At present stage, in the study of photocatalytic CO2 reduction, the reaction rate of the target product is still at the level of mmol·h-1·g-1, and the low reaction rate makes the experimental evaluation results of the photocatalyst activity susceptible to significant interference from external factors. Due to the photoinduced self-decomposition of organic solvent, sacrificant, photocatalyst and seal ring, the experimental results were biased. Based on recent studies, the author summarized the error sources in the evaluation of photocatalytic CO2 reduction activity at the present stage.
Photoinduced self-decomposition of solvent and sacrificial agent
The optimal photocatalyzed CO2 reduction reaction is to use water or water vapor as the electron donor . However, due to the slow kinetics of water oxidation half reaction (2H2O → 4e- + 4H+ + O2), the reaction rate of the whole photocatalyzed CO2 reduction reaction will be limited . In liquid phase photocatalytic CO2 reduction reaction system, sacrificial agents are often used to replace H2O as hole consumptive agents, such as triethanolamine (TEOA) [3, 4], triethanolamine (TEA) , isopropyl alcohol (IPA) [6, 7], etc.
In addition, in order to improve the solubility of CO2 in water, a certain amount of acetonitrile (ACN) [8, 9] or ethyl acetate (EAA)  is often added to the reaction system.
Figure 1. Schematic diagram of photocatalytic CO2 reduction 
Studies have shown that under the irradiation of specific wavelengths of light, several common sacrifice agents ACN, TEOA, TEA and EAA may self-decomposition, and the self-decomposition reaction of sacrifice agents will produce a certain amount of CO, CH4, C2H4 and H2 products. If the target products of photocatalytic CO2 reduction reaction are CO, CH4, C2H4 and H2 products, The gas generated by the self-decomposition reaction will seriously affect the accuracy of the detection of target gas products .
In addition, studies have shown that adding organic solvents or sacrificants into the photocatalytic CO2 reduction reaction system will not only affect the detection results of gas products, but also liquid products, especially alcohol products .
FIG. 2. Product formation rates under different conditions when ACN and EAA are used as solvents/sacrificial agents 
Photoinduced self-decomposition of photocatalysts
Graphite phase carbon nitride (g-C3N4) is a common visible light responsive photocatalyst, which has been widely used in photocatalytic CO2 reduction reaction [11, 12]. However, recent studies have shown that g-C3N4 will undergo photoinduced self-decomposition in gas-phase photocatalytic CO2 reduction reaction, resulting in CO, CO2, NO2 and other products, which seriously affect the experimental results of the evaluation of photocatalytic CO2 reduction reaction activity .
Figure 3. g-C3N4 decomposition in gas-solid phase photocatalytic CO2 reduction reaction and its confirmation 
Photoinduced self-decomposition of sealing ring
In addition to organic solvents, sacrificants and photocatalysts, photoinduced self-decomposition or thermal decomposition reactions may also occur in the sealing ring near the light window of the reactor or reaction system in the photocatalytic CO2 reduction reaction system.
Generally, in the photocatalytic reactor or reaction system, the main material of the sealing ring is NBR, silicone rubber or fluorine rubber. When these sealing rings use xenon lamp as the light source of the photocatalytic reaction, a certain amount of CH4 or CO will be produced, which will cause a certain degree of interference to the detection of the product.
Raw gas purity
Due to the purity of CO2 in the feedstock gas, there will be some hydrocarbons in the feedstock gas, which will affect the experimental results.
It is suggested to use 99.999% CO2 as the raw gas for photocatalytic CO2 reduction reaction。
The above part is the author according to the reference literature translation and summary, the author is limited, if there are mistakes, please correct!
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