**5. Conclusions**

Photosynthesis and artificial photosynthesis system were compared in this study with an emphasis on charge and H transport which is indicated to be the main reason for the difference in resulting carbon dioxide reduction yields and rates. The gap in artificial systems was found to be in the design of the photocatalytic systems which could be developed with a membrane which would enhance charge separation and H transport. H supply to carbon dioxide reduction centers were found to be limiting the existing photocatalytic carbon dioxide reduction rates, indicating the important role of water splitting in artificial photosynthesis systems. Water being in contact with carbon dioxide on photocatalyst surface was found to act negatively on the methanol formation rates by inhibiting carbon dioxide activation. For a better carbon dioxide reduction with existing photocatalysts, separation of the reaction centers was proposed which would enhance the charge and H transport at the same time.
