Single-atom catalysts (SACs) are a rising star in the area of electrocatalysis due to potential merits: (1) economic use of expensive and rare metals through superior metal utilization, (2) stable performance of single metal atoms against agglomeration, (3) tunable activity by modifying metal- ligand configuration. One common structure of SAC is through metal-nitrogen-carbon (M-N-C) arrangements where single metal (M) atoms act as active sites for adsorption and desorption of molecules. These metal atoms are stabilized by coordination with nitrogen atoms. In spite of extensive research of SACs, several critical challenges remain: (1) poor anchoring of single metal atoms on catalyst support causing metallic agglomeration, (2) inability to achieve uniform distribution of metal atoms on support, and (3) limited metal loading (&lt;5wt%) that is a barrier against commercialization of SAC-based technology.<br/>In this seminar, we report an efficient and versatile strategy to synthesize Cu- and Fe- SACs with a high metal loading. Both Cu- and Fe- SACs were tested for performances towards electrochemical oxygen reduction reaction (ORR) in comparison with commercial Pt/C. Our synthesis pre-dominantly formed single-metal-based catalysts where individual metal atoms are uniformly distributed with high metal loading (Cu and Fe loadings of up to 20 wt%). The synthesis employed critic-acid-derived carbon nanodots (CNDs) that captured metal single atoms and then were pyrolyzed in presence of urea. During pyrolysis, nitrogen and metal were incorporated into graphitized carbon and formed metal-nitrogen coordination. The location and distribution of SACs were determined by high-resolution scanning transmission electron microscopy (HR-STEM). The chemical nature and loading of SACs were probed by X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA), respectively. In electrochemical tests of SACs towards ORR, Cu- and Fe- SACs showed comparable overpotentials and limiting currents following four electron pathway to those of commercial Pt/C.

Carbon-nanodots-derived single atom catalysts: Synthesis and catalytic activity for oxygen reduction reaction

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