The future of transportation, at least the clean air kind of transportation, will be powered by electricity. Fully electric cars are being manufactured by some companies most notably Tesla and most manufacturers have plans for them. Even big trucks such as semis are being developed to run on electric motors. Plug-in hybrids and simple hybrids utilize a combination of electric motors and Internal Combustion Engines (ICE) for greater fuel efficiency than straight ICE-powered vehicles.
Vehicles that use electricity for at least part of their motive power use batteries for onboard energy storage. These batteries can be charged from the grid for plug-in hybrids. Hybrids such as the Toyota Prius are charged on the fly by regeneration from braking or alternatively by charging from the ICE.
Under certain circumstances such as rail traffic, the electricity can be provided through the tracks or overhead wires. Depending on the country most to all rail traffic in Europe is powered by motors charged by overhead electric lines.
An as yet exploited alternative to batteries or electric lines are fuel cells powered by hydrogen. A fuel cell is a device which uses hydrogen as the fuel to be converted directly to electricity. The only product of the process is water.
Hydrogen as a fuel has several advantages. As noted it is “clean burning” the only product being water. Important for transportation is its very high energy density. For a given weight Hydrogen has about three times as much energy as gasoline and over 100 times as much as that stored in a battery used in electric vehicles.
Under normal conditions, what chemists call Standard Temperature and Pressure, Hydrogen is a gas but it can be pressurized to decrease its volume. The biggest drawback to Hydrogen as compared say to a fossil fuel is that it can’t be pulled from the air or mined from the ground, it has to be created. Currently, the cheapest way is to strip the Hydrogen from natural gas. Alternately, it can be made from water via a process called electrolysis.
If the energy to make the electricity needed is from wind or solar, it is a way of making a storable form of renewable fuel. And that is a really big area of research. Of course one can always just use solar/wind-generated electrical energy to do electrolysis, but there are inefficiencies.
Two areas of research are microbial biomass conversion and direct photocatalytic production. Microbial production of Hydrogen comes from engineered bacteria that produce Hydrogen when fed. If the feed is something such as fructose made from corn, then the process is renewable.
Likely the best method is the latter, photocatalytic production. Some materials, Titanium Dioxide is one example, when placed in water and exposed to sunlight cleave the water releasing Hydrogen and Oxygen. The problem is low efficiency. Intense research is examining a welter of more exotic materials that are of much greater efficiency.
Currently, Toyota is the only manufacturer selling a Hydrogen fuel cell vehicle. In the United States, they are for sale only in California and Hawaii, and even in these locations, Hydrogen fueling facilities are few and far between.
Dr. Bob Allen is Emeritus Professor of Chemistry, Arkansas Tech University.