Valorisation of Red Mud: Microstructure and Oxide Retention in Stainless Steel 316 L-Based Composites for Direct Carbon Fuel Cells

Red mud has been recognized as an industrial waste that brings significant challenges to recycling since it consists of heavy metal residuals and strong alkaline substances. Nevertheless, the abundance of Fe oxides imparts functional value, making it viable for specific applications. For example, direct carbon fuel cells would benefit from the addition of red mud into the anodic material. Its novel exploitation as a powder feedstock of binder jetting would combine functional properties with higher geometric freedoms in anode design. This work aims to explore the feasibility of producing anodes with stainless steel 316 L and red mud composite via binder jetting and optimize the post-processing parameters to retain and control Fe oxides after sintering. Optimal post-processing cycle is air debinding at 600 °C and sintering at 1360 °C in vacuum, being capable of retaining enough amount of complex Fe-Cr-Mn oxides to enhance the kinetics of carbon activation. The addition of red mud has been proven to provide catalytic effects to the direct carbon fuel cells. 2.5 wt% red mud composite is capable of shortening the stabilization time of 80% and almost doubling both the current and power density (from 13 to 24 mA/cm2 and from 5 to 9 mW/cm2, respectively).