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.