An oxygen-producing device has a power supply with an electrically positive and an electrically negative output, at least one pair of electrodes, one electrode of the pair coupled to the electrically positive output and the other coupled to the electrically negative output, an oxygen-rich material exposed to the electrodes for producing oxygen in response to a voltage generated across the electrodes, and an envelope containing the power supply, the pair of electrodes and the oxygen rich material. The device operates within a human tumor, the envelope— comprises a gas-permeable membrane for releasing the produced oxygen into an environment outside of the envelope and the power supply is enabled to provide a DC voltage of at least 1.2 volts to the electrodes.
