Week of March 14, 2021
Can Ammonia Replace EV Batteries?
Last week I introduced the idea of replacing battery packs for renewables energy storage and zero-carbon cars and trucks with ammonia (NH3). This ammonia would be generated at Windmill and Solar Farms using Clean NH3 units I described last week. These units combine air and water at pressure in the presence of a catalyst to generate ammonia gas which can be liquified by pressurization to 10 atmospheres at room temperature. The Clean NH3 unit I am describing is in the form of a refrigerator-sized device invented by a Canadian, Roger Gordon, and marketed by a small company in Ontario, Canada. This device converts air, water, and electricity into ammonia (NH3) a caustic substance, but a workable fuel that burns and generates only nitrogen and water as by products. The world has been turning air and water into ammonia via the Haber-Bosch process for over a century but at very high pressures and temperatures, and fairly inefficiently. Evidently the Green NH3 process does it with a conversion efficiency of 90% and at a cost of 16 to 18 cents per liter. A prototype conversion unit with its inventors is shown at Ontario Technical University in figure 1 below.
Figure 1 – Dr. Ibrahim Dincer and Roger Gordon with Green NH3 Conversion Unit at Ontario Tech University
I don’t know what exactly is in the conversion unit, but I assume it separates the nitrogen out of air and electrolyzes water to obtain the hydrogen. It then pressurizes these gases and feeds them over a catalyst that generates ammonia, NH3. This is the same as the Haber-Bosch process, but evidently the Green NH3 process is vastly simpler and more efficient. If this is true it could be a game-changer with respect to Global Warming. As you recall the major problem with renewable energy sources is their lack of continuity. Windmills and solar farms only produce their rated power about 35 % of the time. This means we need backup power and in most of the world this ultimately means nuclear fission or natural gas fired turbines.
But assume that our windmills and solar farms are designed so that the surplus power available at any given time is fed into a Green NH3 conversion unit. This unit generates and stores gaseous ammonia which can then be used on-site to generate standby power using an ammonia-fueled fuel cell. Suddenly our totally clean renewable electric powerplants can operate 100 % of the time and easily store energy for the rest of the electrical network. I suspect that storing ammonia is vastly cheaper than building large banks of batteries, but it is still too early for cost comparisons.
Likewise, ammonia can be pumped all over the country as a gas and then liquified and distributed as a liquid to fuel cell powered cars and trucks. Ammonia fuel cells are much cheaper than hydrogen fuel cells and don’t need scarce platinum group metals (PGMS). A summary of ammonia fuel cell characteristics from reference 1 is shown in figure 2 below.
Figure 2 – Ammonia as Fuel Cell fuel
The key data from figure 2 is the 180 kWh of electricity from 15 gallons of ammonia at 50% efficiency. A lithium-Ion battery holding 180 kWh would weigh about 800 kg. A gasoline internal combustion engine at 35% efficiency would get almost identical miles per gallon relative to the ammonia fuel cell because the higher heating value of gasoline relative to ammonia is overcome by the fuel cell’s improved efficiency. While giving identical miles per gallon, the ammonia-powered system should be lighter, cheaper, and has zero carbon emissions.
A direct comparison between fuel cell types is shown in Figure 3 below. Ammonia fuel cells have both low materials construction cost and low electrocatalysts’ cost. It is especially important to avoid the high cost of PGM catalysts required by the hydrogen fuel cells. The fact that they are both cheaper and lighter than comparable gasoline-powered drive trains is critical in selling this concept to current car and truck owners.
Figure 3 - Direct Comparison between Fuel Cell types
The proposed ammonia fuel does operate at elevated temperature which adds insulation weight and complicates startup since we are going to have burn some ammonia to preheat the fuel cell after long shutdowns. However, the added temperature really simplifies our generation process and eliminates unwanted pollution as shown in figure 4 below.
Figure 4 – Protonic Ammonia Fuel Cell
In summary I see some real advantages to embracing ammonia as a lower cost substitute for lithium-Ion batteries, both for renewables energy storage and for zero emission cars and trucks.
Thanks for Reading,
1. Jason C. Ganley, “Ammonia Fuel Cell Systems”, Howard University, Department of Chemical Engineering, Washington, DC