H-2 and O-2 were produced at separate times from water electrolysis by using silicotungstic acid as an electron-coupled-proton buffer. It was found that the redox property of silicotungstic acid in water could be regulate by the introduction of organic solvents (acetonitrile, DMF and ethanol). The redox wave of silicotungstic acid at similar to 0.02 V vs. RHE moved in the negative direction, which was good for the production of hydrogen. A high yield of hydrogen (similar to 85%) was obtained in a water-ethanol system (V/V = 1:1), which was higher than that in water (similar to 45%). And the introduction of ethanol didn't affect the rate of hydrogen evolution. Moreover, the semihydrogenation of organic compounds could be achieved in the present system under mild conditions. The conversion of phenylacetylene and acetophenone are 97% and 80% under optimum reaction conditions, while the selectivity of styrene and 1-phenylethanol are 80% and 82%, respectively. (C) 2019 Published by Elsevier Inc.