In this article, authors demonstrated a temperature effect to electrochemical CO2RR performance in Cu-based MEA electrolyzer, and found that heating method strongly affects product selectivity. Authors used some techniques (for example, in situ ATR SEIRAS) to prove the points. The results are helpful to others especially practical implementations of CO2 electrolysis but some questions remained. I recommend a major revision.
1. Authors used CO as feeding gas and conducted the in situ ATR SEIRAS experiments at different reaction temperatures. In CO saturated aqueous 0.1 M KHCO3, will the solubility of CO decrease with increasing temperature? The CO coverage variation may relate to the changing CO solubility. The results conducted in the same CO concentration could be more plausible.
2. In the IR spectra, the legend should be “Absorbance” not “Transmittance”. In Figure 9, which product does green dot represent?
3. Authors mentioned that “Lower current densities tended to favor higher crossover to the anode” and gave a reference, however, in ref. 30, the authors mostly discussed about the electrode factor and haven’t given conclusion about current density. According to Fick’s first and second law, the crossover of products relates to products concentration and electrolysis duration. Authors should give more experiments and discussion on the temperature effect to the diffusion balance between cathodic and anodic products concentration to support that “temperature rise may represent a strategy to concentrate ethanol at the cathode compartment”.
4. In Figure S17, the stability tests of AEMs only lasted no more than 2 hours, but the duration of MEA electrolyzer stability test in Figure 9 is 50 hours. The membrane stability test results in short-term electrolysis are not reliable in the long-term electrolysis. The stability test of the membrane should be conducted at the same conditions and duration as electrolysis.
5. During electrolysis, the water concentration in anode is much higher than cathode. Thus, according to the Fick’s laws, the water in the anode would inevitably crossover to the cathode in long-term electrolysis which could result in water flooding. In Page 7, authors concluded that water flooding leads to HER and also gave the conclusion of high RH of CO2 inhibits HER. They are paradoxical.
6. The electrolyte penetration rate should be supplemented.
7. The curves of temperature variation against electrolysis duration by three different heating methods should be given to support the point of “heating method impact”.
8. In long-term electrolysis under industrially relevant current density, the membrane may degrade faster at high temperatures. Also, authors mentioned that electrode substrate of the anode was carbon paper, which is terribly instable. In 50-hour electrolysis, the anode substrate can be seriously oxidized. Not only the products selectivity, but also the electrolyzer components after electrolysis need to be shown to convince the long-term stability.

revision is decent