Oriented Films of Conjugated 2D Covalent Organic Frameworks as Photocathodes for Water Splitting

Abstract

Light-driven water electrolysis at a semiconductor surface is a promising way to generate hydrogen from sustainable energy sources, but its efficiency is limited by the performance of available photoabsorbers. Here we report the first time investigation of covalent organic frameworks (COFs) as a new class of photoelectrodes. The presented 2D-COF structure is assembled from aromatic amine-functionalized tetraphenylethylene and thiophene-based dialdehyde building blocks to form conjugated polyimine sheets, which π-stack in the third dimension to create photoactive porous frameworks. Highly oriented COF films absorb light in the visible range to generate photoexcited electrons that diffuse to the surface and are transferred to the electrolyte, resulting in proton reduction and hydrogen evolution. The observed photoelectrochemical activity of the 2D-COF films and their photocorrosion stability in water pave the way for a novel class of photoabsorber materials with versatile optical and electronic properties that are tunable through the selection of appropriate building blocks and their three-dimensional stacking.

Opportunities of Covalent Organic Frameworks for Advanced Applications

“…[46] The remarkable stability of BDT-ETTA in a wide range of pH aqueous solutions and strong absorption of visible light makes it a promising photoabsorber material. Bein and coworkers first explored COFs as photoelectrodes for such applications in the absence of both cocatalyst and sacrificial agent.…”

Acid Exfoliation of Imine‐linked Covalent Organic Frameworks Enables Solution Processing into Crystalline Thin Films

“…The first is solvothermal synthesis, in which the COF is grown directly on a solid support . This method produces highly crystalline films, with pores sometimes oriented perpendicular to the substrate, but suffers from numerous disadvantages, including difficult scale‐up, lack of generality across substrate types, production of powder products in addition to the film, and the inability to transfer films between supports . The second is interfacial polymerization, in which the monomers or catalyst are dissolved separately in two immiscible solvents such that COF formation occurs at the interface .…”

Adsorption of Pharmaceutical Pollutants from Water Using Covalent Organic Frameworks

“…[3] Covalent organic frameworks (COFs), [6][7][8][9][10] crystallinep orousm aterials formed by the self-assembly of purely organic building blocks, have been explored for aw ide range of applications, such as optoelectronics, [11][12][13] gas storage, [14] and catalysis. [15][16][17][18][19][20][21][22] COFs have also shown promise as adsorbents for organic dyes, [23][24][25][26][27] mercury, [28,29] radionuclides, [30] and lanthanides, [31] as carriers for drug delivery, [32][33][34] and isolation of industriallyr elevant compounds. [35] Recently, we demonstrated that COFs can be used to efficientlyc apture marine toxin okadaic acid from seawater.…”