Efficiency of Photoelectrolysis

In a regenerative solar energy conversion system, the device efficiency (r ) is simply given by the ratio of the power delivered by the photovoltaic converter and the incident solar power (Ps in W/m2 or mW/cm2). However, we are concerned here with devices producing a fuel (H2) and several expressions exist for the device efficiency. Thus, this efficiency can be expressed in kinetic terms 70192 

is the standard Gibbs energy for the water splitting reaction generat- 

The bias voltage, that is needed in some cases (c.f., Fig. 3), is Rims and it is the current corresponding to the maximum power point29,66 of the cell. 

4 41 Two-photosystem configuration with two different (optimized) Eg values. 192 

4 For AM 1.5-insolation. Estimated efficiency depends on type of solar conversion system i.e., whether single- or twin-photosystem and whether one- or two-photon driven. 70, 195 

6 38-72 Twin-photosystem at AM l.Oforthe lower limit and a 36 band gap solar cell for the upper limit. 44, 196 

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Fig. 3.20 The ideal limiting solar conversion efficiency for single bandgap devices. The dotted line shows efficiency of photoelectrolysis cells at different values of Eioss in relation (3.6.8) [102].

Similar results of photoelectrolysis of water in cells with n-type SrTi03 single-crystal anode and platinized Pt cathode were reported around the same time in a preliminary communication by Mavroides et al. [53] who measured the maximum quantum efficiency... 

Though equation (3.6.5) is more useful for analyzing the performance of photoelectrolysis cells, for practical purposes the photoconversion efficiency (solar conversion efficiency if sunlight is used) is calculated hy modifying (3.6.5) in the form... 

Fig. 3.22 (a) Current - voltage characteristics of a p-type photocathode and that when it is replaced by a platinum shown to illustrate the efficiency calculation using the power saving approach. The shaded area represents the maximum power saving as a result of photoelectrolysis, (b) The efficiency at various photocurrent densities obtained useing the base graph. 

IPCE enables the estimation of the total photocurrent as well efficiency of a photoelectrolysis cell under any type of... 

IPCE and APCE can have values close to 100%. As discussed before, the maximum attainable photoconversion efficiency in a single bandgap photoelectrolysis cell is 30.7%. Although stable, the photoconversion efficiencies of most oxide semiconductors are low (<2% except the case of 8.35% reported for carbon modified titania [121]) due to their large band gap. 

Hanna MC, Nozik AJ (2006) Solar conversion efficiency of photovoltaic and photoelectrolysis cells with carrier multiplication absorbers. J Appl Phys 100 074510 (8 pages)... 

Varghese, OK Grimes, CA (2007) Appropriate Strategies For Determining The Photoconversion Efficiency Of Water Photoelectrolysis Cells A Review With Examples Using Titania Nanotuhe Array Photoanodes. Solar Energy Materials and Solar Cells, in press. 

Salvador P (1980) The influence of Niobium doping on the efficiency of n-Ti02 electrode in water photoelectrolysis. Sol Energy Mater 2 413-421... 

The principal solar water-splitting models predict dual-band gap photoelectrolysis efficiencies of 16% [40], and 10-18% [41]. 

Woodhouse M, Parkinson BA. Combinatorial approaches for the identification and optimization of oxide semiconductors for efficient solar photoelectrolysis. Chem Soc Rev. 2009 38(1) 197—210. 

Fig. 9. Energy conversion efficiency of solar driven water splitting to generate H2 as a function of temperature for AMI. 5 insolation, with the system minimum bandgap determined at JOH20 = 1 bar.3 The maximum photoelectrolysis efficiency is shown for various indicated values...

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