Recurrently gellable and thermochromic inorganic hydrogel thermogalvanic cells

Thermogalvanic cells (TGCs) draw great attention in the field of heat to electricity conversion, but TGCs were only in the form of liquid or organic gel. Here, we report an all-inorganic hydrogel TGC via simply mixing and stirring two inorganic salt solutions. Benefiting from the hydrogen bonds resultant framework and endogenous Fe^2+/3+ redox couple, the TGC can recurrently pulverize-gel with completely holding its initial thermogalvanic performances after even 60 cycles. As the temperature and pH coregulating Fe³⁺ concentration and reversible transformation between Fe³⁺ and Fe(OH)₃, we boost thermopower and realize thermochromism. This work provides a different perspective for TGCs and offers an avenue for future hydrogel materials research.