Hydrogen peroxide was directly produced from hydrogen and oxygen in a slurry reactor containing a Pd/C catalyst at 5-20 degrees C. Hydrogen and oxygen produced by a solid polymer electrolyte water electrolyzer were fed into the reactor. The effects of reaction temperature, slurry concentration, gas flow rate and solvent on the H2O2 production were investigated. The maximum production rate of H2O2 was obtained at a reaction temperature of 10 degrees C and sharply increased along with the addition of methanol. The results show that H2O2 production is significantly influenced by the solubility of the gas, while excessive catalyst and hydrogen facilitate the decomposition of the accumulated H2O2. Finally, H2O2 production was performed in a catalytic slurry reactor with a pair of platinum electrodes inserted. The in situ feed of hydrogen and oxygen into the reactor improved H2O2 production. This could be due to an increase in gas solubility due to fine bubbles or the electrochemical generation of H2O2.