Thank you, but could you translate this to practical terms? I would like you to imagine some totally off-the-wall usage, I don't know, (this is completely illustrative example), imagine a tiny pacemaker that is self-powered through blood circulation and must charge and discharge itself essentially continuously - so, something like tens of thousands of duty cycles per day (low estimate, this is one cycle every few seconds), or 7m cycles per year.

By the end of one year, would it be totally depleted?

Please note that I did not want to name the application, so don't worry about the specifics of my illustrative example, it's totally made-up and I see the problems with it - just about the timing.

Additionally I am interested in the size and weight as compared with other rechargeable battery types.

I am sorry that I seem to be asking really strange questions. If they are not well-defined could you reply with your questions about my question?

Thank you so much for taking the time to understand my question and and reply. Basically, I'm asking if the effect you describe applies to hundreds of thousands, millions, tens of millions, hundreds of millions, or billions of charge/discharge cycles. Is it a tiny little effect or rather more significant than that?

I want you to really think out of the box, please, so just to expand your mind (as an "anchor"), even though it is not relevant to my application, consider:

>Modern automobile engines are typically operated around 2000–3000 rpm (33–50 Hz) when cruising, with a minimum (idle) speed around 750–900 rpm (12.5–15 Hz), and an upper limit anywhere from 4500 to 10,000 rpm (75–166 Hz) for a road car or nearly 20,000 rpm for racing engines such as those in Formula 1 cars (currently limited to 15,000 rpm)

So if the ctypical cruising speed is 2000 RPM, then in an hour of cruising, a piston would go through 120,000 cycles. If an hour of driving gets you, say, 100 miles (obviously higher than average) then 100,000 miles is 1,000 hours (likely actually more), so that we are at 120 million cycles per 100,000 miles. Obviously this is pretty crazy and I don't envision anything that does anything like that, plus it would need an electric generator, but I just wanted to expand your mind as to why in certain, as-yet unspecified, applications, hundreds of millions, billions, or tens of billions of duty cycles might well be completely reasonable to talk about, and therefore whether the answer to my questions is "tens of thousands" or "infinite" is by no means an equivalent answer!

Please note that both the heart-valve driven pacemaker, and the hybrid engine with per-cycle electric recovery, are not the domains I'm talking about. So I'm interested in a more pure or abstract description of the possible specifications here.

By the way if you happen to know off-hand of other kinds of energy storage (example: graphene supercapacitor; flywheel) that you happen to know are good for the mentioned hundreds of millions of cycles, then you could mention this as well. However, in this thread I was primarily asking about the number of duty cycles (and, to a lesser extent, the possible weight) of a reversible fuel cell - whether via water splitting or some other mechanism.

This is kind of out-there, but it also sounds like you are saying the catalyst may be thought of as an additional "fuel" to be added over time. Like, for the engine made-up example, someone might think of topping up their engine with both petrol and catalyst-fuel, every time they top up. So in this case it would matter how much in quantity we are talking about - if the catalyst is thought of as a consumable that gets used over time and adding some more is part of operations. If it gets used exceedingly slowly, this is no greater a burden than engine oil changes, which are already used regularly.

Thank you so much for your time. I hope I've been clear about my questions.

If all this is pretty crazy, then please just name the number of duty cycles until the catalyst is 50% depleted. (And please name a definition for what 50% depleted means.) Or, any other alternative measure you can think of, as long as it's well-defined. I would just like to know within 1-2 orders of magnitude! Thank you!