After 4500 million years running an optimization algorithm, nature chose to produce hydrogen from the water splitting - photosynthesis - but not to store it or use it as such; Nature chose to produce and transform hydrogen into energy-carrying biomolecules and into biomolecules used to build biological structures. Hydrogen, under ambient conditions, has a low energy density and must be compressed or liquefied to be used as an energy vector, that is, as a substrate for energy transport and storage. At 700 bar, hydrogen exhibits an energy density of 1.3 kWh L^-1, and the compression process requires the equivalent of ca. 13 % of the energy of compressed hydrogen (thermodynamic energy is 6.7 %, assuming isothermal compression, and 10.5 % for adiabatic compression); Liquefied hydrogen has an energy density of 2.3 kWh L^-1, and the liquefaction process requires the equivalent of ca. 36 % of the energy of liquefied hydrogen. Hydrogen is then a bad energy vector, but a very relevant intermediate reagent. Hydrogen should be produced and consumed locally, as Nature realized millions of years ago.

The reaction of methane splitting is:

CH₄ ⇌ C (s) + 2H₂, ∆H⁰ = 75.3 kJ/mol

and produces decarbonized hydrogen and carbon. Intermediate-temperature catalytic methane splitting (IT-CMS) is probably the most efficient and low-cost process for this reaction. If NG is used as a feedstock, it produces decarbonized hydrogen and high-value carbon nanofilament particles with a defined size; if biomethane is used as a feedstock, it produces decarbonized hydrogen, high-value renewable carbon particles, and CO₂ permits. The estimated cost for hydrogen is < 2 € kg^-1 if produced from NG (main assumptions are: NG at 30 € MWh, green electricity at 70 € MWh^-1, CO₂ permits at 70 € kg^-1, graphitic carbon at 1 € kg^-1) and is << 2 € kg^-1 if produced from biomethane (main assumptions are: biomethane at 100 € MWh, CO₂ permits at 70 € kg^-1, graphitic carbon at ≥3 € kg^-1). If hydrogen steam methane reforming (SMR) is replaced by the IT-CMS technology, the world would save 410 Mt y^-1 of CO₂ emissions and 32 000 M€ y^-1 (main assumptions: world’s hydrogen production by SMR of 45.6 Mt y^-1 and hydrogen price, including the required payment of the CO₂ permits, of 2.7 € kg^-1), and if the present entire world’s hydrogen production – ca. 100 Mt y^-1 – were to switch to IT-CMS, the CO₂ emission savings would be ca. 1 Gt y^-1 (ca. 2 % of anthropogenic CO₂ emissions).

The present talk is about this fascinating new technology and when it is expected to be implemented. Also, it will discuss the energy cycle based on direct CO₂ hydrogenation to methanol (load) using biogas, followed by oxy-combustion (unload), using CO₂ as a hydrogen carrier. The first energy cycle has a thermodynamic round-trip efficiency of 89 %.