In situ self-organization of uniformly dispersed Co–N–C centers at moderate temperature without a sacrificial subsidiary metal

Abstract

A one-pot, single step, eco-friendly methodology to promote uniform distribution of Co–N _x–C active centers with suppressed futile nanoparticle formation for electrochemical oxygen reduction.

Abstract

M–N–C centers have garnered tremendous research attention as a potential replacement for the Pt-group metal based cathode catalysts and are expected to be an integral part of the next-generation cathode catalysts for fuel cells and metal–air batteries. Mostly, a Zn based bimetallic organic framework or template is used along with high pyrolysis temperature (>900 °C) and the product is treated with an acid to obtain the uniformly dispersed M–N–C centers. Herein, we report a simple organic solvent free one-step pyrolysis of cobalt phthalocyanine (CoPc) and dicyandiamide (DCDA) at moderate temperature (750 °C) for the synthesis of uniformly dispersed Co–N–C centers in the carbon matrix without any post acid treatment, any subsidiary sacrificial metal like Zn or any NH ₃ treatment. This single step process bypasses any post synthesis manipulation thus making it user friendly and does not induce any burden to chemical waste management facilities which are otherwise required in post synthesis techniques. The introduction of DCDA offers an additional degree of freedom to tune the nitrogen content – an important entity to support the M–N–C institution. Atomically dispersed Co–N–C in carbon matrix exhibits a superior and highly durable oxygen reduction reaction (ORR) performance with suppressed peroxide generation due to the muted outer sphere electron transfer mechanism in comparison with the commercially available state-of-the-art Pt/C electrocatalysts. Though we have reported the synthesis of Co–N–C centers, the methodology can be applied to design a variety of other M–N–C monometallic as well as multimetallic systems.