<div>FIGURE 5 Procedure of the automatic measurement routine with schematic
data for current, cell pressure and H<sub>2</sub> concentration.</div><div>The system was applied to investigate a photocathode of copper indium
gallium selenide in H<sub>2</sub>SO<sub>4</sub>, 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
cm<sup>2</sup> photocathode and a 6.0 cm<sup>2</sup>photovoltaic module. Both efficiencies agree with previous literature
values [16].</div><div>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 mm<sup>3</sup> 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 (<i>e.g.</i> , 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.</div>