Synergy of Dopants and Defects in Graphitic Carbon Nitride with Exceptionally Modulated Band Structures for Efficient Photocatalytic Oxygen Evolution

Abstract

As inspired by natural photosynthesis, semiconductor-based photocatalytic water splitting into hydrogen and oxygen has attracted extensive attention, which provides a promising and clean method to convert solar energy into chemical fuel, for alleviating human's excessive reliance on fossil fuels. [1][2][3] For the water splitting process, the half-reaction of water oxidation to oxygen has been well recognized as the rate-limiting step for its four-electron oxidation process and high activation energy barrier (≈700 mV) for O-O bond formation, [4,5] which thus remains as the main challenge to achieve highly efficient overall water splitting. Although enormous efforts have been dedicated to develop photocatalysts for improved water oxidation performances in the past decades, by far only a few photocatalysts (e.g., WO 3 , BiVO 4 , and Ag 3 PO 4 , etc.) have been proven to be efficient for lightdriven oxygen evolution from water. [5][6][7][8] Worse still, several drawbacks always limit their practical application in oxygen-generating photocatalytic systems, including poor photostability, low charge carrier mobility, and high costs of raw materials. Since the pioneering work reported in 2009 by Wang et al., [9] metal-free graphitic carbon nitride (g-C 3 N 4 ) with a 2D conjugated structure has been intensively investigated for photocatalytic water redox reactions, owing to its earth-abundance, environmental friendliness, chemical stability, and suitable thermodynamical potentials for both hydrogen and oxygen evolution reactions. [10][11][12] In the past ten years, various strategies, including thermodynamic (such as doping with heteroatoms, [13][14][15][16] engineering defects with nitrogen vacancies or carbon vacancies, [17,18] etc.) and kinetic (such as compositing with other semiconductors, [7,[19][20][21][22] morphology design, [23][24][25][26][27] and loading cocatalysts, [28][29][30] etc.) modifications, have emerged to enhance the photocatalytic hydrogen evolution activity of g-C 3 N 4 and a high quantum yield of 34.4% at 400 nm has been achieved. [31] However, only very few results have been reported on g-C 3 N 4 based photocatalysts for water oxidation, and most of them were focused on surface modification by loading cocatalysts, such as cobalt (hydr)oxide and selenide, [32][33][34] etc., onto g-C 3 N 4 . Unfortunately, the photocatalytic oxygen evolution Electronic structure greatly determines the band structures and the charge carrier transport properties of semiconducting photocatalysts and consequently their photocatalytic activities. Here, by simply calcining the mixture of graphitic carbon nitride (g-C 3 N 4 ) and sodium borohydride in an inert atmosphere, boron dopants and nitrogen defects are simultaneously introduced into g-C 3 N 4 . The resultant boron-doped and nitrogen-deficient g-C 3 N 4 exhibits excellent activity for photocatalytic oxygen evolution, with highest oxygen evolution rate reaching 561.2 µmol h −1 g −1 , much higher than previously reported g-C 3 N 4 . It is well evidenced that with c...

Oxygen‐Deficient Birnessite‐MnO2 for High‐Performing Rechargeable Aqueous Zinc‐Ion Batteries

“…This process of thermal hydrogenation of MnO 2 followed by the generation of oxygen defects in MnO 2 eventually caused the nanosheets to be reduced to much smaller nanoparticles as observed in O dc À MnO 2 . [36] Energy Dispersive X-Ray Spectroscopy (EDS) was concurrently conducted during the SEM to illustrate the distribution of Manganese and Oxygen in the as-synthesised samples ( Figure S2).…”

Defect Engineering of Photocatalysts for Solar Energy Conversion

“…Zhang and coworkers developed alkali‐assisted process to synthesize nitrogen defective g‐C 3 N x using KOH, NaOH and Ba(OH) 2 as alkali compounds (Figure d), controlling the bandgap range from 2.68 to 2.36 eV . Shen and coworkers reported defective g‐C 3 N 4 (Figure e,f), regulating the bandgap range from 2.66 to 1.4 eV and achieving the excellent PC oxygen generation rate . Thus, the modulation of the defects is an effective strategy to regulate light absorption and bandgap structures of the photocatalysts.…”

“…e,f) Charge transfer illustration of defective C 3 N 4 . Reproduced with permission . Copyright 2019, Wiley‐VCH.…”

Unveiling real active site for photocatalytic H2O2 evolution: A combined experimental and DFT-TDDFT study

“…In simulation, each MS can be constructed exibly without affecting other factors. Then the role of each MS can be uncovered by analyzing the calculation results of density functional theory (DFT), such as band structure 20,21 , charge density 21,22 and electrostatic potential 23 , etc. This makes up for the lack of experiments to some extent.…”