A Nafion coating lets bicarbonate electrolysis hit 93% CO efficiency at industrial current

Carbon capture has an expensive middle step. Traditional approaches pull CO2 from industrial flue gas, then release it, compress it, purify it, and finally convert it into something useful. Each stage consumes energy. Each stage costs money. What if you could skip the purification entirely?

That is the promise of bicarbonate-mediated integrated CO2 capture and electrolysis, an emerging approach that absorbs CO2 into a bicarbonate solution and then electrochemically converts it directly, without ever isolating pure CO2. The concept is sound, but performance has lagged. Current densities have been too low for industrial relevance, and the energy required per unit of product has been too high.

The ionomer strategy

A team led by Professors Bao Xinhe, Gao Dunfeng, and Zhang Guohui at the Dalian Institute of Chemical Physics, along with Professor Wang Guoxiong at Fudan University, has now demonstrated a way to address both problems simultaneously. Their approach, published in Angewandte Chemie International Edition, focuses on the reaction microenvironment: the immediate chemical neighborhood surrounding the catalyst where the actual conversion happens.

The key move was incorporating a Nafion ionomer into the electrode structure. Nafion is a sulfonated fluoropolymer widely used in fuel cells for its ability to conduct protons while blocking other ions. When deposited onto cobalt phthalocyanine (CoPc) electrodes, the Nafion layer reshapes the local chemical environment in a way that dramatically improves performance.

93% efficiency at 300 milliamps per square centimeter

The numbers tell the story. In a cation exchange membrane-based zero-gap electrolyzer, the Nafion-modified CoPc electrode achieved a CO Faradaic efficiency of 93 percent at an applied current density of 300 milliamps per square centimeter. The system reached a CO partial current density of 410 milliamps per square centimeter at a cell voltage of just 3.09 volts.

For context, previous bicarbonate electrolysis systems have struggled to maintain high selectivity at industrially relevant current densities. The trade-off between speed and efficiency has been a persistent barrier. This system appears to push past that barrier, at least at the laboratory scale.

The mechanism involves proton shuttling. Bicarbonate solutions do not directly provide CO2 to the catalyst surface. Instead, the bicarbonate must first decompose to release CO2 in the immediate vicinity of the electrode. The Nafion ionomer's proton conductivity accelerates this decomposition, increasing the local concentration of in-situ generated CO2 near the CoPc catalyst. More CO2 at the catalyst surface means more efficient conversion to CO and fewer side reactions.

Finite element simulations confirmed this interpretation, showing elevated CO2 concentrations within the Nafion-modified electrode structure compared to unmodified controls.

Closing the loop from flue gas to product

The researchers went a step further, demonstrating a complete closed-loop cycle at the device level. They fed simulated flue gas through a bicarbonate absorption step, then electrolyzed the resulting solution using their Nafion-incorporated CoPc electrode, and recycled the spent solution back to the absorption stage. This closed-loop demonstration is significant because it shows the system can operate continuously rather than as a one-shot laboratory experiment.

Scaling questions and missing data

The study demonstrates impressive laboratory performance, but several questions remain before this approach could reach industrial deployment. Electrode stability over extended operation was not reported in detail, and catalyst degradation under continuous cycling could limit practical lifetime. The simulated flue gas used in the demonstration was cleaner than real industrial exhaust, which contains sulfur compounds, particulates, and other contaminants that can poison catalysts.

The economic case also needs development. While eliminating the CO2 purification step reduces energy consumption, the costs of Nafion membranes and CoPc catalysts are not trivial. A full techno-economic analysis comparing this integrated approach to conventional capture-then-convert pathways would be needed to assess commercial viability.

The CO product itself has value as a chemical feedstock for producing fuels, plastics, and other industrial chemicals, but that value depends heavily on local market conditions and the availability of cheap renewable electricity to power the electrolysis.

Still, the combination of high selectivity, high current density, and closed-loop operation represents a meaningful advance in reactive carbon capture technology. Whether it can survive the transition from bench to plant remains the defining question.