Neodymium nickelate Nd2-xSrxNi1-yCoyO4 ± d (x and y = 0 or 0.05) as cathode materials for the oxygen reduction reaction

The results show that before the ORR, the grains of the undoped material are spherical in shape with a size around 400 nm, while after the oxygen reduction reaction, the grain size increases. In the doped material, on the contrary, the results are reversed and the grain size becomes smaller. In addition, we show that the ORR mechanism proceeds in a single step in the undoped material while it is carried out in two successive steps in the case of the doped one. XPS analysis confirms that the sites responsible for the ORR are the OH− groups. Doping with Sr or Co does not improve the electrochemical properties: this dopant adversely affects the formation of the sites responsible for the dissociation of molecular oxygen. For larger hydroxide groups content (2.30, Nd2NiO4 ± δ) the electrochemical currents are much greater relative to that of the other Nd1.95Sr0.05Ni0.95Co0.05O4 ± δ (0.98) material. This work helps to understand the role of OH− groups, and the reduction mechanisms with 2 and 4 electrons.