One-step synthesis of MN4 molecular electrocatalysts assembled on different nanocarbon architectures for efficient oxygen reduction

Abstract

One-step dry ball-milling method was employed to prepare different electrocatalysts based on cobalt(II) or iron(II) phthalocyanines (CoPc and FePc, respectively) supported on commercial carbon materials (CNovel or a carbon black (Vulcan)), controlling the nominal metal content to 1 or 2 wt %. No pre-treatment (e.g., functionalization of the carbon support), solvent addition or post-processing steps (e.g., heat-treatment, acid-treatment, etc.) were required before, during or after the mechanochemical process. Different characterization techniques have been used to study the morphological, physicochemical and electrochemical properties of the synthesized materials. The as-prepared catalysts can be directly used without involving further procedure. Solid-state ball-milling strategy provides excellent contact of both components, which synergistically improved their electrocatalytic performance. Regarding the carbon materials, the adequate nanoarchitecture and surface chemistry of CNovel permits better distribution of metal phthalocyanines (MPc) compared to a carbon black. The FePc supported on CNovel shows excellent electrocatalytic activity for oxygen reduction reaction (ORR), in terms of good selectivity towards the 4-electron pathway, long-term stability and low overpotential in alkaline medium. This study opens new paths for a simple, scalable and cost-effective catalyst manufacturing through mechanochemistry that can be modulated by selecting the proper nanocarbon support and MPc/carbon ratio.