Tuning the Electronic Bandgap of Graphdiyne by H‐Substitution to Promote Interfacial Charge Carrier Separation for Enhanced Photocatalytic Hydrogen Production

Abstract

Graphdiyne (GDY), which features a highly π-conjugated structure, direct bandgap, and high charge carrier mobility, presents the major requirements for photocatalysis. Up to now, all photocatalytic studies are performed without paying too much attention to the GDY bandgap (1.1 eV at the G 0 W 0 many-body theory level). Such a narrow bandgap is not suitable for the band alignment between GDY and other semiconductors, making it difficult to achieve efficient photogenerated charge carrier separation. Herein, for the first time, it is demonstrated that tuning the electronic bandgap of GDY via H-substitution (H-GDY) promotes interfacial charge separation and improves photocatalytic H 2 evolution. The H-GDY exhibits an increased bandgap energy (≈2.5 eV) and exploitable conduction band minimum and valence band maximum edges. As a representative semiconductor, TiO 2 is hybridized with both H-GDY and GDY to fabricate a heterojunction. Compared to the GDY/TiO 2 , the H-GDY/TiO 2 heterojunction leads to a remarkable enhancement of the photocatalytic H 2 generation by 1.35 times under UV-visible illumination (6200 µmol h −1 g −1 ) and four times under visible light (670 µmol h −1 g −1 ). Such enhancement is attributed to the suitable band alignment between H-GDY and TiO 2 , which efficiently promotes the photogenerated electron and hole separation, as supported by density functional theory calculations.

Site‐Specific Axial Oxygen Coordinated FeN4 Active Sites for Highly Selective Electroreduction of Carbon Dioxide

“…To further understand the intrinsic activity of the axial O group for CO 2 RR, DFT calculations were performed to calculate the free energies of possible intermediates in the reaction pathways from CO 2 to CO by using the computational hydrogen electrode model and parameters reported in the literature. [46][47][48][49] As the counterpart, we created a simulation model with an Fe atom coordinated with 4 N atoms (tetra-nitrogen) by replacing six C atoms in a graphene surface to represent the reported normal FeN 4 catalysts. [50] For the O-Fe-N-C catalyst, an axial OH ligand was added to coordinate with the Fe single atom in the As for the final step of CO desorption, the ΔG over O-Fe-N-C is 0.47 V, which is significantly lower than that over normal FeN 4 (0.89 eV).…”

Band offset engineering at C2N/MSe2 (M = Mo, W) interfaces

“…This would lead to a signicant enhancement in the photocatalytic H 2 generation. 6 The calculated VBO and CBO between C 2 N and MoSe 2 (WSe 2 ) layers are DE v ¼ 0.84 eV (1.05) and DE c ¼ 0.65 eV (0.96) respectively. These values are larger than the CBO (0.54 eV) and VBO (0.67 eV) at WS 2 /C 2 N heterostructure.…”

“…Notwithstanding, comparing at the GGA level the relative values of the bandgap of two different materials and the relative alignment of their valence or conduction band edges are still reasonable, which will not qualitatively affect the interpretation of band values based on my calculations. 6 Indeed, the use of GW induces only a rigid band shi of VBM and CBM by the same amount but in the inverse directions with respect to the same band-gap-center by DFT-calculations. 14,35 The calculated density of states, as shown in Fig.…”

“…14,15 For photocatalytic applications, a heterostructure with a type-II band alignment conguration demonstrated to efficiency separate the photogenerated electron-hole pairs at the interface for highly efficient water reduction and oxidation. 6,16 In such a type-II conguration, the magnitude of the conduction band offset (CBO; dened as the difference in the electron affinities of two constituting components) and valence band offset (VBO; the difference in the ionization potentials) determine the magnitude of the built-in electric at the interface that in turn separates the photogenerated electrons and holes in space. Koda et al demonstrated, by the rst principles calculations, that tailoring the band offsets (CBO and VBO) at phosphorene/ TMDs strongly modulate the electronic properties of heterostructures.…”

“…A new paradigm in photocatalytic devices is to vertically stack 2D materials, with different ionization potentials and electronic affinities to generate a donor–acceptor heterostructure photocatalyst, which has demonstrated to be the most effective approaches for suppressing the electron–hole pairs recombination and improving the photocatalytic performance. 2,6,7 Recently, several C 2 N-based vdW heterostructures such as C 2 N/MoS 2 , C 2 N/Janus monochalcogenides, 8 C 2 N/aza-CMP, 9 C 2 N/h-BN, 10 C 2 N/cobalt-oxide, 2 C 2 N/CdS, 11 C 2 N/g-C 3 N 4 (ref. 12) and C 2 N/WS 2 (ref.…”