Linear Conjugated Polymers for Solar-Driven Hydrogen Peroxide Production: The Importance of Catalyst Stability

Abstract

Hydrogen peroxide (H2O2) is one of the most important industrial oxidants. In principle, photocatalytic H2O2 synthesis from oxygen and H2O using sunlight could provide a cleaner alternative route to the current anthraquinone process. Recently, conjugated organic materials have been studied as photocatalysts for solar fuels synthesis because they offer synthetic tunability over a large chemical space. Here, we used high-throughput experiments to discover a linear conjugated polymer, poly­(3-4-ethynylphenyl)­ethynyl)­pyridine (DE7), which exhibits efficient photocatalytic H2O2 production from H2O and O2 under visible light illumination for periods of up to 10 h or so. The apparent quantum yield was 8.7% at 420 nm. Mechanistic investigations showed that the H2O2 was produced via the photoinduced stepwise reduction of O2. At longer photolysis times, however, this catalyst decomposed, suggesting a need to focus the photostability of organic photocatalysts, as well as the initial catalytic production rates.

Reaction Pathways toward Sustainable Photosynthesis of Hydrogen Peroxide by Polymer Photocatalysts

“…High-throughput experiments have been recently conducted to rapidly screen many linear polymer photocatalysts for photocatalytic production of H 2 O 2 . 32 This approach can accelerate the discovery of organic moieties toward the molecular-level design of high-efficiency polymer photocatalysts for overall photosynthesis of H 2 O 2 . The progress can be further expedited if robotic chemists can participate in the design and synthesis of polymer photocatalysts by integrating with advanced theoretical calculations (e.g., time dependent-DFT, nonadiabatic molecular dynamics, and machine learning).…”

“…In 2014, Shiraishi et al reported that the graphitic carbon nitride ( g -C 3 N 4 ), a metal-free polymer semiconductor, can produce H 2 O 2 under photoirradiation using alcohol and molecular O 2 as the proton and oxygen sources, respectively . Inspired by this seminal work, numerous organic polymer-based photocatalysts have emerged in recent years for photocatalytic production of H 2 O 2 , including g -C 3 N 4 derivatives, − conjugated microporous polymers (CMPs), , covalent triazine frameworks (CTFs), , covalent organic frameworks (COFs), − linear conjugated polymers (LCPs), , and resorcinol-formaldehyde (RFs) resins. − Compared to their inorganic counterparts, these polymeric or “soft” materials are comprised of naturally abundant elements such as C, H, and N. Moreover, recent observation of long-lived charges in organic heterojunctions without electron/hole scavengers suggests that organic polymers are promising for driving kinetically challenging and technologically desirable redox reactions . Thus, they are up-and-coming candidates as low cost and easily processable materials for solar-driven H 2 O 2 production. − …”

“…The fundamental design rules are still missing. High-throughput experiments have been recently conducted to rapidly screen many linear polymer photocatalysts for photocatalytic production of H 2 O 2 . This approach can accelerate the discovery of organic moieties toward the molecular-level design of high-efficiency polymer photocatalysts for overall photosynthesis of H 2 O 2 .…”

Tuning Acceptor Length in Photocatalytic Donor‐Acceptor Conjugated Polymers for Efficient Solar‐to‐Hydrogen Energy Conversion

“…And a variety of organic photocatalysts have been developed, including graphitic carbon nitrides ( g ‐C 3 N 4 ), [ 10‐18 ] covalent organic frameworks (COFs), [ 19‐25 ] conjugated microporous polymers (CMPs), [ 26‐36 ] covalent triazine‐based frameworks (CTFs) [ 37‐43 ] and linear conjugated polymers (LCPs). [ 44‐52 ] Although some of them can achieve hydrogen evolution rate (HER) exceeding 10 mmol·g –1 ·h –1 , [ 22,30‐32,40,47‐49 ] the solar‐to‐hydrogen energy (STH) conversion efficiency is still very low, far from the basic requirement of 10% for their practical application. [ 2,53 ] The development of efficient photocatalysts with wide photo‐acting spectrum is still highly desirable in the field.…”

Efficient Generation of Hydrogen Peroxide and Formate by an Organic Polymer Dots Photocatalyst in Alkaline Conditions

“…With photocatalytic H 2 O 2 generation reaction proceeded, reactivity of PFBT‐PCBM binary Pdots continuously decreased together with its absorbance (Figure S13) and hydrodynamic size (Figure S14). O 2 .− [8a] and 1 O 2 [16] have been reported to degrade polymers. In our system, according to XPS data (Figure S15), the degradation of PFBT‐PCBM system is probably through the opening of thiadiazole rings in PFBT polymers caused by the photogenerated 1 O 2 as discussed in Supporting Information.…”