Reversible Angle Distortion-Dependent Electrochemical CO Reduction on Cobalt Phthalocyanine.

Deducing the local electronic and atomic structural changes in active sites during electrochemical carbon dioxide reduction is essential for elucidating the intrinsic mechanisms and developing highly active catalysts that are stable for a long duration. Herein, utilizing valence-to-core X-ray emission spectroscopy and high energy-resolution fluorescence detected X-ray absorption near-edge structure, combined with spectroscopic calculations, the atomic and electronic structure evolutions of the model cobalt phthalocyanine (CoPc) were quantitatively elucidated. Under real reaction conditions, CoPc undergoes reversible angle distortion while maintaining a constant metal-ligand bond length, causing changes in the energy levels of split d orbitals and electron density of molecular orbitals. The angle distortion further influences intrinsic interactions among the ligands, intermediates, and metal centers. The reversible change in the bond angle with the CO Faraday efficiency was also determined, demonstrating the robustness. The demonstrated findings serve as an important contribution to determine the structure-performance relationship of CoPc which enlightens the further rational design of atomically dispersed site catalysts with high activity and to emphasize the capabilities of the high energy resolution X-ray spectroscopy toward analyzing metal-implanted N-doped carbon catalysts.