MOF-Derived Iron-Cobalt Phosphide Nanoframe as Bifunctional Electrocatalysts for Overall Water Splitting

Abstract

Transition metal phosphides (TMPs) have emerged as an alternative to precious metals as efficient and low-cost catalysts for water electrolysis. Elemental doping and morphology control are effective approaches to further improve the performance of TMPs. Herein, Fe-doped CoP nanoframes (Fe-CoP NFs) with specific open cage configuration were designed and synthesized. The unique nano-framework structured Fe-CoP material shows overpotentials of only 255 and 122 mV at 10 mA cm⁻² for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, overwhelming most transition metal phosphides. For overall water splitting, the cell voltage is 1.65 V for Fe-CoP NFs at a current density of 10 mA cm⁻², much superior to what is observed for the classical nanocubic structures. Fe-CoP NFs show no activity degradation up to 100 h which contrasts sharply with the rapidly decaying performance of noble metal catalyst reference. The superior electrocatalytic performance of Fe-CoP NFs due to abundant accessible active sites, reduced kinetic energy barrier, and preferable *O-containing intermediate adsorption is demonstrated through experimental observations and theoretical calculations. Our findings could provide a potential method for the preparation of multifunctional material with hollow structures and offer more hopeful prospects for obtaining efficient earth-abundant catalysts for water splitting.