Investigating the active sites in molybdenum anchored nitrogen-doped carbon for alkaline oxygen evolution reaction

Developing durable and efficient non-precious-metal based catalysts for oxygen evolution reaction (OER) is highly desirable in the field of electrocatalysis. In this work, a series of novel Mo anchored N-doped carbon catalysts (denoted as Mo/NC-T) were prepared starting from the zeolitic imidazolate framework 8 (ZIF-8) precursor. Firstly, Mo doped ZIF-8 precursor (Mo/ZIF-8) with a regular polyhedron structure was formed through a simple ion-exchange method process between molybdenum pentachloride (MoCl5) and ZIF-8. Afterward, Mo/ZIF-8 was converted to Mo/NC-T through a two-step calcination process in nitrogen (N2) and ammonia (NH3). The as-synthesized Mo/NC-T samples exhibited superior electrocatalytic OER properties. The optimal sample at 650 °C (Mo/NC-650) presented a low overpotential of 320 mV at 10 mA cm-2, a Tafel slope of 71 mV dec-1, and an outstanding long-term stability for 30 h in 1 M KOH solution. The remarkable OER activity of Mo/NC-T could be ascribed to the structural stability of carbon matrix and the synergistic effect between Mo3+ (derived from Mo-C bonds) and pyridinic N. This work provides a novel perspective on the roles of Mo species in the N-doped carbon electrocatalysts for OER.