Insights of single-atom catalysts on nanocarbon support for energy conversion

The fundamental understanding of active sites for various important electrochemical reactions is studied theoretically and experimentally. We synthesized stone-wales (SW) defects rich nitrogen-doped graphene (DG) with specific coordination of carbon atom rings. It reveals that the SW rich defects rings (e.g.,5, 585, or 5775) appear correspondingly with carbon rings that brought active sites during catalytic reactions. Moreover, we anchored dual isolated metallic atoms (Ni/Fe) on DG support via linkers (O/N) to make its hybrids. DFT calculations are used to study the mechanistic understanding of SW defects rich support with dual metal single atoms. Numerous experimental tools such as XAS (XANES, EXAFS), STEM, XPS etc., are used to study detailed experimental insights. The proposed structure exhibits high catalytic activity and stability towards OER and ORR for a longer duration in an alkaline medium, with even better performance and stability than commercial Pt/C. We used laser irradiation techniques to optimize the porous structure of nanocarbon and use it as a supportive matrix via dangling bonding approach to extract metal atoms species from Co and Fe bulk metal foams and demonstrated as SAC for HER-ORR catalysts. The isolated metal SA are confirmed via AC-STEM, XANES and EXAFS. DFT simulations using the GCP-K model has been used to understand the mechanism at varying applied potentials. Moreover, we also applied Mn_SA and Mn_Cluster doped C₂N supported hybrids towards bifunctional (OER-HER) in alkaline media towards stable catalytic performance for 24 hours without deflection. The experimental evidence and theoretical mechanism are highlighted through characterizations, including ADF-STEM, XANES/EXAFS and DFT calculations. Mn_Cluster on C₂N support requires a very low overpotential of 57 mV and 282 mV, a current density of 10 mA cm^-2 towards HER and OER, respectively. Our consistent experimental and theoretical findings inaugurate an avenue towards designing rational catalysts intended for several important reactions like NRR and CO₂RR.