Low-Frequency Electrochemical Pulsing to Manage Flooding and Salt Precipitation in Zero-Gap CO2-to-Ethylene Electrolyzers 

Electrochemical CO₂ conversion has attracted significant attention as a potential way to transform a greenhouse gas into useful chemicals and fuels. One particularly valuable target is ethylene (C₂H₄), a major industrial chemical used to manufacture polyethylene and numerous other products. Ethylene is currently produced primarily from fossil hydrocarbons, so producing it electrochemically from CO₂ could eventually provide an alternative pathway for manufacturing an enormous class of chemicals [1][2].

However, for CO₂ electrolysis to become an industrial technology, an electrolyzer must operate at high current densities for long periods of time without losing performance. Zero-gap electrolyzers are particularly attractive because they minimize the distance between the electrodes and can operate at high reaction rates. Yet these devices can experience catastrophic failures within the first few hours or days of operation.

A 2026 study led by researchers, Michell Marufu et al., at Lawrence Livermore National Laboratory and the University of California, Merced identified two major short-term failure mechanisms in zero-gap CO₂-to-ethylene electrolyzers: flooding and salt precipitation. Rather than redesigning the catalyst to solve these problems, the researchers developed a remarkably simple operational strategy: periodically reduce the electrical current for short periods before returning to normal operation [1].

This low-frequency electrochemical pulsing allows the electrolyzer to temporarily redistribute water, dissolve accumulated salts, and clear liquid products from the cathode. Using operando neutron imaging, Marufu et al. were able to directly observe how the pulsing changed water movement inside the device. The optimized approach ultimately doubled electrolyzer durability compared with constant-current operation.

What is a Zero-Gap CO₂ Electrolyzer?

A zero-gap CO₂ electrolyzer is designed to bring the major components of the electrochemical cell into close contact. “These electrolyzers are called ‘zero-gap’ because there is no gap between the cathodes, anodes, and the electrolyte” [3]. On the cathode side, CO₂ gas is supplied through a gas-diffusion electrode (GDE) to a catalyst layer where the CO₂ reduction reaction occurs. An anode on the opposite side drives the complementary oxidation reaction. 

The membrane in zero-gap CO2 electrolyzers facilitates ion transport between the cathode and the anode. “Currently, CO2 electrolyzers use anion exchange membranes (AEMs), cation exchange membranes (CEMs), or bipolar membranes (BPMs)” [3].

AEMs transport negatively charged ions such as hydroxide (OH-) from the cathode to the anode, CEMs transport positively charged ions such as hydrogen protons (H+) from the anode to the cathode, and BPMs may perform more than one type of ion transport, depending upon the chemistry. 

The advantage of this architecture is high mass transport and low resistance between the components. These characteristics make zero-gap cells promising for operating at industrially relevant current densities.

That complexity also creates a difficult operating environment.

The reaction consumes and produces water, generates hydroxide ions, and produces multiple liquid and gaseous products. Meanwhile, positively charged ions can migrate through the cell. The result is a delicate balance between gas, liquid, and ionic transport inside the catalyst and gas-diffusion layers.

If that balance is disrupted, the electrolyzer can rapidly stop working.

The Problem with Constant-Current Operation

Under constant-current operation, Marufu et al. found that their zero-gap electrolyzer could operate at 200 mA cm⁻² for only around 1-2 hours before salt precipitation caused serious problems. In one experiment, the cell experienced a precipitation-related failure after approximately 2.5 hours. Deposited material was found blocking the gas-flow channels when the cell was disassembled.

The salt forms because CO₂ reacts with hydroxide ions near the cathode to produce carbonate and bicarbonate species. As water moves through the electrode and is consumed by electrochemical reactions, these dissolved species can become concentrated enough to precipitate as solid salts.

Once the salts accumulate inside the gas-flow pathways, they can partially or completely block the movement of CO₂.

The problem can become self-reinforcing: less effective gas transport means poorer reaction conditions, while continued operation allows additional precipitation to occur.

Flooding creates another failure mechanism.

Gas-diffusion electrodes need to maintain pathways through which gaseous CO₂ can reach the catalyst. If excessive liquid water accumulates inside the porous electrode, those gas pathways can become blocked. Instead of efficiently transporting CO₂ to the catalyst, the electrode becomes increasingly filled with liquid; the catalyst has essentially been drowned.

