Cambridge Energy News

The researchers, led by the University of Cambridge, are developing low-cost light-harvesting semiconductors that power devices for converting water into clean hydrogen fuel, using just the power of the sun. These semiconducting materials, known as copper oxides, are cheap, abundant and non-toxic, but their performance does not come close to silicon, which dominates the semiconductor market.

However, the researchers found that by growing the copper oxide crystals in a specific orientation so that electric charges move through the crystals at a diagonal, the charges move much faster and further, greatly improving performance. Tests of a copper oxide light harvester, or photocathode, based on this fabrication technique showed a 70% improvement over existing state-of-the-art oxide photocathodes, while also showing greatly improved stability.

The researchers say their results, reported in the journal Nature, show how low-cost materials could be fine-tuned to power the transition away from fossil fuels and toward clean, sustainable fuels that can be stored and used with existing energy infrastructure.

Copper (I) oxide, or cuprous oxide, has been touted as a cheap potential replacement for silicon for years, since it is reasonably effective at capturing sunlight and converting it into electric charge. However, much of that charge tends to get lost, limiting the material’s performance.

“Like other oxide semiconductors, cuprous oxide has its intrinsic challenges,” said co-first author Dr Linfeng Pan from Cambridge’s Department of Chemical Engineering and Biotechnology. “One of those challenges is the mismatch between how deep light is absorbed and how far the charges travel within the material, so most of the oxide below the top layer of material is essentially dead space.”

“For most solar cell materials, it’s defects on the surface of the material that cause a reduction in performance, but with these oxide materials, it’s the other way round: the surface is largely fine, but something about the bulk leads to losses,” said Professor Sam Stranks, who led the research. “This means the way the crystals are grown is vital to their performance.”

To develop cuprous oxides to the point where they can be a credible contender to established photovoltaic materials, they need to be optimised so they can efficiently generate and move electric charges – made of an electron and a positively-charged electron ‘hole’ – when sunlight hits them.

One potential optimisation approach is single-crystal thin films – very thin slices of material with a highly-ordered crystal structure, which are often used in electronics. However, making these films is normally a complex and time-consuming process.

Using thin film deposition techniques, the researchers were able to grow high-quality cuprous oxide films at ambient pressure and room temperature. By precisely controlling growth and flow rates in the chamber, they were able to ‘shift’ the crystals into a particular orientation. Then, using high temporal resolution spectroscopic techniques, they were able to observe how the orientation of the crystals affected how efficiently electric charges moved through the material.

“These crystals are basically cubes, and we found that when the electrons move through the cube at a body diagonal, rather than along the face or edge of the cube, they move an order of magnitude further,” said Pan. “The further the electrons move, the better the performance.”

“Something about that diagonal direction in these materials is magic,” said Stranks. “We need to carry out further work to fully understand why and optimise it further, but it has so far resulted in a huge jump in performance.” Tests of a cuprous oxide photocathode made using this technique showed an increase in performance of more than 70% over existing state-of-the-art electrodeposited oxide photocathodes.

“In addition to the improved performance, we found that the orientation makes the films much more stable, but factors beyond the bulk properties may be at play,” said Pan.

The researchers say that much more research and development is still needed, but this and related families of materials could have a vital role in the energy transition.

“There’s still a long way to go, but we’re on an exciting trajectory,” said Stranks. “There’s a lot of interesting science to come from these materials, and it’s interesting for me to connect the physics of these materials with their growth, how they form, and ultimately how they perform.”

The research was a collaboration with École Polytechnique Fédérale de Lausanne, Nankai University and Uppsala University. The research was supported in part by the European Research Council, the Swiss National Science Foundation, and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI). Sam Stranks is Professor of Optoelectronics in the Department of Chemical Engineering and Biotechnology, and a Fellow of Clare College, Cambridge.

Reference:
Linfeng Pan, Linjie Dai et al. ‘High carrier mobility along the [111] orientation in Cu2O photoelectrodes.’ Nature (2024). DOI: 10.1038/s41586-024-07273-8

For more information on energy-related research in Cambridge, please visit the Energy IRC, which brings together Cambridge’s research knowledge and expertise, in collaboration with global partners, to create solutions for a sustainable and resilient energy landscape for generations to come. 

