Noble Metal Phosphides Supported on CoNi Metaphosphate for Efficient Overall Water Splitting

Transition metal metaphosphates and noble metal phosphides prepared under similar conditions are potential hybrid catalysts for electrocatalytic water splitting, which is of great significance for H2 production. Herein, the structure and electrocatalytic activity of different noble metal species (i.e., Rh, Pd, Ir) on CoNiP4O12 nanoarrays have been systematically studied. Due to the different formation energies of noble metal phosphides, the phosphides of Rh (RhPx) and Pd (PdPx) as well as the noble metal Ir are obtained under the same phosphorylation conditions perspectively. RhPx/CoNiP4O12 and PdPx/CoNiP4O12 exhibit much better HER activity than Ir/CoNiP4O12 due to the advantages of phosphides. Density functional theory (DFT) calculations reveal that the extraordinary activity of RhPx/CoNiP4O12 originated from the strong affinity to H2O and optimal adsorption for H*. The best RhPx/CoNiP4O12 only requires a low overpotential of 30 and 234 mV to deliver 10 mA cm-2 for HER and OER, respectively, and therefore is effective for overall water splitting (requiring 1.57 V to achieve a current density of 10 mA cm-2). This work not only develops a novel RhPx/CoNiP4O12 electrocatalyst for overall water splitting but also provides deep insight into the formation mechanism of noble metal phosphides.

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.