We present an efficient, easy to construct, air-breathing biocathode for dioxygen reduction using the enzyme bilirubin oxidase encapsulated in a silicate gel film on Toray paper. Functionalised single-walled carbon nanotubes were used for improving electron transfer between the enzyme and the Toray paper. A current density of 1.2 mA cm−2 was measured under air without any mediators. The biocathode was connected with a Nafion-covered Zn-anode to form a zinc–oxygen battery. The biobattery has an open circuit voltage of 1.75 V and gives a maximum power density of 5.25 mW cm−2 at ca 0.4 V, which is the best result published so far for such a device. The device was used to power a two-LED bicycle lamp.