## 3 Results and Discussion
### Life-Cycle Impact Assessment Based on Energy Production
When the different streams were compared, the APG system was more suitable when there was no energy recovery with a percentage of 5% lower, while when the combustion engine is available, the COG system was better, with an improvement of around 20%. Regarding the AP category, practically 100% of the impact was directly attributed to the cell, since the device contained  
Figure 5: Environmental impact results of the COG process (FU = 1 kWh) in the categories (**a**) ADPE, (**b**) ADPF, (**c**) GWP, and (**d**) AP. elements that must be produced by means of manufacturing processes that can release acidifying chemicals to the environment. From the analysis that took into consideration both the hydrogen production stage and the manufacture and operation of the fuel cell, the same conclusions that the case that investigated only the hydrogen production stage were reached. On the one hand, the ADPE category considered that the best conditions were found in scenario 1, and the worst ones in scenario 8. On the other hand, for the rest of the categories, scenario 2 was the most environmentally friendly option, and scenario 7 the least preferable one. Due to the great impact that the fuel cell had in some impact categories, mainly ADPE and AP, the burdens associated with the manufacture of the cell were investigated in detail (Figure 6). As observed, in three of the four categories studied (ADPF is the exception, since in this case, the membrane is the most important contributor), the main impact was caused mainly by the production of the anode and the cathode, with joint contribution percentages close to 100% in ADPE and AP and more than 80% in GWP. These impacts were associated with the employment of platinum in the formulation of these components. In the ADPF, the membrane appeared with a huge contribution, due to the electricity used for its preparation. To have a better understanding of the relevance of the employment of platinum in the fabrication of the anode and the cathode, a sensitivity analysis was carried out. To analyze the sensitivity of the platinum loading, a hypothetical fuel cell without the noble metal was considered to analyze the variation in the environmental impacts. The results revealed that significant reductions were possible, since impact reductions close to 100% were achieved in ADPE and AP categories, while a 84% reduction in the GWP value was possible. However, for the ADPF category, the obtained results were similar to the ones corresponding to a cell with platinum anode and cathode. Figure 6: The relative contribution of the components of the cell to the environmental burdens. A comparison with reference values reported from bibliographic references that applied the LCA methodology to assess the environmental impact of FCs was carried out with two purposes: (i) To know the reliability of the results obtained in the current study comparing with those taken as reference, and (ii) to evaluate the benefits related to the use of H2 recovered from gaseous waste streams in HT-PEMFC. References that have applied LCA for H2 recovery to its use in HT-PEMFC for stationary applications have not been found, so the production method of steam methane reforming has been considered for the comparison. In addition, most references assess the environmental impact of PEMFC for mobile applications, as transportation is currently one of the most polluting sources, whereas, that of HT-PEMFC for stationary applications is underdeveloped. For a stationary FC system, a GWP value of 0.69 kg CO\({}_{2}\) eq/kWh was reported [68]. This value was slightly higher than the one reported in this study considering the APG case, whilst it was in the range of values obtained for the COG case. In scenarios without membrane recovery (scenarios 3, 4, 7, and 8 for COG), higher values in the GWP category are reached in this study. However, the system proposed is generally a competitive alternative; being able to present a larger amount of benefits once the design and operation optimization is carried out.