Researchers have found a way to super-charge the ‘engine’ of sustainable fuel generation – by giving the materials a little twist.

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Researchers led by the University of Cambridge used experimental and computer modelling techniques to study the porous carbon electrodes used in supercapacitors. They found that electrodes with a more disordered chemical structure stored far more energy than electrodes with a highly ordered structure.

Supercapacitors are a key technology for the energy transition and could be useful for certain forms of public transport, as well as for managing intermittent solar and wind energy generation, but their adoption has been limited by poor energy density.

The researchers say their results, reported in the journal Science, represent a breakthrough in the field and could reinvigorate the development of this important net-zero technology.

Like batteries, supercapacitors store energy, but supercapacitors can charge in seconds or a few minutes, while batteries take much longer. Supercapacitors are far more durable than batteries, and can last for millions of charge cycles. However, the low energy density of supercapacitors makes them unsuitable for delivering long-term energy storage or continuous power.

“Supercapacitors are a complementary technology to batteries, rather than a replacement,” said Dr Alex Forse from Cambridge’s Yusuf Hamied Department of Chemistry, who led the research. “Their durability and extremely fast charging capabilities make them useful for a wide range of applications.”

A bus, train or metro powered by supercapacitors, for example, could fully charge in the time it takes to let passengers off and on, providing it with enough power to reach the next stop. This would eliminate the need to install any charging infrastructure along the line. However, before supercapacitors are put into widespread use, their energy storage capacity needs to be improved.

While a battery uses chemical reactions to store and release charge, a supercapacitor relies on the movement of charged molecules between porous carbon electrodes, which have a highly disordered structure. “Think of a sheet of graphene, which has a highly ordered chemical structure,” said Forse. “If you scrunch up that sheet of graphene into a ball, you have a disordered mess, which is sort of like the electrode in a supercapacitor.”

Because of the inherent messiness of the electrodes, it’s been difficult for scientists to study them and determine which parameters are the most important when attempting to improve performance. This lack of clear consensus has led to the field getting a bit stuck.

Many scientists have thought that the size of the tiny holes, or nanopores, in the carbon electrodes was the key to improved energy capacity. However, the Cambridge team analysed a series of commercially available nanoporous carbon electrodes and found there was no link between pore size and storage capacity.

Forse and his colleagues took a new approach and used nuclear magnetic resonance (NMR) spectroscopy – a sort of ‘MRI’ for batteries – to study the electrode materials. They found that the messiness of the materials – long thought to be a hindrance – was the key to their success.

“Using NMR spectroscopy, we found that energy storage capacity correlates with how disordered the materials are – the more disordered materials can store more energy,” said first author Xinyu Liu, a PhD candidate co-supervised by Forse and Professor Dame Clare Grey. “Messiness is hard to measure – it’s only possible thanks to new NMR and simulation techniques, which is why messiness is a characteristic that’s been overlooked in this field.”

When analysing the electrode materials with NMR spectroscopy, a spectrum with different peaks and valleys is produced. The position of the peak indicates how ordered or disordered the carbon is. “It wasn’t our plan to look for this, it was a big surprise,” said Forse. “When we plotted the position of the peak against energy capacity, a striking correlation came through – the most disordered materials had a capacity almost double that of the most ordered materials.”

So why is mess good? Forse says that’s the next thing the team is working on. More disordered carbons store ions more efficiently in their nanopores, and the team hope to use these results to design better supercapacitors. The messiness of the materials is determined at the point they are synthesised.

“We want to look at new ways of making these materials, to see how far messiness can take you in terms of improving energy storage,” said Forse. “It could be a turning point for a field that’s been stuck for a little while. Clare and I started working on this topic over a decade ago, and it’s exciting to see a lot of our previous fundamental work now having a clear application.”

The research was supported in part by the Cambridge Trusts, the European Research Council, and UK Research and Innovation (UKRI).

