To enhance hydrogen production efficiency by in-liquid plasma, the method inserting catalytic metal into in-liquid plasma reaction field was considered. To retain a bubble at the tip of in-liquid plasma electrode, a plate is fixed over the electrode. That plate and electrode are composed of a catalytic metal. Methanol is decomposed by in-liquid plasma, and the gas generation rate and. composition rate are measured. The gas is composed of 67% H-2, 30% CO, and 3% other. This rate is independent of the material of the electrode or plate. The plate enhances the hydrogen production rate. When the plate and electrode are composed of Ni (0.37 Nm(3)/kWh), the maximum hydrogen production rate is obtained. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.