Innovative liquid batteries could revolutionize energy storage

Credit: Journal of the American Chemical Society (2024).

As California rapidly shifts to renewable energy, it faces the challenge of storing power for the electric grid.

Solar energy drops at night and during winter, while wind energy varies. This inconsistency makes the state rely heavily on natural gas to balance renewable power supply.

“The electric grid uses energy as it’s generated. If you can’t store it, you lose it,” said Robert Waymouth, a chemistry professor at Stanford.

Waymouth and his team are exploring a new technology for renewable energy storage called liquid organic hydrogen carriers (LOHCs).

Hydrogen is already used as a fuel and to generate electricity, but it’s difficult to store and transport.

“We’re developing a new method to convert and store electrical energy in liquid fuels,” said Waymouth, the senior author of a study published in the Journal of the American Chemical Society.

“We’ve also discovered a novel catalytic system for storing energy in a liquid fuel without producing hydrogen gas.”

Current energy storage solutions, like lithium-ion batteries used in smartphones and electric vehicles, need supplementing for large-scale energy storage. LOHCs could be a promising alternative.

They store and release hydrogen using catalysts and heat, potentially acting as “liquid batteries” that store energy and return it as fuel or electricity when needed.

Waymouth’s team focused on isopropanol and acetone for hydrogen energy storage and release. Isopropanol, also known as rubbing alcohol, is a high-density liquid hydrogen form that can be stored or transported until needed as fuel or for hydrogen release without emitting carbon dioxide.

However, producing isopropanol with electricity has been inefficient. The process involves converting two protons from water and two electrons into hydrogen gas, then using a catalyst to produce isopropanol.

“But hydrogen gas has low energy density per unit volume,” Waymouth explained. “We need to make isopropanol directly from protons and electrons without producing hydrogen gas.”

Daniel Marron, the study’s lead author and recent Stanford Ph.D. graduate, addressed this issue by developing a catalyst system that combines protons and electrons with acetone to generate isopropanol without producing hydrogen gas, using iridium as the catalyst.

A surprising discovery was that cobaltocene, a cobalt-based compound, was an efficient additive. Cobaltocene delivered protons and electrons directly to the iridium catalyst without releasing hydrogen gas.

Cobalt is already widely used in batteries, so the team hopes their findings on cobaltocene’s efficiency can help develop other catalysts. They’re exploring more abundant, non-precious metals like iron to make LOHC systems more affordable and scalable.

“This is basic science, but we believe we have a new strategy for selectively storing electrical energy in liquid fuels,” said Waymouth. The goal is for LOHC systems to improve energy storage for industries and individual solar or wind farms.

Summing up the process, Waymouth said, “When you have excess energy and no demand on the grid, you store it as isopropanol. When you need the energy, you convert it back to electricity.”

Additional Stanford co-authors include Conor Galvin and Ph.D. student Julia Dressel. Waymouth is also affiliated with several Stanford institutes and initiatives.

Source: Stanford University.