Applied Bias Photon-to-current Efficiency (ABPE) is the ratio of incident solar energy converted to hydrogen energy under certain bias conditions[1].
Distinguished from Solar-to-Hydrogen efficiency (STH), ABPE represents the energy conversion efficiency after deducting the electrical contribution.
When studying the PEC water-splitting performance of a single photoelectrode, a small bias is usually applied using an external power source. At this point, to evaluate the photoelectrode's photoelectrochemical conversion efficiency, the calculation of the ABPE formula for a single photoanode electrolyzer can be simplified using formula (1):
Usually, under the condition of a 100% Faraday efficiency, ABPE can be calculated by substituting jP, Va, and the corresponding Pin into formula (2) through the j-V curve.
For a single photocathode electrolyzer, ABPE is calculated using formula (3):
From formula (2), it can be observed that when Va is set to 1.23 V, the value of ABPE is nearly zero. When Va exceeds 1.23 V (vs. RHE), the value of ABPE becomes negative. Therefore, when measuring the photocurrent density of the photoanode, it is advisable to choose an applied bias value <1.23 V (vs. RHE), and the research objective should focus on improving the photocurrent density within this range.
Notes
Two points to note during calculation:
① The above calculation formulas are only applicable to single-chamber photoelectrochemical reaction cells, where the electrodes need to be in the same electrolyte to avoid the generation of chemical potential.
② The electrolyte solution should not contain electron or hole sacrificial reagents. Although sacrificial reagents can effectively address the transport limitations of charge carriers at the interface, they complicate the reaction in the solution, deviating from the original photoelectrochemical reaction.
Figure 1: ABPE Curve[2-5]
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