Polyampholyte Graft Copolymers as Unimolecular Matrices for Noble Metal-Free and Visible Light-Driven Hydrogen Evolution by Eosin Y and Molybdenum Phosphide

Abstract

Light-driven water splitting is a promising way to produce hydrogen as a renewable energy carrier in a sustainable way. For this, immobilization of different catalytically active building blocks within soft and adaptive matrices plays a key role towards the defined preparation of multi-component hybrid materials. Herein, we present a combination of molybdenum phosphide (MoP, catalyst) and eosin Y (EY, photosensitizer), both immobilized within polyampholytic polydehydroalanine-graft-n-propyl phosphonic acid acrylamide (PDha-g-nPAA) graft copolymers. Analytical techniques such as nuclear magnetic resonance (NMR) and raman spectroscopy confirmed successful graft copolymer formation, while X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analyses further confirmed the immobilization of the EY and MoP, as evidenced by characteristic elemental signals and discrete MoP crystallites within the graft copolymer matrix. The catalytic activity for hydrogen evolution was investigated in aqueous triethanolamine (TEOA) solutions under green light irradiation (λ ≥ 500 nm). This resulted in improved hydrogen production (>1.4 mmol H2/(h.g)) when compared to a system without graft copolymer (~0.9 mmol H2/(h.g)). The catalytic activity is attributed to the ability of the graft copolymer to stabilize and spatially confine the active units, while simultaneously acting as a bridge to facilitate proton and electron transfer between the EY and MoP.