New strategy enables stepwise photo-assisted decomposition of carbohydrates to hydrogen

Hydrogen (H₂), as a clean energy vector, can be produced via biomass photoreforming powered by solar light. For future biomass refining, biomass photoreforming deserves a high decomposition extent of biomass to maximize H₂ production.

Recently, a research team led by Prof. WANG Feng, Dr. LUO Nengchao from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), in collaboration with Prof. Paolo Fornasiero from University of Trieste, proposed a "C-C bond-first" strategy and realized carbohydrates conversion into C₁ liquid hydrogen carriers (LHCs, consisting of HCOOH and HCHO) over Ta-CeO₂ photocatalyst. The LHCs could release H₂ on site that was needed by either photo- or thermocatalysis.

This work was published in Joule on Jan. 31.

Currently, the main obstacle to high H₂ yield is the far insufficient C-C bond breaking to convert biomass carbons into CO₂ with maximization of H₂ production.

In this study, the researchers demonstrated the significance of prioritized scission of C-C bonds in carbohydrates for photocatalytic hydrogen production and storage.

The proposed "C-C bond first" strategy emphasized prioritized biomass conversion to liquid C₁ LHCs via fully breaking the C-C bonds. A synergistic Ta-CeO₂ that utilized the photo- and thermal energy from solar light fully broke the C-C bonds of carbohydrates, producing C₁ LHCs comprising HCOOH and HCHO with yields from 62% to 86%.

They found that during photocatalytic oxidation of carbohydrates, the elevated temperature was adopted to inhibit deleterious radical coupling over the strongly distorted Ta-CeO₂. The resulting C₁ LHCs that could be transported released only H₂ and CO₂, independent of solar light irradiation. The yield of H₂ from glucose was 33%, much higher than that of direct photoreforming of glucose.

"This stepwise method was also exemplified by flow-type photocatalytic oxidation of glucose under concentrated solar light, which enabled 15% yield of C₁ LHCs from glucose via a cumulative irradiation time of 15.5 hours," said Prof. LUO.