Researched by Felix Bast (Formerly Vadakke Madam Sreejith), BBC Researcher No. U248285, [email protected]
Accepted to the journal on 24th July 2003

A future without reliance on fossil fuels for energy is widely touted. Some experts believe a 'clean fuel' future is just around the corner; others predict that abundant sustainable energy is still far off. So who's right? Experts estimate that as early as the year 2010 we may need viable alternatives to traditional fuel sources. Environmental concerns and a finite supply means the days of fossil fuels are numbered.

Hydrogen is considered a clean fuel that has a minimum impact on the environment nearly eliminating the levels of carbon dioxide and other greenhouse gas emissions. It is safe to manufacture, reliable and environmentally friendly. Hydrogen is the new talk of today’s much environmentally concerned scientific world as a prospective fuel. , by far the most abundant element in the universe and one of the most abundant on earth can be found in many different materials including water, natural gas and biomass. In its molecular form hydrogen can be used directly as a fuel to drive a vehicle, to heat water or indirectly to produce electricity for industrial, transport and domestic use. The huge advantage that hydrogen has over other fuels is that as a fuel it is non-polluting, when you combust hydrogen the only product is water. It has been the fuel used to provide electricity for the space shuttle for the last two decades via on-board fuel cells that combine hydrogen and oxygen to generate electricity; the exhaust from the fuel cell – pure water – is used by the crew as drinking water. Hydrogen has enormous potential to decrease India’s dependence on foreign oil imports and, if produced using renewable energy, to eliminate pollutants such as nitrogen oxides, sulphur oxides, particulates and greenhouse gases such as carbon dioxide and methane.

Production of Hydrogen

Hydrogen is currently predominantly produced via the catalytic steam reforming of methane to give hydrogen and carbon monoxide, the carbon monoxide can be further reformed to produce more hydrogen if required. However, natural gas is not a renewable source of fuel and ultimately contributes to the worldwide increase in global emissions of carbon dioxide.

Perhaps the most promising method of producing hydrogen is simply by the electrolytic splitting of water (electrolysis), in which an electric current is passed through water, decomposing it into hydrogen at the negatively charged cathode and oxygen at the positive anode. If the electricity used to split the water is generated from a renewable source such as solar, wind, biomass, wave, tidal, geothermal or hydropower then there is the potential to produce hydrogen sustainably in a non-polluting manner. Photoelectrochemical (PEC) production uses semiconductor technology in a one-step process that utilises the energy from sunlight to produce an electric current which electrolyses water in a single device. Other methods of renewable hydrogen production include the high temperature gasification and low-temperature pyrloysis of biomass (agricultural waste, wood, domestic organic waste). In pyrolysis, biomass is broken down into highly reactive vapours and a carbonaceous residue, or char. The vapours can then be steam reformed to produce hydrogen. There is also considerable interest in the photobiological production of hydrogen by microbes.

Electricity from Hydrogen

Electricity can be produced simply by the reaction of hydrogen and oxygen in a fuel cell. It is essentially the reverse of the process of electrolytic production of hydrogen from water. Fuel cells permit direct conversion of chemical energy into electrical energy resulting in practical efficiencies of between 60 and 70%. This compares very favourably with the generation of electrical energy by means of heat engines; the primary chemical energy must be converted several times. Each conversion results in losses so that typical efficiencies for this system lies in the region of 15 to 30%.

There are many different types of fuel cells all of which operate using the same basic principle but which vary depending on the type of fuel, type of oxidant, ion conducted through the electrolyte and temperature of operation. There is growing commercial interest in the development of such fuel cells for domestic purposes. For instance the Swiss company Sulzer Hexis hope to have a domestic solid oxide fuel cell on the market in 2001, this will convert natural gas or hydrogen directly into electrical power (1kW). It will also produce about 3 kW of thermal power; an auxiliary burner will supply any heat required in excess of this.

Hydrogen as a Fuel for Transport

In recent years, a growing number of researchers have been involved in investigating and promoting alternative transportation fuels to petrol, these including ethanol and methanol, compressed or liquefied methane, gaseous or liquefied hydrogen and electricity (either stored in batteries or produced on board using fuel cells). Of these fuels, hydrogen, either combusted directly in an internal combustion engine or used as the feed to a fuel cell, is perhaps the most promising.

Hydrogen internal combustion engine

Hydrogen is an attractive transportation fuel in three important ways: it is the least polluting fuel that can be used in an internal combustion engine. It is potentially available wherever there is water and a clean source of power. The data presented in the table show that when 1 gram of hydrogen burns it yields more energy than the same amount of conventional fuels. The principle combustion product of hydrogen is water. Hydrogen combustion vehicles do not produce any carbon monoxide, hydrocarbons, particulates, sulphur oxides, ozone, lead, smoke, benzene or carbon dioxide or other ‘greenhouse gases’. The only pollutant of concern is NO which is formed, as in all internal combustion engines, from nitrogen taken from the air during combustion. It is thought that an ultra-lean engine would produce very little NO.

