Feasibility study of a simple unitized regenerative fuel cell

Conventional fuel cells use hydrogen and oxygen as the fuel and oxidant, respectively. Hydrogen and oxygen can be produced through electrolysis of water in an electrochemical cell. A simple unitized regenerative fuel cell (URFC), by combining an electrolyzer and a fuel cell, is constructed to check the feasibility of such a device. In the first cycle, hydrogen and oxygen gases are generated from water containing NaHCO3 when a given dc voltage is applied across Ni–Co/stainless steel electrodes. A solar photovoltaic cell is also used to provide the power. The generated gases are trapped between their respective electrodes and nylon mesh. In the second cycle, the hydrogen and oxygen gases are used in the same electrochemical cell (fuel cell) to produce electricity under a specific load. The current density and voltage are measured by varying different parameters, e.g., time of electrolysis, magnitude of voltage applied, and electrolyte concentration. An open-circuit voltage (OCV) of 1.3 V is obtained from two regenerative fuel cells in series with a total active electrode area of 300 cm2. A current density of about 0.5 mA cm−2 is generated using 0.5N NaHCO3 when 4.5 V is applied for 25 min. A maximum power of 36.5 mW is obtained at 0.21 mA cm−2.