Defective ferrocene-based metal–organic frameworks for efficient solar-powered water oxidation via the ligand competition and etching effect

Two-dimensional metal–organic frameworks are considered to be promising electrocatalytic materials due to their ultrathin lamellar structure, ultrahigh porosity and large surface area, but there are still many challenges such as the embedding of organic ligands leading to low density of active sites and poor conductivity. Herein, we synthesize two-dimensional ferrocene-based metal–organic frameworks nanosheet electrocatalysts via the one-step hydrothermal hydrogen peroxide etching method. The prepared FcNi-BDC-H₂O₂/NF exhibits excellent oxygen evolution reaction performance with a current density of 100 mA·cm^-2 at only 258 mV and a small driving potential of 1.542 V (10 mA·cm^-2) is required to achieve overall water splitting. Significantly, an overall water-cracked cell using a solar cell assembly achieves the solar hydrogen conversion efficiency of 19.5%. The introduction of high electronegativity ferrocene and the etching of H₂O₂ increase the Ni³⁺ content of FcNi-BDC-H₂O₂, and expose more unsaturated active sites, which improve the intrinsic activity of the catalysts and the mass transfer rate during the catalytic process. Moreover, the FcNi-BDC-H₂O₂/NF demonstrates significant urea oxidation reaction performance, achieving a potential of 1.35 V and producing 10 mA·cm^-2. This study presents a viable approach to investigating highly efficient electrocatalysts for oxygen evolution reaction and urea oxidation reaction using MOF-based bifunctional catalysts.