Efficient hydrogen-evolving cathodes based on proton and electron reservoir behaviors of the phosphotungstate [H7P8W48O184]33- and the Co(II)-Containing silicotungstates [Co6(H2O)30{Co9Cl2(OH)3(H2O)9(β-SiW8O31)3}5- and [{Co3(B-β-SiW9O33(OH))(B-β-SiW8O29OH)2}2]22-

Original and simple procedures for glassy carbon electrode modification with polyoxometalates (POMs), phosphotungstate [H7P8W48O184](33-), and Co(II)-containing silicotungstates [Co-6(H2O)(30){Co9Cl2(OH)(3)(H2O)(9)(beta-SiW8O31)(3)}](5-) and [{Co-3(B-beta-SiW9O33(OH))(B-beta-SiW8O29OH)(2)}(2)](22-) give stable and very active surfaces for the hydrogen-evolution reaction (HER). For this purpose, the selected POMs fixed on Vulcan XC-72 were adsorbed on the electrode surface or were directly entrapped in polyvinylpyridine films on the electrode. Cyclic voltammetry and confocal microscopy results converge to indicate that the activation is related to the proton and electron reservoir-like behaviors of these molecular oxides and not to any electrode surface area increase. However, the Tafel parameters of the HER process, which are different from one POM to the next, are in the range of those of the best metallic electrodes.