Phosphorus-Induced One-Step Synthesis of NiCo 2 S 4 Electrode Material for Efficient Hydrazine-Assisted Hydrogen Production.

Rational control of the reaction parameters is highly important for synthesizing active electrocatalysts. NiCo 2 S 4 is an excellent spinel-based electrocatalyst that is usually prepared through a two-step synthesis. Herein, a one-step hydrothermal route is reported to synthesize P-incorporated NiCo 2 S 4 . We discovered that the inclusion of P caused formation of the NiCo 2 S 4 phase in a single step. Computational studies were performed to comprehend the mechanism of phase formation and to examine the energetics of lattice formation. Upon incorporation of the optimum amount of P, the stability of the NiCo 2 S 4 lattice was found to increase steadily. In addition, the Bader charges on both the metal atoms Co and Ni in NiCo 2 S 4 and P-incorporated NiCo 2 S 4 were compared. The results show that replacing S with the optimal amount of P leads to a reduction in charge on both metal atoms, which can contribute to a more stable lattice formation. Further, the electrochemical performance of the as-synthesized materials was evaluated. Among the as-synthesized nickel cobalt sulfides, P-incorporated NiCo 2 S 4 exhibits excellent activity toward hydrazine oxidation with an onset potential of 0.15 V vs RHE without the assistance of electrochemically active substrates like Ni or Co foam. In addition to the facile synthesis method, P-incorporated NiCo 2 S 4 requires a very low cell voltage of 0.24 V to attain a current density of 10 mA cm -2 for hydrazine-assisted hydrogen production in a two-electrode cell. The free energy profile of the stepwise HzOR has been investigated in detail. The computational results suggested that HzOR on P-incorporated NiCo 2 S 4 was more feasible than HzOR on NiCo 2 S 4 , and these findings corroborate the experimental evidence.