Described herein is an apparatus comprising an electrochemical cell that employs a capacitive counter electrode and a faradaic working electrode. The capacitive counter electrode reduces the amount of redox products generated at the counter electrode while enabling the working electrode to generate redox products. The electrochemical cell is useful for controlling the redox products generated and/or the timing of the redox product generation. The electrochemical cell is useful in assay methods, including those using electrochemiluminescence. The electrochemical cell can be combined with additional hardware to form instrumentation for assay methods.