Researchers at the Indian Institute of Science Education and Research (IISER) in Kolkata, India, have for the first time implemented a bio-waste-derived electrode as cathode in a quantum-dot-sensitized solar cell.
Why human hair?
“The materials to be used as cathode in quantum dot solar cells need to be highly catalytic and electrically conducting to facilitate the electron transfer processes,” explains Professor Sayan Bhattacharyya from the Department of Chemical Sciences at IISER. He adds that the lamellar structure of human hair is likely responsible for the graphene-like sheets in the transformed graphitic porous carbon. “Secondly,” he continues, “since hair contains keratin and other amino acids, carbonizing the acid-digested hair under inert conditions likely retains the nitrogen and sulphur hetero-atoms, which are useful to enhance the catalytic propensity of the produced carbon.”
As the professor explains, the idea behind this research project was to use a bio-waste resource like hair in future energy technologies to achieve a win-win situation — i.e., “A smart way to address environmental concerns and also to produce cheaper devices.”
He goes on to explain that waste human hair is an abundant bio waste produced in tons, daily, globally. The disposal of waste hair is an aspect that is particularly neglected in the salons in India, and he says it is a serious cause of environmental degradation. “We, as materials chemists, looked at this hugely collectible free bio-waste from a different perspective and performed a value-added transformation on waste hair to successfully produce cathodes for solar cells,” he says. “Moreover, the realization of metal-free cathode material in solar cells is highly desirable, as it lowers the overall cost of production of the device and also makes them suitable to be integrated into futuristic flexible wearable electronics through roll-to-roll processing.”
To put into perspective the issues concerning disposal of waste hair, Bhattacharyya shares that he and his colleagues were “really surprised” to find that one salon owner offered to pay for cleaning up his day's waste when the authors of this work approached him for samples.
Solving a problem
“By choosing the right conditions and optimizing the process parameters over repeated runs, we have demonstrated for the first time how bio-waste can be harnessed to make metal-free catalytic electrodes in quantum-dot-sensitized solar cells (QDSSCs), which can deliver performances comparable to the best metal-based cathodes,” Bhattacharyya says. Their unique choice for a starting precursor — human waste hair — along with a straight-forward processing method will likely also result in scalable production of this material. Moreover, the metal-free cathodes also solve the issue of photo-anode poisoning induced by metal counterparts, and thereby can improve the device life, according to the expert.
The unique and successful approach could have an impact on the design of the next generation of solar cells. “QDSSCs are an upcoming class of third-generation photovoltaic devices, which can be made through solution-processed methods on a table top, as opposed to the expensive clean-room fabrication techniques associated with traditional silicon-based PVs,” Bhattacharyya points out. “The introduction of this high-performing metal-free cathode derived from free waste can provide additional cost advantages to QDSSCs and make them a competitive technology over other counterparts.”
A result of the research work is that the graphitic porous carbon cathode made from human hair performs at par with metal-based cathodes — a noteworthy milestone. The direct consequence of the high performance of the graphitic porous carbon electrode is that it provides a conceivably inexpensive alternative cathode material without compromising the device performance while simultaneously providing a waste management solution. “Thus, the carbon-cathode-based QDSSCs can now convert sunlight into electricity with similar efficiencies like the traditional metal-based cathodes, but at a lower cost,” Bhattacharyya concludes.
Key applications and large-scale fabrication
“Due to the unique porous microstructure and abundant graphitic edge sites present in the graphitic porous carbon obtained from human hair, the other key applications for this ‘hair cathode’ could also be in producing fuels from water by using electricity produced from PV modules, also known as water-splitting,” Bhattacharyya says. Their catalytic properties can also be harnessed in energy storage devices, such as zinc-air batteries, which operate with similar chemistries at the air electrode.
Regarding manufacturing, the professor notes that their method of transforming waste hair into catalytic carbon is a simple two-step scalable approach that avoids “fancy instrumentation” and can be performed by anyone who knows how to operate a simple furnace. “Our lab efforts have yielded gram-scale quantity of this catalytic material, which is impressive by all standards.”
Bhattacharyya and his collaborators are now establishing a research program on value-added transformation of waste resources for technological applications. “Our group has already demonstrated two fundamentally different applications of processed bio waste: cancer treatment and clean energy,” he says. “With the developed process parameters for producing application-oriented carbon from waste resources, the next steps will be to take this forward to gas capture, metal-air batteries and electrolyzers.”
Written by Sandra Henderson, Research Editor, Solar Novus Today