Coordinated P Atoms Promote Bifunctional Activity for ORR and HER in Atomically Dispersed Fe-N_x Sites

In this study, we report the design and synthesis of a bifunctional Fe-N-P@TDC electrocatalyst derived from renewable precursors, tannin and phytic acid. The catalyst was prepared through a mechanochemical reaction of these precursors with urea and FeCl₃ as nitrogen (N) and iron (Fe) precursors, respectively, followed by simple pyrolysis at 900°C. The innovative integration of phosphorus (P) atoms coordinated to Fe-N_x single-atom sites creates a unique electronic environment that enhances catalytic activity for both ORR and HER. Density Functional Theory (DFT) calculations reveal that FeN₂P₂ and FeNP₃ configurations are the most active sites, showing synergistic effects of P coordination in weakening intermediate adsorption energies and promoting reaction kinetics. The Fe-N-P@TDC catalyst exhibits superior bifunctional activity, with ORR half-wave potentials and HER overpotentials comparable to commercial Pt/C, but at a fraction of the cost and higher stability. This work demonstrates that fine-tuning of Fe-N_x coordination with P atoms in sustainable carbon matrices offers a viable route toward efficient, durable, and low-cost electrocatalysts for clean energy conversion.