Sugar-based catalysts for oxygen reduction reaction. Effects of the functionalization of the nitrogen precursors on the electrocatalytic activity

Non-noble metal catalysts for the electrochemical reduction of oxygen (ORR) in acidic and alkaline solutions have been produced by pyrolysis of a silica gel containing fructose, as a carbon source, and derivatives of guanidine, as nitrogen compounds. The importance of the formation of iron complexes with nitrogen precursors to obtain good oxygen reduction reaction (ORR) catalysts has been investigated by varying the functionalization of guanidine derivatives. The presence of secondary or tertiary amines on guanidine limits or hinders the formation of iron complexes and, as a result, the produced materials are not very active. Conversely, the presence of primary amines promotes the formation of iron complexes, and, during the pyrolysis, of iron nanoparticles and ordered graphitic planes, making the final material very active for ORR. An explanation of this behavior in terms of surface and bulk composition has been proposed. An attempt to find the ORR rate determining step for the samples in both alkaline and acidic solutions has been done.