Aluminium is a promising material as an alternative green energy storage solution thanks to its very high volumetric energy density (23.5 kWh/L) and full recyclability. CO₂-free aluminium could be produced from renewable energy sources through an electrolytic process by using vertical inert anodes and wetted drained cathodes as a sustainable substitute to the Hall-Héroult process with horizontal carbon anodes and cathodes. The use of consumable carbon anodes in the Hall-Héroult process is a significant contributor to greenhouse gas production, with 1.5t of CO₂ produced per tonne of aluminium. Implementation of an inert anode changes the overall chemical reaction as follows:

2Al₂O_3(sol) + 3C(s) → 4Al_(l) + 3CO_2(g)    carbon anodes

2Al₂O3(sol)  → 4Al(l) + 3O2(g)        inert anodes

Ni-Fe-Cu alloys have emerged as a strong candidate for inert anodes [1-3] in vertical electrode cells. Ni-Fe-Cu alloys exhibit good electrical conductivity, thermal shock resistance, corrosion resistance at working temperatures (~800ᵒC for low temperature electrolysis), with a simple FCC structure, in addition to being commercially viable as well. Successful alloy(s) should produce a robust oxide layer and retain anodic function.

Our work aims to undertake a systematic investigation of the anode properties (corrosion resistance, cell stability, purity of resultant aluminium) as a function of the alloy composition to determine an optimal composition range for vertical electrolysis cell performance. Electrolysis tests and oxidation studies at the laboratory scale will be done for optimal upscaled process to industry level. Analysis of the oxide layer on the anode surface is required to understand which oxide formations correlate to optimal cell performance. Fourth and fifth element additions will be considered after the ternary Ni-Fe-Cu composition has been refined to optimise performance in the electrolytic cell.

[1] I. Gallino et al., Corrosion Science, 63 (2012) 293-303

[2] T.R. Beck (1995), Light Metals 1995, Minerals Metals & Materials Society, 355-360

[3] H. Yong et al., Journal of Materials Chemistry A, 9 (2021) 25272