I was looking through an old copy of Moon Miner's Manifesto a while ago and found the concept of a liquid airlock in an early issue.
It is on page 32 of this issue from 1988. It posits this as an option in places with gravity, or simulated gravity on rotating space stations, and suggested 3 possible liquids that could be used: mercury, gallium, or a sodium-potassium alloy known as NaK.
At first glance it seems like it could be really useful in certain situations. I wonder what the likely problems and limitations would be.
In a pinch it even seems like it would be a faster way to get to safety - if your space suit could deal with immersion in liquid. I suppose it would be a good idea to put it inside an alcove or shed, and maybe have a lid on it for when it isn't being used. What else needs to be considered?