Scientists have identified a hidden factor that can determine whether a chemical reaction succeeds or fails, fundamentally changing how chemical manufacturing processes can be engineered. By precisely controlling microscopic changes in acidity near electrodes, researchers at Seoul National University dramatically improved the production of valuable chemical ingredients, raising the proportion of the desired target product from approximately 16% to 97%.
The breakthrough, led by Professor Jaeyune Ryu of the Department of Chemical and Biological Engineering at the Seoul National University College of Engineering, could help make chemical manufacturing significantly safer, cleaner, and more efficient. The research team developed an innovative method that utilizes oxygen and electricity to produce critical compounds used in plastics, medicines, adhesives, and a vast array of everyday materials, all without requiring the separate addition of hazardous peroxide oxidants.
Their discovery centers on a surprisingly overlooked factor known as "local pH," which describes the microscopic acidity or alkalinity in the immediate physical surroundings of an electrode. By redesigning a specialized chemical reactor to strictly control the distance between electrodes and the dynamic movement of liquid through the system, the research team found a highly effective way to manage these localized conditions and greatly elevate the overall performance of the reaction.
The work focused heavily on two critically important families of commercial chemicals: lactones and epoxides. Lactones serve as essential starting materials for the creation of biodegradable plastics and high-performance polyurethanes, while epoxides are widely used to manufacture adhesives, protective surface coatings, and epoxy resins found ubiquitously in electronic materials. Both classes of chemicals also play indispensable roles in the production of pharmaceuticals and other specialized, high-value fine chemicals.
The findings were published in the Journal of the American Chemical Society (JACS), a premier peer-reviewed chemistry journal published by the American Chemical Society (ACS).
The Hidden Chemistry That Can Make or Break a Reaction
The groundbreaking research builds upon an established chemical technique known as organic electrosynthesis, which employs electrical energy to drive chemical reactions that produce carbon-based organic compounds. This electrochemical approach has attracted intense and growing scientific interest because it holds the potential to significantly reduce or eliminate the need for chemical oxidizing and reducing agents that are traditionally relied upon in industrial manufacturing. While such agents help chemical reactions proceed by accepting or donating electrons, many are hazardous to handle, difficult to store, and generate large quantities of unwanted chemical waste.
Until now, the vast majority of research efforts aimed at improving organic electrosynthesis have centered on familiar, macro-level factors. These include controlling the electrical voltage, carefully selecting the materials used for the electrodes, and optimizing the bulk composition of the liquid electrolyte solution in which the reactions occur.
However, Professor Ryu and his colleagues strongly suspected that an essential component was being overlooked: the microscopic chemical environment located directly adjacent to each electrode surface. This is the precise location where molecules exchange electrons and undergo complex chemical transformations. Although the surrounding bulk solution may appear uniform, conditions within this microscopic boundary layer can be dramatically different from the rest of the liquid.
One particularly critical element within this zone is pH, which measures the concentration of hydrogen ions, or protons, and determines how acidic or alkaline a substance is. During an electrochemical reaction, protons can be rapidly produced or consumed right at the electrode surfaces. If these ions are generated or removed faster than they can physically diffuse through the liquid medium, the local pH near the electrode can deviate wildly from the pH measured in the bulk solution.
The researchers discovered that these local disparities can profoundly influence several vital stages of a chemical reaction. They can alter how reactive oxygen species are formed, change the structural behavior of starting molecules, and even determine whether newly synthesized products remain chemically stable or immediately begin to break down. Consequently, a reaction can completely fail even when the overall solution appears to possess the ideal chemical conditions.
An Overlooked Problem May Affect Many Chemical Reactions
To determine whether this phenomenon was an isolated incident or part of a broader trend, the research team conducted a comprehensive review of more than 600 scientific papers on organic electrosynthesis published since 2010. Their analysis revealed that approximately 89% of those studies involved reactions at one or more electrodes where both electrons and protons were simultaneously transferred.
This finding carries significant implications for the broader field of electrochemistry. Because the coupled movement of protons and electrons inherently alters local acidity, overlooked pH gradients near electrodes likely influence a vast range of electrochemical reactions rather than just a few specialized examples.
The team also quantified just how extreme these localized chemical differences can become in practice. Even when the bulk solution was maintained at a neutral state, the researchers estimated that conditions near the cathode—the electrode where chemical reduction takes place—could reach approximately pH 11, creating a strongly alkaline environment. Conversely, the region surrounding the anode, where oxidation occurs, could drop to approximately pH 2.5, establishing a strongly acidic microenvironment.
