Hot π‐Electron Tunneling of Metal–Insulator–COF Nanostructures for Efficient Hydrogen Production

Abstract

A metal–insulator–semiconductor (MIS) photosystem based on covalent organic framework (COF) semiconductors was designed for robust and efficient hydrogen evolution under visible‐light irradiation. A maximal H2 evolution rate of 8.42 mmol h−1 g−1 and a turnover frequency of 789.5 h−1 were achieved by using a MIS photosystem prepared by electrostatic self‐assembly of polyvinylpyrrolidone (PVP) insulator‐capped Pt nanoparticles (NPs) with the hydrophilic imine‐linked TP‐COFs having =C=O−H−N= hydrogen‐bonding groups. The hot π‐electrons in the photoexcited n‐type TP‐COF semiconductors can be efficiently extracted and tunneled to Pt NPs across an ultrathin PVP insulating layer to reduce protons to H2. Compared to the Schottky‐type counterparts, the COF‐based MIS photosystems give a 32‐fold‐enhanced carrier efficiency, attributed to the combined enhancement of photoexcitation rate, charge separation, and oxidation rate of holes accumulated in the valence band of the TP‐COF semiconductor.

Activation of Carbonyl Oxygen Sites in β‐Ketoenamine‐Linked Covalent Organic Frameworks via Cyano Conjugation for Efficient Photocatalytic Hydrogen Evolution

“…Tp‐PDA displays a broad peak which could be divided into two peaks centered at ≈620 and 680 nm, originated from the band‐gap radiative recombination and the layered π–π interactions of the COFs, respectively. [ 31 ] As for Tp‐DBN, the PL quenching confirms a lower recombination or more efficient separation of photogenerated electron–hole pairs, which could be related to more electron localization onto the terminal cyano sites of the COFs through π‐conjugative networks, as is demonstrated in X‐ray diffraction (XRD) analysis. It is believed that this electron relocalization will contribute to the narrowed band gap and the consequent red‐shifts in the optical absorption and PL emission.…”

A Robust Photocatalytic Hybrid Material Composed of Metal‐Organic Cages and TiO2 for Efficient Visible‐Light‐Driven Hydrogen Evolution

“…The utilization of photocatalytic techniques for water splitting to produce “solar fuels” or other useful chemicals is a feasible way to ease the shortage of energy and deterioration of natural environment [1–4] . Various photocatalysts, such as semiconductors, metal complexes, metal‐organic frameworks, metal‐embedded zeolites, covalent organic frameworks, and other composites, have been utilized for photocatalytic hydrogen generation [5–16] . Inspired by the natural enzymes with ingenious structures, metal‐organic cages (MOCs) constructed with multiple redox‐active metal cation centers and coordinated connected optical‐active ligands have been developed due to their well‐defined shapes, specific cavities, nanoscale sizes and symmetrical geometries, which provide a good foundation for artificial photosynthesis.…”

Molecular Engineering of Fully Conjugated sp2Carbon‐Linked Polymers for High‐Efficiency Photocatalytic Hydrogen Evolution

“…The photocatalytic performance for hydrogen evolution was evaluated by suspending polymeric photocatalysts in water at pH 4 under visible‐light ( λ ≥420 nm) irradiation with ascorbic acid (H 2 A) as a sacrificial electron donor, after the optimization of the reaction conditions (Figures S13 and S14). Our group previously reported that the polymeric semiconductor and polyvinylpyrrolidone‐capped Pt nanoparticles (PVP–Pt) can construct a metal–insulator–semiconductor (MIS) photosystem in which the hot π‐electrons in the photoexcited polymeric semiconductors can be efficiently extracted and tunneled to Pt NPs across an ultrathin PVP insulating layer to reduce protons to H 2 . Therefore, homogeneously dispersed PVP–Pt with average particle sizes of approximately 1.34 nm were added into the reaction mixtures as cocatalysts (Figure S8).…”