This manuscript reports a review regarding chitosan-based biopolymer which has been widely used for anion exchange membrane in fuel cell application. This review aims to enhance the cell performance of chitosan-based AEMs by addressing the important factors: mechanical stability, ionic conductivity, water absorption, and expansion rate. The authors have explained their review well, however, revisions considering the comments listed below are required.
1. The last sentence in the abstract section could not be seen in this manuscript. Please revise this matter and also, pay attention to the maximum sentence that could be written in the abstract.
2. Table 1 shows the list of several recently reported composite membranes in AFCs. The authors presented 2 types of polymer matrixes, chitosan and PVA. It is better if the author gives a brief explanation regarding the major differences of these 2 polymer matrixes, and what are the impact of adding various nanoadditives to polymer matrix.
3. The authors stated that adding nanoadditives to a polymer matrix can adjust membrane characteristics such as surface hydrophilicity, increase membrane stability in challenging conditions like high temperature and increase ionic conductivity compared to ordinary ion exchange membranes. Please explain the reason why adding nanoadditives could adjust membrane characteristics? If possible, please also highlight some additives which gave an excellent improvement to the polymer matrix and explain the reason.
4. The authors has divided this manuscript into several parts including the chemical modification of chitosan, chitosan-based interpenetrating polymer networks, and chitosan-based composite membranes. However, the authors have not yet explained the effect (improvement) which this modified chitosan could obtained when used for AEM in fuel cell applications. The authors should discuss the fuel cell results (power density) obtained using this modified chitosan polymers and what are the influence of making some modifications to the chitosan. If possible, the authors could also adding 1 more table to compare many type of modified chitosan and its result when tested in the fuel cell applications.
5. The authors stated that cellulose could be used to replace the use of chitosan because chitosan needs a relatively high cost compared to cellulose. Besides considering the cost aspect, the authors should elaborate the major difference when this cellulose polymer was used as a replacement of chitosan. Also, has this cellulose-based used for AEMFC application? Please also provide the comparison of these 2 types of polymers regarding its result in fuel cell application.
6. The authors should give a brief explanation regarding the future prospects (challenges and perspective) of this chitosan-based polymers for AEMFC.
7. How is the stability of this chitosan-based polymer compare to the commercial AEM used in the fuel cell application? Please elaborate this matter in the manuscript.
8. There are some grammatical errors found in the manuscript, the authors hope the reviewers could consider the words used in this manuscript carefully.