Reference:
Xinyu Liu et al. ‘Structural disorder determines capacitance in nanoporous carbons.’ Science (2024). DOI: 10.1126/science.adn6242

For more information on energy-related research in Cambridge, please visit the Energy IRC, which brings together Cambridge’s research knowledge and expertise, in collaboration with global partners, to create solutions for a sustainable and resilient energy landscape for generations to come. 

The energy density of supercapacitors – battery-like devices that can charge in seconds or a few minutes – can be improved by increasing the ‘messiness’ of their internal structure.

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Funded by the European Union’s Horizon 2020 research and innovation programme, the Bio-inspired and Bionic materials for Enhanced Photosynthesis (BEEP) project, led by Professor Silvia Vignolini in the Yusuf Hamied Department of Chemistry, studied how marine organisms interact with light.

The four-year sustainable energy project brought together nine research groups from across Europe and drew its inspiration from nature, in particular from the marine world, where organisms including algae, corals and sea slugs have evolved efficient ways to convert sunlight into energy. Harnessing these properties could aid in the development of new artificial and bionic photosynthetic systems.

Some of the brightest and most colourful materials in nature – such as peacock feathers, butterfly wings and opals – get their colour not from pigments or dyes, but from their internal structure alone. The colours our eyes perceive originate from the interaction between light and nanostructures at the surface of the material, which reflect certain wavelengths of light.

As part of the BEEP project, the team studied structural colour in marine species. Some marine algae species have nanostructures in their cell walls that can transmit certain wavelengths of visible light or change their structures to guide the light inside the cell. Little is known about the function of these structures, however: scientists believe they might protect the organisms from UV light or optimise light harvesting capabilities.

The team studied the optical properties and light harvesting efficiency of a range of corals, sea-slugs, microalgae and seaweeds. By understanding the photonic and structural properties of these species, the scientists hope to design new materials for bio-photoreactors and bionic systems.

“We’re fascinated by the optical effects performed by these organisms,” said Maria Murace, a BEEP PhD candidate at Cambridge, who studies structural colour in seaweeds and marine bacteria. “We want to understand what the materials and the structures at the base of these colours are, which could lead to the development of green and sustainable alternatives to the conventional paints and toxic dyes we use today.”

BEEP also studied diatoms: tiny photosynthetic algae that live in almost every aquatic system on Earth and produce as much as half of the oxygen we breathe. The silica shells of these tiny algae form into stunning structures, but they also possess remarkable light-harvesting properties.

The BEEP team engineered tiny light-harvesting antennae and attached them to diatom shells. “These antennae allowed us to gather the light that would otherwise not be harvested by the organism, which is converted and used for photosynthesis,” said Cesar Vicente Garcia, one of the BEEP PhD students, from the University of Bari in Italy. “The result is promising: diatoms grow more! This research could inspire the design of powerful bio-photoreactors, or even better

The scientists engineered a prototype bio-photoreactor, consisting of a fully bio-compatible hydrogel which sustains the growth of microalgae and structural coloured bacteria. The interaction of these organisms is mutually beneficial, enhancing microalgal growth and increasing the volume of biomass produced, which could have applications in the biofuel production industry.

Alongside research, the network has organised several training and outreach activities, including talks and exhibitions for the public at science festivals in Italy, France and the UK.

“Society relies on science to drive growth and progress,” said Floriana Misceo, the BEEP network manager who coordinated outreach efforts. “It’s so important for scientists to share their research and help support informed discussion and debate because without it, misinformation can thrive, which is why training and outreach was an important part of this project.”

“Coordinating this project has been a great experience. I learned immensely from the other groups in BEEP and the young researchers,” said Vignolini. “The opportunity to host researchers from different disciplines in the lab was instrumental in developing new skills and approaching problems from a different perspective.”

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under a Marie Skłodowska-Curie grant.

How could tiny antennae attached to tiny algae speed up the transition away from fossil fuels? This is one of the questions being studied by Cambridge researchers as they search for new ways to decarbonise our energy supply, and improve the sustainability of harmful materials such as paints and dyes.

