<p>Precious metals such as Pt are favoured as catalysts for the hydrogen evolution reaction (HER) due to their excellent catalytic activity. However, the scarcity and high cost of precious metals have prompted researchers to explore cheaper alternatives such as Cu. Nevertheless, Cu shows poor catalytic performance due to weak binding with intermediates. Here the catalytic activity of pure Cu is activated via electroreduction-driven modification of the local structure, achieving a HER catalytic performance superior to commercial Pt/C catalysts for working current densities greater than 100 mA cm⁻² in acid electrolyte. Activation involved two steps. First, polycrystalline Cu₂O nanoparticles were prepared via pulsed laser ablation, resulting in grain boundaries within the Cu₂O particles as observed using electron microscopy. Next, the Cu₂O particles were electroreduced to pure Cu, inducing the formation of distorted nanotwins and edge dislocations. These local structures induce high lattice strain and decrease the Cu coordination number, enhancing the interaction between Cu and intermediates—as calculated using density functional theory—leading to the excellent catalytic activity and durability of the catalyst. Our observations show that low-cost pure Cu can be a promising HER catalyst for large-scale industrial applications.</p>