Paving the Way for Commercial Hydrogen Generation From Natural and Artificial Seawater Based on Photocathode of Manganese(II) Oxide–Manganese(IV) Oxide/Poly–1H Pyrrole Nanocomposite Seeded on Additional Poly–1H Pyrrole Film

Abstract

A MnO–MnO₂Poly–1H pyrrole (P1HP) nanocomposite featuring a distinctive semi-pentagonal structure has been synthesized by integrating manganese oxides (MnO and MnO₂) into P1HP through an oxidation process. The resulting nanostructure includes large pentagonal particles ranging from 500 to 600 nm in size, along with smaller dotted particles about 20 nm in diameter. This nanocomposite demonstrates excellent optical absorption across a broad range of spectra, with a bandgap of 1.8 eV. The MnO–MnO₂–P1HP composite is deposited onto a P1HP substrate, forming a MnO–MnO₂–P1HP/P1HP photocathode designed for hydrogen (H₂) production using either natural Red Sea water or an artificial seawater solution free of heavy metals as the electrolyte. H₂ production is evaluated in a three-electrode cell, where the current density under light (J_ph) compared to dark conditions (J_o) serves as the primary indicator of the photocathode’s sensitivity. In natural seawater, J_ph reaches −2.55 mA/cm², while J_o measures −1.6 mA/cm². In artificial seawater, these values decrease slightly to −2.3 mA/cm² and −1.4 mA/cm², respectively. The photocathode’s reproducibility is confirmed through chopped light experiments, which show consistent fluctuations in J values. Its high sensitivity is also demonstrated by its response to varying light energies, ranging from 3.6 to 1.7 eV, with peak J_ph values at 3.6 eV (−2.50 mA/cm²) and a decrease to 2.25 mA/cm² at 2.3 eV. Due to its crystalline structure and cost-efficiency, this MnO–MnO₂–P1HP/P1HP photocathode offers a promising solution for the conversion of Red Sea water into H₂ gas.