Indian scientists have developed a breakthrough sunlight powered energy storage device that can both harvest and store solar energy within a single integrated system, marking a significant advancement in clean and self sustaining power technologies. The innovation, known as a photo capacitor, has been developed by researchers at the Centre for Nano and Soft Matter Sciences in Bengaluru, an autonomous institute under the Department of Science and Technology, Government of India.
The newly developed photo rechargeable supercapacitor addresses a long standing challenge in solar energy systems, which traditionally rely on separate components for energy capture and storage. Conventional systems use solar panels to generate electricity and batteries or supercapacitors to store it, requiring additional power management electronics to balance voltage and current mismatches. These extra components increase system complexity, cost, energy losses and physical footprint, particularly limiting their use in compact, portable and autonomous devices.
The new device integrates solar energy harvesting and storage into a single architecture, significantly simplifying system design while reducing energy losses during conversion and storage. This integration opens new possibilities for efficient, low cost and environmentally friendly power solutions for portable electronics, wearable devices and off grid applications.
The research team, led by Dr Kavita Pandey, developed the device using binder free nickel cobalt oxide nanowires uniformly grown on nickel foam through a simple in situ hydrothermal process. These nanowires, measuring only a few nanometres in diameter and several micrometres in length, form a highly porous and conductive three dimensional network. This unique structure allows efficient absorption of sunlight while simultaneously storing electrical charge, enabling the material to function both as a solar energy harvester and a supercapacitor electrode.
Performance tests demonstrated a substantial enhancement under illumination. The nickel cobalt oxide electrode showed a 54 percent increase in capacitance when exposed to light, rising from 570 to 880 millifarads per square centimetre at a current density of 15 milliamperes per square centimetre. The device also exhibited strong durability, retaining 85 percent of its original capacity even after 10,000 charge discharge cycles, an essential requirement for real world energy storage applications.
To assess practical usability, the researchers assembled an asymmetric photo supercapacitor using activated carbon as the negative electrode and nickel cobalt oxide nanowires as the positive electrode. The device delivered a stable output voltage of 1.2 volts and maintained 88 percent capacitance retention after 1,000 photo charging cycles. It also performed reliably across a wide range of lighting conditions, from low indoor illumination to intense two sun intensity, highlighting its adaptability and robustness.
The ability to function efficiently under varying light conditions and without reliance on grid electricity makes the technology particularly suited for remote and off grid regions. By enabling self charging power systems, the innovation has the potential to reduce dependence on fossil fuels and conventional batteries, contributing to a more sustainable energy ecosystem.
In addition to experimental validation, the team conducted a detailed theoretical study to understand the underlying mechanisms behind the device’s high performance. The analysis revealed that nickel substitution in the cobalt oxide framework narrows the band gap to approximately 1.67 electron volts and induces half metallic behaviour. This rare property allows the material to behave as a semiconductor for one electron spin and metallic for the other, resulting in faster charge transport and higher electrical conductivity. Such spin dependent conductivity is particularly advantageous for photo assisted charge storage.
The study demonstrates strong synergy between experimental results and theoretical insights, offering a comprehensive understanding of how nanostructured materials can be optimised for light responsive energy storage. While laboratory experiments confirmed enhanced capacitance and long term stability, simulations provided atomic level explanations for the observed improvements.
The findings, published in the journal Sustainable Energy and Fuels of the Royal Society of Chemistry, introduce a new class of smart photo rechargeable energy storage devices. With further development and scaling, this technology could play a pivotal role in advancing India’s clean energy ambitions and inspire similar innovations globally.
