This work demonstrates a stretchable and flexible lactate/O 2 biofuel cell (BFC) using buckypaper (BP) composed of multi-walled carbon nanotubes (MWCNTs) as the electrode material. Free-standing BP, functionalized with a pyrene-polynorbornene homopolymer, is fabricated as the immobilization matrix for lactate oxidase (LOx) at the anode and bilirubin oxidase (BOx) at the cathode. This biofuel cell delivers an open circuit voltage of 0.74 V and a high-power density of 520 µW cm-2. The functionalized BP electrodes are assembled onto a stretchable screen-printed current collector with an "island-bridge" configuration, which ensures conformal contact between the wearable BFC and the This article is protected by copyright. All rights reserved. 2 human body and endows the BFC with excellent performance stability under stretching condition. When applied to the arm of the volunteer, the BFC can generate a maximum power of 450 µW. When connected with a voltage booster, the on-body BFC is able to power a light emitting diode under both pulse discharge and continuous discharge modes during exercise. This demonstrates the promising potential of the flexible BP-based BFC as a self-sustained power source for next generation wearable electronics. Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))

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A new concept of hollow electrode based on the assembly of two buckypapers creating a microcavity which contains a biocatalyst is described. To illustrate this innovative concept, hollow bioelectrodes containing 0.16–4 mg bilirubin oxidase in a microcavity were fabricated and applied to electroenzymatic reduction of O2 in aqueous solution. For hemin-modified buckypaper, the bioelectrode shows a direct electron transfer between multi-walled carbon nanotubes and bilirubin oxidase with an onset potential of 0.77 V vs. RHE. The hollow bioelectrodes showed good storage stability in solution with an electroenzymatic activity of 30 and 11% of its initial activity after 3 and 6 months, respectively. The co-entrapment of bilirubin oxidase and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) in the microcavity leads to a bioelectrode exhibiting mediated electron transfer. After 23 h of intermittent operation, 5.66 × 10−4 mol of O2 were electroreduced (turnover number of 19,245), the loss of catalytic current being only 54% after 7 days.