and then to ADN through Kolbe electrolysis, a reaction with a historical background and multiple pathways. Our study utilizes an electrochemical reaction engineering approach to examine the Kolbe electrolysis of CPA to ADN and AN, focusing on a hierarchical research methodology. This approach allowed us to simultaneously accelerate the exploration of numerous reaction parameters while also conducting detailed studies under optimal conditions. This method has enabled us to gain deeper insights into the factors controlling reaction selectivity. We discovered that platinum electrodes favor ADN formation, with selectivity increasing at higher current densities. Optimal CPA concentrations, the presence of larger alkali cations, solvent composition, and controlled pH levels significantly influence ADN production, reducing side reactions such as the oxygen evolution reaction (OER). When using graphite electrodes, an increase in AN production was observed, with the solvent composition playing a crucial role in determining the rate of ADN formation. Our investigation has led to a deeper understanding of the electrochemical conversion of CPA to ADN, revealing key parameters that influence reaction selectivity and rate. The insights obtained from this study are not only pivotal for the specific case of ADN production but also have broader implications for a range of electrochemical decarboxylation reactions. The hierarchical research approach employed here demonstrates its potential for speeding the development of sustainable electrochemical processes. Our insights and methodology used for the electrosynthesis of ADN from biomass-derived feedstocks can be deployed to the deployed to the development of other biomass transformations advancing our ability to produce essential chemicals sustainably. References 1. Tuck, C. O., Pérez, E., Horváth, I. T., Sheldon, R. A. & Poliakoff, M. Valorization of biomass: deriving more value from waste. Science 337 , 695-699 (2012). 2. Dai, J. J., Huang, Y. B., Fang, C., Guo, Q. X. & Fu, Y. Electrochemical synthesis of adiponitrile from the renewable raw material glutamic acid. ChemSusChem 5 , 617-620, doi:10.1002/cssc.201100776 (2012). Figure 1

Electrochemical transformation of biomass feedstocks offers a promising route for sustainable production of fuels and chemicals, enhancing integration with renewable energy sources. Adiponitrile, a key intermediate in Nylon 6,6 production, is mainly produced through thermochemical processes or methods relying fossil fuel feedstocks. Alternatively, it can be produced through Kolbe coupling of biomass-derived 3-cyanopropanoic acid, with its practical implementation hinging on understanding and controlling factors that dictate reaction selectivity. In this study, we establish relationships between electrolyte composition, electrochemical conditions, and performance metrics in this approach, achieving a maximum Faradaic efficiency of 40% towards adiponitrile at current densities up to 500 mA cm-2. Implementing a semi- autonomous high-throughput electrochemical workflow, we tested hundreds of reaction conditions, accelerating the exploration of reaction parameters. Limitations and guidelines obtained from this study apply to a range of electrochemical decarboxylation reactions, and the accelerated research approach shows potential for speeding the development of sustainable electrochemical processes.

Electrochemical synthesis of organic chemical commodities provides an alternative to conventional thermochemical manufacturing and enables the direct use of renewable electricity to reduce greenhouse gas emissions from the chemical industry. We discuss electrochemical synthesis approaches that use abundant carbon feedstocks for the production of the largest petrochemical precursors and basic organic chemical products: light olefins, olefin oxidation derivatives, aromatics, and methanol. First, we identify feasible routes for the electrochemical production of each commodity while considering the reaction thermodynamics, available feedstocks, and competing thermochemical processes. Next, we summarize successful catalysis and reaction engineering approaches to overcome technological challenges that prevent electrochemical routes from operating at high production rates, selectivity, stability, and energy conversion efficiency. Finally, we provide an outlook on the strategies that must be implemented to achieve large-scale electrochemical manufacturing of major organic chemical commodities.

Traditional chemical manufacturing processes are primarily powered by fossil-fuel combustion, and often require operation at elevated temperatures and pressures. Introducing electrosynthesis as an alternative to thermal processes at industrial scale can allow direct integration of renewable electricity with chemical manufacturing, accelerating the decarbonization of large-scale chemical processes. However, there are major challenges that must be addressed before implementing organic electrosynthesis on an industrial level, such as the low solubility of organic reactants in aqueous electrolytes and the existence of multiple reaction pathways that lead to undesired byproducts. In this presentation, we will discuss our work on electrolyte design strategies to enhance the performance of adiponitrile (ADN) electrosynthesis. ADN is a large volume precursor of hexamethylenediamine, which is a monomer used in Nylon 6,6 manufacturing. The most commonly used method for ADN production, the thermochemical hydrocyanation of 1,3-butadiene, is energy intensive and uses hydrogen cyanide, a highly toxic reactant. Alternatively, ADN can be produced electrochemically via the hydrodimerization of acrylonitrile (AN), which is the largest and most successful industrial organic electrochemical process. In this reaction, the addition of tetraalkylammonium (TAA) salts as supporting electrolytes in large concentrations has been widely accepted to enhance the solubility of organic reactants. It has been hypothesized that TAA ions boost the selectivity towards ADN by increasing the AN concentration in the electrical double layer (EDL). Recent studies by our group explored the effect of the molecular size and concentration of TAA ions on the selectivity and efficiency of ADN production. Resulting trends suggest that the reaction is strongly limited by mass transport of organic reactants to the EDL at high current densities. Despite these advances, the local effects of TAA ions on the concentration of reactants and intermediates in the EDL remain unclear. Inspired by prior demonstrations, we developed a spectroelectrochemical method for quantitatively assessing the concentration of species at the electrode/electrolyte interface. This method relies on an electrochemical flow cell integrated with an attenuated total reflection (ATR) Fourier-transform infrared (FTIR) spectrometer to quantify concentrations of reactive species in the near-electrode region. Our results demonstrate that the presence of TAA ions increases the local concentration of AN at the electrode, and that applied potential increases TAA ion concentration. These results provide insights into the effects of supporting ions and potential in organic electrosynthesis selectivity. Figure caption: Schematic view of the enhancement of acrylonitrile (AN) concentration in the electrical double layer (EDL) by the addition of Tetrabutylammonium (TBA) ions to the aqueous electrolyte. Figure 1

In this issue of Chem Catalysis, Zhang et al. describe a method to electrochemically hydrogenate nitriles to primary amines on nanostructured copper electrocatalysts. Through the implementation of CO2-saturated electrolytes, the primary amines are reversibly converted to carbamic acids or carbamates, which prevents their condensation into secondary or tertiary amines.

Dispersing two-dimensional VOx species on β-SiC offers a new approach to scale up propane ODH.