Conversation article- Photocatalysis in Space

Method of making oxygen from water in zero gravity raises hope for long-distance space travel

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Artist’s rendering of a Mars artificial gravity transfer vehicle.
NASA

Charles W. Dunnill, Swansea University

Space agencies and private companies already have advanced plans to send humans to Mars in the next few years – ultimately colonising it. And with a growing number of discoveries of Earth-like planets around nearby stars, long-distance space travel has never seemed more exciting.

However, it isn’t easy for humans to survive in space for sustained periods of time. One of the main challenges with long-distance space flight is transporting enough oxygen for astronauts to breathe and enough fuel to power complex electronics. Sadly, there’s only little oxygen available in space and the great distances make it hard to do quick refills.

But now a new study, published in Nature Communications, shows that it is possible to produce hydrogen (for fuel) and oxygen (for life) from water alone using a semiconductor material and sunlight (or star light) in zero gravity – making sustained space travel a real possibility.

NASA astronaut Kate Rubins works with a Nitrogen/Oxygen Recharge System tank aboard the International Space Station. The tanks are designed to be plugged into the station’s existing air supply network to refill the crew’s breathable air supply.
NASA

Using the unbounded resource of the sun to power our everyday life is one of the biggest challenges on Earth. As we are slowly moving away from oil towards renewable sources of energy, researchers are interested in the possibility of using hydrogen as fuel. The best way to do this would be by splitting water (H2O) into its constituents: hydrogen and oxygen. This is possible using a process known as electrolysis, which involves running a current through a water sample containing some soluble electrolyte. This breaks down the water into oxygen and hydrogen, which are released separately at the two electrodes.

While this method is technically possible, it has yet to become readily available on Earth as we need more hydrogen related infrastructure, such as hydrogen refilling stations, to scale it up.

Sun power

Hydrogen and oxygen produced in this way from water could also be used as fuel on a spacecraft. Launching a rocket with water would in fact be a lot safer than launching it with additional rocket fuel and oxygen on board, which can be explosive. Once in space, special technology could split the water into hydrogen and oxygen which in turn could be used to sustain life or to power electronics via fuel cells.

There are two options for doing this. One involves electrolysis as we do on Earth, using electrolytes and solar cells to capture sunlight and convert this into a current.

Photo catalyst producing hydrogen gas from water.
O. Usher (UCL MAPS)/Flickr, CC BY-SA

The alternative is to use “photo catalysts”, which work by absorbing light particles – photons – into a semiconductor material inserted into the water. The energy of a photon gets absorbed by an electron in the material which then jumps, leaving behind a hole. The free electron can react with protons (which make up the atomic nucleus along with neutrons) in water to form hydrogen. Meanwhile, the hole can absorb electrons from water to form protons and oxygen.

The process can also be reversed. Hydrogen and oxygen can be brought together or “recombined” using a fuel cell returning the solar energy taken in by the “photocatalysis” – energy which can be used to power electronics. Recombination forms only water as a product – meaning the water can also be recycled. This is key to long-distance space travel.

The process using photo catalysts is the best option for space travel as the equipment weighs much less than the one needed for electrolysis. In theory, it should work easily. This is partly because the intensity of the sunlight is far higher without the Earth’s atmosphere absorbing large amounts on its way through to the surface.

Bubble management

Drop tower at the Centre for Applied Space Technology and Microgravity. Bremen University.
Sludge G/Flickr, CC BY-SA

In the new study, the researchers dropped the full experimental set up for photocatalysis down a 120m drop tower, creating an environment similar to microgravity. As objects accelerate towards Earth in free fall, the effect of gravity diminishes as forces exerted by gravity are cancelled out by equal and opposite forces due to the acceleration. This is opposite to the G forces experienced by astronauts and fighter pilots as they accelerate in their aircraft.

The researchers managed to show that it is indeed possible to split water in this environment. However, as water is split to create gas, bubbles form. Getting rid of bubbles from the the catalyst material once formed is important – bubbles hinder the process of creating gas. On Earth, gravity makes the bubbles automatically float to the surface (the water near the surface is denser than the bubbles, which makes them buyonant) – freeing the space on the catalyst for the next bubble to be produced.

In zero gravity this is not possible and the bubble will remain on or near the catalyst. However, the scientists adjusted the shape of nanoscale features in the catalyst by creating pyramid-shaped zones where the bubble could easily disengage from the tip and float off into the medium.

But one problem remains. In the absence of gravity, the bubbles will remain in the liquid – even though they have been forced away from the catalyst itself. Gravity allows for the gases to easily escape from the liquid, which is critical for using the pure hydrogen and oxygen. Without the presence of gravity, no gas bubbles float to the surface and separate from the mixture – instead all the gas remains to create a foam.

This reduces the efficiency of the process dramatically by blocking the catalysts or electrodes. Engineering solutions around this problem will be key to successfully implementing technology in space – with one possibility being using centrifugal forces from rotation of a spacecraft to separate the gases from the solution.

