Pyrolysis-free synthesis of single-atom cobalt catalysts for efficient oxygen reduction

Abstract

Nitrogen-coordinated single-atom catalysts (SACs) have emerged as one of the most promising alternatives to noble metal-containing benchmarks for highly efficient oxygen reduction reaction (ORR). However, the commonly required high-temperature pyrolysis usually results in undesirable structural changes and randomly produced active sites which gives rise to great challenges to the structure–property relationships, inevitably hindering the understanding of the reaction mechanisms. Herein, we demonstrate a simple yet robust pyrolysis-free route to craft single-atom cobalt catalysts with high electrocatalytic ORR activity via judiciously in situ wrapping an electrocatalytically active porphyrin-based thiophene-sulfur site-containing covalent organic polymer (PTS-COP) shell around a highly conductive multiwalled CNT (MWCNT) core, followed by accurately anchoring single-atom Co–N₄ sites onto the macrocyclic porphyrin structure. The resulting Co-PTS-COPs@MWCNTs was exploited as an ORR electrocatalyst and displayed outstanding performance as a direct consequence of the advantageous architecture (i.e., 1D core@shell heterostructures with few-layer-thick PTS-COP shells) and unique active site configurations (i.e., atomically anchored Co–N₄ sites and homogeneously dispersed thiophene-sulfur sites). Remarkably, an alkaline electrolyte capitalizing on Co-PTS-COPs@MWCNTs achieved excellent ORR activity (E_onset, 0.930 V; E_1/2, 0.835 V), and favourable long-term durability, comparable to that of state-of-the-art carbon-based electrocatalysts.