Can we store cut up onions in the fridge or do onions go bad in the fridge? Do they become poisonous? Can onions be safely stored in the refrigerator after peeling? Also how can you tell if an onion is bad?
Restaurants store cut onions refrigerated all the time. They will try to use them in one shift but they can last longer if needed.
They will go soft after time and lose flavor and crispness. As far as going bad it would take over a week. It will be too soft before it actually goes bad.
At home I try and cut on demand. I will halve and make the vertical and horizontal cuts but only finish the dice on demand. My experience is vertical and horizontal cuts on demand causes more damage. Most of the damage is on the exposed surface, which stays the same either way. This assumes proper technique, good knife skills, and a sharp knife.
If you want slices then easy. Just take a slice on demand.
Store them cut side down in a sealed container.
The general rule is, it is safe to keep in the fridge (in a sealed container) for about a week. However, I strongly advise against it, as the taste and flavor will suffer. Cut onions will get more and more pungent as they wait.
Even the direction of the cuts contribute to how pungent it gets after being cut.