2D materials can be classified as single-element, two-element, and multielement. Examples of the first type are graphene, phosphorene, silicene germanene, stanene, arsenene and bismuthene. Hexagonal boron nitride (h-BN), transition metal dichalcogenides (TMDs) and transition metal carbide and nitride (MXene) belong to the second type, while samarium sulfoiodide (SmSI) belongs to the third type. Despite their promising properties, many of these materials do not possess an adequate band gap for electron transport, which is essential in electrochemistry. However, thanks to their tunability their band gap can be closed by the deposition of metallic clusters. The catalytic activity can also be increased in the same way, as previously reported for the inert basal plane of 2H-MoS2. In this context, subnanometer metal clusters have been regarded as functional catalysts to work in tandem with 2D supports. First, due to their small size, clusters possess a huge amount of surface area. In contrast to nanoparticles (NPs), all or most of the atoms are part of the surface, namely, potential active sites, with the possibility of reaching the so-called atomic efficiency. This feature, coupled to the high surface area of the 2D support, permits employing minimal amount of Pt. Second, clusters present many degrees of freedom that can be exploited to tailor the catalytic properties. In this size regime, the catalytic properties become size-dependent to the extent that a single atom can make a dramatic difference: each atom counts. The metal-support interaction (MSI) is also maximized due to their large surface area. This, together with the high thermal stability of 2D supports, may confer the clusters an enhanced resistance to sintering.