Elucidating the Functional Orbital Evolution in Transition Metal-Doped Bi₃O₄Br Platforms for CO₂ Photoreduction

Frontier orbital hybridization plays a vital role in the initial adsorption and activation process during catalysis. A formidable challenge is the precise determination of active orbitals/sites. Herein, 2D Bi₃O₄Br nanosheets are adopted as an operable platform for heteroatom doping of various transition metals (Fe, Ni, Zn/Cd). As the atom number of dopants increases, the capability of selective CO₂ photoconversion is continuously amplified. The intrinsic nature is the variation of active functional orbital as indicated from band center distance (Δd/p-p) indicators. The calculated charge transfer of various CO₂-bound geometries further demonstrates the p-p orbital interaction overwhelms d-p orbital interaction. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy results verify the charged nature of Bi sites with 6p orbitals not fully filled by electrons. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis and Gibbs free energy change profile suggest the rapid emergence of the critical ^*COOH intermediate in a thermodynamically preferred pathway.