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‐C 3 N 4 ) with an atomically thin sheet‐like structure is applied for prominent piezocatalytic and photo‐enhanced piezocatalytic H 2 production. It is revealed that the anomalous piezoelectricity in g‐C 3 N 4 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‐C 3 N 4 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 H 2 evolution rate of 12.16 mmol g −1 h −1 is delivered by the g‐C 3 N 4 nanosheets, far exceeding that of previously reported piezocatalysts and g‐C 3 N 4 photocatalysts. Further, high pure‐water‐splitting performance with production of the value‐added oxidation product H 2 O 2 via photo‐piezocatalysis is also disclosed. This work not only exposes the potential of g‐C 3 N 4 as a piezo‐semiconductor for catalytic H 2 evolution, but also breaks a new ground for the conversion of solar and mechanical energy by photomediated piezocatalytic reaction.