Exploring P-(Fe,V)-Codoped Metastable-Phase β-NiMoO₄ for Improving the Performance of Overall Water Splitting

It is especially essential to develop high-performance and low-cost nonprecious metal catalysts for large-scale hydrogen production. A large number of electrochemical catalysts composited by transition metal centers has been reported; however, it is still a great challenge to design and manipulate target electrocatalysts to realize high overall water-splitting activity at the atomic level. Herein, we develop totally new P-(Fe,V)-codoped metastable-phase β-NiMoO₄. As an electrocatalyst, it can realize oxygen evolution at only 163 mV and hydrogen evolution at only 44 mV at 10 mA cm^-2. It, as both an anode and a cathode, is fabricated into a cell for overall water splitting, which has an ultralow voltage value of 1.48 V to drive a current density of 10 mA cm^-2 and can remain stable for at least 100 h. In the target electrode, the P element plays three important roles: (1) it can stabilize the metastable-phase structure of β-NiMoO₄; (2) it can further optimize the electronic structure; and (3) it can provide more active sites. The synergistic effect for multimetal centers with different redox couples is key for the great improvement of catalytic activity. The related mechanism is discussed in detail.