Institute of Science Tokyo achieves 27.7% quantum yield in artificial photosynthesis by shielding molecular catalysts from light damage

Science Tokyo researchers improve CO2-to-formate conversion efficiency to 27.7% by preventing light-induced damage to molecular catalysts.

By: AXL Media

Published: Mar 31, 2026, 12:25 PM EDT

Source: Institute of Science Tokyo

Overcoming the Efficiency Ceiling in Artificial Photosynthesis

Artificial photosynthesis mimics the natural ability of plants to convert sunlight and carbon dioxide into chemical energy, offering a path toward a carbon-neutral society. While scientists have long used hybrid photocatalysts—pairing light-absorbing semiconductors with highly selective molecular catalysts—efficiency has historically been stalled. Most systems have struggled to exceed a 6% quantum yield, which measures how effectively photons are converted into chemical products. Researchers at the Institute of Science Tokyo (Science Tokyo) have now identified that the primary cause of this limitation is the light-induced degradation of the molecular catalyst itself, which loses its structural integrity when exposed to the very sunlight it is meant to harness.

The Mechanism of Photoinduced Ligand Exchange

The central challenge identified by Professor Kazuhiko Maeda and his team is a process known as photoinduced ligand exchange. In conventional designs using ruthenium (Ru) complexes, the molecular catalyst often absorbs light directly. This energy causes the ligands—molecules attached to the metal center—to detach and be replaced, fundamentally altering the catalyst’s structure. These side reactions effectively "break" the catalyst, significantly weakening its ability to reduce CO2. By recognizing this unrecognized limitation, the Science Tokyo team shifted their design strategy from merely capturing light to carefully managing how that energy is distributed within the hybrid system.

Designing a Shielded Hybrid Photocatalyst

To prevent structural damage, the researchers developed a system that fixes an Ru complex onto a carbon nitride semiconductor loaded with silver nanoparticles. The design ensures that the semiconductor, rather than the molecular catalyst, absorbs the vast majority of incoming photons. Once excited, the semiconductor transfers the resulting electrons to the Ru catalytic site where CO2 reduction occurs. The silver nanoparticles play a vital role by suppressing the trapping of electrons within the semiconductor, acting as a bridge that allows the charge to move readily to the surface-bound catalyst. This architecture shields the molecular component from direct light exposure while maintaining the flow of energy required for the chemical reaction.