Iron Phosphide Doped, Porous Carbon as an Efficient Electrocatalyst for Oxygen Reduction Reaction

Finding alternative catalysts as a replacement for platinum in fuel cells to perform oxygen reduction reaction (ORR) is vital for the widespread use of fuel cell technology. The scarcity and high cost of platinum combined with its vulnerability to poisoning by fuel crossover greatly impede effective use of fuel cells. In this study, a simple and cost-effective synthesis using triphenylphosphine and iron­(II) chloride was developed to produce highly porous P and Fe-doped carbon (PFeC, SA_BET = 967 m² g^–1) with Fe and P contents of 9.8 and 4.1 at. %, respectively. This synthetic route also generates Fe₂P particles, active centers, supported on P-doped porous carbon which was found to be electrochemically active toward ORR in both alkali and acidic media. The optimized PFeC electrocatalyst has a competitive onset and half-wave potential in comparison to commercially available Pt/C (20 wt %), and it selectively reduces O₂ via a single-step 4e^– reaction pathway. The PFeC electrocatalyst exhibits superior long-term stability of 90% for the duration of a 15 h chronoamperometry test and inertness toward the oxidation of methanol. The superior electrocatalytic performance is credited to the synergistic effects between the P and Fe atoms, in the form of well-defined and well-distributed nanoparticles confined in highly porous carbon nanosheets. The enhancement in electrochemical activity is also credited to the exposed active sites on the surface of the PFeC sheets and the high conductivity of the conjugated carbon backbone induced by uniform dopant disruption of the electroneutrality of carbon. The large surface area of PFeC and its well-developed porous structure increase the points of contact for adsorption and rapid transportation of the reactants and improve the overall electrocatalytic activity of PFeC.