# Research Progresses and Application of Biofuel Cells Based on Immobilized Enzymes
## 2 A Variety of Carrier Materials for Enzyme Immobilization in EBFCs
### Some Paper-Based and Other Flexible Materials for Enzyme Immobilization in EBFCs  
Some paper-based and other flexible electrodes have been used more and more widely due to miniaturization, low cost, mechanical flexibility and flexible processing. In order to broaden the application of enzymatic biofuel cells, [PERSON] et al. printed MWCNTs-ionic liquid (IL) nanocomplexes on paper instead of conventional electrodes to immobilize GDH and BOD [42]. The open-circuit voltage of this cell was 0.56 V with a maximum power output of 13.5 \(\upmu\)W cm\({}^{-2}\). After one week of placement, the open-circuit voltage \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Anode** & **Cathode** & \begin{tabular}{c} **Open-Circuit** \\ **Voltage** \\ \end{tabular} & \begin{tabular}{c} **Maximum Current** \\ **Density** \\ \end{tabular} & \begin{tabular}{c} **Maximum Power** \\ **Density** \\ \end{tabular} & **Reference** \\ \hline GOx/N-G@CNT/TIF/GCE & BOD/N-G@CNT/GCE & \begin{tabular}{c} 0.68 V \\ (dual-chamber) \\ \end{tabular} & \begin{tabular}{c} 2 mA cm\({}^{-2}\) \\ (dual-chamber) \\ \end{tabular} & \begin{tabular}{c} 500 \(\upmu\)W cm\({}^{-2}\) \\ (dual-chamber) \\ \end{tabular} & \multirow{2}{*}{[33]} \\ GOx/N-G@CNT/TIF/GCE & BOD/N-G@CNT/GCE & \
\begin{tabular}{c} 0.76 V \\ (single-chamber) \\ \end{tabular} &
\begin{tabular}{c} 1.2 mA cm\({}^{-2}\) \\ (single-chamber) \\ \end{tabular} & \multirow{2}{*}{[33]} \\ MAL@MUT@GOx/CNT/TX/CF & KB/BOD/ABTS/CP & 0.6 V & 17 mA cm\({}^{-2}\) & 2300 \(\upmu\)W cm\({}^{-2}\) & [34] \\ \hline GOx/MR/CTS@CNT/GCE & Pt/C/GCE & 0.64 V & 0.169 mA cm\({}^{-2}\) & 94 \(\upmu\)W cm\({}^{-2}\) & [35] \\ \hline GOx/QN-rG@CNT/Ni foam & Lac/QN-rG@CNT/Ni foam & 0.89 V & 2.25 mA cm\({}^{-2}\) & 900 \(\upmu\)W cm\({}^{-2}\) & [36] \\ GOx/rGO@CNT & Lac/rGO@CNT & 0.88 V & 0.844 mA cm\({}^{-2}\) & 196.04 \(\upmu\)W cm\({}^{-2}\) & [37] \\ \hline LOx/TTF/CN-CHMC & BOD/CN-CHMC & 0.65 V & 0.19 mA cm\({}^{-2}\) & 112.7 \(\upmu\)W cm\({}^{-2}\) & [38] \\ \hline ADH/PDDA/rGO & Pt/CP & 0.756 V & 0.04 mA cm\({}^{-2}\) & 10.35 \(\upmu\)W cm\({}^{-2}\) & [39] \\ \hline ADH/poly (MG-py)/CNT/CP & Pt/C & 0.503 V & 2.1 mA cm\({}^{-2}\) & 275 \(\upmu\)W cm\({}^{-2}\) & [40] \\ \hline GOx/Fe\({}_{3}\)O\({}_{4}\)-rGO & BOD/Fe\({}_{3}\)O\({}_{4}\)-rGO & 0.63 V & 0.24 mA cm\({}^{-2}\) & 73.7 \(\upmu\)W cm\({}^{-2}\) & [41] \\ \hline \hline \end{tabular}  
* N-G@CNT (DNA-derived N-dopped CNT); MAL (maltose oxidase); MUT (mutase); TX (Triton X-100); CF (carbon felt); KB (Ketjen black, conductive carbon black); ABTS (2, 2′′-azio-bis (3-ethylbenzothazoline-6-sulfonic acid)); MR (methyl red); STS (Chitosan); QN-rGO@CNT (Quaternary-N-Dopped-rGO@CNT); CN-CHMC (carbon nanorods assembled coral-like hierarchical meso-macroporous carbon); PDDA (polydiallyIdimethylammonium chloride); poly (MG-py) (polymethylene green pyrrole).  
\end{table} 
Table 1: A part of nanomaterials and nanocomposites applied in EBFCs *. Figure 2: Schematic illustration of spider nest-shaped 3D Gox bioanode and Lac bioachode for glucose/oxygen biofuel cells [31]. was 0.55 V with a maximum power output of 12.2 \(\mu\)W cm\({}^{-2}\) with good stability and successfully obtained energy using some commercially available soft drinks as fuel [42]. Additionally, they developed another miniature origami battery made of a GDH bioanode and a consumable MnO\({}_{2}\)-graphite sheet cathode, which differs from the conventional EBPCs in that it uses MnO\({}_{2}\) as the cathode material to be consumed to accept external electrons, rather than conventionally exhibiting an oxygen reduction reaction [43]. This work is the first attempt to introduce consumable sheet or paper materials as cathodes for EBPCs. It will provide a disposable, cost-effective and clean solution for practical green energy systems. Buckypaper (BP), which is made by dispersing carbon nanotubes and graphene into a slurry and drying them, creates a densely packed carbon material that facilitates efficient electron transfer from the enzyme, resulting in improved cell performance. [PERSON] et al.