We have to know what is platinum. Platinum is a silverish white metal. If there is no gold mixed in it. Then it is not haraam for men to wear.
This question was posed to Sheikh Ibn Uthaimeen and this was his response.
his is allowed on two conditions:
That it is not an extravagance on the part of one who cannot afford to wear this kind of jewellery
That it should not cause any kind of fitnah (temptation), such as the man being young and perhaps causing fitnah by wearing it.
The basic principle with regard to clothing is that everything is permissible except gold rings, which are haraam for men as is well known. And Allaah knows best.