Rational Design of Porous Conjugated Polymers and Roles of Residual Palladium for Photocatalytic Hydrogen Production

Abstract

Developing highly efficient photocatalyts for water splitting is one of the grand challenges in solar energy conversion. Here, we report the rational design and synthesis of porous conjugated polymer (PCP) that photocatalytically generates hydrogen from water splitting. The design mimics natural photosynthetics systems with conjugated polymer component to harvest photons and the transition metal part to facilitate catalytic activities. A series of PCPs have been synthesized with different light harvesting chromophores and transition metal binding bipyridyl (bpy) sites. The photocatalytic activity of these bpy-containing PCPs can be greatly enhanced due to the improved light absorption, better wettability, local ordering structure, and the improved charge separation process. The PCP made of strong and fully conjugated donor chromophore DBD (M4) shows the highest hydrogen production rate at ∼33 μmol/h. The results indicate that copolymerization between a strong electron donor and weak electron acceptor into the same polymer chain is a useful strategy for developing efficient photocatalysts. This study also reveals that the residual palladium in the PCP networks plays a key role for the catalytic performance. The hydrogen generation activity of PCP photocatalyst can be further enhanced to 164 μmol/h with an apparent quantum yield of 1.8% at 350 nm by loading 2 wt % of extra platinum cocatalyst.

A Solution‐Processable Polymer Photocatalyst for Hydrogen Evolution from Water

“…Residual palladium has been suggested to act as cocatalysts in photocatalytic hydrogen evolution in covalent triazine-based frameworks, [37] and in conjunction with g-C 3 N 4 . [38] Low thresholds for the effect of residual palladium on the photocatalytic performance has been reported in conjugated microporous polymers, [22] and for Au loaded onto La-doped NaTaO 3 . [39] It is unclear whether the amount of residual palladium, difference in molecular weight, crystallinity, hydrophobicity or a combination of all of these factors affect the photocatalytic performance in comparison to P8-i.…”

“…[18,19] We have shown that a series of conjugated microporous polymers (CMPs) could facilitate hydrogen evolution from water in the presence of a sacrificial electron donor, without any additional heavy metal cocatalyst. [20,21] Other CMPs have since been studied for photocatalysis [22,23] and recent studies have demonstrated that linear conjugated polymers can have high photocatalytic activities. [24,25] However, as with g-C 3 N 4 , none of these organic materials are soluble in common organic solvents.…”

Visible Light–Driven Hydrogen Production by Carbon based Polymeric Materials

“…Subsequently, Li et al introduced donor-acceptor type microporous polymer by co-polymerization method [44]. Two types of monomeric units, electron-rich units (M2-M4) and electron-deficient (M1) units, were copolymerized with different ration of weak donor biphenyl and weak acceptor bipyridine to produce a series of four polymers (Figure 7).…”

Plausible role of nanoparticle contamination in the synthesis and properties of organic electronic materials

“…Of course, such varying composition of the catalysts makes it difficult to carry out stable and reproducible synthetic procedures [18]. Nanoparticle contamination and the effect of residual metal have been discussed for a variety of catalytic transformations and metal salts used [19][20][21][22][23]. Indeed, structural variations induced by trace metal impurities lead to several difficulties and to irreproducible optoelectronic function [24].…”

“…For example, ICP-MS measurements have shown an increase of the residual Pd content in the range of 0.04-1.88 % upon changing the catalyst/monomer ratio [23]. Several other analytic tools, such as inductively coupled plasmaoptical emission spectroscopy (ICP-OES), ion chromatography (IC), atomic absorption (AA) and X-ray fluorescence (XRF), can also be used.…”