GUWAHATI, Jan 1 - Researchers at the Indian Institute of Technology Guwahati (IITG) have developed materials that can produce energy from water, on a small scale.
These new ways of producing energy can be employed in household environments to support the concept of decentralisation of energy sources. In the centralised energy generation model, one large plant produces energy for an entire region. In contrast, the decentralised energy model introduces a large number of small generation devices that can be employed to generate energy in every household. The excess energy produced in households can be transported to nearby areas where there is an excessive need for energy.
The IITG researchers employed the nanoscale phenomenon called ‘Electrokinetic Streaming Potential’ to harvest energy from flowing water on the small length scale like water flowing through household water taps. Similarly, under the ‘Contrasting Interfacial Activities’, different types of semiconducting materials were employed to generate power from stagnant water.
The research team led by Dr Kalyan Raidongia, Department of Chemistry, IITG, and including Jumi Deka, Kundan Saha, Suresh Kumar, and Hemant Kumar Srivastava, worked on this novel research. Their findings were recently published in the ACS Applied Nanomaterials.
The impending energy crisis that has arisen from the dual problems of dwindling fossil fuel reserves and environmental issues associated with the use of such fuel, has led to considerable research in alternative energy sources such as light, heat, wind, ocean waves, etc. The generation of energy from water in various forms – river flow, ocean tides, stagnant water, and even raindrops – is now known as ‘blue energy’. While hydroelectric power from rivers is the traditional form of blue energy, there have been efforts to harness the power of water in other ways in recent years.
One out-of-the-box blue source is electrokinetic energy. “When fluids stream through tiny channels that are charged, they can generate an electrical voltage, which may be harnessed through miniaturised generators,” Dr Raidongia said.
Although the exploration of such electrokinetic phenomena and their possible use for energy conversion has been known for more than half a century, they have not been harnessed because of low efficiency arising from the unsuitability of channels for the fluid stream. The humble efficiency of electrokinetic streaming potential-based energy generating devices is attributed to the trade-off between high flow rate and nanofluidic confinement.
The IITG researchers demonstrated that power output can be improved by a thousand times by obtaining the best out of these parameters through biconical nanofluidic channels that interconnect tetrahedral and octahedral voids in the close-packed silica spheres. Enhancement in the power density can be brought about through control of multiple parameters such as the diameter of the close-packed spheres, number of the spheres, the contact area of the electrodes, and pH of the streaming water, and the team is currently involved in such optimisation efforts.
In order to extract power from stagnant water, devices were fabricated by employing doped graphene flakes. The complementary charge transfer activities of doped graphene flakes-based devices generate power just upon dipping in any kind of water source, like lake, river or seawater.
Graphene is the sheet produced by oxidation followed by reduction of natural graphite flakes. “What we have done is modified graphene in such a way that its electron density is manipulated; even stagnant water in contact with this form of graphene can produce energy,” Dr Raidongia added.
The researchers doped graphene oxide with boron and nitrogen separately and loaded the two forms of graphene into two filter papers that served as electrodes in an electrochemical cell. Dipping the two filter papers into water produces potential up to 570 millivolt, which was stable for a few days (80 hours).
“We improved the power generated by varying parameters like coating area, the extent of doping, annealing temperature, and ionic conductivity of the medium. We use a lot of stagnant and flowing water in our daily lives,” Dr Raidongia said, adding that water stored in buckets and water flowing from taps can potentially be used to produce energy if such nanogenerators can be developed further.