Electronic Structure Evolution in Tricomponent Metal Phosphides with Reduced Activation Energy for Efficient Electrocatalytic Oxygen Evolution.

Abstract

Non-noble metal catalysts for high-active electrocatalytic oxygen evolution reaction (OER) are essential in large-scale application for water splitting. Herein, tricomponent metal phosphides with hollow structures are synthesized from cobalt-contained metal organic frameworks (MOFs), i.e., ZIF-67, by tailoring the feeding ratios of Ni and Fe, followed by a high-temperature reduction and a subsequent phosphidation process. Excellent OER activity and long-time stability are achieved in 1 m NaOH aqueous solution, with an overpotential of 329 mV at 10 mA cm-2 and Tafel slope of 48.2 mV dec-1 , even superior to the noble metal-based catalyst. It is evidenced that the formed (oxyhydr)oxide/phosphate species by in situ electrochemical surface oxidation are responsible for active OER. Accordingly, the simultaneous introduction of external Ni and Fe elements significantly influences the electronic structures of the parent metal phosphides, leading to the in situ electrochemical formation of surface active layer with decreased OER activation energy for greatly improved water oxidation performance. This electronic structure tuning strategy by introducing multicomponent metals demonstrates a versatile method to use MOFs as precursors for synthesizing high-efficient water splitting electrocatalysts.