Transport fuels are difficult. They need to  to have a high energy density and be liquid, or liquid at reasonably low pressure so they can be easily fed into the motor.

Some liquid transport fuels can be made from electricity, water, CO₂ and or Nitrogen. They include, methane, methanol, diesel, and ammonia.

They have the advantage of producing transport fuels without displacing food crops. They are  a way of storing excess electricity that would normally be "spilled" such as in a wind farm.

Ammonia

Ammonia is the other Hydrogen. It solves the hydrogen storage issue

Ammonia is rarely talked about as a fuel, however it is one of the most likely transport fuels. It has 40% of the energy/kg of petrol. As fertiliser it has been handled, transported and stored safely for decades.

It is made by combining nitrogen and hydrogen in the Haber process. At first the hydrogen came from electrolysis of water. nowadays it comes from the reforming of methane (natural gas). It could be made only from electricity, water, and air.

It can be burnt in an internal combustion engine. It needs a small amount of combustion enhancer  such as petrol / gasoline, diesel or hydrogen.

The internal combustion engine needs a control system that manages the perfect mixture of fuel. At start and idle, the engine requires petrol / gasoline, but as the vehicle accelerates  the fuel mixture transitions to predominately ammonia.

Ammonia can be used in a fuel cell.

 It is stored as a liquid at moderate pressure so is an excellent electro fuel.

Anhydrous ammonia is stored in the same manner as propane, as a liquid under approximately 100 pounds per square inch vapor pressure at room temperature. If released into the atmosphere, ammonia is lighter than air thus dissipates rapidly. In addition, because of its characteristic smell the nose easily detects it in concentrations as low as 5 ppm. Finally, ammonia has such a narrow flammability range that it is generally considered non-flammable when transported. Millions of farms are already equipped to handle ammonia for fertiliser.

Ammonia as a fuel

NH3Car

Wikipedia

Methanol

In the electrolysis of water, an electric current is passed through water, which then breaks down into hydrogen and oxygen.  At room temperature this is an inefficient process and is not economic.

But it is much more efficient at high temperature. A new electrolysis technique using thin, ceramic Solid Oxide Electrolysing Cells (SOECs) enables efficient electrolysis of steam at 750-850 °C.

If the electrolysis is carried out with CO₂ and steam together, then it produces a mixture of  syngas (CO + H₂) and oxygen. The oxygen comes off as a separate stream. Then another process transforms the syngas to methanol or a number of other fuels. Heat is produced during this operation, supplying process heat.

In Iceland, the company Carbon Recycling International (CRI) is already utilising CO₂ from the Svartsengi geothermal power plant to produce methanol which can be blended with petrol in various proportions. The CO₂ is combined with hydrogen to form methanol. Hydrogen is produced at CRI by using electrolysis at a low temperature, below 100 °C.  Source

Iceland produces electrofuel methanol and exports the excess to Holland for blending with petrol. It is marketed as Vulcanol as the energy comes from volcanoes. Source

Butanol from microbial electrosynthesis

The newly discovered  Microbial electrosynthesis  produces butanol from CO₂, water and electricity. It is similar to photosynthesis but 10-1,000 time more efficient.

More...

Soil microbes to produce electrofuels

Research at Berkley Lab 2012.

In the first approach, Logos Technologies is developing a two-liter bio-electrochemical reactor, which is a conventional fermentation vessel fitted with electrodes. The vessel starts with a mixture of bacteria, CO2, and water. Electricity splits the water into oxygen and hydrogen. The bacteria then use energy from the hydrogen to wrest carbon from CO2 and convert it to hydrocarbons, which migrate to the water’s surface.

In the second approach, the scientists want to transform the bacteria into self-reliant, biofuel-making machines. They’re developing ways to tether electro-catalysts to the bacteria’s surface. These catalysts use electricity to generate hydrogen in the presence of water.

The idea is to give the bacteria the ability to produce much of their own energy source. If the approach works, the only ingredients the bacteria will need to produce biofuel would be CO2, electricity, and water.

Source: Berkley Lab

Hydrogen

Using the high temperature electrolysis process means that hydrogen can be made more economically than before. However a viable use needs to be made of the oxygen also produced.

Solid electrofuels

Batteries can be seen as solid electrofuels.

Metals such as aluminium take so much energy to produce by removing the oxygen from alumina, that they are often referred to as solid energy.

Advanced Research Projects Agency - Electrofuels program

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