An electrochemical compressor system, such as an electrochemical refrigeration system includes a sealed vessel that reduces leak issues related to the electrochemical cell. The sealed vessel may be molded or formed from a polymer or a composite polymer having reinforcing materials, such as fibers therein. The sealed vessel may be plated with metal to reduce gas permeation through the wall of the vessel and to accommodate and improve the attachment of conduits, including metal conduits thereto. A metal conduit may be brazed onto a vessel and the brazing material may be selected for polymer to metal joining and for reduced contamination potential of the system. The electrochemical compressor system incorporates a leak sensor configured at least partially within the sealed rigid vessel that measures the pressure within the vessel.