Led by Professor Jaeyune Ryu of the Department of Chemical and Biological Engineering at Seoul National University College of Engineering, the research could help make chemical manufacturing safer, cleaner, and more efficient. The team developed a method that uses oxygen and electricity to produce compounds used in plastics, medicines, adhesives, and other everyday materials without separately adding peroxide oxidants.

The study focuses on local pH—the acidity or alkalinity in the immediate environment around an electrode. By redesigning a chemical reactor to control the distance between electrodes and the movement of liquid through the system, the researchers significantly improved reaction performance.

The findings were published in the Journal of the American Chemical Society (JACS), a leading chemistry journal published by the American Chemical Society (ACS).

Why Local pH Can Make or Break an Electrochemical Reaction

The research builds on organic electrosynthesis, a technique that uses electrical energy to drive reactions that produce carbon-based chemical compounds.

Organic electrosynthesis has attracted growing interest because it may reduce the need for chemical oxidizing and reducing agents commonly used in traditional manufacturing. These substances help reactions proceed by accepting or donating electrons, but some can be hazardous to handle and may generate unwanted waste.

Previous efforts to improve organic electrosynthesis have largely focused on factors such as electrical voltage, electrode materials, and the composition of the reaction solution. The Seoul National University team suspected that another important variable was being overlooked: the microscopic chemical environment directly next to each electrode.

This is where molecules exchange electrons and undergo chemical transformations. Although the surrounding solution may appear uniform, conditions in this tiny region can be dramatically different from those measured throughout the rest of the liquid.

One especially important factor is pH, which measures how acidic or alkaline a substance is. During an electrochemical reaction, hydrogen ions, or protons, can be produced or consumed at the electrodes. If these ions are generated or removed faster than they can move through the liquid, the pH near an electrode can diverge sharply from the overall pH of the solution.

The researchers found that these local pH differences can affect how reactive oxygen species are produced, change the chemical form of starting materials, and influence whether finished products remain stable or begin to break down.

As a result, a reaction can fail even when the overall solution appears to have the correct chemical conditions.

Electrodes Can Create Strongly Acidic and Alkaline Zones

To investigate whether local pH could affect a broad range of reactions, the researchers reviewed more than 600 scientific papers on organic electrosynthesis published since 2010.

Approximately 89% of the studies involved reactions at one or more electrodes in which both electrons and protons were transferred. Because proton movement can change local acidity, this finding suggests that overlooked pH differences may influence many electrochemical reactions, not just a few specialized processes.

The team also estimated how extreme these differences could become. Even when the overall solution was essentially neutral, conditions near the cathode—the electrode where reduction occurs—could reach approximately pH 11, creating a strongly alkaline environment.

At the anode, where oxidation occurs, the local environment could reach approximately pH 2.5, making it strongly acidic.

These changes can have significant consequences. Extreme local conditions may reduce the availability of reactive oxygen species, alter the starting materials, and cause newly formed products to break down more quickly.

Adjusting the acidity of the entire solution may therefore be insufficient. The critical factor is the environment immediately surrounding the electrodes, where the reaction actually takes place.

Using Oxygen and Electricity to Produce Lactones and Epoxides

To demonstrate the importance of local pH, the researchers studied Baeyer–Villiger oxidation, a well-established reaction that adds an oxygen atom to a ketone and converts it into an ester or lactone.

Lactones are ring-shaped compounds used as building blocks for biodegradable plastics and polyurethanes. Epoxides are important in adhesives, protective coatings, epoxy resins used in electronic materials, pharmaceuticals, and other specialized chemicals.

Traditional Baeyer–Villiger oxidation often requires highly reactive oxidizing chemicals, including peroxyacids. Although effective, these substances can create challenges related to safe handling, chemical waste, and unwanted byproducts.

The Seoul National University team developed an alternative method that uses electricity to activate oxygen gas at an electrode. The process produces reactive oxygen species capable of transferring oxygen atoms into organic molecules.

Isotope-tracing experiments confirmed that the oxygen incorporated into the final products came from oxygen gas rather than water.

The two electrodes also worked together. At the cathode, oxygen reduction generated reactive oxygen species that initiated the oxygen-transfer reaction. Hydrogen peroxide formed during this process could then be converted back into reactive oxygen species at the anode, helping sustain the supply needed for the reaction.

However, the process depended heavily on the acidity near the electrodes. When local pH became too extreme, the reaction became far less effective.

