A novel electrochemical reactor for hydrogen production and power generation is proposed based on a fuel cell/battery system. The reactions (hydrogen evolution and oxidation) in the system occur at solid/liquid and solid/gas two-phase boundaries using a metal hydride negative electrode. This leads to high energy efficiency for both hydrogen production and power generation. We thus investigated electrochemical charge/discharge performance at various current densities by fabricating an experimental cell. This cell was composed of negative and positive electrodes with a 1:3 capacity ratio. Hydrogen gas was produced in a linear manner during the charge process and it was completely consumed during the discharge process. The energy conversion efficiencies of hydrogen production and of the complete hydrogen production/power generation process at a current density of 37.0 A/m(2) were 98.3% and 79.6%, respectively. These values are higher than those of conventional water electrolysis and/or power generation systems. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.