For take-off and widespread adoption of low-carbon hydrogen transport, net-zero emission targets imposed by cities and governments would appear to be a necessary prerequisite. Already cities like Berlin, Milan, Singapore and Beijing are planning measures to cut air pollution generated by transport.
London, whose Ultra Low Emission Zone covers the city's central core, has reduced exhaust NOx emissions by up to 45% with its 9,142-strong bus fleet that includes 155 electric, 10 fuel cell buses and 20 hydrogen buses on order.
Countries like China and the EU have increased their emission control standards under the Paris Accord, while ships' sulphur emissions were reduced at the beginning of this year under new regulations from the International Maritime Organisation.
To tackle climate change, a global step-change toward low-carbon transport is essential. The two most promising alternatives to petrol —and diesel— fuelled transport are batteries and hydrogen. While electric vehicles powered by batteries have dominated the attention of mass media, manufacturers such as Van Hool, Hyundai, Siemens and Toyota, are working on hydrogen-powered buses, trucks and trains.
Hydrogen has long been viewed as crucial to achieve zero-emission mass transportation and lower air pollution by the International Energy Agency, the European Commission, governments and cities. For example, Paris, Mexico City and Amsterdam plan to replace their existing buses and trucks with hydrogen or battery power as soon as 2025.
Similarly, freight logistics company DHL, the brewer Budweiser and the French Post Office (La Poste) are adopting hydrogen-powered road-based transportation. As for hydrogen-fuelled trains, French train-maker Alstom has introduced the Coradia LINT, an articulated railcar designed for non-electrified rural lines. Its hydrogen railcar is used in Germany, Canada and Denmark.
At sea, hydrogen technology is less advanced, and progress is slow. One exception is Viking, the cruise ship line, which has ordered hydrogen-fuelled ships. For container shipping, progress is even more tentative, though ABB is working with Hydrogène de France to develop a large-scale hydrogen fuel cell system to power container ships. In the luxury yachting segment, Baltic Yachts has announced plans to build a series of 108-foot WinWin racing yacht to use wind power and hydrogen-fuelled engines.

Nearly all the earth's hydrogen exists in water. Every molecule of water contains one oxygen and two hydrogen atoms that are released through a process called hydrogen electrolysis.
Once the hydrogen is produced, it can be liquefied by cooling it to below -253 °C (-423 °F), compressed and stored in large insulated tanks in the liquefaction plant readily available to power specially designed fuel cells in which a chemical reaction converts hydrogen into electrical energy.

The world's annual output of around 70 million tons of hydrogen is mainly used in oil refining and ammonia and methanol production. However, current hydrogen production is almost entirely powered by fossil fuels with just 4% of power coming from renewables.
Two things are needed to decarbonize the world's transportation. One is an enormous increase in hydrogen production. For example, a single London Transport bus racks up about 57,205 to 57,522 km a year. New fuel cell buses currently use 8 to 9 kilograms of hydrogen per 100 km. Therefore, a back-of-the-envelope calculation shows that London Transport buses today would need 46,582 tons of hydrogen a year.
Current hydrogen production would have to increase by many multiples to achieve worldwide transport with zero carbon emissions. Therefore, it is necessary to show both the technical and commercial viability of producing hydrogen at a larger scale. In addition, large-scale deployment of electrolyser technology is needed to cut costs to compete with petrol and diesel.
Cost is a significant barrier to the widespread adoption of hydrogen-fuelled vehicles. The cost of manufacturing fuel cells for hydrogen is three to four times more expensive than diesel and more expensive than battery-powered cars. In a direct comparison, electric cars batteries and refuelling costs are less costly.

For example, Car Magazine finds that a charge from empty to full using one of the UK's roadside chargers should cost around £35 for a 100kWh battery, while a home power supply would cost just £12. In comparison, a full tank in a hydrogen car could cost anywhere between £50 and £75 notes automobile service, RAC.
Also, unlike the ubiquitousness of petrol stations, hydrogen refuelling stations are scarce. Germany, a leader of sustainability, plans to have just a hundred completed by the end of the year compared with 14,500 petrol stations on the ground.
Adoption of hydrogen-fuelled transport will require a huge worldwide investment in hydrogen refuelling stations. The case for hydrogen is stronger with trucks, however, since this fuel offers longer distance and faster refuelling/charging times than a battery electric truck.
Secondly, massive investment is needed to show that hydrogen has the potential to contribute substantially to the clean energy transition. Australia has just established an A$300 million Advancing Hydrogen Fund to invest in electrolyser technology projects.
In Europe, Belgium, Denmark, Germany and the UK, several joint renewable powered hydrogen production projects have been announced, since producing hydrogen is seen as an excellent way of improving the profitability of renewable energy projects by selling surplus power when demand is low.
But this is all just a start. For short distance journeys, battery power has the advantage of a proven technology, as well as lower upfront and running costs. For long-distance travel on land and sea, hydrogen could become the fuel of the future alongside liquid natural gas.

Journalist who regularly writes about agriculture, aerospace, business, energy, engineering, rail, shipping, technology, transport for clients worldwide.