Ultra-Nanostructured Phenazine Conjugated Porous Polymers as Efficient Photocatalyst for Solar-Driven Hydrogen Production

Herein, a phenazine based ultrananostructured conjugated porous polymer (UN_IEP-27) synthesis by using high-performance microfluidic techniques (HPMT) is described. This fact allows the obtention of small particle sizes, high homogeneities, good dispersions, high surface areas and, therefore, improved processabilities. The phenazine moiety endow to the polymer with redox active sites. These advantages have allowed the preparation of a high-quality thin film for its photoelectrochemical characterization but, above all, an improvement in the photocatalytic activity of its hybrid with TiO2. The hybrid photocatalyst UN_IEP-27@T10 (polymer loading of 10 wt.%) achieved a hydrogen evolution rate of 4.1 mmol g-1 h-1 (ƺ =1.52%) at laboratory scale and 0.11 mmol g-1 h-1 (ƺ =0.58%) at solar-pilot scale plant, being 51-fold and 5.5-fold more active than bare TiO2 alone, respectively. Moreover, due to the redox capacity of the phenazine structure, progressively higher hydrogen production yields were obtained after running the experiment for consecutive days under an inert atmosphere, reaching up to 4.8 mmol g-1 h-1 (ƺ =1.76%) and 0.34 mmol g-1 h-1 (ƺ =1.81%) at lab-scale and solar-pilot plant, respectively. This occurs as phenazine undergoes reversible oxidation-reduction processes, oscillating between phenazine and dihydrophenazine, being the latter more photoactive than the initial one. These values are, so far, one of the best values reported with hybrids based on conjugated porous polymers (CPPs), which contribute a breakthrough in the photocatalytic evolution of hydrogen as a renewable energy.