Halogen‐Doped Carbon Dots on Amorphous Cobalt Phosphide as Robust Electrocatalysts for Overall Water Splitting

Abstract Designing a stable and efficient dual‐functional catalyst for the hydrogen evolution and oxygen evolution reactions (HER/OER) is of great significance to the development of hydrogen production by water splitting. This work reports on novel halogen (X = F, Cl, and Br)‐doped carbon dots modifying amorphous cobalt phosphide (X‐CDs/CoP), which can be tuned by the choice of X‐CDs to have urchin, Pinus bungeana, and Albizia julibrissin type structures. The different characteristics of the various X‐CDs led to different formation mechanisms and final structures. As a bifunctional catalyst, urchin‐shaped F‐CDs/CoP crystals achieve superior electrocatalytic performance, exhibiting excellent HER/OER activity and sustained stability in an alkaline solution. For overall water splitting, they provide current density of 10 mA cm⁻² and require a low cell voltage of 1.48 V in 1 _M KOH. In addition, the catalytic performance shows negligible degradation after 100 h, thus demonstrating excellent long‐term cycling stability. Density functional theory calculations show that the improved electrocatalytic performance of F‐CDs/CoP catalysts is due to the coupling interface between CoP and F‐CDs, which optimizes the hydrogen/oxygen adsorption energy and accelerates the water splitting kinetics. This work provides guidance for the rational design of transition metal phosphide electrocatalysts with outstanding performance.