NOVELTY - Electrochemical conversion assembly comprises electrochemical conversion cells. The electrochemical conversion cells are arranged in a fuel cell stack. The fuel cell stack includes end unit assembly. The end unit assembly comprises an electrically conductive terminal plate and an electrically insulating plate (30) interposed between the terminal plate and end unit plate(s) of end unit assembly. The electrically conductive terminal plate defines an electrical termination of stacked cells.    USE - For use as a source of motive power for vehicle and power supply.    ADVANTAGE - The assembly has thermal insulating characteristic without introducing additional components or plates into the end unit assembly of the stack. The fuel cell stack of the invention can be driven to their operating temperature rapidly than would be the case if the thermally insulating regions were not present and exhibit more stable thermal operating characteristics.    DETAILED DESCRIPTION - Electrochemical conversion assembly comprises electrochemical conversion cells. The electrochemical conversion cells are arranged in a fuel cell stack. The fuel cell stack includes end unit assembly. The end unit assembly comprises an electrically conductive terminal plate and an electrically insulating plate interposed between the terminal plate and end unit plate(s) of end unit assembly. The electrically conductive terminal plate defines an electrical termination of stacked cells. The electrically insulating plate comprises a frontier face configured to engage terminal plate and a backside face configured to engage additional end unit plate. The electrically insulating plate electrically insulates the terminal plate from additional end unit plate. The electrically insulating plate comprises array of thermally insulating regions (35) defined in it. The array of thermally insulating regions defines regions of lower thermal conductivity than remaining regions of electrically insulating plate. The array of thermally insulating regions comprises cavities arranged along front side face, and/or backside face. The cavities define regions of lower thermal conductivity than remaining regions of electrically insulating plate. The array of thermally insulating regions comprises voids arranged along front side face, and/or backside face. The voids define regions of lower thermal conductivity than remaining regions of electrically insulating plate. The voids are defined by an array of posts formed along front side face, and/or backside face. The indirect thermal conductance paths are greater than or equal to 10% longer than a direct thermal conductance path extending directly from front side face to backside face. An INDEPENDENT CLAIM is included for vehicle and power supply comprising electrochemical conversion assembly.    DESCRIPTION OF DRAWING(S) - The figure shows a front side view face of the dry end electrically insulating plate.    Insulating plate (30)    Thermally insulating regions (35)