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.