Lower-temperature synthesis of nitrogen-rich molybdenum nitride/nickel (cobalt) heterojunctional assembly for the effective water electrolysis

The nitrogen-rich molybdenum nitrides (N/Mo > 1) are promising for water electrolysis due to their increased activity and antioxidant ability. However, a higher temperature is needed in the usual synthesis for introducing more N, leading to the formation of large particles and the difficulty in controlling the morphology, thus limiting their catalytic performance. Here, a new strategy is reported based on the synergy of internal/external N sources (INS and ENS) toward Mo${}_5$N${}_6$-based catalysts at a decreased temperature of 450 °C. The PMo${}_{12}$ clusters and Ni${}^{2+}$ (Co${}^{2+}$) are first combined with 2-methylimidazole/melamine (INS) to give a flower-like assembly. The subsequent pyrolysis under NH${}_3$ flow (ENS) gives the flowers composed of small Mo${}_5$N${}_6$/Ni (Co) heterojunctional particles that can expose more surface sites with an optimized electronic structure. The Mo${}_5$N${}_6$/Ni exhibits good HER activity close to Pt/C, and Mo${}_5$N${}_6$/Co shows superior OER performance to IrO${}_2$. The Mo${}_5$N${}_6$/Ni||Mo${}_5$N${}_6$/Co cell drives overall water splitting (OWS) at a low voltage of 1.397/1.74 V to achieve a current density of 10/100 mA cm${}^{-2}$ in the 1.0 M KOH. An anion exchange membrane water electrolyzer (AEMWE) based on the catalysts can achieve a current density of 450 mA cm${}^{-2}$ at 1.8 V with a long-term stability of 120 h. (© 2024 Wiley‐VCH GmbH)