LaF₃ Nanosheet-induced Epitaxial Growth: Hollow (Co, Ni)₂P/LaF₃ Nanotube Arrays Built by Porous Heterojunction Walls Grown on Ni Foam as Active Electrocatalyst for Hydrogen Evolution Reaction

Abstract

Free-standing (Co, Ni)₂P/LaF₃ hollow nanotube arrays are directly grown on Ni foam (NF) (denoted as (Co, Ni)₂P-La4/NF, where "4" refers to 4 g L^-1 of La³⁺ in the starting material), which exhibits efficient electrocatalytic activity for hydrogen evolution reaction (HER) with an overpotential of 94 mV at 10 mA cm², Tafel slope of 88 mV dec^-1, and superior long-term durability in alkaline electrolyte. Investigated was La dosage-induced compositional and morphological evolution of (Co, Ni)₂P/LaF₃, and it was found that suitable La dosage is beneficial for the epitaxial growth of (Co, Ni)₂P on LaF₃ nanosheets (the thickness direction of LaF₃ nanosheet is along the (03i̅) facet), leading to the formation of porous (Co, Ni)₂P/LaF₃ nanotube walls, giving rise to hollow nanotube arrays. The binder-free (Co, Ni)₂P-La4/NF electrode with unique morphology not only provides more active sites exposure to electrolyte ions and accessible ion diffusion path but also favors electron and charge transfer. Density functional theory calculation and experimental data reveal the doping of La into metal phosphide can lead to electron transfer from metal centers to P atoms, make the Δ<i>G</i>_H on the P sites closer to zero with lower H₂O adsorption energy (-0.58 eV), thus improving the HER behavior. The present work gives a novel strategy to design hollow nanotubular microstructure as non-noble-metal HER electrocatalyst.