Correction! 
An attentive reader points out that the oxygen balance in the atmosphere would remain zero if the hydrogen produced were ultimately burnt, either directly or via synthetic fuels. The considerations in this article therefore only concern the most interesting uses of H2, those that produce stable materials, such as steel or other durable goods. This will therefore only be of relative importance.

The philosophical metal of ecologism is hydrogen, the first element on the table, whose virtues are such that it should solve all the ills associated with the chase after fossil fuels. The two chemical equations in the title image depict a perfect world with a carbon-free energy supply. Except that the heretic on duty spots the blind spot of the “climate credulous”: stoichiometry.

The water molecule would therefore have to be broken, for example by electrolysis or, one day, by thermolysis, to obtain hydrogen.

Once enough electricity will have been produced in a more or less efficient but carbon-free way, even more will be lost in the electrolysis process to obtain hydrogen that will be burnt to power cars or turbines, with some heating added on the way. All it produces is water vapour, which nobody is afraid of.

Or, more sophisticated but even less efficient, carbohydrates or ammonia will be synthesised to obtain liquid fuels useful for aviation or for chemicals. H₂ will also be used to reduce iron ore to produce coke-free steel. In this way, CO₂ is recycled in the most expensive way possible, but it sounds virtuous.

Fascinated by these equations, and unaware that stoichiometry requires a full balance sheet, the world’s great leaders decided to ruin it so that a hydrogen sector could be developed. They believe it’s carbon-free! They are indeed capable of anything, and that is how they are recognised.

Their little oversight is that, if a molecule of hydrogen is produced by the electrolysis or thermolysis of water, half a molecule of oxygen will also be formed, i.e. 8 g of O₂ for 2 g of H₂.

What happens to that oxygen? It will be diluted into the atmosphere because there is no point in capturing it. King of oxidisers, it will meet oxidisable substances, mainly biomass. And as with all combustion of organic matter, this will be coupled with the formation of… CO₂ !

In a way that is still not fully understood, nature maintains a constant level of oxygen in the atmosphere with enormous annual inflows and outflows linked to photosynthesis and biomass decomposition or combustion. That O₂ will find its corresponding carbon-containing reducer.

For every 1 tonne of hydrogen produced for non-combustion uses,
around 5.3 tonnes of CO₂ will be emitted.

Anthropogenic!
With hydrogen, “Zero Net” is a long way off, because let’s not fool ourselves: thisCO₂ is definitely anthropogenic, caused by human action, because if there were no electrolysis, there would be no such emissions.

Voir aussi mon billet “Les cancres ne feront pas passer l’hydrogène” du 23 novembre 2023.
Et ce billet en allemand sur le site de Carnot-Cournot-Netzwerk.

Merci de partager et de diffuser cet article !