There are no fundamental limits when compared to batteries. You cannot name them because they don't exist. The point of fuel cells being electrochemical systems is to explain that these limits don't exist.

What you're really arguing is the existence of practical limits. The problem is that most of these practical limits are solvable. Some have long been solved, and most anti-hydrogen claims are attacking an version of the technology that hasn't been true since the 1990s. In reality, FCEVs are already pretty close to BEVs on efficiency. This is especially the case once you look at full lifecycle costs and energy consumption, where battery production and recycling are going to be major penalties.

A hydrogen car is arguably safer than a battery car. The problem is that battery fires continue until they consume the car. But since hydrogen is lighter than air, hydrogen fires are not persistent nor do they surround the car with fire. This argument is basically fearmongering, and is as silly as Edison's attacks on AC power.

Tell me how you get to 90% efficiency (or even 50%) in a system in practice going from not hydrogen (let’s say water, and you don’t even need to pressurize it or filter it for this example) to vehicular thrust.

Hydrolysis maxes out at 65% efficient. Then you need to compress the hydrogen to 700 bar. Don’t forget to transport it unless you are doing hydrolysis and compression in your home. Then you need to convert it back to propulsion.

Do that and make it beat EVs without hand waving at battery recycling (old EV batteries are great for a lot of uses and better than primary products in many lower volume markets, so this argument is nonsense). Please cite your sources.

Electrolysis maxes out at 100% efficiency. And theoretically, so can the fuel cell. So if both sides are 100% efficient, then there's your answer. Also, compressed gas is an energy storage idea. You can in theory extract energy from that.

It's worth noting that electrolysis and fuel cells are electrochemical systems. It is only BEV propagandists that wants you to not be aware of this. If more people knew this, they'd know that FCEVs are eventually going to catch up and surpass BEVs. So instead, they lie and spread FUD like crazy.

Electrolysis cannot hit 100% efficiency. Maybe the approximate math can, if you only consider the first law of thermodynamics, but you’ll violate the second the moment it enters reality.

Alkaline electrolysis maxes out at 66% theoretically. PEM is maybe 80% but that’s neglecting system-level losses.

You cannot extract energy from compressed gas if your fuel cell requires gas at that pressure in order to operate.

There is this weird cult of first principles I keep encountering where people think they’ve cracked the code but they just don’t understand systems.

You are completely wrong. You are not thinking of the laws of thermodynamics. You are thinking of Carnot’s theorem. Which doesn’t apply because electrolyzers are not heat engines. They are electrochemical systems, just like li-ion batteries. What you’re writing is just pseudoscience.

The theoretical limit of both alkaline and PEM electrolysis efficiency is 100%. Real world is somewhat less, but you can get to something like 98% even in the real world: https://www.inceptivemind.com/hysatas-record-breaking-electr...

Fuel cells do not operate at 700 bars of pressure. There is definitely a possibility of extracting energy from compressed gases.

Sorry, but you are spouting total bullshit on all levels here. The only cult is whatever battery/electrification fanbase you’re a part of. You are just repeating BEV propaganda designed to shut down critical thinking and defame all alternative ideas. If anything, this type of tactic is a good sign that we are witnessing the end of the BEV, mainly because its advocates must resort to blatant lies to promote it.