Electrolytic properties and element migration behavior in a Fe-TiB₂/Al₂O₃ composite cathode

Wettable cathodes are a very important part of the non-carbon electrolysis process. This study prepared Fe-TiB₂/Al₂O₃ composite cathode materials by cold pressing and sintering using alumina sol as a binder and metal Fe as a sintering agent for aluminum electrolysis. The electrolytic performance of aluminum electrolysis was studied using a 20 A electrolysis test, and the composite cathode materials before and after the test were analyzed via EDS. The migration behavior of various elements in the electrolysis process was studied by composition analysis. The results show that Fe metal can effectively fill the gap between the aggregates during the sintering process. Hence, the sintering density of the composite cathode material can be significantly improved. In the 20 A electrolysis test, the voltage is stable, the current efficiency is 93.2%, the original aluminum quality is 99.47%, and the impurity in the aluminum liquid is 0.53%. After the electrolysis test, the aluminum liquid can moisten the cathode surface effectively. Therefore, the Fe-TiB₂/Al₂O₃ composite is an ideal wettable cathode material. Based on the EDS analysis of the composite cathode electrolysis, the alkali metal in the liquid electrolyte permeates into the cathode material during the electrolysis process. Subsequently, alkali metals gradually penetrate into the binder phase and fill the voids that are not completely filled by alumina sol or metal sintering additives. As the electrolysis proceeds, the penetration depth of the element K is greater than that of Na. The Al generated at the cathode surface also enters the cathode through the gap of the composite material. However, owing to the gap in the cathode, the Fe metal in the cathode will also be reversely dispersed into the liquid aluminum. This study indicates that the stability of the aluminum liquid layer on the cathode surface is the foundation for efficient and stable operation of the cathode.