Microstructure engineering of bimetal-doped carbon nanospheres for accelerated electrochemical nitrobenzene reduction

Transition metal-doped carbon nanospheres featuring well-defined nanoporous structures are promising electrocatalysts, however, integrating abundant metal active sites while maintaining structural integrity has remained a significant challenge for optimizing metal loading and catalytic efficiency. Herein, we report a template-free strategy to construct Co/Fe-bimetal-co-doped carbon nanospheres (xCoyFe@C) by carbonizing metal-incorporated resorcinol-formaldehyde resins (xCoyFe@RF) with various Fe/Co molar ratio, enabling precise microstructure engineering. Systematic investigations reveal that the iron precursor serves as a morphology-directing agent and, in concert with metal salt identity, dosage, precursor addition sequence, and reaction time, governs the polycondensation kinetics and structural evolution. A progressive transformation from solid to yolk-shell architectures is observed with increasing Fe/Co molar ratio, elucidating the pivotal role of bimetallic interactions in tailoring nanostructures. When evaluated for electrocatalytic nitrobenzene reduction, all bimetal-doped carbon materials exhibit enhanced activity relative to single-metal and metal-free counterparts. Notably, the yolk-shell 1Co1Fe@C achieves a superior conversion of 92.6% and 85.3% selectivity toward azoxybenzene. The improved performance is attributed to the synergistic effects between cobalt and iron species coupled with optimized porous architecture, which facilitates mass transport and active site accessibility. This work provides a versatile platform for designing cost-effective bimetal-doped carbon nanostructures and offers insights into structure-performance relationships for selective nitrobenzene hydrogenation.