Density functional theory study on a nitrogen-rich carbon nitride material C3N5 as photocatalyst for CO2 reduction to C1 and C2 products.

A new-type nitrogen-rich carbon nitride material C3N5 has been synthesized recently, in which the C:N ratio increases from 3:4 in g-C3N4 to 3:5 due to the introduction of azo linkage (NN) connecting segments in two C6N7 units. Herein, C3N5 as a photocatalyst for CO2 reduction was investigated by density functional theory methods. The electronic and optical properties indicate that C3N5 has a longer visible-light region with 2.0 eV of band gap in comparison with g-C3N4. The spatial distributions of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) show that the π network of C3N5 is extended by introducing -NN- linkage, which results in much higher photocatalytic efficiency than g-C3N4. The Gibbs free energies for possible CO2 reaction paths on C3N5 were computed. The results show that CO2 can be reduced to CH4 with a low limiting potential of -0.54 V and to CH3CH2OH with a low limiting potential of -0.61 V, which all driven by solar energy. The present work is expected to provide useful guide for new-type nitrogen-rich C3N5 as promising photocatalyst for CO2 reduction reaction (CO2RR).