Semiconducting Overoxidized Polypyrrole Nano-Particles for Photocatalytic Water Splitting

Abstract

Capturing sunlight to fuel the water splitting reaction (WSR) into O₂ and H₂ is the leitmotif of the research around artificial photosynthesis. Organic semiconductors have now joined the quorum of materials currently dominated by inorganic oxides, where for both families of compounds the bandgaps and energies can be adjusted synthetically to perform the Water Splitting Reaction. However, elaborated and tedious synthetic pathways are necessary to optimize the photophysical properties of organic semiconductors. This study reports here, that when pyrrole dissolved distilled water is exposed to high energy radiation, this leads to the formation of nanostructured spherical polypyrrole (Nano-PPy) particles that are characterized as overoxidized polypyrrole. Electrochemical studies and Tauc's plot highlight the production of a semiconducting material with a bandgap of ≈1.8 eV with the conduction band at ≈−0.5 V and a valence band at ≈+1.3 V vs NHE. When suspended in water and under irradiation at wavelengths higher than 420 nm, Nano-PPy materials lead to O₂ evolution, while electrons and protons can be recovered in the form of reduced quinone. Interestingly, upon intermittent visible irradiation and dark phases, a consumption of the evolved O₂ from oxidation of water is observed. This concomitant O₂ reduction is found to produce H₂O₂.