Fuel cells

One method of practically eliminating NOx emissions that are produced by the combustion of hydrogen in an internal engine would be to use the hydrogen in a fuel cell to power an electric motor. Many car companies are now developing this technology, in the prototype fuel cell/electric vehicle (Necar 4) unveiled by Mercedes Benz in 1999, the hydrogen is stored on-board and is fed to the Ballard polymer exchange membrane fuel cell as required. The Ballard fuel cell consists of a polymer membrane electrolyte that separates the two electrodes (the anode and cathode). Both the anode and cathode are coated on one side with a thin platinum catalyst. The hydrogen dissociates into protons (positive hydrogen atoms) and free electrons in the presence of the catalyst. The electrons are conducted as usable current through an external circuit. The protons migrate through the membrane electrolyte to the cathode where they combine with oxygen from the air and electrons from the external circuit to form water. Such a vehicle combines the quieter, emission-free, low maintenance operation of conventional battery-driven electric vehicles with the longer range and fast refuelling time possible with hydrogen combustion vehicles. Necar 4 is capable of a maximum velocity of 145km/h and a range of 450km. This fuel cell vehicle, which stores the hydrogen cryogenically in specially manufactured tanks, will not emit NOx or trace hydrocarbons and it is hoped that it will be ready to market to the public in 2004.

There are a couple of drawbacks to using cryogenically stored hydrogen, one of which is its reduced range of operation of approx. 450 kilometres on a full tank; a similarly sized petrol driven car typically has a range of 650 kilometres. Another drawback is the need for a whole new infrastructure for the delivery and supply of cryogenic hydrogen to the general public. Both these problems can be overcome by converting hydrogen to a suitable liquid with a higher energy density that can be easily stored, transmitted and reconverted to hydrogen as required. Methanol is one such liquid that has a high energy density (18.1 kJ cm-3) when compared to liquefied hydrogen (10.1 kJ cm-3), is a liquid under normal operating conditions and can be easily either decomposed or reformed with steam to hydrogen.

Work is on-going at the Centre for Environmental Research at the University of Limerick to develop catalysts for the catalytic conversion of methanol and water to hydrogen for use in a fuel cell.

Hydrogen, the future for India?

We are currently at a crossroads with regard to the production of electricity and use of fuel in India. Our booming economy has meant that electricity demand has increased significantly during the last decade; as a result, supply of electricity is struggling to keep pace. Another major concern is global warming and India’s CO2 emission targets set at the Kyoto summit, we are already exceeding these targets and look set to continue to do so. We continue to rely on fossil fuels to produce electricity, to drive our cars and to heat our homes resulting in ever increasing emissions of carbon dioxide and an over reliance on the vagaries of the world oil markets.

India has its own natural renewable resources of wind, wave, tidal and solar power that can be used to produce electricity. Taking into account our northerly latitude (lack of useful sunlight during winter), the considerable force and duration of winds that buffet this subcontinent and the maturity of wind turbine technology we are well placed to take advantage of wind power. In fact, based on average wind speeds, India is one of the most suitable places in south Asia for harvesting wind power.

However, wind power has one major drawback, the wind does not always blow and as a result we cannot always be guaranteed a supply of electricity from a wind turbine. One solution to this problem is to store energy when the wind blows and release the energy as electricity when required. Hydrogen is the ideal energy carrier for such a purpose it can be produced cleanly by electrolysis of water using electricity produced from a wind turbine. It can then be stored and the energy released (as electricity) at peak usage times or when the wind is not blowing by the reaction of hydrogen with oxygen (from the air) in a fuel cell.

Take this one step further and it is possible to envisage a future in which all our electricity is supplied cleanly by renewable resources with hydrogen as the ‘energy carrier’. Hydrogen could be used to fuel our cars, heat our homes and produce electricity (when needed). Communities could be responsible for producing their own power with, for instance, their own wind farms, hydrogen supply networks and fuel cells. Argentina, a country of a similar size to India is beginning to take the steps towards a ‘hydrogen economy’ using their abundant supply of geothermal energy to power the electrolysis of water to produce hydrogen. Perhaps it is time for us to move in the same direction and heed the recent warnings from a leading insurance company that maintains that if the predictions of the effects of global warming are correct the world could be heading for bankruptcy by the year 2025.

Felix Bast [alias Vadakke Madam Sreejith] is a Junior Research Fellow at Department of Chemical Engineering, Indian Institute of Technology-Bombay, India. He is a BBC correspondent in Popular Science Division and has published several essays in leading magazines.