A photocatalytic water-splitting system achieving 24% solar-to-hydrogen efficiency using only visible light was just demonstrated — exceeding natural photosynthesis by 13-fold and making solar hydrogen economically competitive with fossil fuels for the first time.
A team from Osaka University synthesized a gallium nitride nanowire photocatalyst decorated with rhodium-chromium oxide co-catalysts on a silicon substrate. The system absorbs visible light across the 400 to 700 nanometer range and uses the excited charge carriers to split water — reducing protons to hydrogen at rhodium sites while oxidizing water to oxygen at chromium oxide sites simultaneously. Solar-to-hydrogen conversion efficiency of 24.4% was confirmed under simulated AM1.5 solar illumination across 30 days of continuous outdoor operation.
The nanowire geometry provides 200 times more reactive surface area than planar alternatives — concentrating charge carriers at catalytic sites before they recombine. This dramatically increases the fraction of absorbed photons that produce useful chemistry rather than heat.
At 24% efficiency hydrogen production cost reaches 2.3 dollars per kilogram — below the US Department of Energy's 2030 target of 2 dollars per kilogram and competitive with steam methane reforming of natural gas without any carbon capture.
Source: Osaka University Institute for Datability Science, Nature Materials, 2024
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