Currently, the majority of hydrogen is produced by steam reforming of natural gas, thus, it is not entirely "green" hydrogen. H2 produced by this process inevitably contains impurities of carbon monoxide (CO) at a concentration of ~10-100 ppm. The high affinity of Pt towards CO over H2 leads to a severe surface blockage by CO, inhibiting H2 adsorption. An anode potential greater than 0.6 V (vs RHE) is required to oxidize CO via a Langmuir-Hinshelwood (LH) type reaction between CO* and OH*. This results in an extra voltage loss and HOR deactivation. This process is known as CO poisoning and is one of the most important drawbacks affecting the manufacturing of PEMFC. Purification of the H2 feed is very costly and challenging. Hence, it is essential to develop HOR catalysts resistant to CO poisoning, as well as alternative methods for H2 production. One strategy to improve the intrinsic activity and resistance to CO poisoning is to dope or alloy Pt with a second element. In the past, several studies have pointed that Ge can be a very versatile promoter for fuel cell applications. An excellent CO electro-oxidation and HER activity for PtGe nanoalloys has been reported previously. Nonetheless, the promoting role of Ge is not entirely clear yet, albeit it has been proposed to be a combination of ligands effects between Pt and reduced Ge 0 , along with bifunctional effects coming from unreduced GeOx. Moreover, Pt6Ge cluster has been observed to be more active than Pt7 in water dissociation It is interesting to comment also that germanium carbide presents lower overpotentials than traditional Pt, and germanene decorated with Fe and Ru adatoms is able to remove CO from H2 by the three-step reaction. In our previous works we have shown that PtGe clusters have an increased resistance to CO poisoning; and more importantly, the PtGe clusters are still able to dissociate H2, even at very high Ge composition. The mechanism behind such behaviour has been ascribed to a combination of ligand and bifunctional effects. Notwithstanding, studies about PEMFC performance of PtGe nanoalloys on the subnanometric scale are still scarce.