High-pressure synthesis of trimetal phosphide CFNP as highly efficient bifunctional catalyst for alkaline water splitting

Creating highly efficient bifunctional transition metal phosphide catalysts for electrochemical water splitting through cost-effective and universal methods remains an elusive challenge. Here we introduce a universal high temperature and high pressure (HTHP) technique that readily produce phase-pure TMPs, including FeNiP, CoNiP, and Fe 2/3 Co 2/3 Ni 2/3 P (CFNP), which can serve as an ideal model for investigating the relationship between electrocatalytic activity, structure, and chemical composition. The crystal structure of obtained CFNP has been carefully determined for the first time by using single-crystal X-ray diffraction (XRD) and XAS simulations. In the structure of CFNP, iron atoms form an MP4 tetrahedron with Co atoms and a 5-coordination pyramid with Ni atoms. This arrangement synergistically induces an electron-deficient state in the metals and an electron-rich state in phosphorus, enhancing CFNP/NF’s bifunctional catalytic effectiveness, achieving low overpotentials of 92 mV and 239 mV at 10 mA/cm 2 in 1 M KOH environment for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Moreover, an integrated electrolyzer using CFNP/NF as both electrode components can achieve a current density of 10 mA cm −2 at 1.536 V, showcasing a catalytic activity for overall water splitting comparable to those of phosphide-based electrocatalysts. The HTPH technique opens new possibility for exploring pure-phase multimetallics and high-entropy phosphides as potential multifunctional materials for potential applications.