PEM Fuel Cell Electric Vehicles
A number of the world’s leading automobile manufacturers have commenced making Fuel Cell Electric Vehicles (FCEV’s) in recent years. These vehicles have PEM (Proton Exchange Membrane) fuel cells which are fueled by hydrogen gas carried on board in high pressure gas tanks. The fuel cells provide a very efficient conversion of the energy contained in the hydrogen fuel, into electricity to propel the vehicle. This conversion efficiency is much higher than that achieved using the hydrogen fuel in an internal combustion engine and it is therefore likely that the FCEV’s will be the carbon free way forward rather than hydrogen fueled combustion engines. The leading manufacturers of FCEV’s are:
– Toyota with their Mirai
– Hyundai with their Nexo
These FCEV’s have high pressure 700 bar hydrogen gas tanks on board to achieve a reasonable energy density. The vehicles can be re fueled from a hydrogen filling station in several minutes and when full, hold around 5 or 6 Kg of hydrogen, which gives them a range of 500 to 800 km.
Liquid hydrogen fuel is generally not commercially viable due to the amount of energy it takes to liquefy it. Liquefaction consumes about one third of the hydrogen energy stream which means only about 66% comes out as liquid and the rest is lost. This is due to the fact that it must be cooled to well below the critical point (-240C) to about -253C (20K) and this process is very energy hungry and expensive. Consequentially the hydrogen FCEV’s use high pressure compressed hydrogen gas tanks rather than cryogenic liquid hydrogen tanks.
Ammonia is a very good carrier of hydrogen and is easily and cheaply liquefied (+132C critical point) to provide a much higher transportable energy density than hydrogen gas. In August 2018, the CSIRO in Australia demonstrated it’s groundbreaking technology which is able to provide high purity hydrogen gas derived from ammonia to re fuel the FCEV’s. This technology provides a system to crack the hydrogen out of the ammonia then put it thru a metal membrane filter to achieve very high purity hydrogen to comply with the FCEV manufacturers specifications.
This CSIRO development paves the way for hydrogen to be shipped , stored , transported and distributed to the fueling stations as ammonia liquid, and then the hydrogen is cracked and filtered from the ammonia at the fueling station to re fuel the FCEV’s. This will be a far more efficient and cost effective way of distributing the hydrogen than the existing system of using hydrogen gas tube tankers.
Solid Oxide Fuel Cells
In 2017 the Green Ammonia Consortium was formed in Japan and now involves 28 companies. One of the priorities of this consortium is the development of a solid oxide fuel cell which will run directly on ammonia. There is rapid progress on this project and they already have prototypes operating in the lab. The aim is to produce a commercially viable fuel cell with at least similar efficiencies to the PEM fuel cells. Once this new fuel cell is developed, it will open a multitude of options for ammonia energy in areas including transport and electricity generation. We will watch this exciting development with great interest.
In the next instalment we will discuss the manufacture of green and blue ammonia.