Scientists are developing a liquid battery to store renewable energy

As California rapidly implements renewable energy, it urgently needs innovative grid energy storage technologies. Solar energy production decreases at night and in winter, while wind energy is variable. Currently, the state relies heavily on natural gas to offset the intermittent nature of renewable energy.

A team from Stanford University is improving renewable energy storage capabilities by researching a promising technology: liquid hydrogen storage.

“The electrical grid consumes energy at the same rate as you generate it, and if you’re not using it in that time and you can’t store it, you have to throw it away.” said Robert Waymouth, the Robert Eckles Swain Professor of Chemistry in the School of Humanities and Sciences.

Waymouth leads a Stanford team investigating a promising new renewable energy storage technology: liquid organic hydrogen carriers (LOHC). However, hydrogen is already used as a fuel source, and for power generation, its containment and transport pose significant challenges.

“We are developing a new strategy for selective processing and long-term storage of electricity in liquid fuels” said Waymouth, senior author of a study detailing this work in the Journal of the American Chemical Society. “We also discovered a novel, selective catalytic system for storing electricity in liquid fuel without producing hydrogen gas.”

Research is being conducted on new energy storage technologies to complement lithium-ion batteries used in network storage, smartphones and electric vehicles. One promising candidate is LOHC cells, which can efficiently store and release hydrogen, functioning as “liquid batteries” that can store energy and, when necessary, convert it into usable fuel or electricity.

The Waymouth team is investigating the potential of isopropanol and acetone as key components of hydrogen energy storage and release systems. Isopropanol, commonly known as rubbing alcohol, is a promising high-density liquid form of hydrogen that can be efficiently stored or transported via existing infrastructure. When the time comes, it can be used as clean fuel in a fuel cell or to release hydrogen without emitting carbon dioxide.

However, there is currently a need for more efficient methods of producing isopropanol using electricity. The process involves converting two protons from water and two electrons into hydrogen gas, which can then be used by a catalyst to produce isopropanol.

“But hydrogen is not needed in this process” – Waymouth said. “Its energy density per unit volume is low. We need a way to make isopropanol directly from protons and electrons, without producing hydrogen gas.”

Daniel Marron, the lead author of this study, made a significant breakthrough in solving a key problem. Its innovative catalyst system effectively converts acetone into LOHC isopropanol without producing hydrogen gas. This system, using iridium as a catalyst and cobaltocene as a cocatalyst, exceeded previous expectations and offers a promising solution.

The use of cobaltocene as a cocatalyst has proven to be extremely effective, enabling the delivery of protons and electrons directly to the iridium catalyst, marking significant progress in this field of research.

Cobalt is a highly sought-after material in the battery industry, and the Stanford team’s breakthrough in understanding the properties of cobaltocene could pave the way for the development of new catalysts for a variety of processes. By exploring the use of more widely available base-earth metal catalysts such as iron, they hope to make future LOHC systems cheaper and easier to scale.

“It’s basic science, but we think we have a new strategy for storing electricity more selectively in liquid fuels,” he added. Waymouth said.

Improvements in LOHC systems promise to improve energy storage in industrial and residential facilities that use solar or wind energy. Despite the complexity of the work, Waymouth eloquently summarizes the process as incredibly elegant.

“When you have a surplus of energy and there is no demand for it on the grid, you store it in the form of isopropanol. When you need energy, you can return it as electricity.”

Magazine number:

Daniel P. Marron, Conor M. Galvin, Julia M. Dressel, and Robert M. Waymouth. Cobaltocene-mediated catalytic hydride transfer: electrocatalytic hydrogenation strategies. Journal of the American Chemical Society, 2024; DOI: 10.1021/jacs.4c02177