**4. Conclusions**

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Enzymatic bioelectrocatalysis is advancing day by day due to the finding of novel enzymes and the development of electrode nanomaterials. However, there are still issues to be solved such as thermostability, oxygen tolerance, and physical fragility, compared to inorganic electrocatalysts. Further understanding and consideration of the electrode interface and the interaction between enzymes and electrodes from kinetics and thermodynamics are required. Other perspectives, such as the improvement of redox enzymes by protein-engineering approaches, the selection of electrode materials and mediators (including redox hydrogels), the immobilization of enzymes, and the layout of electrodes will be also required for the improvement of present bioelectrochemical devices.

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**Author Contributions:** Conceptualization, T.A. and K.K.; data curation, T.A.; writing—original draft preparation, T.A.; writing—review and editing, Y.K., O.S. and K.K.; supervision, K.K.; project administration, K.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
