How are we going to handle oxygen shortage problem arising due to massive usage of current fossil fuel combustion and future Hydrogen fuel cell tech?

Question

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The current corona pandemic has created a situation where in order to save lives, there is a huge huge requirement for clinical oxygen (which is taken from the environment) all over the world. Now, there is a great hype about (and industrial migration towards) the hydrogen fuel cell tech which can replace the current polluting fossil fuel infrastructure. Which is great and I'm personally an enthusiast of this emerging field.

Traditional hydrocarbons had their chemical reaction as:

hydrocarbon + oxygen => carbon (di/mono)oxide + other harmful residual gases

Which is certainly polluting and is causing climate change and global warming. Whereas hydrogen fuel cell overall (both fuel cell anode and cathode) reaction is:

hydrogen + oxygen => water (vapor) + electricity

Here we become relaxed as we know that water isn't toxic to the environment and some FCEV (fuel cell electric vehicle) manufacturers claim that the water from the exhaust of their vehicles is fit for drinking.

But the common factor in both of the reactions is that the environmental oxygen is entrapped in either some oxide form or water, which will need a definite amount of external energy to again be in the form of oxygen molecule.

The question is, who is going to spend that energy? Hydrogen production, storage and delivery is already a very energy and capital consumptive process and even the businesses that generate hydrogen through mass scale water electrolysis will use/sell the oxygen by product to add to their overall profits.

Tree Plantation/Reforestation cannot compensate for these oxygen losses alone.

It seems that we are not actually solving the whole of the problem and the part which is being ignored, can itself be the next crisis.

Answer 1

What oxygen shortage?

Earth's atmosphere contains 20.9 percent oxygen. There's a lot of oxygen in the atmosphere and its depletion rate from burning fossil fuels has been small. Humans have been burning fossil fuels on an industrial scale for a long time: coal fired power stations, internal combustion engines in cars, trucks, train locomotives, aircraft and ships, steam engines, oil and coal fired boilers for domestic heating, coal, oil and gas as sources of heat for industrial purposes, etc.

The atmosphere has a mass of about 5.15×10¹⁸ kg, which means the amount of oxygen in the atmosphere is 1.07×10¹⁸ kg.

Concerning hydrogen fuel cells and other forms of usage of hydrogen as an energy source, the hydrogen that would be used would be derived from electrolysis. Water molecules are split by applying electricity to them, hence the system makes both hydrogen and oxygen gas.

All the proposals I have seen for industrial scaled electrolysis derived hydrogen plants intend to use either wind power or solar power as the source of electricity. Most of the proposals intend to use sea water.

When hydrogen derived from splitting water is used in a fuel cell or burned by other means as a source of energy it will consume atmospheric oxygen, but any oxygen derived from splitting water, when used for medical purposes or otherwise means that that amount of atmospheric oxygen will not be used.

My concerns about the use of hydrogen as an energy source are the safety aspects and the potential rise in localized humidity, particularly in warmer parts of the world. This would have implications concerning localized temperatures and the ability of people and animals to sweat and lose body heat when they need to if there was a lot water vapor produced from a high concentration of hydrogen consuming devices.

Answer 2

Atmospheric oxygen levels have in fact been declining. Current estimates indicate that the level is decreasing at a rate of approximately 19 parts per million per year. This would mean that it would take approximately 500 years, at current rates of consumption, for the the oxygen concentration of the atmosphere to decrease by 1% relative to its current levels. However, best estimates indicate that if we continue burning fossil fuels at the current rate, we will exhaust the known reserves of coal in a little over 100 years, and oil and gas before that. So even if we kept burning fossil fuels at today's rates (which seems increasingly unlikely), we would not be able to exhaust atmospheric oxygen via the combustion of fossil fuels.

As far as the combustion of hydrogen in a hydrogen economy goes: let's do a worst-case scenario analysis.

• The current world energy consumption is around $5.7 \times 10^{20}$ joules per year. Let's imagine a future where it is 10 times larger, or $5.7 \times 10^{21}$ joules per year. Let's further imagine (and here's where it gets totally unrealistic) that the world's entire energy supply goes through hydrogen.
• One kilogram of hydrogen releases 142 MJ of energy when burned. This means that this hypothetical world would need about $4 \times 10^{13}$ kg of hydrogen each year. Accounting for inefficiency losses, let's bump that up by a factor of 5, to a world hydrogen production of $2 \times 10^{14}$ kg per year.
• Each $\text{H}_2$ molecule, when formed from water, would also create one oxygen atom as a byproduct. Let's assume that the hydrogen manufacturers sequester 100% of this oxygen somehow. Since water is 8 parts oxygen to 2 parts hydrogen by weight, this would mean that $1.6 \times 10^{15}$ kg of oxygen per year would be removed from the atmosphere.
• The atmosphere contains (per Fred's answer) about $10^{18}$ kg of oxygen.

Putting these numbers together, we find that it would take about 600 years to exhaust the atmosphere's oxygen supply. So even under this worst-case scenario, it would not be a pressing concern.

But here's the other question in a scenario like this: what on Earth would humanity do with $1.6 \times 10^{15}$ kg of oxygen per year? In 2018, global sales of industrial oxygen were about 380 million tons, or about $4 \times 10^{11}$ kg. To believe in this scenario, you would have to believe that there would somehow be a market for four thousand times more industrial and medical oxygen than we currently consume. It seems likely that long before we got to a point like this, the price of oxygen would fall substantially, to the point where at least some producers would find it more economical to vent the oxygen back into the atmosphere rather than bother with storing and selling it. Which would push the time-frame for this to become a problem even further into the future.