Typically, the cost of photons generated by LEDs is significantly lower compared to the cost of organic molecules – the products of photochemical and photocatalytic processes. Therefore, it is logical to use concentrated light generated by LEDs to make photochemical reactions to proceed faster. For example, we can achieve easily photon flux density that is up to ten times higher than that of solar radiation on Earth’s surface.

The main idea behind the area of research “solar fuels” is to use real Sun light to generate molecules that are used as fuels and have added value. Sun light on Earth’s surface is diluted. On a typical sunny day, power flux density is ~100 mW cm-2. Therefore, efficient use of photons is of paramount importance for solar fuels. The efficiency of photons utilization in photocatalysis (and photochemistry) is estimated by the apparent quantum yield (AQY) – a number of product molecules generated per photon. High AQY is the key to scaling up solar fuels production and transition to higher technology readiness level.

In GH2 project (funded by the European Innovation Council) we cooperate with several partners from Europe, Hong Kong and China. Dr. Vitaliy Shavalagin (located at the Max Planck Institute of Colloids and Interfaces, Potsdam, Germany) has been leading a part of this project that focuses on development of a poly(heptazine imide)-based photocatalyst that operates under visible light.

Until now, we achieved AQY of H2 from bioethanol 73% at 410 nm. Simultaneously with H2 Vitaliy’s photocatalyst generates 1,1-diethoxyethane from ethanol with selectivity over 90%. The photocatalyst uses only 0.05-0.1 wt. % Pt nanoparticles as a H2-evolution catalyst, which is approx. 30 times lower than that typically used in H2 evolution reactions mediated by graphitic carbon nitride-based photocatalysts.

The most spectacular aspect of this reaction is that due to high AQY, we can observe reaction progress by a naked eye – hydrogen bubbles are formed rapidly even in a small 5 mL reactor.

High AQY prompted us to scale up the reaction and make a photoreactor, which could use real solar light. The photocatalytically active sheet (~550 cm2) was prepared by soaking a piece of commercial sponge made of cotton and cellulose in a dispersion of photocatalyst particles in ethanol.

These results have been published in ACS Catalysis. Link to read the article.