Rare earth metals are an essential part of our daily lives. They are present in more application than we realize, some of these include cell phones, all computer or electronic devices, ovens, cars and fuel additives to name a few. This article will focus on a specific rare earth metal called Cerium. Cerium bonds with oxygen forming cerium oxide a highly useful industrial material. Cerium oxide has two primary applications, first it is often used to coat self cleaning ovens. In terms of a self cleaning oven, cerium oxide acts as a hydrocarbon catalyst during the high-temperature cleaning process. Cerium oxides primary use is in fuel cells. Cerium oxide is useful for fuel cells because of its unique ability to rapidly reduce from a 4+ cation to a 3+ cation. Cerium oxide has a large oxygen storage capacity which has been explored in numerous scientific papers. Its oxygen storage capacity is a function of particle size, it has been demonstrated that a 2 nanometer (nm) particles have the greatest ability to store oxygen.
Cerium oxide exists as Ce2O and Ce2O3 oxides, research is currently being conducted into Cerium oxide particles that are doped with Iron in the 2+ and 3+ cation states. The ongoing research has shown that the oxygen storage capacity can be increased 10 fold in a 2 nm (1x10^-9 m) particle. Cerium oxide exhibits the cubic fluorite structure and experimentation has shown that a 1 nm is too unstable to yield a large oxygen storage capacity. Cerium oxide is a candidate for solid oxide fuel cells (SOFCs) because of its high oxygen storage capacity (OSC). It is worth noting that during the reduction process the lattice constant of cerium oxide expands due to the transition from a 4+ cation state to a 3+ state cause by the oxygen vacancy. For this reason cerium oxide is considered for use as a fuel additive.
Cerium oxide is also used in catalytic converters. Cerium oxide exhibits non-stoichiometric properties meaning that it can give up oxygen atoms while keeping its cubic fluorite structure. Doping cerium oxide with quantities of Iron (Fe) cause a reduction in the lattice constant due to the smaller ionic radius of Fe. This causes accessible Ce 3+ ions to appear on the surface which allows for the nanoparticle to act as a catalytic center for activity through chemical processes. Increasing the OSC of the lattice gives rise to increase catalytic activity and oxygen transport properties, making better fuel cells and other battery types.