N, F Codoped FeOOH Nanosheets with Intercalated Carbonate Anions Rich in Oxygen Defects for Enhanced Alkaline Electrocatalytic Water Splitting

Alkaline water splitting is a highly efficient and clean technology for hydrogen energy generation. However, in alkaline solutions, most catalysts suffer from extreme instability. Herein, a cross-nanostructured N, F, and CO32– codoped iron oxyhydroxide composite (N,F–FeO(OH)–CO3–NF) rich in oxygen defects is designed for water splitting in the alkaline solution. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations show that the introduction of F and CO32– can induce electron redistribution around the active center Fe, accelerate the four-electron transfer process, and optimize the d-band center, thereby improving the efficiency and stability of HER and OER. In a 1 M KOH solution, N,F–FeO(OH)–CO3–NF only needs the overpotential of 248 mV for OER and the overpotential of 199 mV for HER to reach the current density of 10 mA·cm–2. Meanwhile, it can reach 100 mA·cm–2 current density at 1.55 V vs RHE and maintains a current density of 10 mA·cm–2 for 120 h in a two-electrode electrolytic water device. Compared with bulk hydroxides, the heteroatom and anion codoped composite hydroxides are more stable and have dual functions in the electrolyte solution. This is of great significance for designing a new stable water-splitting electrocatalyst.