I’m continually surprised that the HYPER lab remains the only cryogenic hydrogen research lab in US academia. But then again, I find myself continually having to fight for liquid hydrogen, even to hydrogen experts. Hydrogen liquefies at atmospheric pressure only after cooling below 20 K (-420°F), you cannot liquefy hydrogen by increasing pressure. This requirement to make something that cold (a.k.a. cryogenics) is technically challenging. However, in 2012, liquid hydrogen accounted for over 90% of small merchant hydrogen utilization in the US. Yet, only a few legacy companies have the knowledge base necessary to handle liquid hydrogen, and the last academic lab in the US in this area shut it’s doors in the 1970’s. Liquid hydrogen is largely considered mature, monopolized, fossilized, and generally unpopular (that’s all about to change). Looking back over the posts on this website, I haven’t answered this simple question: Why, of all things, did I choose to commit my career to researching liquid hydrogen?
The value of an energy resource can be related to:
- Purity (%): we want just the pure energy and no other waste to filter or byproducts like CO2 that reduce efficiency. All contaminants freeze out of liquid hydrogen. It’s the quickest way to ensure the >99.999% purity required of many fuel cell systems. These fuel cell systems generate only water as the by product — water so pure we have to contaminate it to make it safe to drink. No other fuel is as pure.
- Mass density (kg/m^3) and specific energy (W/kg): we want our energy to take up no space and weigh nothing (or at least as close as we can). A liquid hydrogen tanker truck delivers about 4,000 kg in a shipment. The best high pressure gas composite tube trailers deliver up to 750 kg per shipment. When it comes to energy per weight, liquid hydrogen is nearly 2 times better than any other fuel and batteries are not even close because they require host atoms/molecules.
- Power density (W/m^3) and specific power (W/kg): how quickly can you extract the energy? Very. This is why liquid hydrogen is the best rocket fuel. A hydrogen refueling station transfers energy at approximately 4 MW to refuel a tank in under 5 minutes. Even the battery electric ‘superchargers’ are only rated around 100-120 kW — this means that hydrogen is 40x faster. This is one reason why hydrogen energy is roughly 40x more valuable than electricity.
- Safety: liquid hydrogen has been shipped over US highways without a single death since the 1960s. Leaks are straightforward to detect with sensors and dissipate to outer space. We handle liquid hydrogen on a weekly basis in HYPER. We are founding members of the AIChE Center for Hydrogen Safety. So just how dangerous is hydrogen fuel?
- Availability/resiliency and utility: You want fuel to be available at a reliable price when you need it. Hydrogen is the most abundant element in the universe and can be made from water or methane (among many others). Once formed, chemical reactions are driven by hydrogen and it’s needed in just about any synthetic fuel production process. No fuel has more potential for availability or end uses. Being able to bottle it and ship it where you want to without the need for a pipeline is another advantage. However, the price of liquid hydrogen is highly volatile lately due to supply and demand for the transportation sector. In the last 5 years the capacity for hydrogen liquefaction in the US has increased ~50% with 5 new liquefiers being announced (we had just 8 prior). I’ve heard quoted prices for liquid hydrogen approaching $40/kg. Considering that a kg of hydrogen has roughly the same raw energy as a gallon of gasoline (which weighs 3.8 kg), liquid hydrogen may be the highest value energy product — given all of the points in this list that makes some sense.
- Efficiency: Efficiency can be defined as (What you got/What you paid) or (What you got/What you could’ve). The efficiency of hydrogen liquefaction is abysmally low. The current best systems on the planet are rated at 10 kW-hr/kg of liquid hydrogen, which is approximately 30% of the fuel’s energy content. Our best $XXXM hydrogen liquefiers are only 30-40% efficient! However, the theoretical minimum efficiency of hydrogen liquefaction is just 3.84 kW-hr/kg. This is comparable to the best electrochemical compressor efficiencies (90%), but scales to higher densities (you need to compress to 22,000 psi to have densities at room temperature approaching liquid hydrogen). This means that developing low-cost, high efficiency, hydrogen liquefiers could be the biggest opportunity for improvement in all of clean energy. More on this here.
While nature took care of the first three above, it’s up to humanity to take care of the last three. Thankfully, nature has given hydrogen some unique tools that it’s up to us to engineer. Given the abundance of hydrogen in the universe, and our challenges with climate change and space, Humanity’s continued evolution necessitates mastery of hydrogen. So, as a student, when I realized nobody was doing research in this area, the decision was easy. I hope you now know why we chose and continue to choose liquid hydrogen. I hope you will too.