Covalent Organic Framework Nanoplates Enable Solution-Processed Crystalline Nanofilms for Photoelectrochemical Hydrogen Evolution

Abstract

As covalent organic frameworks (COFs) are coming of age, the lack of effective approaches to achieve crystalline and centimeter-scale-homogeneous COF films remains a significant bottleneck toward advancing the application of COFs in optoelectronic devices. Here, we present the synthesis of colloidal COF nanoplates, with lateral sizes of ∼200 nm and average heights of 35 nm, and their utilization as photocathodes for solar hydrogen evolution. The resulting COF nanoplate colloid exhibits a unimodal particle-size distribution and an exceptional colloidal stability without showing agglomeration after storage for 10 months and enables smooth, homogeneous, and thickness-tunable COF nanofilms via spin coating. Photoelectrodes comprising COF nanofilms were fabricated for photoelectrochemical (PEC) solar-to-hydrogen conversion. By rationally designing multicomponent photoelectrode architectures including a polymer donor/COF heterojunction and a hole-transport layer, charge recombination in COFs is mitigated, resulting in a significantly increased photocurrent density and an extremely positive onset potential for PEC hydrogen evolution (over +1 V against the reversible hydrogen electrode), among the best of classical semiconductor-based photocathodes. This work thus paves the way toward fabricating solution-processed large-scale COF nanofilms and heterojunction architectures and their use in solar-energy-conversion devices.

Photoelectrochemical water splitting with a triazine based covalent organic framework

“…The broad peak for the TFBB–TAT COF at ∼25° (2 θ ) stipulates the (001) facet, which is usually observed for amorphous polymers, indicating the presence of strong interlayer π–π stacking, which also suggests that the periodicity of the 2D COFs is extended to the third dimension. 33 Although both the COF materials (Scheme 1) are non-planar, the large stacking of the TFBB–TAT COF is due to the planar triazine unit (coming from TAT) in the COF crystallites, which is absent for the TFBB–TAB COF. Due to the presence of the non-planar central phenyl ring (coming from TAB), interlayer stacking for the TFBB–TAB COF is very poor.…”

A Heterostructure Photoelectrode Based on Two-Dimensional Covalent Organic Framework Film Decorated TiO2 Nanotube Arrays for Enhanced Photoelectrochemical Hydrogen Generation

“…On the other hand, oriented films of conjugated 2D COFs grown on transparent conducting fluorine-doped tin oxide and indium tin oxides were also reported as photocathodes for generating hydrogen [ 34 ]. Recently, solution-processed COF nanoplates were proposed to construct centimeter-scale-homogeneous COF films for fabricating a complex cascading photoelectrode for PEC hydrogen evolution [ 35 ]. Although these efforts have been made, constructing the 2D COF-based PEC system for hydrogen generation remains in the early stages of development.…”

Antiaromatic Covalent Organic Frameworks Based on Dibenzopentalenes

“…This class of well-defined porous materials can serve as a platform to translate the properties of molecules to bulk insoluble materials. The combination of a high surface area, accessible pores, and efficient electronic delocalization makes COFs ideal candidates for applications in energy storage, [41][42][43] as well as gas storage and separation, 44,45 (photo)catalysis, [46][47][48][49] and optoelectronics. [50][51][52][53][54][55][56][57][58] Analogous to crystalline COFs, amorphous porous organic polymers (POPs) are constructed of functional monomers.…”