RecycLiCo Battery Materials and Zenith Chemical announce US$25M Li-ion battery recycling JV in Taiwan
Porsche and Frauscher developing electric sports boat; PPE drive technology

KIT team designs low-cost photoreactor for efficient solar-driven synthesis

Researchers from the Karlsruhe Institute of Technology (KIT) and their Canadian partners have designed a low-cost photoreactor design for solar-driven synthesis. The photoreactors have a low level of complexity, are readily manufacturable via mass fabrication techniques in polymers, and are easy to adapt to diverse photocatalysts. An open-access paper on the work is published in the journal Joule.

In artificial photosynthesis, chemical reactions are carried out with the help of sunlight. As with the natural model, photons are absorbed by a photocatalytically active material in such a way that their energy directly drives a chemical reaction.

Different photocatalysts can be used, for example, to split water into hydrogen and oxygen, but climate-neutral fuels can also be produced from water and carbon dioxide, says Paul Kant from the Institute of Microprocess Engineering (IMVT) of KIT.

Until now, however, the technology has mainly been found in the laboratory because the costs of producing solar hydrogen were simply too high. However, with a concept for highly efficient photoreactor panels that can be installed in cost-effective modules, the research group has now taken a decisive step towards practice.

An efficient photoreactor module for practical use must essentially have two components: On the one hand, a suitable photocatalyst must be available that drives the actual chemical reaction. On the other hand, a photoreactor must be present—i.e. a “container” for the photocatalyst as well as the starting materials of the chemical reaction.

he photoreactor should ideally direct incident sunlight to the photocatalyst with low loss, no matter from which direction it occurs, or no matter where in the sky the sun is, explains Kant. It is also important that the photoreactor ensures optimal operating conditions for the photocatalyst due to its structure and the material used, such as the right temperature or the right intensity when absorbing light at the photocatalyst.

The photoreactor concept presented by the research team addresses this double challenge: It consists of microstructured polymer panels that are coated with aluminum for high reflectivity and enables both optimal operating conditions and efficient transport of light to the photocatalyst throughout the day. The researchers developed the system with the help of computer-aided geometry optimization and a photocatalytic model system and were already able to demonstrate it on a laboratory scale.

The base design is an extrudable array of reaction channels… The cross section of a single channel comprises a V-shaped concentrator capturing light from various incident directions and guiding it into a tube-like, mirrored cavity, enclosing the reaction volume… The precise shape of a single concentrator cavity channel is optimized in a way that the achieved UV-vis photocatalytic efficiency… is maximized. The optimization is based on a 3D optical model that employs Monte Carlo ray tracing coupled to a plug flow reactor model that maps the chemical conversion. The optimization, thus, considers the specific optical and reaction engineering properties of the employed reaction system and reactor component materials. Kant et al.


Computer-aided design (CAD) model rendering of the single-channel lab photoreactor employed for the demonstration of the proposed photoreactor concept. Kant et al.

On the basis of a generally valid guideline, which was developed by the researchers on the basis of a detailed analysis of their reactor concept, future photoreactor modules can now be designed relatively easily for maximum efficiency for different purposes.

However, high efficiency in the chemical reaction is only part of the challenge to establish artificial photosynthesis as an economic technology. For relevant product quantities, extremely large areas must be covered with photo reactor panels. According to initial calculations, the researchers estimate the price at about US$2 per square meter of photoreactor module.

2023_044_Energiewende mit Wasserstoff vom Dach_1

Concept for highly efficient photo reactor panels for equipping inexpensive modules. (Photo: Amadeus Bramsiepe, KIT)

In further work under the leadership of Anselm Dreher, a suitable photocatalyst will now be developed in the next steps at the IMVT in Karlsruhe and in the working group led by Professor Geoffrey Ozin in Toronto, which efficiently splits water into hydrogen and oxygen. The photocatalyst is then integrated into the presented photoreactors. In addition, current work includes studies on the mass production of the presented panels.


  • Paul Kant, Shengzhi Liang, Michael Rubin, Geoffrey Alan Ozin, Roland Dittmeyer (2023) “Low-cost photoreactors for highly photon/energy-efficient solar-driven synthesis.” Joule doi: 10.1016/j.joule.2023.05.006


Bernard Harper

If green hydrogen is produced in vast quantities, will the inevitable leakage be a disastrous greenhouse gas too?


It'll be far worse than CO2.


' It'll be far worse than CO2.'

This is to confuse leakage and inefficiencies, which are at most a few percent of production and can be minimised, with our present production, which is largely in spite of progress in renewables dependent on fossil fuels, which inherently produce CO2 with every KWh of production.


Far worse than hydrogen is natural gas


What about when it rains?
Also, bird droppings and general dirt - much harder to clean than a flat PV panel.


Good point, Jim.
Many seemingly great notions fall down due to even on the face of it small sounding issues.


@ Davemart:
"This is to confuse leakage and inefficiencies, which....."
When considering all the calamities occurring in the past with raw oil production (off-shore oil rigs, oil tankers, pipe lines etc. etc.) resulting from negligence, carelessness, ignorance, stupidity, greed and profit dreaming, are you really convinced that all this will change overnight when the same idiots switch to an H2 based industry??? If you believe that, then you are really a fantastic day dreamer.



One could make the same comments regarding the electricity supply industry, which historically has run on coal and natural gas, or batteries which have been toxic, use scarce elements and are and often dumped in landfills.

To do so however would just be to pick random and not particularly relevant analogies, as would appear to be the case for your critique.


"One could make the same comments regarding the electricity supply industry"
I assume from your line of reasoning that because Putin is a mass-murder it's OK to murder without fearing any consequences.



And that assumption would be even more erroneous and downright daft than those you made in your original argument.

For the record, I support sending F16 and Grippen fighter planes, and Apache helicopters, to Ukraine, and have done since the invasion.

The comments to this entry are closed.