One of the interesting aspects of climate change is the number of proposals put forward to solve it that do not take into account adverse consequences. There is a strong association of wishful thinking with some of these. On the other side are the gloomy ones, and maybe I fall into that category. What brought that thought to the fore was I have seen further claims for hydrogen as a solution. Why? Well, there are wild claims that wind and solar will solve everything. One problem with these is they tend to deliver their energy in pulses: solar during the day, wind when it is blowing. The net result is that if these can deliver adequate power for all times, there is serious overproduction required at other times. The problem then is how to store this energy. One way is to pump water uphill, but that requires large storage. In a country like New Zealand, where much of the electricity is hydro generated, you would just turn off that generation and use the hydro to manage power demand. However, that assumes there is not a large increase in electricity demand. One proposed solution is to generate hydrogen by electrolysing water. This is a well-understood technology, with no problems, given the power. There are, however, significant economic ones.
This is claimed to solve another problem; a very significant amount of domestic heating is obtained from burning gas. Now, all we have to do is burn hydrogen. We could also use hydrogen in vehicles. My big problem, having worked with hydrogen before, is that it leaks, and is extremely flammable. According to Wikipedia, the flammability range of hydrogen in air is between 4% and 75%; to detonate, the limits are 18.3 – 59% (each by volume), and a leak can support combustion at flow rates as low as 4 micrograms/second. Mixtures can ignite with very low energy input, 1/10 of that needed to ignite gasoline/air, and any static electric spark can ignite it.
The leak problem is made worse by the fact that hydrogen can embrittle metals, and thus create a way for it to escape. It is lighter than air, so it tends to accumulate at the ceilings of buildings, and its very wide explosive range is a broad hazard. The idea that hydrogen could be piped into houses to provide heating is not something I would want to see. The problem is made worse in that you might be sensible and cautious and not take it up, but your neighbour might. The consequences of that can impinge on you. Recently, in Christchurch, a house blew up, and reduced itself to a collection of boards, roofing material, etc., with only the foundations remaining more or less where they started. Several neighbours houses were severely damaged, and made effectively unliveable, at least without major repairs. By some miracle, nobody was killed, although a number had injuries. What apparently happened was a registered gasfitter had done some work on the house’s gas system, there was a natural gas leak, and something ignited it. My guess is, he has some explaining to do, but my point is if this can happen to a registered tradesman, what will happen if there is widespread use of something that leaks with orders of magnitude more ease?
There is a further irony. The objective behind using hydrogen is to help the greenhouse effect by reducing the amount of carbon dioxide we emit. Unfortunately, leaked hydrogen also magnifies the greenhouse effect. At first sight, this does not look right because greenhouse gases work because there is a change of dipole moment in the vibrational mode. This is needed because unless the transition involves a change of electric moment, it cannot absorb a photon. Hydrogen has only one vibrational mode and no electric moment, and no change of electric moment when it is stretched because of its symmetry, i.e.one end of H2 is exactly the same as the other end. There is a minor effect in that the molecule can be polarised for an instant in a collision with something else, but that is fairly harmless.
The problem lies in downstream consequences. One of the important greenhouse gases is methane, emitted by natural gas leaks, farm animals, other farm processes, anaerobic fermentation, etc. Methane is about 35 times more powerful than carbon dioxide as a greenhouse gas, and worse, it absorbs in otherwise transparent parts of the infrared spectrum. (The otherwise does not include other hydrocarbon gases.) However, methane is not as serious as it might be because it is short-lived. UV radiation in the upper atmosphere breaks water, directly or indirectly, into hydroxyl radicals and hydrogen radicals. The hydroxyl radicals rapidly degrade methane, and the hydrogen radicals react with oxygen in the air to make peroxyl radicals that also degrade methane. Molecular hydrogen reacts with both these sort of radicals, and thus indirectly preserves the methane.
There are, of course, other ways of using hydrogen, such as in chemical reactions, including upgrading biofuels, and it can be stored in chemical compounds. Hydrazine (N2H4) is an example of a liquid that could make a very useful fuel. (In the book, and film “The Martian”, the hero has hydrazine from the fuel tank of a rocket, so he catalytically converts it to hydrogen to burn to make water, and blows up his “dome”. It would have been so much easier to burn hydrazine, as it was, after all, from a rocket fuel tank.) Other options include storing hydrogen as hydrides, e.g. borohydrides, or as ammonia, which is cheaper to make than hydrazine, but it is also a gas, unlike hydrazine. The problem is usually how to deliver the hydrogen at a regular and controllable rate.
The use of hydrogen in a chemical manufacturing plant, or when handled with expertise, such as when used by NASA, is no problem. My concern would be for the average person doing repairs themselves to pipes conveying hydrogen, or worse still, plumbing incorrectly. As for having hydrogen as a fuel to be delivered at refuelling stations, I used this concept in my ebook “Puppeteer” to illustrate the potential danger if there are terrorists on the loose.
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