Unusual enhancement in the electroreduction of oxygen by NiCoPt by surface tunability through potential cycling

Abstract

Chemically ordered interconnected nanostructures of NiCoPt alloy have been prepared using a simple solvothermal process and studied for oxygen reduction reaction (ORR) kinetics. NiCoPt/C catalyst has demonstrated an interesting trend of enhancement in the ORR activity along with long-term durability. The specific activity of 0.744 mA cm⁻² for NCP10/C (NiCoPt/C prepared at reaction time of 10 h) is ∼3.7 times higher than that of Pt/C (0.2 mA cm⁻²). The durability of the catalyst was evaluated over 30k potential cycles in the lifetime regime. More significantly, a novel trend in the enhancement in the ORR activity during stability cycles has been observed for the first time, where a remarkable enhancement of 82% in the specific activity has been observed after 30k potential cycles. Thus, ∼7-fold higher activity of NCP10/C@30k over initial activity of commercial Pt/C would make a tremendous impact on fuel cell technology. Systematic X-ray diffraction studies were performed to supplement subsequent improvement in the ORR activity during potential cycling, where structural changes due to alloying and de-alloying taking place with formation of tetrahexahedron-like surfaces after 15k cycles. Furthermore, transmission electron microscopy (TEM) analysis after 30k durability cycles reveals better stability of NCP10/C nanostructure signifying the retention of Ni and Co due to the chemically ordered structures of NiCoPt alloy catalyst. The observed enhancement in durability might be due to the ordered arrangement of Pt and Ni/Co within the alloy.