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Sustainable hydrogen: still a long way to go?

“Turquoise hydrogen” a viable solution without CO2

Cécile Michaut, Science journalist
On July 8th, 2021 |
3 mins reading time
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“Turquoise hydrogen” a viable solution without CO2
Laurent Fulcheri
Laurent Fulcheri
Research director at PERSEE, MINES-ParisTech
Key takeaways
  • Black, brown and grey hydrogen are made from fossil fuels, and blue hydrogen is a similar process combined with CO2 capture and storage to reduce emissions.
  • Green hydrogen is produced via electrolysis of water, but it requires large amounts of electricity from the grid or renewable energy.
  • Turquoise hydrogen uses both electricity and methane, but with 4–7.5 times less electricity than electrolysis depending on the technology used – making it a hopeful technology for the future.
  • Moreover, if the methane comes from biogas it has captured CO2from the air, meaning it actually has a negative carbon footprint.

Though the use of hydro­gen ener­gy is clean, its pro­duc­tion is high­ly pol­lut­ing, par­tic­u­lar­ly when it comes to COemis­sions. Green­er solu­tions, such as elec­trol­y­sis, do exist but they are still too expen­sive. Nev­er­the­less, new, effi­cient low-emis­sion tech­nolo­gies are emerg­ing, such as methane pyrol­y­sis. Here is a quick run­down of the colours of hydro­gen: grey, blue, green or turquoise?

Is hydro­gen the ide­al ener­gy solution?

Hydro­gen is inher­ent­ly a ‘clean’ ener­gy: when you burn it or you use it in a fuel cell, it only pro­duces water and ener­gy. How­ev­er, it is almost non-exis­tent in gaseous form on Earth so it must there­fore be pro­duced some­how. Unfor­tu­nate­ly, hydro­gen pro­duc­tion requires a lot of ener­gy, which makes it far less clean. As such, today about 95% of hydro­gen is made from fos­sil fuels. Pro­duc­ing 1 ton of hydro­gen results in 10 tons of CO2 emis­sions. It is one of the ener­gies with the worst car­bon foot­print and so the chal­lenge is to find a way of pro­duc­ing hydro­gen with­out emit­ting CO2.

Today, this is pos­si­ble thanks to water elec­trol­y­sis, which rep­re­sents 5% of glob­al hydro­gen pro­duc­tion. It is called “green” hydro­gen. The process involves split­ting water into oxy­gen and hydro­gen, but it uses huge amounts of elec­tric­i­ty. Ener­gy con­sump­tion is there­fore inevitable: the chem­i­cal reac­tion requires at least 40kWh to pro­duce each kilo­gram of hydro­gen, if elec­trol­y­sers oper­ate at max­i­mum effi­cien­cy. But today, their per­for­mance is only about 60% of max­i­mum, mean­ing that pro­duc­ing 1kg of hydro­gen con­sumes as much as 60 kWh. 

It is easy to under­stand why methane reform­ing (using fos­sil fuels) is the pre­dom­i­nant method com­pared to elec­trol­y­sis. At cur­rent elec­tric­i­ty prices, 1kg of green hydro­gen costs 4–6 €. In con­trast, hydro­gen pro­duced through reform­ing costs less than 1€. Giv­en the cur­rent mar­ket, a mas­sive deploy­ment of green hydro­gen is hard­ly possible. 

Table pre­sent­ing the sources and tech­niques used as well as the amount of CO2 emit­ted dur­ing the pro­duc­tion of each type of hydrogen.

What are the options to make hydro­gen pro­duc­tion “green­er”?

One of the options is to com­bine COreform­ing with the cap­ture and stor­age of CO2 (see our dossier on CO2 cap­ture and stor­age). The sce­nar­ios show that it would dou­ble or triple the cost of hydro­gen, that is a price of 2–3 €/kg. This is called “blue” hydro­gen. “Grey” hydro­gen is pro­duced by methane reform­ing, and “black” hydro­gen is made from coal.

But there is a dif­fer­ent way. Indus­tri­al and polit­i­cal cir­cles recent­ly dis­cov­ered this process, but it is not new: I have been work­ing on it since 1995 and have based my whole car­ri­er on this sub­ject. Referred to as “turquoise” hydro­gen, it uses both elec­tric­i­ty and methane. It involves decom­po­si­tion of methane by pyrol­y­sis at very high tem­per­a­tures (1 000 to 2 000 °C). Hence, it still requires elec­tric­i­ty, but 4–7.5 times less than elec­trol­y­sis depend­ing on the tech­nol­o­gy used. This process pro­duces car­bon and hydro­gen, but not CO2. One kilo of methane is used to pro­duce 250g of hydro­gen and 750g of car­bon, a prod­uct with high added val­ue. More impor­tant­ly, this reac­tion requires 7 times less elec­tric­i­ty than water elec­trol­y­sis for each quan­ti­ty of pro­duced hydro­gen (but it pro­duces two times less hydro­gen than water reform­ing per methane molecule).

How far along is indus­tri­al pro­duc­tion for turquoise hydrogen? 

This pyrol­y­sis process is cur­rent­ly under indus­tri­al devel­op­ment in the USA, with our Amer­i­can indus­tri­al part­ner Mono­lith Mate­ri­als. They devel­oped a con­clu­sive pilot between 2012 and 2017 in Cal­i­for­nia and have start­ed indus­tri­al­i­sa­tion. The first unit has been built and 11 oth­er units are soon to fol­low. Tech­no­log­i­cal prob­lems relat­ed to change of scale have been solved, and first mar­ket­ing is expect­ed in the com­ing months. This unit will con­sume 20,000 tons of nat­ur­al gas and will pro­duce 15,000 tons of black car­bon as well as 5,000 tons of hydrogen.

At first, the eco­nom­ic mod­el will con­sist of adding val­ue to the car­bon pro­duced, which is wide­ly used in tyre man­u­fac­tur­ing and sold at approx­i­mate­ly 1€/kg. A tyre con­tains about 30% of black car­bon, which increas­es resis­tance to wear, UV radi­a­tion or heat. In the sec­ond phase, hydro­gen will become promi­nent from an eco­nom­ic per­spec­tive. Today, the tech­nol­o­gy is opti­mised for black car­bon pro­duc­tion (the tem­per­a­ture is set accord­ing to the desired grade for black car­bon). In the future, it will be opti­mised for hydro­gen pro­duc­tion, and new appli­ca­tions for black car­bon will need to be devel­oped. For instance, it could be used in con­struc­tion mate­ri­als, road infra­struc­tures, or even in agri­cul­tur­al soils. It is cheap­er and safer than stor­ing CO2!

Bet­ter yet: if the methane comes from bio­gas (obtained by the decom­po­si­tion of organ­ic mate­ri­als, in bio­gas plants or land­fill sites, for exam­ple), it has cap­tured CO2 from the air. In this case pyrol­y­sis actu­al­ly has a neg­a­tive car­bon foot­print since it reduces the quan­ti­ty of CO2 in the atmosphere.

Are there oth­er tech­nolo­gies for turquoise hydro­gen pro­duc­tion technologies? 

Yes, but only at the lab­o­ra­to­ry or demon­stra­tor stage. There are “liq­uid met­al bath” meth­ods in which methane is inject­ed and decom­posed in columns con­tain­ing molten met­al. Pilots were built in Cal­i­for­nia and in Aus­tralia. For its part, the Ger­man indus­tri­al­ist BASF stud­ies the decom­po­si­tion of methane using cat­a­lysts. These are seri­ous com­peti­tors, but they must still over­come sev­er­al tech­no­log­i­cal challenges.