Experiments on chaotically oscillating arrays of nickel electrodes in sulfuric acid were carried out. A global periodic forcing is added to a base state of 64 weakly coupled elements by means of variations in the applied potential. Intermittent, unstable chaotic clusters are observed at low forcing amplitudes. Stable clusters, first chaotic and then periodic, form as the forcing amplitude is increased. Stable cluster states consisting of two, three, and four different clusters are observed at forcing amplitudes below that at which synchronization occurs.