# Research Progresses and Application of Biofuel Cells Based on Immobilized Enzymes
## 3 Applications of EBFCs
### Wearable EBFCs  
Wearable devices have been changing how we live and work when tracking our life physically and physiologically. Flexible and biocompatible electrode materials are often required as enzyme carriers in EBFCs for wearable devices. EBFCs in wearable devices can convert molecular chemical energy inside body fluids such as sweat, tears and blood into electrical energy to produce reasonable power output [7]. [PERSON] et al. prepared paper -based EBFCs based on a screen-printing array structure toward wearable energy storage devices [48]. [PERSON] et al. developed the wearable self-powered biosensor system integrated with diaper for detecting the urine glucose of diabetic patients (Table 2) [51]. The 2D-GP nanosheets were assembled in a paper-like architecture with good mechanical strength and high conductivity for potential applications of EBFCs in wearable and implantable devices [53]. The implantable needle-type biofuel cell using enzyme/mediator/carbon nanotube composite fibers has been developed towards wearable electronics [68]. [PERSON] et al. prepared a nanoporous gold-based EBFC for wearable microelectronic device applied on contact lenses (Figure 4) [75]. Nanoporous gold (NPG) electrodes were mechanically stable and flexible. The resulting flexible EBFC loaded with LOx and BOD was placed between two commercially available contact lenses, exhibiting a maximum power density of 1.7 \(\pm\) 0.1 uW cm\({}^{-2}\) and an open-circuit voltage of 380 \(\pm\) 28 mV when tested in air-equilibrated artificial tear solutions [75]. [PERSON] et al. reported a high-performance EBFC based on flexible carbon cloth loading with MgO-templated porous carbon [76]. The open-circuit potential was 0.75 V and the maximum output power density was 2 mW cm\({}^{-2}\). The resulting flexible composite carbon cloth exhibited very promising for the development of wearable EBFCs [76]. [PERSON] et al. developed an integrated EBFC based on laser-scribed N-doped graphene (LSNG) [77]. The integrated EBFC produced a maximum power density of 27 \(\pm\) 1.7 uW cm\({}^{-2}\) at open-circuit voltages of 0.45 \(\pm\) 0.03 V. LSNG displayed excellent mechanical robustness, conductivity and electrocatalytic performance for the development of wearable device [77]. [PERSON] et al. prepared a CTS-protected, TTF-mediated, CNTs-based lactate oxidase anode electrode (CNTs/TTF/LOx/CTS) with Pt as cathode [78]. The resulting wearable battery placed on a human arm produced a power density of 5-70 uW cm\({}^{-2}\) under exercise sweating conditions [78]; [PERSON] et al. assembled a battery with a CC electrode loaded with LOx as the anode and Pt as the cathode [79]. A filter membrane was sandwiched between the two electrodes as the diaphragm of the battery, allowing the anode to be in contact with sweat and the cathode to be exposed to air. The battery was attached to the skin surface with a maximum output power of 938 uW and successfully provided electrical power to the wearable sensor and was able to operate stably for two weeks [79]. [PERSON] et al. prepared an Au/CNTs/NO/LOx/CTS biological anode. The anode was based on CTS-coated carbon nanotubes with NQ as the electron transfer mediator. The Au/CNTs/Ag\({}_{2}\)O was used as the cathode. The resulting cell was assembled into a wearable battery with an open-circuit voltage of 0.5 V, producing a power density of 1.2 mW cm\({}^{-2}\) at 0.2 V [80]. [PERSON] and [PERSON] et al. also used NQ as an electron transfer mediator and integrated MWCNTs onto CC to produce a CC/ MWCNTs/NQ/LOx anode [81]. Pt was mixed with conductive carbon black on CC to produce a cathode. The resulting EBFCs produced a power density of 62.2 \(\pm\) 2.4 uW cm\({}^{-2}\). [PERSON] et al. integrated poly (methylene green) (PMG), LOx and  
Figure 4: Schematic diagram of the assembly of the modified contact lens (**A**) and the configuration of the EBFC (**B**) [75]. electron mediator NAD+ on BP paper to make an anode [82].