Abstract Electrochemical oscillations previously shown to occur during hydrogen peroxide reduction of natural samples of copper-containing sulfides (e.g. Cu 5FeS 4) have also been produced with synthetic chalcopyrites (CuMeX 2 with Me=Fe, In, X=S, Se). It is possible partly to control this cooperative phenomenon by photoexcitation of p-type CuInS 2 and p-type CuInSe 2, semiconductor electrodes. With illumination as a key factor in the control of cooperative phenomena it should be possible to explore non-linear photoelectrochemical mechanisms with possible applications to solar energy conversion. The cooperative phenomenon studied involves the interaction of electrons with copper (in oxidation states I, II and III) and oxygen and thus might be related to the cooperative mechanism causing high-temperature superconduction in copper oxide phases.