Phosphidation treatment of surfactant-tuned iron polyphthalocyanine grown in situ on nickel foam: An efficient bifunctional catalyst for overall water splitting

Abstract

Developing robust electrocatalysts for overall water splitting is vital for industrial hydrogen production on a large scale. Herein, we obtain a bifunctional electrocatalyst NF@FePPc-s/p (where s represents surfactant and p stands for the phosphidation treatment) by phosphorization of surfactant (F127)-tuned iron polyphthalocyanine (FePPc) grown in situ on the nickel foam (NF) substrate. The as-obtained NF@FePPc-s/p exhibits the golden needle mushroom-like morphology, which is conducive to fully exposing the active sites and boosting the electron-transfer kinetics at the reaction interface. The physicochemical characterization and electrochemical measurements demonstrate that the active Fe2P and Ni2P phases formed during the phosphidation treatment are intrinsically active catalytic sites for hydrogen evolution reaction (HER), and the FeOOH formed from phase transformation of Fe2P during the oxygen evolution reaction (OER) process contributes a lot to enhancement of the OER activity. Furthermore, the electronic interaction between Fe and Ni further improves the electrocatalytic performances for both reactions. The optimized NF@FePPc-s/p catalyst exhibits remarkable OER (293 mV@100 mA cm−2) and HER (190 mV@100 mA cm−2) activities in 1.0 M KOH electrolyte. The water electrolyzer assembled with the NF@FePPc-s/p as the cathode and anode electrodes, respectively, only requires a low cell voltage of 1.743 V to obtain the current density of 100 mA cm−2 for overall water splitting, outperforming the precious NF@RuO2–Pt/C based electrolyzer (1.852 V).