A method and apparatus are provided for polishing a substrate surface. In one aspect, an apparatus for polishing a substrate includes a conductive polishing pad and an electrode having a membrane disposed therebetween. The membrane is orientated relative the conductive pad in a manner that facilitates removal of entrained gas from electrolyte flowing towards the conductive pad. The apparatus may be part of an electro-chemical polishing station that may optionally be part of a system that includes chemical mechanical polishing stations.