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• Enzymatic bioelectrode characterized for energy generation and biosensing purposes. • Bilirubin oxidase immobilized on carbon paper using PBSE as bifunctional crosslinker. • Biobattery successfully applied in powering a digital watch for over 2 h. • Biosensor revealed high sensitivity (606 μA mM−1 cm−2) and low LOD (1.3 μM) for O 2. • Response maintained (88%) for 34 days through constant bioelectrode reutilization. Biological systems can be envisaged as energy-sustainable solutions for both microenergy production to power small electronics and sensing purposes. In the present work, an enzymatic bioelectrode was characterized as biocathode in the fabrication of a biobattery and as biosensor for dioxygen detection. Carbon fibre paper was selected as transducer given its unique tailoring and electrocatalytic characteristics, being modified with carbon nanotubes for subsequent attachment of bilirubin oxidase enzyme. The immobilization process was based on a simple but effective method using the crosslinker 1-pyrenebutanoic acid N-hydroxysuccinimide ester, which creates stable bonds by maintaining a good response (88%) for over 34 days. The biobattery, that consisted of a zinc anode coupled with the developed biocathode, produced an open circuit potential of 1.69 V and maximum power of 40 μW, being capable of powering a digital watch for over 2 h. When applied as a dioxygen biosensor, the biocathode revealed high sensitivity of 606 ± 22 μA mM−1 cm−2 and low limit of detection of 1.3 ± 0.2 μM in chronoamperometric measurements at +0.4 V. The application of bilirubin oxidase in the fabrication of biobatteries is scarcely studied even given its advantages over other dioxygen reduction enzymes. Likewise, the use of the remarkable features of CP in dioxygen biosensing is yet to be explored. Therefore, this work stands as an interesting opportunity in the development of relatively simple and affordable bioelectrodes viably intended for energy and biosensing applications. [Display omitted] [ABSTRACT FROM AUTHOR]