Halogen-doped carbon dots regulated Co/Co2P heterostructured electrode for efficient alkaline water and simulated seawater electrolysis

The development of electrocatalysts exhibiting high activity, long-term stability, and tolerance to a wide range of electrolytes remains a key challenge for practical water electrolysis. Three-dimensional Co/Co 2 P heterostructures regulated by halogen-doped carbon dots (X-CDs) were constructed on self-supported nickel foam via a two-step hydrothermal and phosphorization process. The incorporation of different halogen-doped carbon dots influences the growth behavior of the catalyst and yields unique hierarchical morphologies. Fluorine-doped carbon dots (F-CDs) promote the formation of well-defined nanoflower structures that provide abundant exposed active sites. The Co/Co 2 P heterojunction enhances catalytic kinetics and facilitates efficient charge transfer. The improved F-CDs-derived catalyst exhibits remarkable durability and bifunctional catalytic performance in alkaline media, requiring overpotentials of only 185 mV for HER and 354 mV for OER at 100 mA cm −2 . It maintains exceptional performance at elevated current densities, exceeding that of commercial noble-metal-based catalysts. The catalyst demonstrates stable OER performance at 100 mA cm⁻ 2 over a duration of 300 h. When assembled in a two-electrode electrolyzer, a cell voltage of only 1.91 V is needed to drive overall water splitting at 100 mA cm⁻ 2 in simulated alkaline seawater. The electrolyzer operates stably for 100 h and displays tolerance to chloride-containing environments. This work demonstrates a general strategy that integrates halogen regulation with heterostructure engineering and three-dimensional self-supported architectures, offering insights into the fabrication of durable water-splitting electrocatalysts.