Monday, October 8th was the fourth annual Hydrogen and Fuel Cell Day celebration, and if you heard the sound of partying from natural gas stakeholders, there’s a good reason for that. Hydrogen is touted as a zero-emission fuel and the primary source of hydrogen today is natural gas, which means that natural gas stakeholders will be looking to grow their foothold on the hydrogen fuel cell market.

Well, not so fast. Hydrogen from natural gas and other fossil sources has a lot of baggage to carry in the form of fugitive greenhouse gas emissions. As the latest IPCC report makes clear, natural gas is not a sustainable solution. In any case, the race is already on to push fossils aside in favor of renewable sources.

Get Ready For Renewable Hydrogen … Eventually!

Renewable hydrogen is not a particularly new thing. The real challenge is getting the cost of renewable hydrogen down to parity with fossil-sourced H2.

For the transportation sector, the US Department of Energy looks at the problem from the perspective of cost parity with gasoline:

In order for fuel cell electric vehicles to be competitive, the total untaxed, delivered and dispensed, cost of hydrogen needs to be less than $4/gge. A gge, or gasoline gallon equivalent, is the amount of fuel that has the same amount of energy as a gallon of gasoline. One kilogram of hydrogen is equivalent to one gallon of gasoline.

So, how close are renewables to reaching that target? Getting closer! The Energy Department ran the numbers back in 2015 and listed several funding streams on track to bring down the cost of renewable H2. As of this writing, the agency is still hammering away on the mission of getting hydrogen production out fossil dependency and into renewables.

In particular, the Energy Department foresees that renewable hydrogen from landfill and wastewater gas (not to be confused with biomass gasification, which is another potential source) could become a significant source for transportation fuel in the US.

Forget The Hydrogen Economy — Here Comes The Ammonia Economy

Another area of strong interest for the Energy Department is “splitting” water with an electrical current to produce hydrogen. CleanTechnica has already spilled a bunch of ink on that topic, so let’s move on to something else that has begun to sail across our radar: H2 from ammonia.

If you know your ammonia, you’ll spot the greenhouse gas problem. Ammonia is three parts hydrogen and one part nitrogen, so where does the hydrogen come from? Well, mostly natural gas, for now.

Fortunately, renewable ammonia is becoming a thing. One pathway is to extract nitrogen from the air and combine it with H2 sourced from water, through electrolysis.

Then the question becomes, why would you want to go through all of the trouble of producing renewable hydrogen to make renewable ammonia and then turn right around and pull the hydrogen out again?

The answer is pretty straightforward: transportation and storage costs for hydrogen gas are relatively high. If you could transport and store H2 in a more stable form — say, as renewable ammonia — you could significantly reduce the “delivered and dispensed” part of your fuel costs.

Think of ammonia as an energy storage system and you get to the “Neighborhood Energy Station” concept, in which a facility the size of a conventional gas station provides for local energy needs.

What’s Next For The Ammonia Economy

As for the dispensing part of the plan, that’s where a recent development in the ammonia-to-H2 field comes in.

A team of scientists at Rice University is on to a new catalyst based on copper with a bit of ruthenium thrown in. The new catalyst could lower the cost of breaking up ammonia molecules. That opens up the potential for engineering commercial ammonia-based systems that generate hydrogen fuel on demand.

Here’s the rundown from Namoi Hala, Stanley C. Moore Professor of Electrical and Computer Engineering at Rice and director of the school’s Laboratory for Nanophotonics:

A generalized approach for reducing catalytic activation barriers has implications for many sectors of the economy because catalysts are used in the manufacture of most commercially produced chemicals. If other catalytic metals can be substituted for ruthenium in our synthesis, these plasmonic benefits could be applied to other chemical conversions, making them both more sustainable and less expensive.

Got all that? If you caught that thing about catalytic activation barriers, that’s the key to the whole thing. Catalysts generally work better under high temperature and high pressure, which effectively chains higher efficiency to higher costs.

Decoupling cost from efficiency is a particularly sticky challenge when it comes to breaking up ammonia molecules. With a conventional catalyst, additional energy is needed to keep the nitrogen from clogging the surface of the catalyst.

The Rice team’s solution was to leverage the properties of light to raise the temperature at key points on the catalyst. Loosely speaking (very loosely speaking), it’s like warming up a metal pan by putting it out in the sun, rather than putting it inside an oven.

If you’re familiar with plasmonics and hot-carrier driven photocatalysis, you can guess where this is going. Here’s a snippet from the study:

Photocatalysis based on optically active, “plasmonic” metal nanoparticles has emerged as a promising approach to facilitate light-driven chemical conversions under far milder conditions than thermal catalysis…We introduce the concept of a light-dependent activation barrier to account for the effect of light illumination on electronic and thermal excitations in a single unified picture. This framework provides insight into the specific role of hot carriers in plasmon-mediated photochemistry, which is critically important for designing energy-efficient plasmonic photocatalysts.

For more details check out the article “Quantifying hot carrier and thermal contributions in plasmonic photocatalysis” in the journal Science.

Thanks, USAF!

The research is early stage, so don’t hold your breath for that fancy new ammonia-based hydrogen dispenser to make its way into your garage any time soon.

Meanwhile, it’s worth noting that the US Air Force Office of Scientific Research is one of the funders behind the Rice project.

The Air Force has a strong track record on EVs and renewable fuel and they have had a renewable H2 demo project running in Hawaii since 2006. They provided an update on the goings-on in Hawaii just last winter. Here’s the money quote:

AFCEC [the Air Force Civil Engineer Center] is extremely interested in developments in clean and efficient energy production and storage that may enhance energy resilience for critical Air Force missions…

You don’t say! We’re is reaching out to the Air Force to see if they’re working the ammonia angle on Hawaii or anywhere else, so stay tuned for more on that.

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Image: “Scientists with Rice’s Laboratory for Nanophotonics have shown how a light-driven plasmonic effect allows catalysts of copper and ruthenium to more efficiently break apart ammonia molecules, which each contain one nitrogen and three hydrogen atoms. When the catalyst is exposed to light (right), resonant plasmonic effects produce high-energy “hot carrier” electrons that become localized at ruthenium reaction sites and speed up desorption of nitrogen compared with reactions conducted in the dark with heat (left)” by LANP/Rice University.