Construction of nickel phosphide/iron oxyhydroxide heterostructure nanoparticles for oxygen evolution

Active and stable oxygen evolution electrocatalysts are essential in increasing the efficiency of the water electrolyzers. The Ni2P/Fe(O)OH heterostructure nanoparticles are prepared via solvothermal phosphidization of Ni metal-organic frameworks (MOF) followed by immersing in Fe3+ aqueous solution. Characterizations reveal that the Ni2P/Fe(O)OH heterostructure nanoparticles are 12.83 nm in size averagely, and the heterointerface induces electron interactions between the Ni2P and Fe(O)OH phases. When used to catalyze OER in alkaline solutions, the Ni2P/Fe(O)OH-40/nickel foam (NF) is the most active and exhibits 240 mV overpotential to reach 10 mA cm-2 oxygen evolution (OER) current densities, which is significantly better than the Ni2P/NF. Lower apparent activation energy, charge transfer resistance, and Tafel slope, along with higher electron rate constant are observed at Ni2P/Fe(O)OH-40/NF, which suggests that the OER kinetics is more facile at the heterostructure surface. Both Ni2P/Fe(O)OH-40/NF and Ni2P/NF involve decoupled electron and proton transfer process, and higher degree of lattice oxygen oxidation mechanism (LOM) participation is observed at Ni2P/Fe(O)OH-40/NF, which results from the increased acidity of the Ni3+ sites. Density functional theory calculations prove that the formation of heterostructure with Fe(O)OH alters the band structure and the OER intermediate adsorption energies, that lead to lower energy barrier in the rate-determining step. The Ni2P/Fe(O)OH-40/NF is also stable towards OER in alkaline solutions.