Inorganic Hydrogels can be Flexible and Highly Extensible.

Abstract

Inorganic hydrogels have great potential in many applications as sustainable materials, but lack flexibility due to rigid network structures. Here, a novel strategy is proposed-an inorganic polymer hydrogel, prepared by crosslinking long-chain polyphosphate (LPP) with M²⁺ ions (Ca²⁺, Mn²⁺, Mg²⁺, Ni²⁺), which effectively address the rigidity and fragility issues commonly associated with traditional inorganic gels. With the most stable hydration shell among those ions, Ni²⁺ tends to interact indirectly with LPP through hydrogen bonds rather than coordination bonds. The unique Ni²⁺-phosphate interaction endows the Ni-LPP hydrogels with ultrahigh elongation at break (≈15 000×). Further experiments reveal that the Ni²⁺-phosphate motif can be applied to other hydrogels as an extension enhancement factor. The highly extensible, good conductive (1.06 ± 0.08 S m^-1), self-healing (within 30 s and without stimulation), arbitrarily shapeable, and nonflammable Ni-LPP inorganic hydrogel indicates a bright future in flexible electronics, environmental remediation, and beyond.