Mimicking photosynthesis using has been attempted to convet CO2. The reaction scheme consists of electrochemical NADH regeneration and enzymatic CO2 reduction. Carbon and metal electrodes were not suitable for electrochemical NADH regenreation because the inactive NADH formation by dimerization of NADH was not avoidable. Electron mediators were required to get nearly 100% active NADH by the electrochemical method. Rh carbene