In our previous issue, we discussed the description of quantum yield-related parameters in photocatalysis. In this issue, we will describe the parameters related to the efficiency of photo-electric energy conversion in photocatalytic research.
Quantum Efficiency in Photocatalytic Experiments
1. External Quantum Efficiency (EQE), also known as Incident Photon-to-Current Efficiency (IPCE)[1]: The ratio of the number of electrons generated by photons of a specific wavelength to the number of incident photons, essentially representing photon efficiency. The formula for calculation is as follows:
jph: Photocurrent density (mA·cm-2), measured by 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: Optical power density of monochromatic light (mW·cm-2);
λ: Wavelength of monochromatic light.
It should be noted that in the calculation of IPCE/EQE, the Faradaic efficiency η is assumed to be 100%, meaning that all generated photogenerated electrons are used for the production of the target product. IPCE measurements allow the application of bias, while no bias is allowed in STH measurements in photocatalysis.
Quantum Efficiency in Photocatalytic Experiments
2. Internal Quantum Efficiency (IQE), also known as Absorbed Photon-to-Current Efficiency (APCE)[1]: The ratio of the number of electrons generated by photons of a specific wavelength to the number of absorbed photons, essentially representing quantum efficiency. The formula for calculation is as follows:
A: Absorbance of the reaction system.
EQE/IPCE and IQE/APCE are primarily used in photocatalytic 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.
Quantum Efficiency in Photocatalytic Experiments
3. Applied Bias Photon-to-Current Efficiency (ABPE)[1]: Under certain bias conditions, the proportion of input solar energy converted into hydrogen energy[1]. Unlike STH, ABPE is the energy conversion efficiency that deducts the contribution of electrical energy.
Vredox: Thermodynamic potential (V) of the reaction, in the case of water splitting, Vredox=1.23 V;
Vapp: Applied bias (V) relative to the counter electrode, should be less than 1.23 V;
ηF: Faradaic efficiency for H₂ generation;
Plight: Optical power density of AM 1.5G standard solar spectrum (100 mW·cm-2).
The above content describes the definitions and calculation methods of common activity evaluation parameters in photocatalysis research, known as quantum yields. In the study of photocatalytic water splitting, we most commonly use AQY and STH as quantum yields. In the study of photocatalytic water splitting, the most commonly used quantum yields are IPCE and STH or ABPE. In summary, efficiency emphasizes specific wavelength incident light, while yield emphasizes monochromatic light. EQE/IPCE emphasizes incident light, while 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. Journal of Materials Research, 2010, 25, 3.
