Coupling a Low Loading of IrP₂, PtP₂, or Pd₃P with Heteroatom-Doped Nanocarbon for Overall Water-Splitting Cells and Zinc–Air Batteries

Noble metal-based catalysts are currently the most advanced electrocatalysts for many applications, such as for energy conversion and for chemical industry. Because of the high cost and scarcity of noble metals, reducing the usage is a practical way to achieve scalable applications. Herein, for the first time, three novel electrocatalysts composed of noble metal phosphide (IrP2, Pd3P, or PtP2) nanoparticles with N,P-codoped nanocarbon were synthesized by the pyrolysis of mixtures of IrCl4, PdCl2, or PtCl4 with phytic acid under an ammonia atmosphere. With an ultralow loading of Pd (1.5 μg), Pt (1.4 μg), or Ir (1.6 μg) on the electrode, the Pd3P/NPC, PtP2/NPC, and IrP2/NPC catalysts, respectively, exhibited excellent trifunctional catalytic activities for the oxygen reduction reaction, hydrogen evolution reaction, and oxygen evolution reaction. Notably, the IrP2/NPC-, Pd3P/NPC-, and PtP2/NPC-based water-splitting cells required only 1.62, 1.65, and 1.68 V, respectively, to deliver the current density of 10 mA cm–2. Furthermore, the IrP2/NPC-, Pd3P/NPC-, and PtP2/NPC-based zinc–air batteries exhibited higher specific capacities than that of Pt/C. IrP2/NPC exhibited a comparable performance to that of Pt/C-IrO2 for use in rechargeable zinc–air batteries.