Morphological engineering of monodispersed Co₂P nanocrystals for efficient alkaline water and seawater splitting

Developing feasible synthetic strategies for preparing advanced nanomaterials with narrow size distributions and well-defined structures represents a cutting-edge field in alkaline water and seawater electrolysis. Herein, the monodispersed Co₂P nanocrystals with tunable morphologies, namely one-dimensional nanorods (Co₂P-R), nanoparticles (Co₂P-P), and nanospheres (Co₂P-S), were controllably synthesized by using a Schlenk system through optimizing the reactivity of cobalt- and phosphorus-based sources. The resulting Co₂P-R exhibited superior electrocatalytic activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1.0 M KOH, simulated seawater, and natural seawater. Impressively, the reconstructed active species effectively avoid the chlorine evolution on Co₂P-R surface and facilitate OER process. Density functional theory (DFT) calculations revealed that Co₂P-R exhibited an optimal d-band center (ε_d) and a lower energy barrier for the rate-determining steps in both HER and OER processes in comparison with Co₂P-P and Co₂P-S. Additionally, the Co₂P-R showed a more favorable water adsorption energy (E_H2O) over Cl^- adsorption energy (E_Cl-), which contributes to its enhanced seawater electrolysis performance. The Co₂P-R||Co₂P-R electrolyzer achieves a low voltage of 1.70, 1.76, and 1.76 V at 100 mA cm^-2 in alkaline freshwater, simulated seawater, and natural seawater, respectively, and demonstrates stable operation for 200 h at 100 mA cm^-2.