Exceptional Cocatalyst‐Free Photo‐Enhanced Piezocatalytic Hydrogen Evolution of Carbon Nitride Nanosheets from Strong In‐Plane Polarization

Abstract

Utilizing mechanical energy to produce hydrogen is emerging as a promising way to generate renewable energy, but is challenged by low efficiency and scanty cognition. In this work, graphitic carbon nitride (g‐C3N4) with an atomically thin sheet‐like structure is applied for prominent piezocatalytic and photo‐enhanced piezocatalytic H2 production. It is revealed that the anomalous piezoelectricity in g‐C3N4 originates from the strong in‐plane polarization along the a‐axis, contributed by the superimposed polar tri‐s‐triazine units and flexoelectric effect derived from the structured triangular cavities, which provides powerful electrochemical driving force for the water reduction reaction. Furthermore, the photo‐enhanced charge transfer enables g‐C3N4 nanosheets to reserve more energized polarization charges to fully participate in the reaction at the surface reactive sites enriched by strain‐induced carbon vacancies. Without any cocatalysts, an exceptional photo‐piezocatalytic H2 evolution rate of 12.16 mmol g−1 h−1 is delivered by the g‐C3N4 nanosheets, far exceeding that of previously reported piezocatalysts and g‐C3N4 photocatalysts. Further, high pure‐water‐splitting performance with production of the value‐added oxidation product H2O2 via photo‐piezocatalysis is also disclosed. This work not only exposes the potential of g‐C3N4 as a piezo‐semiconductor for catalytic H2 evolution, but also breaks a new ground for the conversion of solar and mechanical energy by photomediated piezocatalytic reaction.

2D Graphitic Carbon Nitride for Energy Conversion and Storage

“…[44] The thin layer of g-C 3 N 4 nanosheets has a large number of polar tri-s-triazine groups in the layers, allowing it stronger piezoelectricity than the bulk g-C 3 N 4 . [45] As expected, along with these changes in physical properties, the chemical properties of g-C 3 N 4 nanosheets have also changed. The most intuitive performance is that the UV-vis absorption peak and photoluminescence (PL) band of ultrathin g-C 3 N 4 nanosheets show a blue shift compared with that of bulk g-C 3 N 4 (Figure 2d-i).…”

“…Our group recently discovered that the ultra-thin g-C 3 N 4 nanosheets exfoliated from the non-piezoelectric bulk material exhibit strong piezoelectricity due to the broken symmetry. [45] Without the aid of a co-catalyst, the photo-piezocatalytic H 2 evolution rate of g-C 3 N 4 nanosheets can reach 12.16 mmol g −1 h −1 (Figure 7e). DFT calculations show that the orderly arrangement of polar tri-s-triazine group in the g-C 3 N 4 atomic layer along the a-axis direction induces strong in-plane polarization (Figure 7f).…”

“…g) FEM simulation for the piezoelectric potential distribution of bulk g-C 3 N 4 (left) and UT-g-C 3 N 4 (right) with the cavitation pressures of 100 MPa. Adapted with permission [45]. Copyright 2021, Wiley-VCH.…”

High Efficiency Water Splitting using Ultrasound Coupled to a BaTiO3 Nanofluid

“…Due to the existence of the intrinsic internal‐built electric field in the ferroelectric, it has also been utilized as a hybrid piezo‐photo‐catalyst. [ 26 , 28 , 29 , 30 ] The majority of work to date has focused on morphological design, such as the formation of microfibers, [ 10 , 11 , 25 ] nanowires, [ 27 ] nanosheets, [ 9 , 28 , 29 ] and nanoparticles. [ 16 , 31 , 32 ] Other work has been reported on the exploitation of noble metals as the co‐catalyst [ 29 , 30 , 33 ] and maximizing the polarization change when the working temperature is close to the Curie temperature, T c , of a ferroelectric.…”

Morphology engineering of type-II heterojunction nanoarrays for improved sonophotocatalytic capability

“…The interaction between the polarization field and charge carriers in ferroelectric, pyroelectric, and piezoelectric nanomaterials has received considerable critical attention across many areas, including photocatalysis, field-effect transistors, sensors, and self-powered systems [1] , [2] , [3] , [4] , [5] , [6] , [7] , [8] , [9] , [10] . As one of the most significant outcomes, ultrasound sonication-promoted photocatalysis (named sonophotocatalysis) has been developed using a sonication-induced piezoelectric field by suppressing the recombination of photoexcited electron–hole pairs [11] , [12] , [13] , [14] .…”