HybridSolarFuels

Extracting the value from CO2 Carbon dioxide is not just a greenhouse gas, but also a potential source of valuable products, such as chemicals and fuels. Researchers in the HybridSolarFuels project are developing hybrid materials to photoelectrochemically convert CO2, which could lead to the development of novel technologies that provide a more sustainable source of fuels, as Dr Csaba Janáky explains.

Many of us think of carbon dioxide (CO 2) primarily as a greenhouse gas, yet it’s also a potential source of transport fuels and useful chemicals. Based at the University of Szeged in Hungary, Dr Csaba Janáky is the Principal Investigator of the HybridSolarFuels project, an ERC-backed initiative which is exploring the possibility of using solar energy to generate chemicals or fuels. “The idea in the project is to use semiconductor photoelectrodes to generate chemicals from CO 2,” he says. This research in the field of photoelectrochemistry can

be thought of as lying roughly halfway between photovoltaics and photochemistry (or photosynthesis). “With photovoltaics, semiconductors are used to generate electricity, while in photosynthesis sunlight is used to generate chemicals,” explains Dr Janáky. “With photoelectrochemistry we use an electrode like in photovoltaics.

We have a semiconductor, we shine light and generate the electron-hole pairs – but instead of extracting them as current, we drive chemical reactions with these charge carriers, similarly to photosynthesis.”

Photoelectrochemistry A lot of techniques used in these two fields can be applied in photoelectrochemistry, as most of the optical phenomena are similar to those which occur in photovoltaics, while the chemical reactions are driven at a solidliquid interface, similarly to photochemistry.

Meeting these dual requirements in an electrode is a significant scientific and technical challenge however, a topic which lies at the core of the project’s research. “The difficulty is that the same materials need to fulfil the requirements of both photovoltaics,

Labwork with a custom-developed electrolyzer test station. Photo: SZTE INFO, Ilona Újszászi.

and also photochemistry,” says Dr Janáky.

Researchers do not expect to find a single material which meets these requirements, so Dr Janáky is working to assemble hybrid electrode materials with multiple components, where each component has its own function. “The electrode material itself needs to have multiple components, because we need to absorb sunlight, to transport charge carriers inside the electrode, and to transfer these charge carriers to the chemical species on the surface,” he explains. “We can achieve the highest level of efficiency if these three phenomena are de-coupled, meaning that we have different materials for each function.”

There are essentially three main considerations in terms of maximising conversion efficiency. One is optical conversion, so the proportion of photons which are converted to charge carriers, while Dr Janáky says transport efficiency and charge-carrier transfer are also important considerations. “We multiply these efficiencies by each other to calculate the overall efficiency of the conversion process. If any of these efficiencies are low, then the overall efficiency is very low,” he outlines. A lot of attention in research is focused on developing new design concepts to improve these efficiencies, particularly related to interfaces between materials in

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the electrode. “Our project is not about the individual materials themselves, it’s more about the integration of these materials into one electrode. We want to understand how we can combine these materials and harvest all the benefits of the individual components in the system,” continues Dr Janáky. “If we simply combine the best optical absorber, conductor, and catalyst material, it would not be an effective electrode material. We need to design these electrodes in a rational manner.”

in practical applications,” explains Dr Janáky.

A lot of progress has been made in these terms, while Dr Janáky has also made some exciting new discoveries outside the scope of the project’s initial plans, particularly around perovskite materials. “This is a very exciting family of materials. In principle they can be very cheap, because the active layer is extremely thin in comparison to silicon, and they are very easy to make,” he outlines. “There is a lot of interest in using perovskite materials in photovoltaics, but

In photoelectrochemistry we use an electrode like in photovoltaics. We have a semiconductor, we shine light and generate electron-hole pairs – but instead of extracting them as current, we drive chemical reactions with these charge carriers, similarly to photosynthesis.

The primary aim here is to design the interfaces between the components in such a way that the flow of charge carriers is appropriate and that there is minimal recombination. The materials used in these electrodes must be active, robust and scalable if they are to be applied more widely, which is an important consideration in research. “We are analysing the key descriptors, or success factors, for a given photoelectrode material

very few people have looked into using them as electrode materials, or as photoelectrode materials.”

This is a topic that Dr Janáky and his colleagues have been able to investigate further over recent years, demonstrating the benefits of having the freedom to explore interesting avenues of research rather than sticking rigidly to pre-determined plans.

