Behind the Paper

Pushing solar fuels to the next level

There is a personal story behind every scientific project. Behind this very successful project that deals with simultaneous photocatalytic production of hydrogen and 1,1-diethoxyethane from ethanol is a dramatic personal story of its main author.
Published in Chemistry and Materials
Go to the profile of Oleksandr Savateev
Oleksandr Savateev
Vice-Chancellor Associate Professor, The Chinese University of Hong Kong
Pushing solar fuels to the next level
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ACS Publications ACS Publications

Simultaneous Photocatalytic Production of H2 and Acetal from Ethanol with Quantum Efficiency over 73% by Protonated Poly(heptazine imide) under Visible Light

In this work, protonated poly(heptazine imide) (H-PHI) was obtained by adding acid to the suspension of potassium PHI (K-PHI) in ethanol. It was established that the obtained H-PHI demonstrates very high photocatalytic activity in the reaction of hydrogen formation from ethanol in the presence of Pt nanoparticles under visible light irradiation in comparison with K-PHI. This enhancement can be attributed to improved efficiency of photogenerated charge transfer to the photocatalyst’s surface, where redox processes occur. Various factors influencing the system’s activity were evaluated. Notably, it was discovered that the conditions of acid introduction into the system can significantly affect the size of Pt (cocatalyst metal) deposition on the H-PHI surface, thereby enhancing the photocatalytic system’s stability in producing molecular hydrogen. It was established that the system can operate efficiently in the presence of air without additional components on the photocatalyst surface to block air access. Under optimal conditions, the apparent quantum yield of molecular hydrogen production at 410 nm is around 73%, the highest reported value for carbon nitride materials to date. The addition of acid not only increases the activity of the reduction part of the system but also leads to the formation of a value-added product from ethanol–1,1-diethoxyethane (acetal) with high selectivity.

Generation of hydrogen (H2, "solar fuel") by sustainable methods is one of the strategic topics of the European Union. Therefore substantial resources are invested into creating new materials, method and processes, which can deliver this chemical.

In the project "GreenH2 production from water and bioalcohols by full solar spectrum in a flow reactor" (abbreviated as GH2 and funded under the European Innovation Council), one of our goals is to produce of H2 from bioalcohols with quantum efficiency >60%.  Simultaneously with H2 we aim to obtain a product of a bioalcohol dehydrogenation with selectivity >90%. In case of bioethanol, such a product  is 1,1-diethoxyethane. This molecule is used as a solvent, but has a potential as a fuel-additive. 

Dr. Vitaliy Shvalagin has been working on the implementation of the abovementioned goals. He designed and prepared a photocatalyst, which is based on graphitic carbon nitride - poly(heptazine imide).

Vitaliy's photocatalyst generates H2 and 1,1-diethoxyethane in nearly 1:1 molar ratio. AQY of H2 is 73% at 410 nm and 85% at 365 nm. The photocatalytic system requires only 0.05-0.1 wt. % of Pt as nanoparticles, which is approx. 30 times lower than typically used in H2 evolution reactions driven by graphitic carbon nitride photocatalysts. The selectivity of 1,1-diethoxyethane synthesis is up to 90%. The reaction mechanism involves conversion of ethanol into H2 and acetaldehyde by means of photocatalysis. Under the conditions of acidic catalysis acetaldehyde reacts with two ethanol molecules, which gives 1,1-diethoxyethane. These steps are accomplished in one pot.
A culmination of this part of the project is a 550-cm2 photoreactor that operates under real solar light. The setup generates approx. 130 mL of hydrogen per hour.

Readers who follow developments in the field of solar fuels have probably noticed similarities of our setup and a flat panel reactor developed by  Prof. Kazunari Domen and colleagues. Indeed, we were inspired by their design. After all, immobilizing a photocatalyst on a flat surface is the most rational and straightforward photoreactor design when using natural sunlight.

This part of the GH2 project was completed in a cooperation with ETH Zurich, Hong Kong University and Tsinghua University. The results are now published in ACS Catalysis.

Before joining my group at the Max Planck Institute of Colloids and Interfaces in Potsdam, Germany, Vitaliy has been working as a senior research associate at the Institute of Physical Chemistry, National Academy of Sciences of Ukraine - a stable job and an advanced carrier stage within Ukrainian scientific community. After Russia's full-scale invasion of Ukraine, on 24th of February 2022, Vitaliy and his family had to leave Kyiv. Unplanned relocation and a new environment were the challenges they faced.

This project is not just about photocatalysis and hydrogen generation; it is a testament to the researcher’s determination in the face of adversity. Truly per aspera ad astra.

Go to the profile of Oleksandr Savateev
Oleksandr Savateev (He/Him)
Vice-Chancellor Associate Professor, The Chinese University of Hong Kong

Photocatalysis, organic chemistry, materials chemistry

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Photocatalysis
Physical Sciences > Chemistry > Materials Chemistry > Catalytic Materials > Photocatalysis
Hydrogen Energy
Physical Sciences > Chemistry > Industrial Chemistry > Hydrogen Energy
Heterogeneneous Catalysis
Physical Sciences > Chemistry > Organic Chemistry > Catalysis > Heterogeneneous Catalysis

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