Magnesium Transfer between Atomic Force Microscopy Probes and Metal Electrodes in Aqueous Alginate Electrolytes.

The upcoming energy transition requires not only renewable energy sources but also novel electricity storage systems such as batteries. Despite Li-ion batteries being the main storage systems, other batteries have been proposed to fulfil the requirements on safety, costs, and resource availability. Moving away from lithium, materials such as sodium, magnesium, zinc, and calcium are being considered. Water-based electrolytes are known for their improved safety, environmentally friendliness, and affordability. The key, however, is how to utilize the negative metal electrode, as using water-based electrolytes with these metals becomes an issue with respect to oxidation and/or dendrite formation. This work studied magnesium, where we aimed to determine if it can be electrochemically deposited in aqueous solutions with alginate-based additives to protect the magnesium. In order to do so, atomic force microscopy was used to research the morphological structure of magnesium deposition at the local scale by using a probe-the tip of a cantilever-as the active electrode, during charging and discharging. The second goal of using the AFM probe technology for magnesium deposition and stripping was an extension of our previous study in which we investigated, for lithium, whether it is possible to measure ion current and perform nonfaradaic impedance measurements at the local scale. The work presented here shows that this is possible in a relatively simple way because, with magnesium, no dendrite formation occurs, which hinders the stripping process.

Iron and Manganese Alginate for Rechargeable Battery Electrodes.

We present a sustainable, inherently safe battery chemistry that is based on widely available and cheap materials, that is, iron and manganese hosted in alginate bio-material known from the food and medical industry. The resulting battery can be recycled to allow circularity. The electrodes were synthesised by the alginate caging the multi-valent metals to form a hydrogel in an aqueous environment. Characterisation includes FTIR, XPS and Mössbauer spectroscopy. The electrochemical performance of the electrodes was investigated by performing cyclic voltammetry (CV) and (dis)charge experiments. Mn and Fe ions show good co-ordination with the alginic acid with higher oxidation states demonstrating complex bonding behaviour. The non-optimised iron and manganese alginate electrodes already exhibit a cycling efficiency of 98% and 69%, respectively. This work shows that Fe and Mn atomically disperse in a bio-based host material and can act as electrodes in an aqueous battery chemistry. While demonstrated at cell level, it is furthermore explained how these materials can form the basis for a (semi-solid) flow cell.