PolyNanoCat · Polymer Nanoparticle for Hydrogen Evolution

Polymer Nanoparticle for Hydrogen Evolution

Global energy supply, and its impact on the environment, is one of the biggest technological challenges to be addressed. The synthesis of fuels and chemicals from sunlight, water and carbon dioxide is an important route to sustainable development beyond fossil fuels. Organic semiconductors materials have emerged as potentially low-cost photocatalysts for hydrogen evolution with promising efficiencies, including carbon nitrides, conjugated polymers, and covalent organic frameworks. However, the photophysics of such organic semiconductors photocatalysts and how these determined photocatalytic performances remain limited. Discovering the correlation between the photocatalytic activity and the photophysical properties of polymer photocatalysts will guide the design of novel, stable and efficient catalysts for solar-to-fuel conversion. In PolyNanoCat project, we focused on state-of-the-art polymers donor:acceptor heterojunction nanoparticles for hydrogen evolution, addressing their previously unexplored photophysical properties which determine their function. Advanced transient optical emission and absorption spectroscopies were used to investigate how the structure of the polymer heterojunction nanoparticles affects the photocatalysis mechanism. We reported highly efficient polymer donor/acceptor heterojunction nanoparticles with hydrogen evolution rate (HER) up to 73.7 mmol h−1 g−1 under simulated solar irradiation, and quantum efficiencies of ~ 9 % across the visible spectrum, among the most efficient organic hydrogen evolution photocatalysts reported. The photophysical studies of such nanoparticles revealed that organic semiconductor nanoparticles photocatalysts containing a donor/acceptor heterojunction structure can intrinsically generate remarkably long-lived and reactive charges in the timescales need it for photocatalysis (milliseconds) even in the absence of added metal cocatalyst or sacrificial electron donors. This demonstrates that in heterojunction nanoparticles the mechanism does not rely on a rapid reductive exciton quenching by a sacrificial reagent to drive charge separation as observed in single polymers. Our studies also revealed that the nanomorphology of the donor/acceptors domains in the nanoparticle strongly influences the charge recombination and therefore their activity. These photophysical studies most likely represent the state-of-the-art for organic semiconductors heterojunction photocatalysts leading to guidelines for designing more efficient organic nanoparticles.

Data: CORDIS, © European Union