These dramatic shifts can have severe consequences for chemical synthesis. Under such extreme conditions, the reactive oxygen species required to drive the desired reactions may become depleted or unavailable. Starting materials can alter their chemical forms, and newly created products can degrade rapidly. Simply adjusting the overall acidity of the entire solution fails to solve the underlying problem, because what dictates the success or failure of the process is the immediate environment directly adjacent to the electrodes where the chemistry actually occurs.
Making Valuable Chemicals With Oxygen and Electricity
To demonstrate the practical utility of their discovery, the scientists investigated a well-known chemical process called Baeyer-Villiger oxidation. This classic reaction introduces an oxygen atom into an organic molecule known as a ketone, effectively converting it into an ester or a lactone. Lactones are vital ring-shaped compounds that serve as fundamental building blocks for sustainable materials like biodegradable plastics and versatile polyurethanes.
Traditionally, Baeyer-Villiger oxidation often requires the addition of highly reactive oxidizing chemicals, such as peroxyacids. While effective at driving the reaction, these substances introduce significant operational hurdles regarding safe handling, hazardous chemical waste disposal, and the costly treatment of unwanted byproducts.
To circumvent these challenges, the Seoul National University team engineered an alternative, cleaner approach. Instead of supplying external oxidants from outside the system, the researchers utilized electricity to directly activate oxygen gas at an electrode surface. This electrochemical activation produced reactive oxygen species capable of seamlessly transferring oxygen atoms directly into the targeted organic molecules.
To verify the exact origin of the oxygen incorporated into the final products, the team conducted meticulous isotope-tracing experiments. These analytical tests confirmed conclusively that the oxygen atoms came directly from ambient oxygen gas rather than from the water molecules in the solvent.
The scientists also uncovered a crucial cooperative mechanism between the two electrodes in the system. At the cathode, the reduction of oxygen generates reactive oxygen species that initiate the oxygen-transfer reaction. Furthermore, hydrogen peroxide formed during this electrochemical process can be transported and converted back into reactive oxygen species at the anode. This synergistic loop helps sustain a continuous and reliable supply of the reactive chemical species necessary to keep the reaction moving forward.
However, the efficiency of this entire cooperative pathway remains tightly bound to the localized acidity near the electrodes. If the local pH drifts into extreme ranges, the chemical machinery breaks down and the process loses its effectiveness.
A Simple Reactor Redesign Boosts Selectivity From 16% to 97%
Armed with a deep understanding of the critical role played by local pH, the researchers set out to find a practical way to control it. Combining advanced computer simulations with precise electrochemical measurements, they developed a novel reactor architecture that positions the electrodes significantly closer together while forcing the electrolyte—the electrically conductive liquid carrying the reaction ingredients—to flow continuously between them.
The primary objective of this design was to prevent extreme acidity gradients from accumulating. Because the area near the anode naturally tends to become acidic while the area near the cathode becomes alkaline, bringing these contrasting zones into closer proximity and actively circulating the liquid helps counterbalance and neutralize their opposing effects.
The empirical results were striking. Under conventional conditions where local pH variations were left unmanaged, only about 16% of the resulting products consisted of the desired target compound. With the newly optimized reactor design in place, that reaction selectivity soared to approximately 97%. This dramatic increase means the reaction became vastly more efficient at producing the intended substance while avoiding the creation of unwanted chemical byproducts.
The team also observed that manipulating the flow rate of the electrolyte had a powerful impact on overall production efficiency. Across the various flow rates tested, the amount of product generated per unit of time increased by approximately 14 times from the lowest flow rate to the highest. Furthermore, reducing the physical distance between the electrodes from 20 millimeters down to 4 millimeters produced a 2.2-fold increase in the reaction rate.
Perhaps the most telling demonstration of the reactor’s design occurred when the liquid was purposefully kept stagnant. Even though the applied voltage and the chemical composition of the solution remained entirely unchanged, the researchers obtained virtually none of the desired product when flow was eliminated.
This stark contrast underscored just how crucial the immediate chemical environment is to electrochemical synthesis. The ultimate success of a reaction depends on far more than simply mixing the right ingredients, applying the correct voltage, and choosing appropriate electrode materials. The physical configuration of the reactor and the microscopic conditions it fosters are equally decisive.
