The electron transport to the catalytically active species from the surface can be monitored with this technique. We found that the electron transport is faster in 0.5 M NH3 solution than in aqueous solution without ammonia substrate (only 0.2 M NaClO4 supporting electrolyte). Moreover, the electron-transporting naphthalene backbone of guest 2 showed a faster electron transport rate (86.6 s -1 ) than those from guest 1 (46.4 s -1 ). However, since the catalytic process is slower than the electron transport to the electrode surface, the catalysis is the rate-limiting step. This explains the better performance of guest 1 despite the clearly lower electron transfer rate.