Photocatalytic Water Splitting System SolarH2 Deep Dive: Efficiency of Using Sunlight to Split Water into Hydrogen and Oxygen Surpasses 15%

A research team led by University of Tokyo special professor Kazunari Domen, in collaboration with Toyota Motor Corporation, announced that its SolarH2 photocatalytic water splitting system has achieved 15.3% solar-to-hydrogen conversion efficiency under real sunlight conditions, surpassing the 10% practical threshold set by the International Energy Agency for the first time.

Photocatalytic water splitting is a one-step hydrogen production technology. Photocatalyst powder is dispersed in water, and sunlight directly splits water molecules into hydrogen and oxygen. Compared to electrolysis, which requires first generating electricity and then electrolyzing water, the photocatalytic method eliminates the intermediate electrical step and is theoretically cheaper.

SolarH2s core is a set of three-layer photocatalyst panels that absorb ultraviolet, visible, and near-infrared light respectively. Each layer uses different semiconductor materials, achieving broad-spectrum absorption of sunlight through band-gap engineering.

Domen stated at a Tokyo press conference that 15.3% STH efficiency is a historic breakthrough in photocatalytic hydrogen production. The previous laboratory record was 9.2%, and the team improved efficiency by 66% in just two years. The key breakthrough was introducing atomically dispersed iridium-based co-catalysts in the third-generation photocatalyst.

The team has built a 100-square-meter SolarH2 demonstration unit at the University of Tokyo Kashiwa campus, producing approximately 1.2 kilograms of hydrogen per day. The next step is a 10,000-square-meter pilot plant planned for 2029.

However, the fundamental challenge for photocatalytic hydrogen production remains catalyst long-term stability. In actual operation, photocatalysts gradually deactivate due to photocorrosion. Current catalyst lifespan is approximately six months, requiring periodic replacement. The team is developing self-healing catalyst coatings targeting a lifespan of over three years.