Sulphur smell from only one faucet

Since the smell is only at one faucet, it may not be the faucet at all. As water runs into a drain, sewer gas is displaced. That gas typically escapes through a roof vent. If the roof vent is plugged, the sewer gas looks for the next path of least resistance. That path is the drain where the water in the the U-trap is being disturbed. If your bathroom has it's own vent, you would only notice the smell in the kitchen. It is also possible that your kitchen and bath have seperate grey tanks, again each having their own vents.

EDIT Try filling a large pan from the offending faucet. If the water in the pan doesn't smell, the problem is the drain.