While the project’s research has centered on

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HybridSolarFuels Efficient Photoelectrochemical Transformation of CO2 to Useful Fuels on Nanostructured Hybrid Electrodes

Project Objectives

The three main goals of the HybridSolarFuels project are to (i) gain fundamental understanding of morphological-, size-, and surface functional group effects on the photoelectrochemical (PEC) behavior at the nanoscale (ii) design new functional hybrid materials for PEC CO2 reduction, (iii) develop flow-reactors for PEC CO2 reduction.

Project Funding

HybridSolarFuels, H2020 - European Research Council (ERC) Grant agreement ID: 716539.

Overall budget: €1 498 750 https://cordis.europa.eu/project/id/716539 https://cordis.europa.eu/project/id/899747

Collaborating Partners

• Prof. Krishnan Rajeshwar (UT Arlington) • Prof. Prashant Kamat (University of Notre Dame) • ThalesNanoEnergy Inc

Contact Details

Dr Csaba Janáky Principal Investigator Photoelectrochemistry Research Group Fellow of the Young Academy of Europe University of Szeged Department of Physical Chemistry and Materials Science Szeged, Aradi square 1. HUNGARY T: +36 62 546393 E: janaky@chem.u-szeged.hu W: www.elchem.hu W: http://www2.sci.u-szeged.hu/physchem/ MTA_PERG/index.html : @JanakyLab

Dr Csaba Janáky

Dr Csaba Janáky is an Associate Professor at the University of Szeged, Hungary.

He is an emerging expert of materials science oriented electrochemistry and photoelectrochemistry. He has developed new electrode materials and systems for energy applications, such as CO2 reduction, water oxidation, O2 - reduction, and H 2 evolution. He has published over 90 articles with an overall impact factor of over 600.

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We use electrochemical methods, to assess (photo)corrosion at irradiatied perovskite/liquid interfaces.

photoelectrochemistry, Dr Janáky says their results also hold relevance to other fields.

“We can also provide very useful feedback to the photovoltaics community on the stability of these perovskite materials, and the source of the instability of these materials, through the use of our electrochemical and photoelectrochemical tools,” he says.

However, the main priority in the project is to develop a set of design concepts, which can then be used to produce efficiently performing photoelectrodes, which could then spur further research. “If many other people, other groups, also implement these design concepts, then it’s much more likely that somebody will eventually come up with an efficient electrode material,” continues Dr Janáky.

PEC_Flow project A method of efficiently converting CO 2 into chemicals and fuels holds clear importance in the context of ongoing concern about climate change and the impact of carbon emissions, so Dr Janáky is also looking to explore the wider potential of the project’s research. While the focus in HybridSolarFuels has been primarily on discovery and fundamental research, Dr Janáky is also considering how this can be translated into technological development.

“If everything progresses well, then this research will be translated to CCU (carbon capture and utilisation) technologies, where CO 2 can be converted into economically useful products,” he outlines. With HybridSolarFuels entering the last year of its funding term, Dr Janáky has been awarded a proof-of-concept grant by the ERC for the PEC-Flow project, in which he will investigate the commercial possibilities of continuous flow photoelectrochemical cells. “We are doing different types of techno-economic analysis and lifecycle analysis,” he says.

The intention here is to assess how this novel photoelectrochemical technology compares to other approaches like photosynthetic and photovoltaic+electrochemical methods. Researchers have conducted a number of tests on these cells, looking to assess the performance of different device architectures. “We have continuous flow cells, where we continuously feed the CO 2 and also continuously convert it.

We have generated some data regarding the performance,” says Dr Janáky.

Researchers have observed enhanced photoelectrochemical performance in cuprous oxide/graphene nanohybrids, while other architectures are also under investigation. “We are looking to identify the most attractive approach, to identify those descriptors which describe the performance best, and we are looking at how sensitive the business case is for these parameters,” continues Dr Janáky. “This is the kind of techno-economic analysis work that we are doing. And if it works out and proves effective then it can be further developed towards CCU applications.”

This research is still ongoing and will inform decisions on which materials will be studied further in long-term tests, which could eventually pave the way towards commercialisation. There are still many challenges to deal with before this point however, particularly around the design of a photoelectrochemical system. “The answer depends to a degree on the timescale,” says Dr Janáky. Alongside this work in introducing a novel technology, Dr Janáky also plans to pursue further fundamental research in future, and to work closely with colleagues in complementary fields.

“We have collaborators who are very active in the photovoltaics field, and we continuously share our findings with them,” he stresses.

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