ZIF‐67‐Derived Carbon‐Doped Cobalt Composites With Dominant Pseudocapacitance as Solid Transducing Layer for High‐Sensitivity Solid‐Contact Ion‐Selective Electrodes

Carbon‐doped cobalt composites (CDC‐67s: Co@C, Co 3 O 4 @C, and Co 3 O 4 ) have been synthesized via controlled pyrolysis and oxidation of ZIF‐67 (a metal–organic framework) precursor. These composites exhibit both electrical double‐layer capacitance and pseudocapacitance, making them promising materials for high‐performance ion–electron solid transduction layers (STLs). Herein, the efficient transduction mechanism of CDC‐67s has been systematically analyzed. Specifically, the Co 3 O 4 @C material leverages its mesoporous carbon framework to facilitate additional charge storage through reversible Co 3+ /Co 2+ redox reactions. This mechanism results in a high specific capacitance of 103.44 F g –1 , with pseudocapacitance accounting for up to 83% of the total capacitance. Furthermore, solid‐state contact ion‐selective electrodes (SC‐ISEs) fabricated with Co 3 O 4 @C as STLs show the highest sensitivity of 68.03 mV decade –1 among the CDC‐67s, significantly surpassing that of SC‐ISEs based on commercial materials like graphene and multiwalled carbon nanotubes (MWCNTs). This pseudocapacitance‐dominated charge storage mechanism, thus, greatly enhances SC‐ISE sensitivity, expanding the design paradigm for traditional carbon‐based SC‐ISE materials and opening new avenues for developing high‐performance SC‐ISEs. The stability of the CDC‐67‐based SC‐ISEs has been assessed by water layer tests; the Co 3 O 4 ‐based SC‐ISE demonstrates superior resistance to this interfacial interference, indicating the promising application of Co 3 O 4 @C as ion–electron solid transduction layer for solid‐contact ion‐selective electrodes.