This is especially problematic because the researchers were attempting to operate at high current density, where water and ion transport become substantial. A reactor that performs extremely well for an hour but then floods or clogs is not useful for industrial chemical production.

Giving the Electrolyzer a “Rest”

The researchers' solution was to stop treating the electrolyzer as a system that must operate at exactly the same current every second.

Instead, they introduced a low-frequency pulsing protocol.

During normal operation, the electrolyzer runs at a high primary current density, designated (JP). At regular intervals, the current is temporarily reduced to a lower value, (JR). After the relaxation period, the current returns to (JP).

Marufu et al. systematically varied the lower current density and timing of these pulses to determine how much relaxation was necessary without sacrificing too much ethylene production.

Their initial experiments used a 15-minute reduced-current period followed by 45 minutes at the primary current. The 15-minute interval was selected partly because it was the shortest period that allowed reliable gas-chromatography measurements, while the 45-minute high-current period remained below the approximate timescale at which precipitation occurred under constant-current operation.

The pulsing strategy substantially improved the electrolyzer’s operating lifetime. Under constant-current operation at 200 mA cm⁻², the researchers observed salt precipitation and flooding within only a few hours, with one cell experiencing a precipitation-related failure after approximately 2.5 hours. In contrast, optimized low-frequency pulsing allowed the electrolyzer to operate for roughly twice as long before significant performance degradation. Importantly, the improved durability was achieved without eliminating the high-current operating periods responsible for rapid ethylene production. 

The results demonstrate that strategically introducing short periods of reduced current can preserve the high-rate performance of the electrolyzer while mitigating the physical processes that ultimately cause it to fail.

The Reduced-Current Period

The key to the technology is understanding that the reduced-current period changes the physical and chemical environment inside the electrode.

When the current returns to its higher value, the electrode is therefore in a more favorable state for CO₂ reduction. The pulse has essentially acted as a short self-cleaning cycle.

Seeing Water Move Inside the Electrolyzer

One of the most important aspects of the study was not simply demonstrating that pulsing works, but determining why it works.

To investigate the internal water dynamics, Marufu et al. used operando neutron radiography (NR), an imaging technique that uses a beam of neutrons to take real-time pictures of the inside of a device while it is actively working.

Neutron imaging is particularly useful for this problem because neutrons interact strongly with hydrogen. Since water contains hydrogen, neutron radiography can provide information about where water is located inside a functioning electrochemical device.

“Using operando NR, we observed that our optimized low-frequency pulsing protocol allowed water to pass through the GDE and clear hygroscopic liquid products and salt through the flow fields” [1].

Instead of disassembling the electrolyzer after an experiment and guessing where water had accumulated, the researchers could observe water distribution while the device was operating.

The imaging revealed substantially different water distributions during constant-current and pulsed operation. Under pulsed conditions, the relaxation periods allowed water to move through the gas-diffusion electrode and helped clear accumulated liquid and salts from the cathode region.

This provided direct experimental evidence for the proposed water-management mechanism.

Extending Lifetime

The innovation works because flooding and salt precipitation are not independent problems. They are connected through the movement of water and ions within the electrode.

If too little water is available in one region, dissolved salts can become concentrated and precipitate. If too much water accumulates in another region, the gas-diffusion electrode can flood and restrict CO₂ transport.

The pulsing protocol helps maintain a more favorable balance.

During the lower-current period, reduced water consumption allows accumulated water to redistribute and helps remove salts and liquid products. When the higher current resumes, the electrode has regained more of its gas-transport capacity.

“Both the step-up and step-down experiments showed that operating for 15 minutes at any of the tested reduced currents (10–100 mA cm−2) extended the electrolyzer lifetime compared to continuous operation at JP” [1].

Marufu et al. therefore describe pulsing as a method for managing water movement, rather than simply manipulating the electrochemical reaction itself.

The technology does not require a fundamentally new catalyst or membrane. Instead, it changes the operating protocol of an existing type of electrolyzer.

A Unique Approach

Much of CO₂-electrolysis research focuses on developing better catalysts: materials that produce more ethylene, operate at lower voltages, or achieve higher Faradaic efficiency.

