A new and stable Keggin-type phosphomolybdate based hybrid compound, [Ag4(FKZ)2][HPMo12O40] (HFKZ = [1-(2,4-difluorophenyl)-1,1-bis [(1H-1,2,4-triazol-1-yl)-methyl]methanol], was synthesized and structurally characterized. The flexible coordination mode of HFKZ molecules and Ag ions generate high-connected PMo12 polyanions, as well as synergistically contribute to the formation of quadruple meso-helical structure. The new compound exhibits excellent stability in aqueous solution and different organic solvents and even high pressure, which is expected as an ideal electrocatalytic material due to the multi-electron redox ability of PMo12 polyanions and synergistic effect of all components. The result of the electrochemical behavior indicates that the new compound as active substance exhibits good electrocatalytic activity toward the reduction of nitrite.