Porphyrin Conjugated Polymer with Periodic Type II‐Like Heterojunctions and Single‐Atom Catalytic Sites for Broadband‐Responsive Hydrogen Evolution

Abstract

A novel heterometallic Zn‐/Co‐porphyrin conjugated polymer (ZnCoP‐F CP) with its Co‐porphyrin bridging unit bearing two perfluorophenyls is synthesized via a Sonogashira coupling reaction. The resulting ZnCoP‐F CP without the Pt cocatalyst exhibits broadband (UV–vis–NIR) light‐driven hydrogen evolution activity of 83 µmol h−1, which is more than twice that (39 µmol h−1) of its counterpart (ZnCoP CP) with the Co‐porphyrin unit bearing two phenyls. Furthermore, an apparent quantum yield of 6.92%, 5.50%, 5.78%, 3.17%, and 0.73% is achieved from the ZnCoP‐F CP illuminated at 400, 500, 550, 700, and 850 nm monochromatic light, respectively. The enhanced performance of ZnCoP‐F CP can be attributed to the high electron‐withdrawing capacity of its perfluorophenyls and the highly dispersed Co centers in Co‐porphyrin bridging units serving as single‐atom catalytic sites (CoN4), which facilitate the formation of periodic type II‐like heterojunctions and the fast charge transfer from Zn‐porphyrin to Co‐porphyrin units for hydrogen evolution reaction. The broadband‐responsive feature is due to the large π‐conjugated system through the whole 2D internal framework of the porphyrin polymer. This work opens a new path to fabricate porphyrin‐based polymer with an efficient and broadband‐responsive hydrogen evolution system.

Electronic and energy level engineering of directly fused porphyrin-conjugated polymers – impact of the central metal cation

“…optoelectronic and catalytic properties) can be further enhanced by assembling them into large p-conjugated systems, e.g. porphyrin-based metal-organic frameworks (MOFs), 6,7 bridged porphyrin conjugated polymers (CPs) 8 and directly fused porphyrin CPs. 9,10 In contrast to inorganic semiconductors, even a small modification of the chemical structure of conducting and semiconducting coordination and covalent polymers can lead to a significant change of their optoelectronic properties and hence, the extension of their functional applications.…”

“…2,6,11 In particular, the modification of the central metal ion and/or meso-substituents can alter the band gap and band edge positions of porphyrin-based MOFs 6 and porphyrinbased CPs. 8 In addition, the metal cation chelated at the center of the metalloporphyrin macrocycle -magnesium(II) in chlorophyllcan act as a single-atom catalytic site, boosting the efficiency of a targeted chemical reaction. For example, cobalt(II)-bridged porphyrin CPs have been demonstrated as excellent earthabundant element heterogeneous catalysts for the oxygen evolution reaction (OER) 12 from water oxidation and the oxygen reduction reaction (ORR).…”

“…13 When combining with zinc(II) porphyrins in a bridged porphyrin conjugated polymer, cobalt(II) porphyrins are also active for the hydrogen evolution reaction (HER) from water splitting. 8 In this latter example, the periodically distributed type II-like heterojunction between adjacent zinc(II) and cobalt(II) porphyrins ensures the charge separation and transfer from zinc(II) porphyrins to cobalt(II) porphyrins. 8 Directly fused porphyrin assemblies are also active catalysts.…”

“…8 In this latter example, the periodically distributed type II-like heterojunction between adjacent zinc(II) and cobalt(II) porphyrins ensures the charge separation and transfer from zinc(II) porphyrins to cobalt(II) porphyrins. 8 Directly fused porphyrin assemblies are also active catalysts. 14,15 In particular, bimetallic copper(II)-fused porphyrin dimers were shown to be a highly active HER catalyst, demonstrating the direct fusion of the porphyrin macrocycles to be a promising strategy for enhanced electrocatalyst design.…”

In situ grown TiN/N-TiO2 composite for enhanced photocatalytic H2 evolution activity

“…This energetic alignment is thermodynamically favorable for hot carrier injecting to the CB of N-TiO 2 [21], and those injected electrons and the photoexcited ones of N-TiO 2 are further transferred to the Pt cocatalyst to participate in the H 2 evolution reaction [43,44]. Meanwhile, the photogenerated holes remain in N-TiO 2 transfer to the photocatalyst for the oxidation reaction of hole scavenger [45].…”