Effects of using two transition metals in the synthesis of non-noble electrocatalysts for oxygen reduction reaction in direct methanol fuel cell

Abstract

Five different bimetallic non-precius metal catalysts for oxygen reduction reaction (ORR) are synthesized by different combinations of two transition metal (Fe, Co, Cu, Zn) phthalocyanine precusrsors. The aim of this study is to investigate the effects of the different combinations of two transition metals on the physico-chemical and ORR electrocatalytic activity of the catalysts. The precursors were mixed, impregnated on a mesoporous silica used as a hard template, and pyrolyzed under inert atmosphere at 800 °C. After the template removal, the catalysts were characterized via BET, FESEM, and XPS. TGA-MS analysis was also performed on the catalysts precursors to simulate their behaviour during the pyrolysis, detecting the evolved gases. The results show that both the physico-chemical features and the ORR activity and selectivity in acidic medium (measured by RDE-RRDE technique) are strongly influenced by the transition metals pair used. In particular, the most effective transition metals pair to get a more performing ORR catalyst is Co-Zn. The catalysts are also tested in direct methanol fuel cell, including a short-term durability test. The durability of the best perfroming Co-Zn catalyst is improved compared to a similar catalyst synthesized using Fe. The possibility of tuning the catalysts features by combining different transition metals enables to increase the catalyst durability, the production yield during the synthesis (enabling to recover more material after the pyrolysis), and the surface N fixation.