Inert Anodes for the Hall-Héroult Cell: the Ultimate Materials Challenge

Introduction The principal obstacles to improving the productivity of the Hall-Héroult cell derive from limitations imposed on its design by the lack of suitable materials. Alternatively, the discovery of a material that could serve as an inert anode, especially if combined with a wettable cathode and a ledge-free sidewall, would enable major changes in cell design and operating practice with attendant improvements in energy and resource utilization as well as in environmental impact. The search for this elusive material has taken over 100 years. Indeed, Charles Martin Hall himself lamented that in the absence of an inert anode he feared that aluminum would have difficulty attaining the status of a structural metal on a competitive footing with steel. The purpose of this article is to review the current status of inert anode materials and suggest possible directions for future work. Table I lists the performance requirements of an inert anode. Taken in sum they represent a formidable challenge, and it is evident why the search for the inert anode has gone for so long. The efforts to date have focused on three materials classes: ceramics, cermets, and metals.