Tip-concentrated electric fields steer hydroxide migration to suppress cathodic scaling in urchin-like NixMoy–MoO2 for seawater electrolysis

Abstract

Direct seawater electrolysis for green hydrogen production is critically impeded by cathodic scaling caused by Mg²⁺/Ca²⁺ hydroxide precipitation under alkaline interfacial conditions. We report an urchin-like Ni_xMo_y–MoO₂@NF cathode that overcomes this limitation through tip-enhanced electric field engineering. The nanostructured tips induce a specific tip-enhanced electric field effect (up to 1.52 × 10⁶ V m⁻¹) that electrostatically repels cathodically generated OH⁻ ions, shifting precipitate nucleation from the electrode surface to the bulk seawater. Density functional theory calculations and in situ Raman spectroscopy reveal that the Ni_xMo_y–MoO₂ heterointerface synergistically lowers the water dissociation barrier to 0.14 eV and optimizes hydrogen adsorption free energy, while promoting ordered interfacial water configurations that simultaneously enhance HER kinetics and impede Mg²⁺/Ca²⁺ diffusion. The optimized electrode achieves an ultralow overpotential of 123 mV at 10 mA cm⁻² in natural seawater. Systematic modulation of nanopillar diameters quantitatively establishes that reduced feature size correlates with enhanced local field strength, which not only accelerates interfacial charge transfer to boost reaction kinetics but also ensures superior anti-scaling durability. COMSOL simulations corroborate that sharper tips steepen interfacial pH gradients and accelerate OH⁻ migration into the bulk electrolyte. This work establishes a mechanistic framework that links nanoscale morphology, tip-enhanced electric field modulation, and interfacial reaction dynamics, presenting a transformative additive-free strategy for durable seawater electrolysis.