A team of researchers from PNNL explores the properties of a widely available salt for energy storage.
In an era of escalating global temperatures, the consensus is clear: energy sources must have minimal or no carbon emissions. This necessitates a transition away from coal, oil, and natural gas, toward harnessing more energy from renewable sources.
Among the most promising carriers of renewable energy is clean hydrogen, which can be produced without fossil fuels.
The allure of hydrogen lies in its abundance as the most prevalent element in the universe, constituting 75 percent of all matter. Additionally, hydrogen molecules consist of a pair of non-toxic and highly combustible atoms, making them a compelling focus for energy researchers worldwide.
At the Pacific Northwest National Laboratory (PNNL), a team is delving into the potential of hydrogen as a medium for energy storage and release, primarily through the process of breaking its chemical bonds. Much of their work is linked to the Hydrogen Materials-Advanced Research Consortium (HyMARC) at the Department of Energy (DOE).
Unoptimized hydrogen storage
One area of focus for PNNL researchers is optimizing hydrogen storage, an ongoing challenge. To date, there is no completely safe, cost-effective, and energy-efficient method for large-scale hydrogen storage.
Recently, PNNL scientists co-authored a paper that explores the use of a baking soda solution as a means of hydrogen storage. This study has garnered significant attention and has been labeled a “hot paper” by the Royal Society of Chemistry’s Green Chemistry journal, indicating high levels of interest.
The hydrogen storage efforts at PNNL receive funding from the DOE’s Hydrogen and Fuel Cell Technologies Office in the Office of Energy Efficiency and Renewable Energy (EERE). This research aligns with the DOE’s H2@Scale initiative and the Hydrogen Shot program.
Chemist Tom Autrey, a Laboratory Fellow at PNNL, and his colleague Oliver Gutiérrez, an expert in enhancing the speed and cost-effectiveness of chemical reactions, are the main authors of the research.
Autrey acknowledges the need for creativity, finding it intriguing how a common, inexpensive, and mild substance like baking soda could potentially address a significant challenge. He emphasizes the importance of working with the resources provided by nature in the search for efficient hydrogen storage solutions.
Clean hydrogen for long-term energy requirements
Autrey, Gutiérrez, and their colleagues at PNNL view long-duration energy storage as the key to unlocking hydrogen’s potential as a renewable energy carrier.
Existing battery technology is designed for several hours of storage and can satisfy approximately 80 percent of storage needs in a renewable energy grid.
However, the remaining 20 percent necessitates unique approaches. Autrey states that excess energy must be stored to prepare for periods of low solar and wind energy generation, referred to as Dunkelflaute.
Hydrogen possesses attractive characteristics for seasonal storage and is considered “geographically agnostic” since it does not require specific geographical conditions, unlike other energy storage methods like hydropower, which relies on elevation differences.
Furthermore, Autrey highlights that as the scale increases, hydrogen becomes more cost-effective. Instead of investing in a large number of batteries, it is more economical to acquire a few additional hydrogen storage tanks.
Searching for optimal hydrogen storage solutions
Clean hydrogen holds great promise as an energy source. Electrolysis, for example, can separate water into hydrogen and oxygen, and the electricity used in the process can be sourced from renewable energy generators like solar, wind, or geothermal power.
Nevertheless, there is a persistent challenge to produce hydrogen at a lower cost.
To address this issue, the DOE introduced the Energy Earthshots initiative in 2021, a series of steps aimed at advancing breakthroughs in clean energy technology. The Hydrogen Shot, the first initiative launched, aims to reduce the cost of hydrogen from $5 to $1 per kilogram within a decade, representing an 80 percent reduction.
However, achieving cost-effective hydrogen production is only part of the equation. Autrey emphasizes the importance of finding efficient methods for moving and storing hydrogen, as these steps can impact the overall cost.
Discovering the ideal medium for hydrogen storage has proven elusive.
Hydrogen can be compressed into a gas, but this requires extremely high pressures, necessitating thick steel walls for safe storage or expensive carbon fiber materials.
Cryogenic liquid hydrogen is another storage option, but it involves maintaining ultra-low temperatures (-471°F or -279.4°C), which significantly increases peripheral energy costs.
Molecules in liquid form appear to hold the most promise for storing and releasing hydrogen. Jamie Holladay, an expert in sustainable energy, has recently led PNNL research on simpler and more efficient strategies for liquefying hydrogen.
Using liquid substances as storage media offers the advantage of leveraging existing energy infrastructure, such as pipelines, trucks, trains, and tankers, which is beneficial for practical implementation, according to Gutierrez.
The bicarbonate-formate cycle
Baking soda, commonly known as sodium bicarbonate, may hold the key to both baking cookies and storing hydrogen energy. This non-toxic and abundant salt is currently being investigated by the PNNL team for its potential in hydrogen energy storage. Specifically, they are exploring the properties of the bicarbonate-formate cycle, a well-studied concept involving formate, a safe and mild liquid organic molecule.
