Transition metal carbides and nitrides as oxygen reduction reaction catalyst or catalyst support in proton exchange membrane fuel cells (PEMFCs)

Fuel cells are potentially efficient, silent, and environmentally friendly tools for electrical power generation. One of the obstacles facing the development and the commercialization of fuel cells is the dependence on the precious metal catalyst, i.e., Platinum (Pt) and Pt - alloy, especially at the cathode where high catalyst loading used to compensate the sluggish oxygen reduction reaction (ORR). Pt is not only an expensive and rare element but also has insufficient durability. The development of an efficient non-precious catalyst, i.e., electrochemically active, chemically and mechanically stable, and electrically conductive, is one of the basic requirements for the commercialization of fuel cells. The bonding to carbon and nitrogen to form metal carbides and nitrides modify the nature of the d-band of the parent metal, thus improve its catalytic properties relative to the parent metals to be similar to those of group VIII noble metals. In this article, we summarize the progress in the development of the transition metal carbides (TMCs) and transition metals nitrides (TMNs) relative to their application as catalysts for the ORR in fuel cells. The preparation of TMCs and TMNs via different routes which significantly affects its activity is discussed. The ORR catalytic activity of the TMCs and TMNs as a non-precious catalyst or catalyst support in fuel cells is discussed and compared to that of the Pt-based catalyst in this review article. Moreover, the recent progress in the preparation of the nano-sized (which is a critical factor for increasing the activity at low temperature) TMCs and TMNs are discussed.