Atomic Manipulation to Create High-Valent Fe⁴⁺ for Efficient and Ultrastable Oxygen Evolution at Industrial-Level Current Density.

Abstract

Manipulating the electronic structure of a catalyst at the atomic level is an effective but challenging way to improve the catalytic performance. Here, by stretching the Fe-O bond in FeOOH with an inserted Mo atom, a Fe-O-Mo unit can be created, which will induce the formation of high-valent Fe⁴⁺ during the alkaline oxygen evolution reaction (OER). The highly active Fe⁴⁺ state has been clearly revealed by in situ X-ray absorption spectroscopy, which can both enhance the oxidation capability and lead to an efficient and stable adsorbate evolution mechanism (AEM) pathway for the OER. As a result, the obtained Fe-Mo-Ni₃S₂ catalyst exhibits both superior OER activity and outstanding stability, which can achieve an industrial-level current density of 1 A cm^-2 at a low overpotential of 259 mV (at 60 °C) and can stably work at the large current for more than 2000 h. Moreover, by coupling with commercial Pt/C, the Fe-Mo-Ni₃S₂∥Pt/C system can be used in the anion exchange membrane cell to acquire 1 A cm^-2 for overall water splitting at 1.68 V (2.03 V for 4 A cm^-2), outperforming the benchmark RuO₂∥Pt/C system. The efficient, low-cost, and ultrastable OER catalyst enabled by manipulating the atomic structure may provide potential opportunities for future practical water splitting.