Rational Synthesis of Metal-Organic Framework-Derived Noble Metal-Free Nickel Phosphide Nanoparticles as a Highly Efficient Cocatalyst for Photocatalytic Hydrogen Evolution

Facile preparation of metal-organic framework (MOF) derived earth-abundant nickel phosphide (Ni₂P) by a simple, cost-effective procedure is described. Ni₂P is recognized as a suitable replacement for expensive noble metal cocatalysts used for H₂ production by water splitting. Ni₂P nanoparticles were used to prepare a Ni₂P/CdS composite with improved photocatalytic properties. Crystal structure and surface morphology studies showed that Ni-MOF spheres readily transform into Ni₂P particles, and TEM images indicated the presence of Ni₂P nanoparticles on CdS. The optical properties and charge carrier dynamics of the composite material exhibited better visible light absorption and improved suppression of charge carrier recombination. X-ray photoelectron spectra confirmed the presence of Ni₂P on CdS. The synthesized materials were tested for photocatalytic hydrogen production with lactic acid as a scavenger under irradiation in a solar simulator. The rate of H₂ production with Ni₂P/CdS was 62 times greater than that with pure CdS. The superior activity of the composite material is attributed to the ability of Ni₂P to separate the photoexcited charge carriers from CdS and provide good electrical conductivity. The optimized composite material also exhibited better photocatalytic activity than Pt cocatalyzed CdS. Based on the experimental results, a possible electron-hole transfer mechanism is proposed.