NOVELTY - Combinatorial screening system for array of electrochemical cells, comprises an electrolyte, anode and cathode common to each of the cells of the array; and electrochemical probe configured to supply a first electrochemically reactive species to individual members of anode catalyst library, where each of the cells is in a non-active condition with the exception of the cell that is receiving the electrochemically reactive species.    USE - For combinatorially screening an array of electrochemical cells such as array of fuel cells (claimed).    ADVANTAGE - The system is capable of efficiently testing and evaluating catalyst libraries. No electrical isolation between cells of the array is necessary because the electrical output from the array is equal to the individual cell being addressed by the probe.    DETAILED DESCRIPTION - Combinatorial screening system (50) for array of electrochemical cells (47E), comprises:    (1) an electrolyte common to each of the cells of the array;    (2) anode common to each of the cells of the array, and an anode catalyst library positioned between the anode and the electrolyte such that the anode catalyst library defines the individual electrochemical cells of the electrochemical cell array;    (3) cathode common to each of the cells of the array, and a common cathode catalyst layer positioned between the cathode and the electrolyte;    (4) common reservoir (51) for supplying a second electrochemically reactive species to at least a portion of the common cathode catalyst layer; and    (5) electrochemical probe (60) configured to address each of the cells of the array individually, and to supply a first electrochemically reactive species to the individual members of the anode catalyst library, where each of the cells of the array are in a non-active condition with the exception of the cell that is receiving the electrochemically reactive species from the probe.    An INDEPENDENT CLAIM is also included for a method of combinatorially screening an array of electrochemical cells, comprising:    (1) supplying a second electrochemically reactive species to the common cathode catalyst layer;    (2) providing an electrochemical probe configured to address each of the cells of the array individually, and supplying a first electrochemically reactive species to one of the cells defined by the anode catalyst library; and    (3) measuring an open circuit voltage and a load current from the electrochemical cell under test.    DESCRIPTION OF DRAWING(S) - The figure is a combinatorial screening system.    Electrochemical cells (47E)    Combinatorial screening system (50)    Reservoir (51)    Electrochemical probe (60)    Current measuring device (61)    Electrical load (62)