Photocatalytic water splitting for solving energy crisis: Myth, Fact or Busted?

Reaping hydrogen energy by utilising eternal sunlight offers a good fit to the theme of popularly-hype sustainable and carbon-free energy future. Contrary to that belief, this review unveils the impracticality of photocatalytic water splitting (solar energy for H₂ energy) to fuel global advancement. Despite some success with idealized laboratory-scale studies, the past research works also mutually evinced an extreme low solar-to-hydrogen efficiency (STH < 1.0%). Hitherto, multifarious endeavours, such as advanced reactor design, facilities to eliminate diffusional restrictions, advanced photocatalyst design and an inclusion of sacrificial reagents, are incapable to raise STH efficiency to the practical threshold of STH > 10%. Regardless of the epitome and modifications of photocatalysts, the intrinsic limitation of charges recombination remains a sturdy obstacle, leading to an appreciable energy losses and low STH. For consequential solar-driven H₂ production, the bandgap energy of photocatalyst employed must stay below 2.36 eV. Meanwhile, most photocatalysts are capped by the theoretical maximum STH of 18%, even with the assumption of 100% quantum yield of corresponding spectrum. Nonetheless, the theoretical maximum STH is unattainable at this juncture due to the inevitable solar energy dissipation associated to the scattering effects of reactor and water. From economy standpoint, H₂ production via photocatalytic water splitting is pricey at 10.36 $/kg with exorbitant upfront costs, which is far beyond the practicable price range of 2 – 4 $/kg. In conclusion, we assert that the H₂ production from solar-driven photocatalytic water splitting is an industrially impractical pathway for solar energy harnessing, despite technically-feasible.