Researchers at Pennsylvania State University have developed a larger, more efficient reactor that converts carbon dioxide and renewable electricity into methane, offering a possible way to store renewable energy for long periods.

The international team, led by Bruce Logan, scaled up a microbial electrosynthesis system without losing performance, addressing one of the biggest challenges facing the technology.

The reactor uses electricity from renewable sources such as solar and wind to split water and generate hydrogen. Microorganisms called methanogens then consume the hydrogen and convert carbon dioxide into methane, the main component of natural gas.

Researchers said the methane could be stored and transported using existing gas infrastructure, potentially creating a new pathway for long-duration renewable energy storage.

“Traditionally, large-scale, long-term storage means pumping water uphill and letting it flow back down through turbines,” Logan said. “If you’re talking seasonal storage, you really need to put that energy into a chemical form.”

Bigger reactor, same efficiency

Microbial electrosynthesis systems have typically struggled to move beyond laboratory-scale devices because efficiency drops as systems become larger.

To solve that issue, the team developed an up-scaled “zero-gap” reactor design in which the electrodes are separated only by a membrane. The configuration reduces internal resistance and improves energy transfer inside the system.

The researchers expanded the electrode area by roughly tenfold and increased the internal flow path to nearly 12 inches. Despite the larger design, the reactor maintained strong methane production and high energy efficiency.

“Even though we made the system much bigger, the internal resistance didn’t get worse,” Logan said. “That’s because we were able to use the hydrogen coming off the electrodes much more efficiently.”

The reactor also uses multiple flow ports to distribute fluids and gases more evenly across the system, helping maintain stable operating conditions.

In tests conducted at 30 degrees Celsius, the reactor produced up to 6.9 liters of methane per liter of reactor volume per day. The system also achieved coulombic efficiencies above 95 percent, meaning most of the electrical energy was converted directly into methane rather than wasted in side reactions.

Researchers reported energy efficiency levels of around 45 percent to 47 percent, which they said ranks among the highest achieved for microbial electrosynthesis systems operating under standard conditions.

Hydrogen speeds methane output

The study also clarified how methane production occurs inside the reactor.

Instead of microbes directly collecting electrons from electrodes, the system first generates hydrogen through water splitting. Methanogens then rapidly consume the hydrogen to produce methane at higher rates.

“We split water to make hydrogen, and the methanogens are right there to use it immediately,” Logan said. “You can think of it as a water electrolyzer, which uses electricity to split water into hydrogen and oxygen, combined with a biological system.”

The researchers believe future methane-generation facilities could be built alongside renewable energy plants and directly connected to gas pipeline networks.

“I see methane generation plants built next to solar or wind farms,” Logan said. “Instead of putting electricity onto the grid, you use it on site to produce methane and inject that into gas lines.”

The study was published in the journal Water Research.