Recent development of black TiO2 nanoparticles for photocatalytic H2 production: An extensive review

Hydrogen is increasingly acknowledged as a promising sustainable energy carrier to fulfill the global energy demand due to its superior energy density, cleanliness, and storability. Besides, it finds extensive application in various industries including oil refining, steel/metal production, chemical production, and transportation. Currently, greater than 95 % of H2 is produced from fossil fuels or renewable resources with release of CO2 as a by-product. To mitigate this CO2 emission, extensive attempts have been undertaken to develop environmentally friendly H2 production methods. The photocatalytic process stands out as a green chemical process, which can produce H2 at atmospheric condition without the emission of CO2 or other toxic substances. Due to its outstanding attributes such as high visible light absorption capacity and remarkable thermal-chemical resistance, black TiO2 (bTiO2) exhibiting defects is currently being developed and applied for photocatalytic H2 production. This review focuses on the recent advancements in the laboratory-scale development of bTiO2, outlining several strategies including defective self-doping, metal and non-metal doping, and conductive material or semiconductor coupling. Among the various strategies applied, the coupling of bTiO2 with semiconductors exhibited the highest photocatalytic H2 production. The mesoporous TiO2/CeO2 nanocomposite aerogel, synthesized by thermal treatment in 5 % H2/Ar atmosphere, produced approximately 182 mmol/g⋅h of H2 under the visible light illumination. This review could broaden the horizon on the design and tailoring of bTiO2 nanocomposites for further practical applications.