In many applications, chromium is not utilized to directly replace scarce and expensive noble metals such as platinum, palladium, or rhodium. Noble metals are coveted for their distinct features, such as high catalytic activity, corrosion resistance, and high-temperature stability. These characteristics make them indispensable in a variety of industrial operations, including as catalysis, electronics, and automotive applications.
Expensive noble metals are frequently used to illuminate screens or convert solar energy into fuels. Chemists at the University of Basel have now succeeded in substituting these rare components with a much less expensive metal. The new materials have qualities that are remarkably comparable to those employed in the past.
We’re all familiar with chromium from common uses like chromium steel in the kitchen and chrome-plated motorcycles. However, the element may soon be found in ubiquitous mobile phone screens or used to convert solar energy. Researchers at the University of Basel’s Department of Chemistry, led by Professor Oliver Wenger, have produced chromium compounds that can substitute the noble metals osmium and ruthenium – two elements that are nearly as scarce as gold or platinum – in luminous materials and catalysts.
The team writes in Nature Chemistry that the luminous features of the novel chromium materials are nearly as good as some of the osmium compounds utilized previously. Relative to osmium, however, chromium is about 20,000 times more abundant in the earth’s crust – and much cheaper.
At the moment, it seems unclear which metal will ultimately win the race when it comes to future applications in luminescent materials and artificial photosynthesis.
Professor Oliver Wenger
The novel materials are also proving to be effective photochemical catalysts, including processes activated by light exposure, such as photosynthesis. This process is used by plants to transform sunlight energy into energy-rich glucose and other compounds that serve as fuel for biological processes.
When the novel chromium compounds are exposed to a red light, the energy from the light is stored in molecules, which can subsequently be used as a power source. “Here, there’s also the potential to use our new materials in artificial photosynthesis to produce solar fuels,” Wenger says.
Tailor-made packaging for chromium
The researchers built the chromium atoms into an organic molecular framework of carbon, nitrogen, and hydrogen to make them shine and convert energy. This organic structure was engineered to be exceptionally stiff, allowing the chromium atoms to be well wrapped. This tailored environment aids in minimizing energy losses caused by unwanted molecule vibrations and optimizing luminous and catalytic characteristics. The drawback of the new materials is that chromium requires a more sophisticated framework than noble metals, necessitating additional research in the future.
Encased in its rigid organic framework, chromium proves to be much more reactive than noble metals when exposed to light. This paves the way for photochemical reactions that are otherwise difficult to initiate. A potential application could be in the production of active pharmaceutical ingredients.
Competition with other alternatives
For a long time, the search for sustainable and cost-effective materials that did not contain noble metals was predominantly centered on iron and copper. Other research groups have already had encouraging results with both of these elements, and chromium has been used in the past to make luminous materials.
However, in many situations, the luminous and catalytic capabilities of these materials fell well behind those of materials containing rare and expensive noble metals, rendering them ineffective as a viable replacement. The novel chromium materials are distinct because they contain a type of chromium that is particularly similar to noble metals, reaching luminous and catalytic efficiencies that are comparable to those of materials containing such metals.
“At the moment, it seems unclear which metal will ultimately win the race when it comes to future applications in luminescent materials and artificial photosynthesis,” says Wenger. “What is certain, however, is that the postdocs Dr. Narayan Sinha and Dr. Christina Wegeberg have made important progress together.”
Following that, Wenger and his research team intend to develop their materials on a wider scale to allow for more extensive testing of prospective applications. They intend to accomplish light emission in many spectrum colors ranging from blue to green to red by making additional modifications. They also want to improve the catalytic characteristics to get us one step closer to converting sunlight into chemical energy for storage, as in photosynthesis.
