FIGURE 5 Procedure of the automatic measurement routine with schematic data for current, cell pressure and H2 concentration.
The system was applied to investigate a photocathode of copper indium gallium selenide in H2SO4, for which a Faradaic efficiency of (95.4±7.7) % was determined (Figure 6). The STH efficiency was calculated to be (1.9±0.1) % for a system of a 25.0 cm2 photocathode and a 6.0 cm2photovoltaic module. Both efficiencies agree with previous literature values [16].
A quantitative error analysis with consideration of the propagation of uncertainty shows that the free gas volume of the electrochemical cell is an important contribution to the overall error, for which an individual measurement uncertainty of 2 mm3 results in an absolute error of 0.9 % in the Faraday efficiency. The determination of the absorber area, variations in the reaction temperature and non-ideal behavior of the gas/liquid system (e.g. , trapped gas bubbles) are significant contributions to the error. The GC measurement itself has a high accuracy with an error of less than 0.01 % but relies on the quality of the calibration.