High‐Performance Quasi‐Solid‐State Thermogalvanic Cells with Metallized Fibril‐Based Textile Electrodes and Structure‐Breaking Salts

Abstract Thermogalvanic cells (TGCs) convert heat into electricity through thermoelectrochemical reactions of redox couples, generating a millivolt‐scale Seebeck coefficient. However, TGCs based on liquid electrolytes are prone to leakage, whereas quasi‐solid‐state TGCs (QTCs) using gel‐based electrolytes typically have low power outputs due to slow ion diffusion and limited reaction rates. Herein, we present novel strategies for developing high‐performance all‐flexible QTCs using both metallized fibril‐based textile electrodes with extremely large surface area, (specifically Ni textiles), and structure‐breaking salts for hydrogel electrolytes. The electrodes are oxidized to create Ni and Ni oxide heterostructures, forming numerous O vacancy defects that enhance redox reactions. Meanwhile, the structure‐breaking salts facilitate redox reactions and improve ion diffusion by disrupting water structures in the hydrogel electrolyte. These advancements significantly enhance the performance of the QTCs without the need for precious‐metal electrodes, achieving a remarkable maximum power density of 4.05 mW m −2 K −2 and a record‐high effective cell conductivity of 17.3 S m −1 , compared to previously reported QTCs. Finally, the proposed QTCs can generate a stable open‐circuit voltage and output power for wearable applications owing to the flexibility of the electrodes and electrolyte, achieving successful electronic device operation using body heat from the forearm (Δ T ≈ 2 K).