Effect of Acid-Leaching on the Electrochemical Performance of Carbon-Supported Copper Phthalocyanine Tetrasulfonic Acid Tetrasodium Salt (CuTSPc/C) Catalys

Since the strong O=O bond (498kJ mol^-1) with very slow oxygen reduction reaction (ORR) rate at the cathode has a much larger overpotential (or polarization) than that of hydrogen oxidation reaction (HOR) at the anode, the cathodic ORR has become the most challenging step in a fuel cell¹. Up to now, Pt is still the best catalyst candidate for the ORR due to its high catalytic activity. As yet, there are still two major challenges for the Pt-based catalysts, one is high cost, and the other is insufficient electrochemical durability^2-3. Therefore, the major effort in fuel cell research and development have been put on reducing Pt loading by exploring more effective synthesis technologies, and/or replacing Pt metal using other non-precious metals such as Fe, Co and Cu.  

In this regard, carbon-based transition metal macrocycle complexes catalysts have become one of the most promising candidates to replace Pt/C catalyst, especially these catalysts synthesized after thermal treatment show high catalytic activity^3,4. For revealing the mechanism of ORR and improving the ORR activity, one should know the active site in these catalysts. So far, there is a consensus that carbon, nitrogen and transition metals are all considered to be indispensable elements for the ORR activity⁵. However, for the transition metals, there is few report clearly point out whether it is a part of the active sites in these macrocycle complexes. In this work, with carbon-supported copper phthalocyanine tetrasulfonic acid tetrasodium salt, CuTSPc/C, as a target, the role of transition metal in macrocycle complexe was investigated by acid-leaching procedures.