Accelerated Water Oxidation Kinetics Triggered by Supramolecular Porphyrin Nanosheet for Robust Visible‐Light‐Driven CO₂ Reduction

Abstract

Water oxidation is one of the most challenging steps in CO2 photoreduction, but its influence on CO2 photoreduction is still poorly understood. Herein, the concept of accelerating the water oxidation kinetics to promote the CO2 photoreduction is realized by incorporating supramolecular porphyrin nanosheets (NS) into the C3N4 catalyst. As a prototype, porphyrin‐C3N4 based van der Waals heterojunctions with efficient charge separation are elaborately designed, in which the porphyrin and C3N4 NS serve as the water oxidation booster and CO2 reduction center, respectively. Theoretical calculations and relevant experiments demonstrate that the added porphyrin NS reverses the rate‐limiting step in the water oxidation while reducing its energy barrier, thus resulting in faster reaction kinetics. Therefore, the optimal sample shows excellent performance in visible‐light‐driven CO2 reduction with a maximum CO evolution rate of 16.8 µmol g−1 h−1, which is 6.8 times that of the C3N4 NS and reaches the current state of the art for C3N4‐based materials in CO2 photoreduction. Overall, this work throws light that accelerating water oxidation kinetics can effectively improve the CO2 photoreduction efficiency.

Constructing Z-scheme WO3/C3N4 heterojunctions with an enlarged internal electric field and accelerated water oxidation kinetics for robust CO2 photoreduction

“…1i). 9,36 Compared with C 3 N 4 NS, the peaks of 10% WO 3 / C 3 N 4 in the C 1s and N 1s spectra shied slightly towards higher binding energies by 0.2 eV. For WO 3 NS, the two peaks at 36.2 and 38.3 eV are attributed to W 4f 7/2 and W 4f 5/2 of W 6+ , respectively.…”

“…2c and d clearly demonstrated that CO and O 2 were indeed produced from CO 2 and H 2 O, respectively. 9 The control experiments (Fig. S11 †) indicated it was a light-driven CO 2 reduction reaction.…”

“…Moreover, the four-electron-involving H 2 O oxidation half-reaction is kinetically sluggish. [9][10][11][12] Given the above, the H 2 O oxidation half-reaction is the essential bottleneck in overall CO 2 photoreduction, both thermodynamically and kinetically. Recent studies have proved that boosting H 2 O oxidation can effectively improve CO 2 photoreduction efficiency.…”

“…For example, Chen et al introduced a porphyrin as a H 2 O oxidation booster into C 3 N 4 to reduce the H 2 O oxidation energy barrier, which accelerated the H 2 O oxidation kinetics and further promoted CO 2 photoreduction. 9 Yin et al demonstrated that the Svacancies on SnS 2 could directly enhance the rate-determining H 2 O oxidation half reaction in the overall CO 2 photoreduction. 10 Additionally, the rapid recombination of photogenerated e −h + pairs is unable to satisfy the kinetics required for overcoming the high chemical inertness of CO 2 molecules and the sluggish H 2 O oxidation half-reaction.…”

Elucidating protonation pathways in CO2 photoreduction using the kinetic isotope effect

“…Upon light exposure, a comprehensive CO 2 photoreduction process typically encompasses water oxidation (or organic sacrificial agents, if utilized) and CO 2 reduction half-reactions. The water oxidation half-reaction is often regarded as analogous to the oxygen-evolving reaction (OER) in water-splitting 9 , 10 . The CO 2 reduction reaction encompasses multiple step-wise proton/electron transfer processes.…”