Effect of pH, temperature, and low light flux on the performance (16% STH) of coupled triple junction solar cell to water electrolysis

Abstract

A triple junction (3J) solar cell having 33% efficiency at one Sun condition is integrated with an electrolyzer containing Pt wire electrodes to study the effect of pH, temperature and low flux solar light on H2 production from water. Results indicate that electrolyte conduction affects the rate of reaction mostly due to the large voltage at maximum power (Vmpp) of the PV-cell. Measurements are performed both indoors, under 100–500 mWcm−2 insolation, and outdoors. Electrochemical impedance measurements indicate that the exchange current, ji, depends largely on the electrolyte resistance, r (ji = (Vapp-Veq)/r); where Vapp is applied voltage provided from the cell and Veq is the equilibrium potential for water electrolysis (1.23 V). The small increase in the hydrogen production rate with temperature (Ea = 4.4 kJ mol−1) is largely because of the high Vapp, where above 1.6 V the IV curve enters into the Tafel slope region. The maximum solar-to-hydrogen conversion efficiency (STH) outdoor is found to be about 16% under acidic conditions. The high Vmpp (2.5 V) of the PV cell compared to Vopp (1.7 V) makes the current at maximum power (Impp) the limiting factor.