From Metal-Free to Metal-Lean: Synergistic Ni-Chelation in a Thiazolothiazole-Linked Porous Organic Polymer for Cost-Effective Green Hydrogen Evolution

Electrocatalytic water splitting can deliver sustainable H₂ when paired with renewables, yet deployment is constrained by noble-metal reliance. Here, we report a thiazolothiazole-linked porous organic polymer (POP) that incorporates N and S chelating sites within a conjugated, high-surface-area network, enabling the efficient anchoring of earth-abundant metals for the hydrogen evolution reaction (HER). The metal-free POP achieves an overpotential of 230 mV vs Reversible Hydrogen Electrode (RHE) at a current density of 10 mA cm⁻². Postsynthetic coordination of ultralow Ni (0.83 atomic %) reduces the overpotential to 69 mV vs RHE at 10 mA cm⁻², approaching the performance of commercial Pt/C while using significantly less metal by mass. Kinetic analysis reveals a low Tafel slope of 56.4 mV dec⁻¹ for the Ni-POP, consistent with a fast proton-electron transfer process. The catalyst exhibits excellent durability under chronopotentiometry at -20 mA cm⁻² for 22 h, with negligible performance loss. Gas quantification by the Hofmannn voltameter (dispersion method) confirms 27.12 mL of H₂ in 4 h at a rate of 6.78 mL/h and a Faradaic efficiency of nearly 99%. We attribute the near-Pt activity to the synergistic interplay between the electron-rich thiazolothiazole backbone and chelation-stabilized, highly dispersed Ni centers that promote rapid charge transport and optimized adsorption energetics. This chelation-guided, minimal metal-doping strategy provides a general route to scalable POP electrocatalysts that minimize noble-metal content without sacrificing performance, advancing cost-effective green hydrogen production.