[Image source: Roland Tanglao, Flickr]
Hydrogen is a very clean fuel that is increasingly being used as vehicle fuel and to generate electricity. The problem is how to produce it efficiently without generating significant carbon emissions and at a competitive cost. A team of researchers at Imperial College is currently looking at the problem and think they know how to do it.
Fuel Cell vehicles
Vehicles can be fitted with a hydrogen fuel cell which converts the chemical energy of hydrogen to mechanical energy. Fuel cells do this through a chemical reaction between hydrogen and oxygen which in turn runs an electric motor. This method of powering vehicles is now an important part of the European hydrogen economy.
In September 2009, a European group of companies, government organisations and a non-government organisation (NGO) undertook a study on passenger cars with the aim of developing alternative power-trains, i.e. those not powered conventionally using fossil fuels. Some of these companies have a specific interest in the development of fuel cell electric vehicles (FCEVs) and hydrogen, alongside an interest in other renewable vehicle technologies, such as battery electric vehicles (BEVs), plug-in hybrids (PHEVs), as an alternative to their conventionally manufactured fossil-fueled vehicles powered by an internal combustion engine (ICE). The main advantage of these types of vehicles is that, over time, they could be potentially developed as completely emissions-free vehicles. For the reason, development of such vehicles forms an important part of the decarbonization efforts being undertaken currently by countries all around the world.
Technological breakthroughs in fuel cell and electric systems have significantly increased the efficiency and cost-competitiveness of EVs and fuel-cell vehicles in recent years, such that they are now ready for commercialization and mass production in order to take advantage of economies of scale. The EU has also now set realistic targets for the decarbonization of the transport sector by 2050. Hydrogen fuel cell vehicles form an important part of those targets.
The cost of fuel cell systems is expected to decrease by 70 percent by 2025, largely due to increased utilization of the refueling infrastructure and economies of scale. The refueling infrastructure represents about 5 percent of the overall cost of FCEVs, or between 1000 euros and 2000 euros (£703-£1407) per car. The value of FCEVs therefore becomes increasingly positive beyond 2030, both in terms of the Total Cost of Ownership (TCO) and emissions. Consequently, FCEVs are already beginning to appear on the European vehicle market.
How to produce hydrogen
Hydrogen does not occur naturally, although it is an energy carrier. The vast majority of existing stocks are made from methane. Production from renewable energy sources is viable but expensive. Furthermore, when produced from natural gas, hydrogen has a high emission intensity.
In an attempt to address these issues, researchers at Imperial College in London, UK are now starting to look at algae as a means of producing hydrogen with help from the sun. Algae is one of the oldest organisms on the planet, having been present on Earth for billions of years. Algae converts sunlight to energy extremely efficiently, producing hydrogen as part of the process.
“I don’t think we could have asked for a better starting point” said Pongsathorn Dechatiwongse, a PhD student at Imperial College. “Nature has provided an amazing blueprint and if we can harness the process we get clean, renewable energy.”
Pongsathorn is studying at Imperial College’s Reaction Engineering and Catalytic Technology group, which is a multi-disciplinary team of scientists looking at chemistry, chemical engineering and materials science. The aim of the group is to conceive, design, construct, model, characterize, control and optimize catalysts, reactors and processes for chemical and fuel synthesis, energy conversion and for treating effluents, wastes and spent catalysts. It uses computational modelling as an important part of its advanced experimental studies. Pongsathorn himself is looking at designing and building machines that use algae as part of a bioreactor that produces hydrogen. However, the problem is how to do this on an industrial scale, and for this reason, he is particularly interested in both the underlying mechanisms of this process and the conditions required for algae to work effectively.
“It’s like a workflow and we need to know each step and what could speed it up or slow it down” Pongsathorn added. “You wouldn’t believe the difference subtle changes in the shape of a container can make.”
Unfortunately, the ideal conditions for producing hydrogen are toxic to the algae, which means that most systems have a limited life span. The solution to this would be to keep feeding algae into the system, but that requires continual manual intervention.
Or does it?
Pongsathorn has been researching a system with two bioreactors, one of which is suitable for algal growth and the other suitable for hydrogen production. The trick is then to ensure that the second system is fed algae at the same rate at which algae dies. By achieving this, the team at Imperial College have successfully managed to keep a reliable rate of continuous hydrogen production, but it’s a pretty delicate balancing act. So far, the team have managed to maintain hydrogen production for 31 consecutive days, producing six times more hydrogen than a single chambered reactor.
The team now intends to scale up the process from its present laboratory stage to an outdoor system. At present, they are attempting to develop a plastic bag bioreactor that could be placed on some of the rooftops at Imperial College’s campus in South Kensington. They have also published the results of their research, thus far, in the journal Algal Research.
Written by Robin Whitlock