Hydrogen Generation through Solar Photocatalytic Processes: A Review of the Configuration and the Properties of Effective Metal-Based Semiconductor Nanomaterials

[...]an efficient photocatalyst should reduce the likelihood of photogenerated electron/hole recombination (reaction time range 10−12–10−6 s) and promote the migration of photogenerated charge carriers to the surface of the photocatalyst (migration time scale: 10−8–10−1 s) where they may be involved in the half reactions of interest. [...]of this process, excess negative charges and more negative energy levels promote proton ion reduction from a kinetic and thermodynamic point of view, respectively. [...]a phenomenon, also known as “Local Surface Plasmonic Resonance” (LSPR) [36,37], occurs when the electromagnetic field has an oscillation frequency in phase with free electrons on the metal [38]. [...]nanosized metal particles (i) act as antennas by promoting visible light absorption and (ii) sensitize titanium dioxide by favoring the flux of charge carriers on to the conduction band of the semiconductor in the so-called “Process of Plasmon-Induced Resonance Energy Transfer” (PIRET) [39]. In particular, the adoption of specific solar collectors could allow employing the beneficial effect of higher operating temperatures on hydrogen evolution. [...]with the aim of implementing photocatalytic hydrogen production in real applications, cost reduction and toxicity assessment of the photocatalytic composites should be also considered.