“Making the catalysts work for us”

Plant photosynthesis is a highly complex process that is still not fully understood even today – this was something that Roger Alberto, who initiated the URPP LightChEC, was very conscious of at the start of the 12-year research project. Following many years of detailed study across multiple disciplines, his successor, the chemistry professor and current director Greta Patzke, is now able to report significant progress: “We’ve understood fundamental aspects and produced a number of new catalysts.”

Eco-friendly catalysts
Catalysts play a key role in the process of artificial photosynthesis, but producing them is a challenging task. The biggest challenges are that the catalysts need to be efficient and stable, and be able to adapt to the different pH levels needed to produce H2 and O2. “We’ve managed to achieve this,” says Patzke. “The learning years in which we discovered the dynamics of how catalysts work are now behind us. We’re hopefully now entering an era where our catalysts can work for us and provide products on a larger scale.”

The URPP researchers developed novel, efficient and eco-friendly catalysts whose structural, electronic and optical characteristics can be optimized for their specific applications – for direct photocatalytic water splitting or for traditional water electrolysis. “We’ve created a range of substances that we can now draw from,” says Patzke. “We can produce molecules, nanoparticles, solid bodies, coatings – all kinds of things.”

Everything under one roof
The URPP researchers managed to combine the individual steps for producing energy – light harvesting, oxidation and reduction of water – into functional systems in the laboratory. What’s more, thanks to its cooperations with selected partners, the research team is able to carry out almost all the required synthesis and analysis techniques itself.

A low-threshold scientific collaboration has been established with the Swiss Federal Laboratories for Materials Science and Technology (Empa) in Dübendorf and, according to Patzke, this complements the URPP’s expertise perfectly. For example, Empa has analytical techniques that can be used to study the way hydrogen interacts with materials at a new level – this is particularly vital for storage and transport. The LightChEC researchers have also built close links with business chemistry scientists at UZH, who can perform technical economic analyses to establish possible applications. “We’ve set up a hub here, and it’s fantastic,” says Patzke. As the program comes to an end, the URPP LightChEC boasts a wide array of expertise and cooperations that allow the components to be studied in respect of their mechanisms, production, efficacy, longevity and efficiency under one and the same roof.

Scientists with a mission
Patzke says that the value of a university education should not be underestimated either. The URPP participants included almost 90 young scientists “who are passionate about the idea of making greater use of sunlight in a controlled process for generating a product”. Even if graduates from UZH go on to take up a different position, “they carry our mission all over the world as ambassadors of ‘human’ photosynthesis that is eco-friendly, low-tech, affordable and clean” – and ideally they will also sell the idea to potential partners in industry.

What surprised the director of the URPP the most during the last 12 years of research? “How dynamic and receptive to change catalysts are. And how much we still have to learn about supposedly simple inorganic systems.”

The benefit of the URPP LightChEC to society is obvious. Artificial photosynthesis could be used to convert virtually unlimited solar energy into useful materials. A clean, sustainable and inexpensive process would solve lots of problems: humans could move away from oil and gas and meet a large proportion of their demand for energy and raw materials by producing climate-neutral hydrogen. That’s why the shared objective after concluding the URPP is to make sure that the process of converting light into chemical energy not only works in the laboratory, but also becomes an interesting proposition for industrial applications. 

Patzke says that the comprehensive approach adopted by the LightChEC team has gained widespread recognition in a highly competitive international research landscape, and this is also reflected by the fact that outstanding researchers from all over the world have come to speak and give talks at summer schools and symposia. “The brilliant team has made the URPP LightChEC a flagship project that has a real resonance internationally.” 

As well as conducting research, Patzke herself has done plenty of PR work: she has gained a foothold in academies and business-oriented associations and promoted her work widely to get the public, and increasingly also industry, excited about her concept. As an “ambassador for human photosynthesis”, as she likes to describe her work, she regularly manages to get people interested in chemistry and make it clear to them that this “is based on clearly understandable principles that they too can share in”. 

When Greta Patzke helped to set up the URPP LightChEC, she had a very traditional view of solid-state chemistry. “Over the course of the URPP studies, we’ve shown how dynamic these solid-state catalysts are, when previously they were considered to be extremely stable.” For example, molecules underwent what were in some cases major changes under the action of light and when a voltage was applied. But solid-state materials that were previously considered to be much more stable can also undergo massive restructuring. “This reveals an incredible complexity and a new, dynamic picture of solid materials,” says Patzke, “that is the subject of intense discussion within the community.” The chemistry professor thinks the fact that even established theories in textbooks can change is very exciting. “Science would not be so thrilling if it only ever reaffirmed your own ideas and beliefs.”

The fact that the LightChEC researchers have almost no need to outsource anything because of their local cooperations gives them a real edge over their rivals when it comes to implementing their research in practical photochemical applications. In the long term, they envisage an inexpensive, sustainable, low-tech technology with simple reactors – “ideally, the reactors would be recyclable plastic-bag reactors with a compressor-driven, solar-powered separation technology,” reflects Patzke. Their vision is to establish a European technology: “an innovation that is marketed from our continent”. 

At UZH, Patzke will now be focusing on optimizing the developed catalysts – especially their longevity – to make them marketable. The plan is to expand the range of products. For example, the eco-friendly catalysts developed in the URPP could also be suitable for converting biomass into hydrogen or other valuable materials like plastic precursors.

In 2023, Greta Patzke and David Tilley reached the final of the Werner Siemens Foundation “project of the century competition” – they were one of the six finalists from a total of 123 teams that had entered. Although they only received one million francs rather than the hundred million that went to the winner, this success heralded the launch of the new solar reactor project. “In around six years, we want to produce a reactor prototype with the aim of finding production partners that can ramp up the process to an industrial scale,” says Patzke. 

As things stand at present, it is possible to implement a medium-scale to large-scale technology for converting the solar spectrum into hydrogen in countries that get plenty of sunshine, according to Patzke. Yet the situation is different in less sunny countries like Switzerland. “But if we expand the knowledge we have gained in relation to photocatalysis to other reactions, so move away from hydrogen and develop catalysts for producing other valuable materials, for example for refining biomass or producing polymer components, such as ammonia, fine chemicals or similar products, then we’ll be able to carry out our processes in Switzerland as well,” says Patzke.