The development of efficient and cost-effective water splitting electrolyzers is a fundamental step to support the achievement of climate neutrality by using renewable energy sources to produce green H2 as a form of clean fuel. In this work, we investigated Pt-based nanostructured cathodes for high-performance alkaline electrolyzers (AELs), showing the beneficial effect of graphene over traditional carbon black as nanocatalysts support. By relying on a water-based, scalable, synthetic method, surface-cleaned Pt nanoparticles were successfully produced and strongly anchored to defect-free graphene flakes, the latter produced through wet-jet milling exfoliation of natural graphite. Once deposited on conventional gas diffusion layers, Pt/graphene catalysts outperform traditional Pt on Vulcan (Pt/C) in terms of hydrogen evolution reaction (HER) activity and performance durability. The two-dimensional morphology of graphene flakes strongly retains the catalysts in the electrode even in the absence of any binder, while intrinsically ensuring the exposure of the catalytic sites for the HER. This rationale enables the fabrication of high-performance AELs based on Pt/graphene cathodes. By using commercially available cost-effective anodes (stainless-steel meshes), our AELs reached current densities of 1 A cm− 2 at a voltage of as low as 1.71 V. These AELs can even operate up to more than 2 A cm− 2 (e.g., 2.2 A cm− 2 at 1.90 V), with stable performance during accelerated stress tests. Our study discloses two main aspects: (1) graphene is an effective conductive support for 1–10 nm-scale catalysts for the development of nanostructured cathodes with elevated catalytic properties and durable performance; (2) the use of efficient nanostructured cathodes can boost the AEL’s performance to state-of-the-art values reported for proton-exchange membrane electrolyzers, avoiding the use of expensive anodes (e.g., Ir-based ones).