Previously, we discussed the description of quantum yield-related parameters in photocatalysis. In this issue, we will delve into the description of energy conversion efficiency parameters in photoelectrocatalysis research.
Quantum Efficiency in Photoelectrocatalysis Experiments
1. External Quantum Efficiency (EQE), also known as Incident Photon-to-Current Efficiency (IPCE)[1]: The ratio of electrons generated by photons of a specific wavelength to the number of incident photons, essentially representing photon efficiency. The calculation formula is as follows:
jph: Photocurrent density (mA·cm-2), measured using chronoamperometry (constant potential);
h: Planck's constant (6.62 × 10-34 J·s);
c: Speed of light (3.0 × 108 m·s-1);
e: Charge of a single electron (1.6 × 10-19 C);
Pmono: Power density of monochromatic light (mW·cm-2);
λ: Wavelength of monochromatic light.
It's important to note that in the calculation of IPCE/EQE, the assumption is made that the Faradaic efficiency η is 100%, meaning that all generated photo-induced electrons are used for the desired product. IPCE measurements allow the application of bias voltage, while photoelectrocatalytic measurements of STH do not allow any bias voltage.
Internal Quantum Efficiency in Photoelectrocatalysis Experiments
2. Internal Quantum Efficiency (IQE), also known as Absorbed Photon-to-Current Efficiency (APCE)[1]: The ratio of electrons generated by photons of a specific wavelength to the number of photons absorbed, essentially representing quantum efficiency. The calculation formula is as follows:
A: Absorbance of the reaction system.
EQE/IPCE and IQE/APCE are primarily relevant to photoelectrocatalysis research. Similar to photon efficiency and quantum efficiency, EQE/IPCE emphasizes the concept of "incident light," while IQE/APCE emphasizes "absorbed light." EQE/IPCE can be directly calculated.
Applied Bias Photon-to-current Efficiency in Photoelectrocatalysis Experiments
3. Applied Bias Photon-to-current Efficiency (ABPE)[1]: The proportion of incident solar energy converted to hydrogen energy under a certain bias condition[1]. Unlike STH, ABPE is an energy conversion efficiency that subtracts the contribution of electrical energy.
Vredox: Thermodynamic potential of the reaction (V), in water splitting reactions, Vredox = 1.23 V;
Vapp: Relative bias applied to the electrodes in the two-electrode system (V), should be less than 1.23 V;
ηF: Faradaic efficiency for hydrogen generation;
Plight: Power density of AM 1.5G standard solar spectrum (100 mW·cm-2).
The above content explains the definitions and calculation methods of commonly used quantum yield parameters for activity evaluation in photoelectrocatalysis research. In the study of photocatalytic water splitting, the most commonly used quantum yields are AQY and STH. In photoelectrocatalytic water splitting research, the most commonly used quantum yields are IPCE and STH or ABPE. In summary, efficiency emphasizes incident light of specific wavelengths; yield emphasizes monochromatic light; EQE/IPCE emphasizes incident light; IQE/APCE emphasizes absorbed light.
[1]Chen Zhebo, Deutsch Todd G., Jaramillo Thomas F.* et. al., Accelerating materials development for photoelectrochemical hydrogen production: Standards for methods, definitions, and reporting protocols[J]. Journal of Materials Research, 2010, 25, 3.
