Plasmonic Au-based junctions onto TiO2, gC3N4, and TiO2-gC3N4 systems for photocatalytic hydrogen production: Fundamentals and challenges

Solar energy and photocatalysis will undoubtedly play a key aspect in the energy transition. In this background, hydrogen emerged as the ideal photocatalysis-driven solar fuel due to the simplicity of the water-splitting reaction. But finding a single catalyst with sufficient solar-to-photon conversion efficiency remains an important bottleneck of this technology. A constraint that prompted the advancement of multi-phase composites with broader capabilities. Owing to their unique properties, plasmonic Schottky junctions and Z-scheme heterojunctions arose as promising approaches to enhance hydrogen production. But the selection of suitable components towards multi-phasic composites remains challenging due to the absence of standardization in literature and proper characterization of existing materials. Characterization is especially important since components' plasmon wavelength (visible or NIR) and electronic properties have a significant influence on light-harvesting properties and charge carriers separation of the resulting composites. Plus, the optoelectronic properties of the semiconductors determine the resulting type of heterojunction with potential influence in the charge carrier separation via photosensitization. Recent studies suggest that the combination of TiO2 (broad band gap), gC(3)N(4) (narrow band gap), and gold may achieve efficient plasmonic and Z-scheme heterojunctions. In this review, we cover the synthesis and implementation of these materials (alone or in combination), including key technical aspects in photocatalysis, plasmonics, and hydrogen production subjects. We also address pertinent knowledge, experimental gaps, and point to future perspectives to further improve the development of photocatalytic-driven hydrogen technologies. Globally, this multi-phasic composite Au/TiO2-gC(3)N(4) could be used as a platform to continue reinforcing TiO2 efficiencies via photosensitization, co-catalysis, and surface plasmon resonance.

Automated summary

Solar energy and photocatalysis are key players in the energy transition, with hydrogen emerging as an ideal solar fuel due to its simplicity in the water-splitting reaction. However, the challenge lies in finding a single catalyst with sufficient conversion efficiency. The development of multi-phase composites, plasmonic Schottky junctions, and Z-scheme heterojunctions are promising approaches to enhancing hydrogen production.