What a subject, pages could be written, yes engines are not as reliable as they could be certainly Lycomings have many uncorrected design flaws, so that many never make TBO, without some work.
To make Hydrogen with electricity needs clean water not sea water and platinum for the electrodes ( have to mine an asteroid for the amount needed)
at the moment it is made from natural gas which produces 9kg of CO2 for every Kilo of it. So not so clean.
Also as it costs about a million pounds to build a Hydrogen filling station, I don't see airfields rushing to install them.
Electric motor/battery combination has to be consider as a package and compared to the weight of ICE and fuel together to be compared.
So the extra weight of the battery can be offset against a lighter electric motor. So when batteries reach about 2.5 Klw/hour/Kilo then liquid fuel is dead.
Note there is a 300hp 15kg electric motor on the market but it does rev at 20,000rpm so the gear box would add extra weight.
A bit off subject Lycoming have a certified electronic Mag on the market and are fitting one on new engines along with a normal mag as backup
this means ships power is required to run but it does produces a higher spark voltage and cheaper automotive spark plugs can be used.
Improves starting and more reliable. The next item to improve things would be dumping the 14 volt lead acid battery for a LiFePo4 Lithium (they don't burn)
but would would require a small redesign of the alternator regulator for the correct charge voltages and must have overvoltage protection.
These changes are relatively low cost but I believe would improve reliability.