- PhD researcher develops polymer films with two functions for energy systems
- Porphyrin-based materials combine electrochromic switching with electrical energy storage
- Nickel, zinc and metal-free films show different optical behavior
A PhD researcher at the University of Turku has developed multifunctional materials that could eventually be used in smart windows capable of storing energy while adjusting indoor light levels.
The work focused on porphyrins, naturally occurring molecules found in biological systems such as chlorophyll and hemoglobin.
These molecules are known for their ability to participate in energy transfer and other important chemical processes.
Nature-inspired materials combine two functions
The polymer films developed in the work combine electrochromic behavior with electrical energy storage in a single material.
In this system, electrochromic materials change color when electricity is applied, while energy storage materials capture and release electrical charge.
Combining both features can expand the use of smart surfaces in energy-efficient technologies and other applications.
Doctoral researcher Sachin Kochrekar said porphyrins provided a useful starting point because of their natural ability to transfer electrons and change their electronic states under controlled conditions.
“For example, thanks to the porphyrin structure found in chlorophyll, the plant is able to recover energy from sunlight through photosynthesis,” said Sachin Kochrekar.
“The ability of this natural molecule to transfer electrons and change its state in a controlled way is also an interesting starting point for us materials scientists.”
The study uses two different approaches – a method combining porphyrins with electrically conductive compounds.
The second method connects porphyrins through molecular bridge structures to form polymer membranes without requiring specially modified starting materials.
Both methods resulted in polymer membranes that exhibit combined electrochromic and energy storage properties, although their performance depends on the synthesis route.
Small structural changes produced different results
The study also investigated how changing the central component of the porphyrin structure affected the performance of the material.
It incorporated nickel, zinc, or no metal at all into the molecular framework and observed remarkable differences in behavior.
The results showed that the nickel-containing film could reversibly switch between three different colors, while the zinc-containing and metal-free versions switched between two states.
The color changes happened quickly, generally within two seconds, while the materials maintained a strong visual contrast during operation.
The films retained their color after electrical current was removed, a property that could reduce energy consumption in practical applications where continuous current is undesirable.
In addition to color-changing behavior, the materials were evaluated as electrochromic supercapacitors using water-based electrolytes.
Such systems are generally considered to be safer and environmentally preferable than many conventional electrolyte technologies.
The experimental films demonstrated measurable energy storage capabilities and maintained performance across thousands of charge and discharge cycles.
According to the University of Turku, this is the first study of these specific porphyrin-based polymer films acting as electrochromic supercapacitors in an aqueous electrolyte environment.
Smart windows remain a future option
There are several potential applications of this study, and the relatively low cost of producing the materials makes them relevant for further evaluation.
“The materials are cheap to produce, easy to control and highly adaptable, and can be integrated into a wide range of applications, including flexible and stretchable substrates,” said Kochrekar
“In the future, these materials can be used, for example, in sensor technology, flexible electronics, smart clothing and solar energy solutions.”
One potential application involves window systems capable of adjusting transparency while simultaneously storing solar energy collected during the day.
“For example, new types of smart windows could simultaneously store solar energy and darken in the bright sun, which would reduce the need for cooling in the building.”
However, the research remains at the materials development stage and further engineering work will be required before it can appear in commercial buildings or consumer products.
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