Template-Free Synthesis of Hollow Iron Phosphide–Phosphate Composite Nanotubes for Use as Active and Stable Oxygen Evolution Electrocatalysts

The oxygen evolution reaction (OER) is a half-cell reaction that is of importance to many electrochemical processes, especially for electrochemical and photoelectrochemical water splitting. Developing efficient, durable, and low-cost OER electrocatalysts comprising Earth-abundant elements has been in the focus of electrocatalysis research. Herein, we report a cost-effective, scalable, and template-free approach to the fabrication of hollow iron phosphide–phosphate (FeP–FeP x O y ) composite nanotubes (NTs), which is realized by hydrothermal growth of iron oxy-hydroxide nanorods (NRs) and a subsequent postphosphorization treatment. The hollow interior of NTs results from the Kirkendall effect occurring upon phosphorization. When used to catalyze the OER in basic medium, the as-synthesized FeP–FeP x O y composite NTs exhibit excellent catalytic activity, delivering the benchmark current density of 10 mA cm –2 at a low overpotential of 280 mV and showing a small Tafel slope of 48 mV dec –1 and a high turnover frequency of 0.10 s –1 at the overpotential of 350 mV. Moreover, the composite NTs demonstrate outstanding long-term stability, capable of catalyzing the OER at 10 mA cm –2 for 42 h without increasing the overpotential, holding substantial potential for use as active and inexpensive anode catalysts in water electrolyzers.