Metal energy carriers

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Metal Energy Carriers (MEC) are recyclable energy carriers in which elementary metals are used to store and transport energy. The energy is chemically stored through the reduction of metal oxides to their metallic form, a process that requires an energy input. This stored energy can later be released by oxidizing the metal back to its oxide. The resulting metal oxide can then be reused in another reduction-oxidation cycle, making the process inherently recyclable or rechargeable.

A subcategory of MECs are Renewable Metal Energy Carriers (ReMECs), which fulfill the same recyclability criteria but are produced exclusively using renewable energy sources such as solar, wind, and hydropower.

Key characteristics of metal energy carriers include their high energy density, long-term storability, and potential for circular use.

insert infobox such as this one here; circularity schematic? Iron powder?

Process

The use of metals as energy carriers is based on redox cycles, in which reduction reactions chemically store energy and oxidation reactions release energy.

Energy release

For the energy release via metal oxidation, typically two main routes are considered:

Dry cycle

In the dry cycle, metals oxidize/combust with air to release their energy as high-temperature heat:

$x\mathrm{M}{\phantom{A}}_{(\mathrm{s})}+\mathrm{y}\frac{1}{2}\mathrm{O}{\phantom{A}}_2{\phantom{A}}_{(\mathrm{g})}⟶{\mathrm{M}}_{\mathrm{x}}{\mathrm{O}}_{\mathrm{y}}{\phantom{A}}_{(\mathrm{s})}+\mathrm{Q}{\phantom{A}}_1$

Wet cycle

In the wet cycle, metals react with water at high temperatures to produce heat and hydrogen:

$x\mathrm{M}{\phantom{A}}_{(\mathrm{s})}+y\mathrm{H}{\phantom{A}}_2\mathrm{O}{\phantom{A}}_{(\mathrm{g}/\mathrm{l})}⟶\mathrm{M}{\phantom{A}}_x{\mathrm{O}}_{\mathrm{y}}{\phantom{A}}_{(\mathrm{s})}+\mathrm{y}{\mathrm{H}}_{\mathrm{2}}{\phantom{A}}_{(\mathrm{g})}+\mathrm{Q}{\phantom{A}}_2$

Energy storage

Energy can be stored chemically by reducing metal oxides, which may originate from previous oxidation reactions as energy carriers, to metals. Possible pathways include thermochemical reduction using renewable and fossil reduction agents, such as hydrogen and carbon, and electrochemical reduction using direct electrolysis.

$\mathrm{M}{\phantom{A}}_x{\mathrm{O}}_{\mathrm{y}}{\phantom{A}}_{(\mathrm{s})}\stackrel{\mathrm{r}\mathrm{e}\mathrm{d}\mathrm{u}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}{\to }x\mathrm{M}{\phantom{A}}_{(\mathrm{s})}+\mathrm{y}\text{1/2}{\mathrm{O}}_{\mathrm{2}}{\phantom{A}}_{(\mathrm{g})}$

Materials

Iron

Crosslink to Iron-Steam Process

Reduction: Direct electrolysis, green steel production

flame temperatures

Aluminium

Reduction: Hall-Hèroult-Process, carbon and inert anodes; specifics of aluminium oxidation (homogeneous combustion, pressurized combustion, processes and conditions to break the oxide layer).

History

Metals such as aluminium have been used as energy carriers for a long time in fireworks and in the space industry for the propulsion of spacecraft in solid rocket propellants. The concept of using oxidation and reduction reactions of metals is also the base for the construction of electric batteries. However, using metals outside a battery as bulk material to store energy, release this energy by oxidation and recycle the oxidized metal by converting it into its elementary state again, differs from these approaches. This concept of metal energy carriers goes back to at least 2015. Systematic analysis of the periodic table of elements have been performed and it has been found that aluminium and iron are suitable candidates for recyclable and renewable metal energy carriers.

Research initiatives

Applications and Use Cases

Hydrogen Production

Industrial Heat Generation

District Heating

Electricity Power Plants (Grid-Scale Electricity Storage and Dispatchable Power Plants)

References

This article "Metal energy carriers" is from Wikipedia. The list of its authors can be seen in its historical and/or the page Edithistory:Metal energy carriers. Articles copied from Draft Namespace on Wikipedia could be seen on the Draft Namespace of Wikipedia and not main one.

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