Chronoamperometric measurements were also performed in order to evaluate in detail the effect of SnO2 modification on the ammonia NHS-LC-Biotin activity of Pt. The CAs obtained at 25 °C for C–Pt/SnO2, SnO2–Pt/C, and Pt/C are compared in Fig. 6. It can be clearly seen that the two SnO2–modified Pt catalysts maintained a high current density during the analysis. In particular, the current density for C–Pt/SnO2 after 3 min was approximately three times higher than that for Pt/C. A series of measurements was also performed at 5, 45, and 60 °C, and the Arrhenius plots were constructed using the current density after 3 min for each catalyst (see Fig. 7). The estimated apparent activation energies for C–Pt/SnO2, SnO2–Pt/C, and Pt/C were 52, 58, and 67 kJ mol−1, respectively. The activation energy for C–Pt/SnO2 was slightly lower than that for SnO2–Pt/C due to the difference in the numbers of Pt particles in contact with the SnO2 in each catalyst. Therefore, these results demonstrated that SnO2 activated the ammonia oxidation reaction over Pt. With regard to the role of SnO2 in ammonia oxidation, it is thought that the SnO2 provides OH species to the Pt surface, which accelerates the dehydrogenation of NH3 and/or intermediates, i.e., NH2 and NH, as is the case for ethanol oxidation according to Kowal et al. .