P-doped CoS/NiS heterostructures embedded in N-doped carbon nanoboxes: Synergistical electronic structure regulation for overall water splitting.

Water splitting using transition metal sulfides as electrocatalysts has gained considerable attention in the field of renewable energy. However, their electrocatalytic activity is often hindered by unfavorable free energies of adsorbed hydrogen and oxygen-containing intermediates. Herein, phosphorus (P)-doped CoS/NiS heterostructures embedded in N-doped carbon nanoboxes were rationally synthesized via a pyrolysis-sulfidation-phosphorization strategy. The hollow structure of the carbon matrix and the nanoparticles contained within it not only result in a high specific surface area, but also protects them from corrosion and acts as a conductive pathway for efficient electron transfer. Density functional theory (DFT) calculations indicate that the introduction of P dopants improves the conductivity of NiS and CoS, promotes the charge transfer process, and creates new electrocatalytic sites. Additionally, the NiS-CoS heterojunctions can enhance the adsorption efficiency of hydrogen intermediates (H*) and lower the energy barrier of water splitting via a synergistic effect with P-doping. These characteristics collectively enable the titled catalyst to exhibit excellent electrocatalytic activity for water splitting in alkaline medium, requiring only small overpotentials of 150 and 257 mV to achieve a current density of 10 mA cm for hydrogen and oxygen evolution reactions, respectively. This work sheds light on the design and optimization of efficient electrocatalysts for water splitting, with potential implications for renewable energy production.