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Semiconductors, also known as microchips, are a key component in nearly every electrical device from mobile phones and medical equipment to electric vehicles.

They are increasingly being recognised as an area of global strategic significance due to the integral role they play in net zero, AI and quantum technology.

Co-created and delivered with industry, the REWIRE IKC is led by the University of Bristol, in partnership with Cambridge and Warwick Universities.

The IKC will accelerate the UK’s ambition for net zero by transforming the next generation of high-voltage electronic devices using wide/ultra-wide bandgap (WBG/UWBG) compound semiconductors.

The project is being led by Professor Martin Kuball and his team at the University of Bristol. Cambridge members of the IKC team include Professors Rachel Oliver, Florian Udrea and Teng Long.

The centre will advance the next generation of semiconductor power device technologies and enhance the security of the UK’s semiconductor supply chain.

Compound semiconductor WBG/UWBG devices have been recognised in the UK National Semiconductor Strategy as key elements to support the net zero economy through the development of high voltage and low energy-loss power electronic technology.

They are essential building blocks for developing all-electric trains, ships and heavy goods electric vehicles, better charging infrastructure, renewable energy and High Voltage Direct Current grid connections, as well as intelligent power distribution and energy supplies to telecommunication networks and data centres.

“Power devices are at the centre of all power electronic systems and pave the way for more efficient and compact power electronic systems, reducing energy loss,” said Kuball. “The REWIRE IKC will focus on power conversion of wind energy, electric vehicles, smart grids, high-temperature applications, device and packaging, and improving the efficiency of semiconductor device manufacture.”

Our home electrical supply is at 240 Volts, but to handle the power from offshore wind turbines, devices will have to operate at thousands of Volts. These very high voltages can easily damage the materials normally used in power electronics.

“Newly emerging ultra-wide bandgap materials have properties which enable them to handle very large voltages more easily,” said Oliver, who Director of the Cambridge Centre for Gallium Nitride. “The devices based on these materials will waste less energy and be smaller, lighter and cheaper. The same materials can also withstand high temperatures and doses of radiation, which means they can be used to enable other new electricity generation technologies, such as fusion energy.”

“The REWIRE IKC will play a prominent role within the UK’s semiconductor strategy, in cementing the UK’s place as a leader in compound semiconductor research and development, developing IP to be exploited here in the UK, rebuilding the UK semiconductor supply chain, and training the next generation of semiconductor materials scientists and engineers,” said Professor Peter Gammon from the University of Warwick.

Industry partners in the REWIRE IKC include Ampaire, BMW, Bosch, Cambridge GaN Devices (CGD), Element-Six Technologies, General Electric, Hitachi Energy, IQE, Oxford Instruments, Siemens, ST Microelectronics and Toshiba.

REWIRE is one of two new IKCs announced being funded by the Engineering and Physical Sciences Research Council (EPSRC) and Innovate UK, both part of UK Research and Innovation. The second IKC at the University of Southampton will improve development and commercialisation of silicon photonics technologies in the UK.

“This investment marks a crucial step in advancing our ambitions for the semiconductor industry, with these centres helping bring new technologies to market in areas like net zero and AI, rooting them right here in the UK,” said Minister for Tech and the Digital Economy Saqib Bhatti. “Just nine months into delivering on the National Semiconductor Strategy, we’re already making rapid progress towards our goals. This isn’t just about fostering growth and creating high-skilled jobs, it's about positioning the UK as a hub of global innovation, setting the stage for breakthroughs that have worldwide impact.”

Adapted from a University of Bristol media release.

For more information on energy-related research in Cambridge, please visit the Energy IRC, which brings together Cambridge’s research knowledge and expertise, in collaboration with global partners, to create solutions for a sustainable and resilient energy landscape for generations to come.

The University of Cambridge is a partner in the new £11m Innovation and Knowledge Centre (IKC) REWIRE, set to deliver pioneering semiconductor technologies and new electronic devices.

The text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright ©University of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Students at this year's Green Careers Fair nibbled edible crickets, cuddled plush pink octopi, and met industry experts for advice on landing a job in the green sector.