• A cactus-like NC/CoxP@NF electrode was synthesized via in-situ ZIF-67 formation and phosphorization, exhibiting abundant active sites and ion transport channels.
• The electrode achieves low overpotentials of 107 mV (alkaline) and 133 mV (alkaline saline) at 10 mA cm−2, outperforming many non-noble metal catalysts.
• The NC nanosheet protective layer and surface phosphate polyanions enhance anti-corrosion resistance, ensuring superior durability in saline water splitting.
• This in-situ transformation strategy offers a promising route for designing efficient and stable HER catalysts for direct seawater electrolysis.