O-2 electroreduction catalysis: effects of sulfur addition on some cobalt macrocycles

In the present paper the effects of sulfur additions under thiourea form we re examined in the case of two macrocycle precursor catalysts (Cobalt tetaa zaannulene and Cobalt tetramethoxyphenyl porphyrin) after heat treatments a t 600 degrees C and 800 degrees C. Rotating disk Experiments (RDE) were app lied. A beneficial effect was found in both cases for S/Co=1 initial value which turned out to be amplified in the case of CoTAA precursor to about 50 mV at constant I. As imides and their protonated forms were evidenced from XPS techniques on the macrocycle precursor catalysts, RDE were also conduct ed on four distinct imide precursor catalysts including a thione derivative . The thione has also been found to be more active than the other one imide s. From XPS experiments on the mast active macrocycle precursors a binuclea r cobalt site is suggested and the active site density reveals to be propor tional to the cobalt and to the oxygen percentage which can be fixed on the active site with the additional sulfur.