Microscope image of the metal oxides. Image: Imperial College London.
Microscope image of the metal oxides. Image: Imperial College London.

Metal oxides are compounds that play a crucial role in processes that reduce carbon dioxide (CO2) emissions. These processes include carbon capture, utilization and storage (CCUS), purifying and recycling inert gases in solar panel manufacturing, thermochemical energy storage, and producing hydrogen for energy.

All these processes are based on reactions where metal oxides gain or lose electrons, known as redox reactions. However, the performance of metal oxides suffers when they undergo redox reactions at the high temperatures required for chemical manufacturing.

Now, a team led by researchers at Imperial College London in the UK has developed a new materials design strategy for producing copper-based metal oxides that perform better under high temperatures. This technology is already having a global impact on argon recycling in solar panel manufacturing and is expected to help unleash even more power from existing energy technologies that fight the climate crisis.

“As the world transitions to net zero, we need more innovative industrial processes for decarbonization,” said Qilei Song in Imperial’s Department of Chemical Engineering, and senior author of a paper on this work in Nature Communications. “To enhance energy security, we must diversify the electricity supply, from renewable energy generation and storage to clean use of fossil fuels with CCUS technologies. Our improved metal oxides hold great potential for use in the energy processes that are helping us reach net zero.”

Metal oxides are key players in a relatively new process called chemical looping combustion (CLC). This is an alternative way of burning fossil fuels that uses metal oxides, such as copper oxides, to transport oxygen from the air to react with the fuel. This reaction produces CO2 and steam, which is condensed to allow the efficient capture of CO2 to prevent it entering the atmosphere

By capturing the CO2 that is produced, CLC can allow fossil fuels to be used in a cleaner way, and is already employed in the EU, the US and China. However, a key issue that has held back CLC from use on a larger scale is the inability of metal oxides to maintain good oxygen-releasing performance over multiple redox cycles at high temperatures.

To solve this problem, the researchers examined the fundamental structures of the metal oxides used in CLC. They reasoned that the precursor chemistry to metal oxides was poorly understood, limiting their rational design.

“To solve the question of how metal oxides maintain their performance, we looked to the basics of the chemical processes involved in CLC,” explained co-lead author Michael High, a PhD candidate in Imperial’s Department of Chemical Engineering. “This is a key example of combining fundamental research and smart design to produce a strategy that’s applicable to a wide range of engineering processes.”

The researchers utilized an alternative method for engineering the metal oxide structure from well-known precursor compounds known as copper-magnesium-aluminium-layered double hydroxides (LDHs). By tailoring the chemistry of the LDH precursors, they were able to produce metal oxides that could still perform well under remarkably high temperatures. They demonstrated this by putting the oxides through 100 chemical cycles in a widely used type of reactor known as a fluidized bed reactor for 65 hours.

Their greater ability to withstand heat means that metal oxides produced in this way can be used to unleash more power from purifying and recycling inert gases like argon in the manufacture of solar panels, capturing and storing carbon, storing chemical energy, and producing clean hydrogen. To demonstrate this, the researchers scaled up the production of metal oxides for use in fluidized bed reactors. They found that the process for creating these materials is simple and readily suitable for upscaling using existing industrial manufacturing methods.

“The world must reach net zero carbon emissions by 2050,” said senior author Paul Fennell from Imperial’s Department of Chemical Engineering. “Renewable energies are developing rapidly, but in the short term we need to develop cost-effective carbon-capture technologies that can be applied to decarbonize the industry. Our work will help solve this global challenge.”

Next, the researchers will study the long-term stability of the materials during the combustion of different types of fuels, explore new applications for thermochemical energy storage, and extend this approach to other metal oxide systems for producing clean hydrogen via thermochemical redox cycles.

This story is adapted from material from Imperial College London, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

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