Spontaneous dissociation of excitons in polymeric photocatalysts for overall water splitting

Poly (Triazine Imide) (PTI), like other polymeric semiconductors, suffers from the high exciton binding energy, which intrinsically impedes the separation of photo-induced charge carriers. Herein, we present a crystal structure engineering strategy that exploits the lattice mismatch between the CaCl₂ ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover><mml:mrow><mml:mn>1</mml:mn></mml:mrow> <mml:mo>¯</mml:mo></mml:mover> </mml:math> 12) growth template and basal planes of PTI to synthesize unusual PTI nanoplates featuring spontaneous exciton dissociation. The measured exciton binding energy of 15.4 meV in PTI is much lower than the room-temperature thermal fluctuation energy (25.7 meV), which is an indicator of realizing spontaneous exciton dissociation. The in-plane lattice contraction and the interlayer Ca²⁺ doping are revealed as the underlying reasons for the desirable delocalization and anisotropic distribution of energy states. Correspondingly, the resulting PTI-based photocatalyst delivers a nearly 5 times enhancement of the photocatalytic overall water-splitting activity compared with commonly available PTI. Moreover, the chemically traceable spatial separation of the photo-induced electrons and holes has been evidenced in PTI-based photocatalysts. This success in modifying the properties of photo-induced charge carriers in PTI sheds light on how to make polymeric semiconductors more efficient by dissociating excitons into free charges.