By Dr Bruno G Pollet, head of the Proton Exchange Membrane Fuel Cell Research Group, Centre for Hydrogen and Fuel Cell Research, University of Birmingham
Decarbonising transport is proving to be one of the largest research and development projects of the early 21st century.
Motor vehicles are one of the greatest purchases that a person will make, with around 800 million vehicles in use worldwide.
The motor industry is therefore one of the largest global forces, employing millions of people and generating a value chain in excess of £2.5 trillion per year.
A consequence of this colossal industry is that road transportation emits 4.6 billion tonnes of CO2 per year, approximately 17% of mankind’s greenhouse gas emissions.
The ever-increasing demand for personal mobility and near total dependence on liquid hydrocarbons means that emissions reductions from this sector will be particularly difficult.
The development of alternative fuels to petrol and diesel has been ongoing since the 1970s, initially in response to the oil shocks and concerns over urban air pollution.
Efforts have gained momentum more recently as the volatility of oil prices and stability of
supplies, not to mention the consequences of global climate change have risen up political agendas the world over.
Low-carbon technologies are therefore rapidly advancing, with petrol and diesel hybrids, battery electric, hydrogen fuel cell, and hybrids of the two being developed by nearly every major manufacturer.
Concerns about up-scaling production and the true environmental and social costs of biofuels means that hydrogen and electricity are widely regarded as the sustainable transport fuels of the future.
Despite this interest in low carbon vehicles, there is still no consensus over which technology can offer the greatest environmental benefits, and different studies arrive at polar opposite conclusions.
However, for the past five years, the fuel cell industry has received a lot of interest, as fuel cells are zero-emission technologies at point of use with much higher efficiencies than internal combustion engines.
Demand is expected to increase well into the 21st century.
Indeed, latest projections estimate that the European fuel cell market is expected to reach nearly £42 million by 2020. The current focus is on the development of hydrogen and fuel cell technologies and their associated supply chains for stationary, transport and portable markets (www.hydrogen-wm-scratch.info) that offer significant quantitative improvements in performance, reliability and durability at a much lower cost.
Challenges related to hydrogen generation, storage and utilisation and the acceleration of hydrogen and fuel cell technology deployment to markets such as vehicles and buildings are also being addressed.
Up to now, hydrogen and fuel cell technologies have been identified as priorities for direct investment by the UK Government.
These technologies will potentially contribute to tackling the UK climate change targets (80% reduction in CO2/greenhouse gases by 2050) and security of energy supply challenges, while providing significant market opportunities to a strong UK capability base.
With the current coalition Government, the Liberal Democrats are in charge of the Department of Energy and Climate Change and have a clear green agenda that could help the hydrogen and fuel cell industries with commitments to set a target for 40% of UK electricity originating from clean, non-carbon emitting sources by 2020, rising to 100% by 2050.
The UK Technology Strategy Board has also set targets for fuel cell and hydrogen technologies such as increasing durability and performance levels up to 8,000 hours for transport applications and up to 40,000 hours for stationary applications with cost targets for longer term sustainable hydrogen production below £4/kg.
Novel hydrogen fuel cell vehicles
Microcab Industries, in collaboration with the University of Birmingham has developed a novel hydrogen fuel cell-battery electric vehicle.
The vehicle has a 1.2kW proton exchange membrane fuel cell stack (PEMFC) (less than 1g of platinum is used compared with 60g for a 100kW system) used as a secondary power source to charge up a series of lead-acid batteries and a pressurised hydrogen tank that takes only three minutes to fill up. This hybrid system has the following benefits:
- The range of the vehicle is extended to 150 miles (a current state-of-the-art lithium-ion battery vehicle can only do up to 100miles)
- Short refuelling time (battery vehicles have a domestic charging time of 5-8 hours)
- Cost reduction
- The lifetime of the PEMFC stack is increased
- Economically, if 500,000 hydrogen fuel cell battery electric vehicles (HFCBEV) were produced per annum, less than 0.5 tons of platinum would be required assuming a platinum loading of 0.6g/kW.
Of course, the main key issues are cost, lifetime and reliability in both start-up and duty cycles, which still require some attention.
Lower production costs make fuel cell-electric hybrids a very attractive option for commercial deployment.
Recently, performance, range, efficiency and system cost of these HFCBEVs were evaluated and compared to ‘pure’ lithium-ion BEVs (Mitsubishi iMiEV,47 kW electric motor, 58 MJ of battery storage, 1100kg, £26,700) and conventional internal combustion engine (ICE) diesel vehicles.
The 11 kW electric motor in these HFCBEVs are powered directly by an inexpensive 1.5 kWh lead acid battery pack (£1,000) which is constantly charged up by a 1.2 kW PEMFC stack Ballard Nexa (£4,000) running on a 350 bar hydrogen composite tank (£4,000).
The BEVs showed better efficiency with a higher range (up to 80 miles) and speed (80mph) to that of the HFCBEVs.
Overall, all hydrogen and pure BEVs offer better efficiency and performance than ICE diesel vehicles.
Finally, the test clearly demonstrated that a hydrogen PEM Fuel Cell can be used as an ‘effective’ range extender when used with some batteries.
Production, usage and infrastructure
Hydrogen has a very good energy content by weight; around three times more than gasoline and almost seven times that of coal (hydrogen has the highest energy content of all fuels on a weight basis.
However, the energy density of hydrogen per unit volume is quite low.
Given that five kilograms of hydrogen is equivalent to five gallons or 22 litres of petrol, to store it under ambient conditions would require a five metre diameter vessel, which is impractical for most applications.
Its volumetric energy density can be increased by storing the hydrogen under either increased pressure, at extremely low temperatures as a liquid or in metal-hydride systems.
The efficiencies of a hydrogen internal combustion engine (ICE) is 25% and a hydrogen fuel cell vehicle is 60%, which is three times better than today’s petrol fuelled engines (18-20% for a petrol ICE).
Fifty million tons of hydrogen are produced globally, mainly through the reformation of fossil fuels, and around 100,000 tons of hydrogen are produced in the UK annually.
Recent worldwide hydrogen production totals show that 48% of hydrogen is produced from natural gas, 30% from oil, 18% from coal and only 4% from renewable sources, mainly by electrolysis.
Hydrogen is currently used in the chemical processing and petroleum industries, for the production of fats, oils, metals and electronics and as a fuel in space flight.
There is currently little hydrogen infrastructure in the UK.
There are around 10 functional hydrogen refuelling stations in the UK with three located in the Midlands at University of Birmingham, Loughborough University and Coventry University.
However, plans are underway to implement a further series of hydrogen refuelling stations in the Midlands, later spreading to the rest of the UK.
The installation of a network of refuelling stations across Europe capable of servicing 40 million hydrogen and fuel cell vehicles would cost £5-20 billion, which is comparable to the installation cost of mobile phone and broadband infrastructure.