Applications for Biodegradable Plastics, Medicines, and Electronics
Building upon their initial success, the researchers explored whether their localized pH control strategy could be successfully generalized to manufacture a wider array of useful chemical products. Using their optimized reactor conditions, they successfully synthesized lactones from 18 distinct ketone compounds.
One notable achievement was the successful production of $epsilon$-caprolactone with an 82% yield. This specific compound serves as a vital precursor for polycaprolactone, a biodegradable polymer extensively utilized in advanced medical applications such as surgical sutures and controlled drug-delivery systems.
In addition to lactones, the team applied their local pH management strategy to the synthesis of epoxides, successfully obtaining high-value products from six different alkene starting materials. Epoxides are indispensable ingredients in industrial adhesives, durable surface coatings, and epoxy resins utilized throughout the electronics industry. They also function as essential intermediate compounds in the synthesis of pharmaceuticals and fine chemicals.
Together, these experiments demonstrated that controlling the microscopic environment surrounding electrodes is not limited to a single specialized reaction. Instead, the findings suggest a versatile, widely applicable methodology for improving the commercial synthesis of numerous industrially important chemical ingredients.
Toward Cleaner and More Sustainable Chemical Manufacturing
One of the most promising aspects of this electrochemical technique is its inherent alignment with green chemistry principles. By utilizing clean electricity and oxygen gas, the approach successfully circumvents the need for externally added peroxide oxidants. Furthermore, the reactions take place smoothly at room temperature and under normal atmospheric pressure, eliminating the energy-intensive equipment traditionally required to heat or pressurize industrial chemical systems.
These operational characteristics could render certain chemical manufacturing processes considerably simpler and inherently safer. Because electricity supplies the fundamental energy required to drive the transformations, the methodology could eventually be integrated seamlessly with renewable energy generation sources, thereby supporting the transition toward truly sustainable chemical manufacturing.
The researchers believe that the synthesis of pharmaceutical ingredients and other high-value specialty chemicals represents a particularly promising avenue for future commercial adoption. These sensitive products demand meticulous control over reaction conditions and rigorous adherence to safety standards. Electrochemical methods offer distinct advantages by reducing the necessity of handling hazardous oxidizing agents and enabling production within relatively compact, modular equipment.
At the same time, the technology has not yet reached the stage of widespread industrial deployment. Further engineering optimization, rigorous long-term testing, and pilot-scale trials will be necessary to establish whether these impressive laboratory results can be reliably and economically reproduced at full commercial manufacturing scales.
A New Way to Think About Chemical Reactions
Beyond its immediate practical applications, the discovery offers a paradigm shift in how electrochemists and chemical engineers approach the design of electrochemical systems. Traditionally, research has focused heavily on selecting the ideal starting materials, catalysts, electrode compositions, applied voltages, and bulk solution mixtures.
The findings from the Seoul National University team indicate that engineering the tiny, microscopic environment where molecules actually undergo transformation may be just as important as the macro-scale components of the system. This insight redirects scientific attention toward the deliberate design of the local reaction environment.
"This study transforms ‘local pH’ near the electrode from a hidden variable into a controllable design principle," Professor Ryu noted.
He emphasized that to truly maximize the efficiency of organic electrosynthesis, researchers must look beyond conventional parameters. "To improve the efficiency of organic electrosynthesis, we need to design not only the reaction substrates and catalysts, but also the environment in which the molecules actually react," Ryu added.
The research team believes this overarching principle will unlock new opportunities to improve a wide variety of other electrochemical processes, particularly those involving the coupled transfer of electrons and protons. Rather than treating localized acidity as an unavoidable nuisance or side effect, future chemical reactors can be intentionally engineered to maintain micro-environmental conditions that actively favor desired synthetic outcomes.
The study was co-authored by Seonghyeon Min and Junghoon Lee, both Master of Science students in the Department of Chemical and Biological Engineering at Seoul National University, alongside integrated M.S./Ph.D. student Hanju Kim. Professor Ryu supervised the investigation.
Min and Lee intend to build upon this work by continuing to explore how local reaction environments dictate the pathways of organic electrosynthesis, with the long-term goal of expanding the methodology to encompass an even broader spectrum of chemical reactions and industrial manufacturing processes. The research received financial support from Seoul National University, the National Research Foundation of Korea, and the Institute for Basic Science (IBS).