Reactor Redesign Increases Selectivity From 16% to 97%

After identifying local pH as a critical factor, the researchers investigated how to control it. Using computer simulations and electrochemical measurements, they developed a reactor design that placed the electrodes closer together while allowing the electrolyte—the electrically conductive liquid carrying the reaction ingredients—to flow between them.

The design was intended to prevent extreme acidity differences from developing. Because the region near the anode tends to become acidic while the region near the cathode becomes alkaline, reducing the distance between the electrodes and circulating the liquid helps counterbalance these effects.

The results were substantial. When local pH differences were not effectively controlled, approximately 16% of the relevant products were the desired target compound. With the redesigned reactor, selectivity increased to approximately 97%.

Higher selectivity means the reaction produced much more of the intended substance and fewer unwanted products.

Electrolyte flow also had a major effect on production. Across the flow rates tested, the amount of product generated per unit time increased by approximately 14 times from the lowest flow rate to the highest.

Reducing the distance between the electrodes also improved performance. When the gap was reduced from 20 millimeters to 4 millimeters, the production rate increased by approximately 2.2 times.

When the liquid was not allowed to flow, the researchers obtained almost none of the desired product—even though the applied voltage and solution composition remained unchanged.

The result demonstrated that electrochemical reaction performance depends on more than ingredients, voltage, and electrode materials. Reactor design and the microscopic chemical conditions it creates can be equally important.

Applications in Biodegradable Plastics, Medicine, and Electronics

The researchers next tested whether their local pH control strategy could produce different useful chemicals.

Using optimized conditions, they synthesized lactones from 18 different ketone compounds. One important example was ε-caprolactone, which they produced with an 82% yield.

ε-Caprolactone is a starting material for polycaprolactone, a biodegradable polymer used in medical applications such as surgical sutures and drug-delivery systems.

The team also applied the method to epoxide production and successfully obtained products from six different alkene starting materials.

Epoxides are used in adhesives, surface coatings, and epoxy resins found in electronic materials. They are also valuable intermediates for producing pharmaceuticals and fine chemicals.

Together, the experiments suggest that controlling the microscopic environment around electrodes could improve more than one type of reaction and may offer a versatile method for producing commercially important chemical ingredients.

Potential for Cleaner and Safer Chemical Manufacturing

One of the most promising features of the technique is that it uses oxygen and electricity while reducing the need for externally added peroxide oxidants.

The reactions also occur at room temperature and normal atmospheric pressure, eliminating the need for separate equipment to heat or pressurize the system. These characteristics could make some chemical processes simpler and potentially safer.

Because electricity supplies the energy needed to drive the reactions, the approach could eventually be combined with renewable energy sources to support more sustainable chemical manufacturing.

The researchers believe pharmaceutical ingredients and other high-value specialty chemicals could be particularly promising applications. These products often require precise reaction control and strict safety measures. Electrochemical methods may help by reducing the need to handle hazardous oxidizing agents and potentially enabling production in relatively compact equipment.

However, the technology is not yet ready for widespread industrial use. Additional optimization and larger-scale testing will be needed to determine whether the laboratory results can be reproduced economically and reliably in commercial manufacturing.

Local Reaction Environment Becomes a Reactor Design Principle

Beyond its immediate applications, the discovery offers a new way to think about electrochemical reaction design.

Researchers have traditionally concentrated on selecting the right starting materials, catalysts, electrode surfaces, voltages, and solution compositions. The Seoul National University team’s findings indicate that controlling the tiny environment where molecules actually react may be just as important.

Professor Jaeyune Ryu, who supervised the research, said, “This study transforms ‘local pH’ near the electrode from a hidden variable into a controllable design principle.”

He added, “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.”

The researchers believe this principle could help improve other electrochemical processes, particularly those involving the movement of both electrons and protons. Instead of treating local acidity as an unavoidable side effect, future chemical reactors could be engineered to maintain conditions that favor the desired reactions.

The study’s co-first authors were Seonghyeon Min and Junghoon Lee, both M.S. students in Seoul National University’s Department of Chemical and Biological Engineering. Hanju Kim, an integrated M.S./Ph.D. student, participated as a co-author, with Professor Ryu overseeing the research.

Min and Lee plan to continue studying how local reaction environments influence organic electrosynthesis, with the goal of extending the approach to a broader range of chemical reactions and manufacturing processes.

The research was supported by Seoul National University, the National Research Foundation of Korea, and the Institute for Basic Science (IBS).