The ConversationNevertheless, thanks to this new study we are a step closer to long-duration human spaceflight.

Charles W. Dunnill, Senior Lecturer in Energy, Swansea University

This article was originally published on The Conversation. Read the original article.

Scientific Reports Paper 2017

SUMMARY: A novel, non-hazardous photocatalytic material developed by scientists in the Energy Safety Research Institute (ESRI) at Swansea University is shown to effectively remove dye pollutants from water, adsorbing more than 90% of the dye and enhancing the rate of dye breakdown by almost ten times using visible light.

 

 

Rapid removal of harmful dye pollutants by a novel, non-hazardous composite

Exciting new material developed by Swansea scientists uses solar energy to remove man-made dye pollutants from water

 

 

Swansea – (June 22, 2017) – A novel composite material has been developed which shows promise as a catalyst for the degradation of environmentally-harmful synthetic dye pollutants, which are released at a rate of nearly 300,000 tonnes a year into the world’s water.  

The researchers, led by Dr. Charles W. Dunnill and Dr. Daniel Jones at the Energy Safety Research Institute in Swansea University, reported their discovery in the Nature open access journal Scientific Reports (https://www.nature.com/articles/s41598-017-04240-4).

By heating the reaction mixture at high pressures inside a sealed container, the composite is synthesised by growing ultra-thin “nanowires” of tungsten oxide on the surface of tiny particles of tantalum nitride.  As a result of the incredibly small size of the two material components – both the tantalum nitride and tungsten oxide are typically less than 40 billionths of a metre in diameter – the composite provides a huge surface area for dye capture.  The material then proceeds to break the dye down into smaller, harmless molecules using the energy provided by sunlight, in a process known as “photocatalytic degradation”.  Having removed the harmful dyes, the catalyst may simply be filtered from the cleaned water and reused.

While the photocatalytic degradation of dyes has been investigated for several decades, it is only relatively recently that researchers have developed materials capable of absorbing the visible part of the solar spectrum – other materials, such as titanium dioxide, are also able to break down dyes using solar energy, but their efficiency is limited as they only absorb higher energy, ultra-violet light.  By making use of a much greater range of the spectrum, materials such as those used by the ESRI team at Swansea University team are able to remove pollutants at a far superior rate.

Both of the materials used in the study have attracted significant interest in recent years.  Tungsten oxide, in particular, is considered one of the most promising materials for a range of photocatalytic applications, owing to its high electrical conductivity, chemical stability and surface activity, in addition to its strong light absorbance.  As a low band-gap semiconductor, tantalum nitride is red in colour due to its ability to absorb almost the entire spectrum of visible light and therefore extracts a high amount of energy from sunlight to power the degradation processes. 

However, the true potential of the two materials was only realised once they were combined into a single composite.  Due to the exchange of electrons between the two materials, the test dye used within the study was broken down by the composite at around double the rate achieved by tantalum nitride on its own, while tungsten oxide alone was shown to be incapable of dye degradation.  In contrast to other leading photocatalytic materials, many of which are toxic to both humans and aquatic life, both parts of the composite are classed as non-hazardous materials.

The scientists responsible for the study believe that their research provides just a taster of the material’s potential.  “Now that we’ve demonstrated the capabilities of our composite, we aim to not just improve on the material further, but to also begin work on scaling up the synthesis for real-world application.” said Dr. Jones.  “We’re also exploring its viability in other areas, such as the photocatalysed splitting of water to generate hydrogen.”

In addition to Drs. Dunnill and Jones, co-authors of the paper are Drs. Virginia Gomez, James McGettrick and Serena Margadonna and PhD students Bertrand Rome, Francesco Mazzali and Aled Lewis, who are all fellow researchers in the College of Engineering at Swansea University, in collaboration with Dr. Joseph Bear from the Materials Chemistry Centre at University College London and Dr. Waheed Al-Masry from the Department of Chemical Engineering at King Saud University, Saudi Arabia.  Financial support for the study was provided by the Welsh Government Sêr Cymru Programme and the FLEXIS project, which is part-funded by the European Regional Development Fund (ERDF) through the Welsh Government, as well as through collaboration with King Saud University.

The Energy Safety Research Institute (www.esri-swansea.org) is positioned to discover and implement new technology for a sustainable, affordable, and secure energy future and is housed on Swansea University’s new world class Bay Campus. ESRI provides an exceptional environment for delivering cutting edge research across energy and energy safety-related disciplines with a focus on renewable energy, hydrogen,  carbon capture and utilisation as well as new oil and gas technologies.

Read the open access article at https://www.nature.com/articles/s41598-017-04240-4.

Big Bang Fair 2017

This report concerns the activities of the Human to Hydrogen Experience @TheHydrogenBike at the Big Bang Fair 2017 in March 2017.

We attended the fair with a sponsorship from the RSC who gave us £4000 towards the stand in the Birmingham NEC.

