Poly(dehydroalanine)‐Based Hydrogels as Efficient Soft Matter Matrices for Light‐Driven Catalysis

Abstract

Soft matter integration of photosensitizers and catalysts provides promising solutions to developing sustainable materials for energy conversion. Particularly, hydrogels bring unique benefits as spatial control and 3D‐accessiblity of molecular units as well as recyclability. Herein, we report the preparation of polyampholyte hydrogels based on poly(dehydroalanine) (PDha). Chemically‐crosslinked PDha with bis‐epoxy poly(ethylene glycol) lead to a transparent, self‐supporting hydrogel. Due to the ionizable groups on PDha, this 3D polymeric matrix can be anionic, cationic, or zwitterionic depending on the pH, and its high density of dynamic charges has a potential for electrostatic attachment of charged molecules. We realized the integration of the cationic molecular photosensitizer [Ru(bpy)3]2+ (bpy = 2,2′‐bipyridine), which is a reversible process controlled by pH, leading to light harvesting hydrogels. They were further combined with either a thiomolybdate catalyst ([Mo3S13]−2) for hydrogen evolution reaction (HER) or a cobalt polyoxometalate catalyst (Co4POM = [Co4(H2O)2(PW9O34)2]10−) for oxygen evolution reaction (OER). Under the optimized condition, the resulting hydrogels showed catalytic activity in both case upon visible light irradiation. In case of OER, we observed higher photosensitizer stability compared to homogeneous systems, as the polymer environment seems to influence decomposition pathways.This article is protected by copyright. All rights reserved

Noble Metal-Free Light-Driven Hydrogen Evolution Catalysis in Polyampholytic Hydrogel Networks

“…This behavior is typical for polyelectrolyte hydrogels due to charge screening by the addition of salt . Similar effects have been observed in pristine PDha hydrogels despite the polyzwitterionic feature . In the current work, the net charge of the hydrogel is positive due to the introduced quaternary ammonium side groups, and this contributes to the degree of swelling, also by repulsive Coulombic interactions .…”

“… 53 Similar effects have been observed in pristine PDha hydrogels despite the polyzwitterionic feature. 41 In the current work, the net charge of the hydrogel is positive due to the introduced quaternary ammonium side groups, and this contributes to the degree of swelling, also by repulsive Coulombic interactions. 54 Besides water, the herein described cross-linked PDha- g -GTMAC also showed a DS of 30 ± 5 in DMF as a highly polar organic solvent.…”

“…The chemical cross-linking of poly­(dehydroalanine) allows us to obtain pH-responsive, transparent, and self-supporting hydrogels featuring a high density of pH-dependent charges, and these hydrogels were already successfully utilized as scaffold matrix for immobilizing [Ru­(bpy) 3 ] 2+ photosensitizers and H 2 or O 2 evolution catalysts. , In this work, we integrate an organic photosensitizer derived from PMI into PDha-based hydrogels bearing quaternary ammonium side chains to obtain a fully organic light-harvesting hybrid hydrogel. To this end, we used a PMI derivative with a negatively charged anchoring group for attachment and modified PDha before cross-linking to increase the adsorption capability.…”

“…Another prime example described by Okeyoshi et al involves a H 2 -evolving gel obtained by incorporating a HER catalyst into a cross-linked network comprising comonomers derived from [Ru­(bpy) 3 ] 2+ (bpy = 2,2′-bipyridine) and viologen. , While this gel system offers flexibility in usage and potential adaptation to catalytic systems for O 2 production, the demanding preparation of monomers involved in the catalytic process (e.g., light-harvesting, electron relay) poses a significant challenge. Inspired by this, we have reported a polyampholyte hydrogel designed for immobilizing a PS and CAT only via electrostatic attachment, demonstrating the capability for both visible light-driven HER and water oxidation. , These networks, based on polydehydroalanine (PDha), form hydrogels with dynamic charges arising from ionizable groups (−NH 2 and −COOH). Therefore, they can accommodate both positively and negatively charged guest molecules, making them suitable matrices for various PS/catalyst combinations through attractive electrostatic interactions.…”

“…Inspired by this, we have reported a polyampholyte hydrogel designed for immobilizing a PS and CAT only via electrostatic attachment, demonstrating the capability for both visible light-driven HER and water oxidation. 40 , 41 These networks, based on polydehydroalanine (PDha), form hydrogels with dynamic charges arising from ionizable groups (−NH 2 and −COOH). Therefore, they can accommodate both positively and negatively charged guest molecules, making them suitable matrices for various PS/catalyst combinations through attractive electrostatic interactions.…”