Chemical Dealloying-Derived Porous FeCoNiMoZn High-Entropy Alloy Electrode for Alkaline Overall Water Splitting

Abstract

The development and use of hydrogen energy are important initiatives to alleviate the global energy crisis. Bifunctional overall water splitting electrodes play an important role in the work of hydrogen production from electrocatalytic water splitting. High-entropy alloys (HEAs) prepared by transition group metals have shown very excellent performances in terms of both the OER/HER. In this paper, FeCoNiMoZn high-entropy alloys were prepared by spark plasma sintering (SPS), and then, a multilayered porous structure was constructed through chemical dealloying with hydrochloric acid to obtain an overall water splitting electrode. After 20 min of dealloying treatment, the porous FeCoNiMoZn electrode has excellent overall water splitting performance. The surface of the electrode shows an ice-crystal-like corrosion structure, which is mainly composed of FCC, BCC, and Mo phases and contains a large number of stacking faults. The elements of the electrode after dealloying exist in the form of high valence metals, which can accommodate more electrons and have more active sites. In addition, the metals in a high valence state have a stronger adsorption effect on OH^- in solution and promote ion transfer. The OER and HER overpotentials of the porous electrode are 240 and 171 mV, respectively, at a current density of 100 mA cm^-2, and their Tafel slopes are 36.54 and 78.57 mV dec^-1. The charge-transfer resistance (R_ct) of the porous FeCoNiMoZn electrode is greatly reduced after the dealloying treatment, while the electrochemically active surface area is obviously increased as well as the reaction kinetics. The porous FeCoNiMoZn electrode can achieve overall water splitting at a cell voltage of 1.79 V at a current density of 100 mA cm^-2 with minimal potential change in a 230 h stability test.