Hi Sebastian,
You need to use jQuery.sap.require("sap.ui.core.IconPool") to load the reference to ICON pool
A similar discussion can be found in http://scn.sap.com/thread/3369327 with examples http://jsbin.com/aku-test-icon-url/3/edithttp://jsbin.com/aku-test-icon-url/2/edit ..
Regards,
Atanu