  Humankind produced 63.7 million metric tons of aluminium in 2019, nearly all
via an electrochemical process in which electrical current liberates molten Al
from dissolved alumina. That year, Al production required 848 TWh of
electricity1, 3% of the worldwide total, and caused 1% of human greenhouse gas
emissions. Much of the electricity and emissions originate from energy loss in
the poorly conducting electrolyte where aluminum oxide is dissolved. Thinning
the electrolyte layer could decrease loss but has been limited by the Metal Pad
Instability (MPI), which causes Al cells to slosh out of control if the
electrolyte is not sufficiently thick. Here we show that adding an oscillating
component to the current disrupts the MPI in realistic simulations, allowing
stable operation with electrolyte layers at least 12% thinner. This occurs when
oscillation excites standing waves, which decouple the resonance that drives a
growing traveling wave, characteristic of the MPI. Maintaining oscillation can
prevent MPI; initiating oscillation can halt an MPI in progress. Our findings
could significantly increase the efficiency of virtually all aluminium refining
cells without the need for expensive reconstruction, thereby decreasing energy
use by 34 TWh/year (2.1 MJ/kg Al) or more and greenhouse gas emissions by 13
Mton/year or more.
