A biomimetic photoelectrocatalyst of Co–porphyrin combined with a g-C3N4 nanosheet based on π–π supramolecular interaction for high-efficiency CO2 reduction in water medium

Abstract

Aiming at high-efficiency biomimetic CO₂ photoelectrochemical conversion, a photoelectrocatalyst with excellent CO₂ catalytic activity was designed and prepared by immobilizing CoTPP (cobalt meso-tetraphenylporphyrin) onto g-C₃N₄ conveniently via self-assembly based on π–π supramolecular interaction. The quasi 3-D structure of CoTPP showed a suitable hole with a size of 3.8 Å × 9.6 Å which favoured CO₂ adsorption. The pores formed by the π–π stacking of CoTPP and g-C₃N₄ also provided additional space for CO₂ adsorption, which was confirmed by the appearance of a desorption peak at 250 °C in the temperature programmed desorption measurement for CoTPP/g-C₃N₄. As a normal efficient homogeneous catalyst in organic media, CoTPP commendably maintained outstanding CO₂ photoelectrocatalytic activity in heterogeneous aqueous solution, even at a low overpotential of −0.6 V (vs. normal hydrogen electrode, NHE). Under 8 h PEC CO₂ reduction, formic acid generation on CoTPP/g-C₃N₄ reached 154.4 μmol with a TON of 137 and high selectivity of nearly 100% in liquid products. The formation of CoTPP–COO⁻ and CoTPP–COOH intermediates by the Co(II) active site and CO₂ was investigated by in situ UV-vis and Raman spectra. Moreover, an isotopic labelling experiment indicated that water supplied abundant protons for the production of formic acid.