Tuning the Intrinsic Properties of Carbon Nitride for High Quantum Yield Photocatalytic Hydrogen Production

Abstract

The low quantum yield of photocatalytic hydrogen production in carbon nitride (CN) has been improved upon via the modulation of both the extrinsic and intrinsic properties of the material. Although the modification of extrinsic properties has been widely investigated in the past, recently there has been growing interest in the alteration of intrinsic properties. Refining the intrinsic properties of CN provides flexibility in controlling the charge transport and selectivity in photoredox reactions, and therefore makes available a pathway toward superior photocatalytic performance. An analysis of recent progress in tuning the intrinsic photophysical properties of CN facilitates an assessment of the goals, achievements, and gaps. This article is intended to serve this purpose. Therefore, selected techniques and mechanisms of the tuning of intrinsic properties of CN are critically discussed here. This article concludes with a recommendation of the issues that need to be considered for the further enhancement in the quantum efficiency of CN photocatalysts.

Boosting Oxygen Evolution Kinetics by Mn–N–C Motifs with Tunable Spin State for Highly Efficient Solar‐Driven Water Splitting

“…[41][42][43] Kohn-Sham singleparticle wave functions were expanded in the plane wave basis set with a kinetic energy cutoff at 500 eV. [45] The binding energy was defined as b M n CN t otal 3 4 The thickness of vacuum space was set to be 20 Å to prevent the artificial couplings between adjacent periodic images.…”

“…[44] Long-range correlation was included in evaluating vdW interaction by DFT-D2 method. [45] The binding energy was defined as b M n CN t otal 3 4…”

“…Here we focus on Mn-based centers as OER species since natural CaMn 4 O 5 complex in photosystem II can efficiently oxidize water, [22] and some other artificial Mn complexes such as Mn 3 3 ], and mononuclear Mn embedded N-doped graphene (Mn-NG) also show high activity toward water oxidation. And our concept is to intercalate active oxygen-evolving units into a photoresponsive matrix.…”

“…Under this condition, a portion of solar energy is consumed in the conversion of sacrificing agents, which often leads to extra economic cost and secondary pollution. [3,4] Therefore, direct water splitting into stoichiometric H 2 and O 2 is in urgent need, yet still remains challenging. Although great implementations have been made, most of them require either ultraviolet irradiation (only ≈4% of full spectrum) or a two-photon Z-scheme excitation process (with half of photoinduced charges directly combined at the junction interface), severely limiting the solar conversion efficiency.…”

“…[14,23,24] Moreover, the π-conjugated carbon nitride (C 3 N 4 ) is chosen to incorporate with Mn centers, acting as both photo responsive semiconductor and ideal ligand, since it is capable of visible light driven one-step photocatalytic water splitting with easily tunable electronic and structural properties, and its six lone-pair electrons from nitrogen in the tri-s-triazine structure provide ideal coordinative sites for the inclusion of Mn atoms. [3,25] Afterward, the e g occupancy of Mn 3+ center is tuned by controlling the Mn concentration on C 3 N 4 , which is essentially based on the bond length of MnN. And for the first time, the photocatalytic OER activity of Mn is found to follow a volcano trend toward e g occupancy with the peak located at e g ≈ 0.95.…”