Here’s how it works: Solutions containing formate ions (hydrogen and carbon dioxide) in water act as carriers of hydrogen using non-corrosive alkali metal formate. When these ions react with water in the presence of a catalyst, hydrogen and bicarbonates are produced. Autrey compares these bicarbonates to baking soda due to their lack of environmental impact.
By slightly adjusting the pressure, the bicarbonate-formate cycle can be reversed, enabling an aqueous solution to alternately store or release hydrogen, serving as an on-off switch.
Before exploring baking soda, the PNNL hydrogen storage team investigated ethanol as a liquid organic hydrogen carrier, a term used in the industry to describe storage and transport media. In parallel, they developed a catalyst that facilitates the release of hydrogen.
Catalysts are additives designed to accelerate chemical processes for making and breaking bonds in an energy-efficient manner.
In a related project, EERE awarded $2.5 million in funding over two years to OCOchem, a company based in Richland, Washington. The grant aims to develop an electrochemical process that converts carbon dioxide into formate and formic acid. This process binds carbon dioxide with hydrogen from water’s chemical bond (H2O). PNNL will collaborate with OCOchem to explore methods of releasing hydrogen from their products.
Hydrogen storage resembling water
The bicarbonate-formate cycle has been a topic of interest in the field of hydrogen storage for quite some time. It is founded on materials that are abundant, non-flammable, and non-toxic.
This cycle relies on an aqueous storage solution so mild that it closely resembles water, as Autrey points out, even being capable of extinguishing fires.
However, for formate-bicarbonate salts to become a practical means of storing hydrogen energy, economically viable scenarios need to be developed. Currently, the technology can store only 20 kilograms of hydrogen per cubic meter, while the industry standard for liquid hydrogen is 70 kilograms per cubic meter.
Furthermore, Autrey emphasizes the need for a comprehensive understanding of the required electrochemistry and catalysis at a systems level. Achieving a workable bicarbonate-formate cycle is still at a low technical readiness level.
“If we can overcome the challenges in catalysis,” Autrey adds, “we could generate significant interest.”
An exciting prospect
The salt solutions under consideration at PNNL, based on the bicarbonate-formate cycle, offer several advantages. They release hydrogen when reacted with water, operate at moderate temperatures and low pressures, and are relatively safe.
Theoretical discussions in Autrey and Gutiérrez’s 2023 paper describe the bicarbonate-formate cycle as a “viable green alternative for storing and transporting energy” in the form of hydrogen.
The baking soda idea intersects with several urgent scientific challenges, as outlined in the paper. It explores the possibility of creating a hydrogen storage medium from captured excess carbon dioxide and even utilizing the same medium for electron storage, which holds the potential for direct formate fuel cells.
Additionally, the PNNL research could provide insights into catalysis in aqueous phases. Currently, the team employs palladium as their catalyst of choice and seeks ways to enhance its stability, reusability, and longevity.
Overall, the baking soda concept represents an exciting prospect for hydrogen storage, with Autrey describing it as “an amazing shiny thing.” The possibilities it presents are truly intriguing.
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Frequently Asked Questions (FAQs) about Renewable energy storage
What is the focus of the research conducted by PNNL?
The research conducted by PNNL focuses on exploring the potential of using baking soda as a solution for renewable energy storage, specifically in the context of hydrogen storage.
Why is hydrogen considered a promising renewable energy carrier?
Hydrogen is considered a promising renewable energy carrier because it is abundant in the universe and can be produced without relying on fossil fuels. It is a highly combustible and non-toxic element that holds great potential for clean energy applications.
What are the challenges associated with hydrogen storage?
One of the main challenges in hydrogen storage is finding a safe, cost-effective, and energy-efficient method for storing hydrogen at large scales. Current storage options such as compressed gas or cryogenic liquid hydrogen have limitations in terms of pressure requirements and energy costs.
How does the bicarbonate-formate cycle work for hydrogen storage?
The bicarbonate-formate cycle involves using a solution of formate ions (hydrogen and carbon dioxide) in water to carry and store hydrogen. These ions react with water in the presence of a catalyst, producing hydrogen and bicarbonates. The process can be reversed, allowing for the controlled release of hydrogen from the solution.
What advantages does baking soda offer for hydrogen storage?
Baking soda, or sodium bicarbonate, offers advantages such as being abundant, non-toxic, and environmentally friendly. The bicarbonate-formate cycle based on baking soda as a storage medium shows promise due to its mild operating conditions, moderate temperatures, and low pressures.
How does long-duration hydrogen storage contribute to renewable energy goals?
Long-duration hydrogen storage is crucial for addressing periods of low renewable energy generation, such as when solar and wind resources are limited. By storing excess energy in the form of hydrogen, renewable energy systems can ensure a stable and reliable energy supply even during extended periods of low generation, reducing reliance on traditional energy sources.
More about Renewable energy storage
- PNNL – Pacific Northwest National Laboratory
- DOE – Hydrogen and Fuel Cell Technologies Office
- DOE – H2@Scale Initiative
- DOE – Hydrogen Shot
- Green Chemistry – Royal Society of Chemistry
- Hydrogen Materials-Advanced Research Consortium (HyMARC)
- Energy Earthshots Initiative
