<p>Adsorption and corrosion caused by Cl⁻ are the main reasons for the low performance of Pt-based catalysts for the hydrogen evolution reaction (HER) in seawater. Although the introduction of hydroxyl species is an ideal approach to enhance HER kinetics and resist harmful Cl⁻, achieving this goal in Pt-based catalysts is challenging. In this study, we developed a high-temperature reduction process to generate PtNi alloy particles that contain Ni vacancies (Lewis acid sites) that participate in transforming lattice hydroxyls to dissociative hydroxyls on Ni layered double hydroxides (Ni-LDH). The hydroxyls in Ni-LDH bind with Lewis acid active sites to form hydroxyl rich species, a process which enhances the hydrophilicity of PtNi/Ni-LDH to promote water adsorption and enhance resistance to Cl⁻ absorption. Owing to these properties, PtNi/Ni-LDH exhibits superior performance as an electrocatalyst for the HER in alkaline natural seawater as reflected by a low overpotential of 19 mV to drive a current density of 10 mA cm⁻², a low Tafel slope of 31 mV dec⁻¹, and an only slightly elevated overpotential after 100 h of operation. This study throws light on the development of new strategies for the design of high-performance catalysts for hydrogen production by electrolytic seawater splitting.</p>