Based on the above analysed results, we estimated the CO2 emission of a smart phone use. Here, we considered the indirect and the direct CO2 emissions. The direct CO2 emission is equivalent to the fuel consumption origin. On the other hand, the indirect one is mainly on the device of a smart phone. In this study, we focused on HTC Desire X06HT made in Taiwan as a model phone. The indirect CO2 emission is calculated by Input-Output (IO) table, and this emission referred to the prior result. Also, we estimated the conventional smart phone including Li-ion battery in order to compare to the new one. Assuming that the holding time (life time: LT) when one user has a smart phone until he or she change the new one is 2.6 years, the indirect CO2 emission of HTC Desire X06HT including Li-ion battery would be 15.32 kg-CO2/unit. The emission of a smart phone with a PEFC unit would be 15.30 kg-CO2/unit. Although there are uncertainties on the storage tank of H2 to some extent, referring to the data of DMFC storage tank which has already developed, we estimated the emission as almost same as the conventional case (Dowaki et al., 2010a).

Next, the direct CO2 emission is affected by the specific CO2 emission of each fuel. Here, the CO2 emissions of conventional electricity, H2 fuel of natural gas origin (on-site) and Bio-H2 are assumed to be 123.1 g-CO2/MJ, 121.3 and 39.6 g-CO2/MJ-H2, respectively. The CO2 emission per one life cycle is shown in Fig. 9. Note that the specific emission of Bio-H2 is a minimum level (see Fig. 5).

According to this result, due to application of a PEFC unit to the smart phone, we would be able to reduce CO2 emissions of 3.9% to 6.1 % in comparison to the conventional phone. Especially, in the category of younger generation, the CO2 reduction benefit would be effective.