Nano- and micro-sized TiN as the electrocatalysts for ORR in Li–air fuel cell with alkaline aqueous electrolyte

Due to its higher electrical conductivity compared with carbon and its outstanding corrosion resistance, titanium nitride (TiN) has recently been studied intensively for applications as an active electrode as well as catalyst support materials in supercapacitors, fuel cells and Li–air batteries. In this work, we studied the electrocatalytic activities of nano- and micro-sized TiN toward the oxygen reduction reaction (ORR) in an alkaline media using a thin film–rotating-disk electrode (RDE) technique, and investigated their performances as active air electrodes on a newly developed Li–air fuel cell with a hybrid electrolyte. The results show that both nano- and micro-sized TiN exhibit electrocatalytic activities toward ORR in alkaline media but with different mechanisms. The ORR catalyzed by micro-sized TiN proceeds via the serial “2e− + 2e−” pathway in a consecutive manner with the reduction of HO2− starting at a higher electrode potential as a discrete step. On the other hand, the ORR catalyzed by nano-sized TiN proceeds via a dual-path, where the two serial “2e−” steps proceed with smaller intervals and manifest an overall mixed appearance by coexistence of the parallel and serial “2e−” steps. The extent to which the two steps are in parallel or consecutive reveals a potential-dependent feature. Furthermore, both nano- and micro-sized TiN particles demonstrate evident electrocatalytic activities toward ORR in the Li–air fuel cell, with the nano-sized TiN showing a much better catalytic activity, which is comparable to that of the nano-sized Mn3O4.