Metal‐Free Photocatalytic CO2 Reduction to CH4 and H2O2 under Non‐sacrificial Ambient Conditions

Abstract

AbstractPhotocatalytic CO2 reduction to CH4 requires photosensitizers and sacrificial agents to provide sufficient electrons and protons through metal‐based photocatalysts, and the separation of CH4 from by‐product O2 has poor applications. Herein, we successfully synthesize a metal‐free photocatalyst of a novel electron‐acceptor 4,5,9,10‐pyrenetetrone (PT), to our best knowledge, this is the first time that metal‐free catalyst achieves non‐sacrificial photocatalytic CO2 to CH4 and easily separable H2O2. This photocatalyst offers CH4 product of 10.6 μmol ⋅ g−1 ⋅ h−1 under non‐sacrificial ambient conditions (room temperature, and only water), which is two orders of magnitude higher than that of the reported metal‐free photocatalysts. Comprehensive in situ characterizations and calculations reveal a multi‐step reaction mechanism, in which the long‐lived oxygen‐centered radical in the excited PT provides as a site for CO2 activation, resulting in a stabilized cyclic carbonate intermediate with a lower formation energy. This key intermediate is thermodynamically crucial for the subsequent reduction to CH4 product with the electronic selectivity of up to 90 %. The work provides fresh insights on the economic viability of photocatalytic CO2 reduction to easily separable CH4 in non‐sacrificial and metal‐free conditions.