In the quest for sustainable energy storage solutions, a new contender has emerged from the shadows of traditional fossil fuels: metal fuels. According to a recent review published in the journal “Next Energy” (formerly known as “Next Energy”), these metals, including aluminum, iron, magnesium, and zirconium, are gaining traction as high-energy-density, carbon-free alternatives for storing renewable energy. The review, led by independent scientist Alberto Boretti from Johnsonville, Wellington, New Zealand, explores the potential of these metals within a circular economy framework, offering a fresh perspective on how they might complement existing energy storage technologies.
The review highlights the oxidation of metal fuels in air, steam, and carbon dioxide, with air and steam oxidation proving particularly effective for heat generation and facilitating hydrogen production. “The beauty of metal fuels lies in their ability to store energy in a dense, recyclable form,” Boretti explains. “When you oxidize these metals, you release energy, and the resulting metal oxides can be recycled back into reusable fuels through processes like electrolysis.”
One of the key advantages of metal fuels is their potential to support the circular economy. By recycling metal oxides into reusable fuels, these metals can address specific energy storage needs while supporting the recycling of metal oxides. However, the technology readiness level (TRL) for metal fuel combustion for power generation remains relatively low, estimated to be between TRL 3 and 4. In contrast, processes for recycling metal oxides, such as the Hall-Héroult process for aluminum, exhibit higher TRLs, around TRL 9.
Despite their promise, metal fuels face limitations due to the restricted availability of metal oxides compared to the abundance of water for hydrogen storage. As such, metal-based energy storage should not be seen as competing with hydrogen-based solutions but as a complementary approach. “Metal fuels offer a unique set of advantages, particularly in terms of storage density and recyclability,” Boretti notes. “They won’t replace hydrogen, but they can play a crucial role in specific applications where their properties are particularly beneficial.”
The review also highlights the fact that several of these metals, such as magnesium and potentially zirconium, are considered critical raw materials, adding complexity to their large-scale use as energy carriers. This underscores the need for careful consideration of supply chain dynamics and the potential for geopolitical and economic implications.
As the energy sector continues to evolve, the role of metal fuels in renewable energy storage and the circular economy is likely to gain prominence. By aligning with circular economy principles, metal fuels can address specific energy storage needs while supporting the recycling of metal oxides. This research not only sheds light on the potential of metal fuels but also underscores the importance of a diversified approach to energy storage, one that leverages the unique advantages of different technologies to create a more sustainable and resilient energy landscape.