The development of a negative electrode for supercapacitors is a critical challenge for the next‐generation of energy‐storage devices. Herein, two new electrodes formed by the coordination polymers Ni(itmb)4(HPMo12O40)·2H2O (1) and Zn(itmb)3(H2O)(HPMo12O40)·4H2O (2) (itmb = 1‐(imidazo‐1‐ly)‐4‐(1,2,4‐triazol‐1‐ylmethyl)benzene), synthesized by a simple hydrothermal method, are described. Compounds 1 and 2 show high capacitances of 477.9 and 890.2 F g−1, respectively. An asymmetric supercapacitor device assembled using 2 which has novel water‐assisted proton channels as negative electrode and active carbon as positive electrode shows ultrahigh energy density and power density of 23.4 W h kg−1 and 3864.4 W kg−1, respectively. Moreover, the ability to feed a red light emitting diode (LED) also demonstrates the feasibility for practical use. The results allow a better elucidation of the storage mechanism in polyoxometalate‐based coordination polymers and provide a promising direction for exploring novel negative materials for new‐generation high‐performance supercapacitors. Water‐assisted proton channels in a polyoxometalate polymer‐based asymmetric supercapacitor device is reported for boosting capacitance and achieving ultrahigh energy density. What's more, this work allows a better elucidation of the storage mechanism in polyoxometalate polymers and provides a promising direction for exploring novel negative materials for new‐generation supercapacitors.