Harnessing energy stored in water from raindrops

Using nanocapillaries to understand the fundamental structure and behaviour of water

  • Water is everywhere. It’s essential to all life forms, so is ubiquitous. 
  • It also carries enormous energy. 70% of solar radiation that reaches the surface of earth gets absorbed by water. This energy circulates with water around the globe and transfers into other forms of energy. 
  • But most of the energy – for example, osmotic energy, stored in water is not exploited yet. Imagine if we could harness energy stored in water? 
  • In Manchester – a city known for its rain – research led by Dr Qian Yang explores the fundamental questions around the structure and behaviour of water at the molecular level. 
  • Using nanocapillaries made from graphene she is progressing underpinning research that could lead to the development of a brand-new form of renewable energy that could revolutionise sustainable living. 

The potential of water as a source of energy is vast. Hydroelectric power plants, for example, have been explored in large scale to harvest the kinetic energy of water, yet this technology causes significant changes to the local ecosystem. Which means, we still can’t harness the enormous amount of energy stored in water. As a result, this endless energy resource is largely untapped. 

The water-solid interface is the key to harnessing energy toward more efficient water-energy nexus. This requires better understanding of the interfacial water structures and their interactive properties. So far, this progress has been hampered largely because lack of understanding of water at the nanoscale. As a general rule of thumb, structure determines properties and therefore the best applications. Therefore, our first priority is to figure out the structure of nanoscale water. But how do we do it? 

Nanocapillary confinement: analysing water molecules at atomic level 
The answer is using nanocapillary confinement, a tool first identified by Sir Professor Andre Geim in 2016, and now the focus of Dr Qian Yang’s research. 

Using a 2D material capillary, Dr Yang is able to confine a single layer of water molecules. This enables Dr Yang’s team to start to detect the structure of water, and determine its properties, advancing our understanding of key fundamental questions such as how water molecules arrange themselves and transport, and how it responds to light and behaves under electric fields. This will further enable single molecular detection which is essential for many chemical and biological applications. 

Understanding the unique interaction between water and graphene 
In parallel, she is also exploring the unique interactions between water and graphene at the water-graphene interface. Graphene carries charges; and the charges interact with the ions in water solutions at the interfacial area. This means if you pour water through graphene surface, and attach electrodes alongside, you can generate electricity. Through her research, Dr Yang is determining how to make this process work more efficiently, in order to design the materials that best harvest flow induced electricity – either from rain droplets or water flow in a river. 

Leveraging the Manchester’s expertise, equipment and connections 
While researchers across the world are undertaking similar fundamental analysis, Dr Yang’s research has an advantage. The nanocapillary devices conceptualized by Professor Geim and housed in Manchester is extremely sophisticated, enabling atomic confinement that’s proving difficult for other institutions to replicate. Alongside, to accelerate discovery Dr Yang has access to: the National Graphene Institute, the biggest academic cleanroom facility in Europe; the expertise of Manchester’s graphene community, the highest-density research and innovation community in the world; and a network of international collaborations. 

Leading discovery 
As a result of this capabilities, her team’s discoveries include capillary condensation under atomic scale confinement. For example, using a van der Waals assembly of two-dimensional crystals to create atomic-scale capillaries – less than four ångströms in height and can accommodate just a monolayer of water – Dr Yang has proven that the century-old Kelvin equation stands, rather than breaks down as expected. Dr Yang shows that this can be attributed to elastic deformation of capillary walls, which suppresses the giant oscillatory behaviour expected from the commensurability between the atomic-scale capillaries and water molecules. This finding provides a basis for an improved understanding of capillary effects at the smallest scale possible, which is important in many real world situations. For instance, for estimating the oil reserve worldwide. Her work also helps us to have better understanding of sandcastles, which are also hold tightly together by capillary force. 

Further to this, she has also explored ionic transport inside two-dimensional nanocapillaries to understand the mass transport and charge transfer process, for potential deionization and water purification applications. Overall, using combined nanocapillary devices with microfluidics system, together with precise electrical measurements, she examines: (i) capillary condensation inside nanocavities and modulated ionic transport; (ii) electricity generation induced by liquid flow through graphene surface; (iii) nanoconfined water structure and their properties. 

The future of energy harvesting 
Dr Yang’s work explores new physics and phenomena arise inside nanocapillaries, aiming at both better fundamental understanding of water at the atomic scale and working principles for designing more efficient energy harvesting devices at scale. 

By taking the research down to the atomic scale, she is progressing global understanding, and often confounding expectations – as in the case with the Kelvin equation. 

Her research will enable technologies in a wide range of fields, including single molecular sensing, medical diagnostics and energy harvesting. 

Dr Qian Yang 
Dr Qian Yang is a Royal Society University Research Fellow and Dame Kathleen Ollerenshaw Fellow at the Department of Physics and Astronomy. Her research explores the mass transport in 2D nanocapillaries enabled by van der Waals technology, molecular properties under spatial confinement, nanofluidics and electrokinetic phenomena at the water-graphene interface. She is also the recipient of the Leverhulme Early Career Fellowship in 2019, Royal Society University Research Fellowship and the European Research Council Starting Grant. 

Recent relevant papers 

To discuss this research further contact Dr Qian Yang.

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