Those improvements are important, but they do not automatically solve the problem of durability; a catalyst can be highly selective for ethylene while the device surrounding it still floods or becomes clogged with salts.

Rather than attempting to eliminate every source of water and salt accumulation through materials design, Marufu et al. use the electrochemical current itself as a process-control variable. That creates an important shift in how electrolyzers can be designed; the current is not merely the input that drives the chemistry.

It can also be used to actively manage the physical conditions inside the reactor.

The study’s results therefore demonstrate a form of electrochemical process control in which the operating conditions are deliberately varied to maintain the health of the device.

Why This Innovation Matters

The importance of this innovation becomes clearer when considering what industrial CO₂ electrolysis actually requires. Laboratory demonstrations can achieve impressive current densities and product selectivities, but industrial chemical processes must operate reliably for thousands of hours. An electrolyzer that performs exceptionally well for a few hours but then floods or becomes clogged with salt cannot provide a practical route to large-scale chemical production.

The researchers' pulsing strategy addresses this gap by treating durability as an operating problem as well as a materials problem. Rather than requiring a fundamentally new catalyst or reactor architecture, the system periodically adjusts its current to manage the internal environment of the electrolyzer. These brief relaxation periods allow water to redistribute, salts to dissolve, and liquid products to move away from the cathode before they can cause more severe transport problems.

This is particularly significant because flooding and salt precipitation can occur before longer-term forms of degradation, such as catalyst deactivation or loss of electrode hydrophobicity, become important. Preventing these early failures gives the electrolyzer a better chance of reaching the much longer operating times needed for meaningful industrial evaluation.

The approach also highlights an important principle for scaling electrochemical technologies: the operating conditions themselves can be engineered as part of the technology. Instead of designing an electrolyzer to operate at one fixed condition indefinitely, researchers can use controlled changes in current to actively maintain the environment inside the reactor.

The relaxation periods temporarily reduce the rate of ethylene production, so the ideal pulsing schedule must balance durability with productivity. But this tradeoff illustrates a broader reality of industrial scale-up: maximizing instantaneous performance is not always the same as maximizing useful production over the lifetime of a system. A slightly lower average production rate may be worthwhile if it allows the electrolyzer to operate reliably for substantially longer.

The study therefore demonstrates an approach that could complement advances in catalysts, membranes, gas-diffusion electrodes, and reactor design. As CO₂ electrolyzers become more sophisticated, integrating materials engineering, electrochemistry, and real-time process control could become increasingly important for maintaining performance over long operating periods. Solving the scale-up problem does not always require inventing an entirely new material. Sometimes, understanding how a reactor physically changes during operation can reveal a much simpler intervention.

References 

1. Michell Marufu, Maxwell Goldman, R. Dominic Ross, Jongmin Lee, Jack Davis, Michael Troksa, Eric Krall, Auston Clemens, Aditya Prajapati, Andrew A. Wong, Pavel Trtik, Po-Ya Abel Chuang, Eric B. Duoss, Sarah E. Baker, Christopher Hahn; Low-frequency electrochemical pulsing to manage flooding and salt precipitation in zero-gap CO2-to-ethylene electrolyzers. EES Catal. 2026; 4 (3): 708–716. https://doi.org/10.1039/d6ey00012f

2. Berkelaar, L., Linde, J. van der, Peper, J., Rajhans, A., Tiemessen, D., Ham, L. van der, & Berg, H. van den. (2022). Electrochemical conversion of carbon dioxide to ethylene: Plant design, evaluation and prospects for the future. Chemical Engineering Research and Design, 182, 194–206. https://doi.org/10.1016/j.cherd.2022.03.034

3. Cell Store, F. (2024, February 15). Membrane Properties and Characterization for Zero-Gap CO2 Electrolyzers. Fuelcellstore.Com. https://www.fuelcellstore.com/blog-section/membrane-information/membrane-properties-characterization-zero-gap-co2-electrolyzer

4. Ma, W., Xie, S., Liu, T. et al. Electrocatalytic reduction of CO2 to ethylene and ethanol through hydrogen-assisted C–C coupling over fluorine-modified copper. Nat Catal 3, 478–487 (2020). https://doi.org/10.1038/s41929-020-0450-0