Analysis of the potential of four reactive metals as zero-carbon energy carriers for energy storage and conversion

Reactive metals are emerging as potential zero-carbon energy carriers. The recent increase in fundamental knowledge on this topic calls for an assessment of the actual potential of the different metals proposed to fulfil this role on a commercial scale. In the present study, a Multi-Criteria Decision Analysis (MCDA) is performed for iron, aluminium, magnesium and silicon. The nine Selection Criteria (SC) cover the entire metal energy cycle and allow for a practical comparison of the metal candidates. A particular attention was given to the technology readiness of the key processes (energy charge through metal oxide reduction, and energy discharge through metal-air combustion). The study suggests that despite better intrinsic characteristics of the other metals, the much greater availability of iron makes it the most suitable to become a global zero-carbon energy carrier on a short term, especially for stationary applications. For mobile applications however, the energy densities of aluminium make it a better alternative. Our review gives a practical overview of the current knowledge on the metals cycles, and discusses current major roadblocks, such as nanoparticle emissions during combustion, that should be the focus of future research.