The Hydrogen Bike is an outreach project by Swansea University that enables participants to donate their energy via a static bike and observe in real time their energy stored as hydrogen gas.  It facilitates real understanding and discussion as to the issues surrounding our renewable energy future and the use of hydrogen to store and move energy.

The team of chemists and engineers were amazing and full of enthusiasm for the full 4 days of intense activity.  6 of us went up and we spoke to more than 1500 people every day with at least a third of them actually getting on the bike.  The event was totally exhausting in a good way with at times groups of 20 small children peddling for 30 seconds, seeing their bubbles and then jumping off. While others spent longer on the bike making a substantial amount of hydrogen. The flame was well behaved and really opened the eyes of loads of people as to the cutting edge science that we do at Swansea and the benefits of Hydrogen as a potential store for renewable energy.

We counted people in two categories those on the bike and those actively watching the display and discussions.  Broken down daily:

  • Wednesday –  1193 recorded interactions with an additional 359 on the bike
  • Thursday – 1451 recorded interactions with an additional 679 on the bike
  • Friday – 965 recorded interactions with an additional 549 on the bike
  • Saturday ~1000 recorded interactions with an additional 500 on the bike

Giving us a total of more than 6500 interactions with people.

The age range was across the board with most being of school age.  The youngest child on the bike was probably about 3 years old and sat on the bike seat while here brothers turned the peddles long below her feet, while the oldest interaction would have been one of the grandparents taking their grandchildren to the show.  There were people from all backgrounds and ethnicities involved, reflecting the diverse backgrounds from which our school children originate.

There were a number of highlights for me. People declaring that we were the “Best event at the whole show” were pretty touching, as was the young lad who climbed out of his wheel chair and onto the bike in order to see his own hydrogen bubbles. Some of the more in-depth conversations about sustainable living and energy transfer were great, as was the animated argument about how we should ignore the laws of physics and run the bike off the hydrogen energy in order to make more hydrogen…..

We also came up with loads of improvements for the display and are now trying to implement them before our next outing.

I am extremely grateful to the RSC for their contribution and to the dedicated helpers on our team and look forward to the next encounter for The Hydrogen Bike.

 

Charlie Dunnill                                                                               @TheHydrogenBike

HEA Fellowship Application

I was bored, so I did a wordle of my HEA Fellowship application.

wordle-hea

Gas Safety

Gas safety gassafe

Joseph Bear’s poster MC12

S-Polymers MC12_2MB

Tower of London guide

This must be the best tour guide for the Tower of London ever..

Right click the mouse and select play.

 

 

I didn’t take this video and I make no claim to it, or the accuracy of it’s contents.  It is just funny..

Why space should not be measured in metric

Space in mteric

PhD in Renewable Energy Storage and Vectoring

With the modern shift to renewable energy supplies, there remains a significant problem in the buffering of supply and demand. Traditional renewable forms of energy such as wind wave and solar do not correlate in their supply with the demand for energy. Electricity is very difficult to store on a large scale so new forms of energy storage are required to smooth the supply and demand issues. Hydrogen is a fantastic possibility.

The project will look into the application of water splitting devices for the implementation of renewable energy storage in the form of hydrogen gas. Alkaline electrolysers will be engineered and modified with Matlab modelling used to guide the process.

Test cell2 Tests cell

This project will also  have an outreach element where members of the public can be enthused as to the benefits of hydrogen.

More details from the Swansea Post graduate pages HERE

Apply for the post by sending a CV and cover letter to me. C.Dunnill@Swansea.ac.uk

PhD in Solar Energy Harvesting

Fig 1

Solar energy harvesting is the direct conversion of sunlight to fuels.  My methods involve the use of bi-phasic catalysts to split water when under the influence of sunlight.

TiO2 has for many years been the pinnacle of photocatalytic research.  Doped TiO2 has shown much promise in applications with wide ranging consequence.  Another source of interest is in pure TiO2 but using the synergistic relationship between the different crystal structures.  Mixtures of both anatase and rutile have shown promise and are indeed the main composition of the commercial P25.

My new synthetic procedures allows for the production of bi-phasic nanoparticles.  Single particles consisting of half anatase and half rutile. These nanoparticles have allowed some interesting measurements to be carried out and helped to answer one of the big questions of semiconductor photocatalysis.  This is regarding the band alignment in a composite system of Anatase and Rutile.  Our Nature Materials paper on the revision of the band alignments of anatase and rutile we showed how this works.2015-01-16 10.20.43

This project will explore the plethora of different materials that could be married together using this synthetic technique and assess the composites for the use as solar energy harvesting photocatlaysts.

This project will also involve the design modification and optimization of an engineering device that will measure hydrogen produced in these reactions.  as well as having an outreach element where members of the public can be enthused as to the benefits of hydrogen.

More details from the Swansea Post graduate pages HERE

Apply for the post by sending a CV and cover letter to me. C.Dunnill@Swansea.ac.uk

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