Efficiency Definitions in the Field of PEC

In general, a UV-Vis transmission experiment offers the fastest and most direct method of estimating the optical bulk band gap and should be a priority for any newly synthesized material. A diffuse reflectance or absorption configuration can be used if the sample is not transmissive. If a diffuse reflectance experiment is not available, then photocurrent spectroscopy (as described in Chapter Efficiency definitions in the field of PEC ) with extremely facile redox couples can be performed, though errors in this method may arise from poor charge carrier mobilities or lifetimes and from slow kinetics at the sample-electrolyte interface. 

An important limitation is that the three-electrode j-V measmement cannot be utilized to calculate a power conversion efficiency because the three-electrode scale represents only the half-cell voltage between the WE and RE (see Chapter Efficiency Definitions in the Field of PEC ). To emphasize why a half-cell efficiency is insufficient, Fig. 6.9a illustrates the case for two distinctly different hypothetical photoanodes. Photoanode A possesses a small Vonset, oer and large jfc OER while Photoanode B possesses a large Vonset,OER and small oer- Both photoanodes in this case would seemingly yield the same half-cell efficiency described by in Eq. (2.10) in Chapter Efficiency Definitions in the Field of PEC using the operating points Vop and jop that correspond to the point of maximum fill factor. However, further analysis in Fig. 6.9b reveals that a complete device which includes the addition of a photocathode would clearly distinguish Photoanode B as the superior component. 

The general equation for calculating IPCE is Eq. 2.5 from Chapter Efficiency Definitions in the Field of PEC ... 

The peak area given by the TCD signal correlates linearly with the concentration of each gas. Based on the calibration for the GC-TCD, the area of the H2 peak can be converted to mol H2. When divided by the measurement time, the rate of H2 evolution is obtained. (Area under H2 peak) x (Conversion factor mol H2/area)/ Time (s) = (rate mmol H2 s ). This rate is then used with Eq. 2.1 of Efficiency Definitions in the Field of PEC to determine the STH. 

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