Abstract
Electrochemical reduction of 
under high pressure (>50 atm) on a Pt gas diffusion electrode (Pt—GDE) was studied. When the Pt catalyst layer was directed toward the 
gas phase (the reverse arrangement), methane was produced as the main 
reduction product at high faradaic efficiency and at large partial current density. Ethanol, ethylene, ethane, carbon monoxide, and formic acid were also produced. The effects of the Pt catalyst, electrode arrangement, 
pressure, reaction temperature, and hydrogen pretreatment of the electrode were investigated for this electrocatalytic reaction. Faradaic efficiencies of the formation of 
reduction products such as methane, carbon monoxide, and formic acid depended significantly on the 
pressure and temperature. The yield of 
reduction products was increased by hydrogen pretreatment of the Pt—gas diffusion electrode.