1. Thank you very much Chairman. Good afternoon,
Today I’d like to talk about the electrochemical carbon dioxide conversion into formate using a catholyte-free method
as a strategy to overcome the CO2 solubility problem.

2. Since it was mentioned in the previous talk, I will briefly introduce about the electrochemical conversion.
Nowadays, many people interested in the CO2 conversion technology.
In particular, the electrochemical CO2 conversion using renewable electricity is regarded as a promising way to reduce carbon emissions and produce valuable products.

3. Because, it has several advantages and can produces various chemicals with different catalyts.

4. Among the various products, formic acid and carbon monoxide have been particular attention over the past few years
Because those are the only profitable products under current technology level.
However, those are not enough to consume a huge amounts of CO2. Thus conversion technology into commodity chemicals which have large market size is required.
Recently, many efforts has been reported to synthesize C2 and C3+ compounds such as ethylene and propnanol.

5. in recent years, the field has advanced remarkably with the development of new catalysts, which provide better selectivities and efficiencies.
Many results have been reported including size & composition effects, oxide-derived materials, metal & metal oxides as well as mechanism study.

6. The challenges in electrochemical co2 conversion are the reducing OP, and the increasing FE, EE, CD & durability.
For the formate synthesis, remarkable improvement has been reported in recent years for OP, FE, and EE.
Despite these significant results, the current density is still limited by poor transport of CO2,

7. This limitation is due to the low solubility of CO2 in the catholyte, which significantly limits the current density.
In addition, the mass transfer overpotential & electrolyte resistance increase the cell potential and reduce the energy efficiency.
Furthermore, the liquid electrolytes have to be separated for product recovery.

8. Some efforts have been reported to overcome the solubility problems using GDE system.
Castillo et al.[5] achieved a high current density and formate concentration using GDE system. But they still suffered from a high cell voltage of 3.7 V, a low FE of 70 %, and the need for product separation.

9. We proposed a facile strategy of catholyte-free method that can avoid the solubility problems by introducing a water vapor instead of bulk catholyte.
This improves the reaction rate & EE by reducing the mass transfer OP & electrolyte ressistance
In addition, concentrated liquid products can be obtained as 1-path product, because very small amount of water vapor is used for the reaction.

10. This is the construction of full flow cell system, and this shows the configuration of the unit cell.
Aqueous anolyte was used for anode and CO2 gas was supplied to the cathode channel through a bubble-type humidifier.
The gas & liquid products were analyzed by GC & LC respectively.

11. Here we can see the benefits of CF method
Here we can see the benefits of CF method. These graphs show the electrolytic performances with the reaction temperature.
As you can see, in the traditional method using aq. Catholyte, the FE, PCD and Conc are decreased by temperature.
While in the case of CF method, high FEs are maintained at a high temp., the CD was increased with temperature.
Moreover, the formate concentration was increased by hundreds times than the traditional case.
This clearly shows that the cathode reaction~~~~

12. The vapor supply was determined by the temperature of a bubble-type humidifier. Thus the formate concentration can be controlled by the amount of vapor supply,
By reducing the vapor supply, very high formate concentration of g L-1 was obtained with high FE about 78%.

13. The performances of CF-CO2R also depend on the applied cell voltage.
The maximum FE of 95.0% was obtained at a low cell voltage of 2.1 V, at which the highest energy efficiency of 64.7% was achieved.
In addition, a low cell overpotential of 0.67V was observed, inclucing anodic & cathodic overpotentials.

14. This slide shows the effect of gas diffusion layer property.
GDL is the medium for mass & electron transfer to the catalyst layer.
Thus the GDL should ensure sufficient supply of gaseous reactants & release of liquid products.
Especially, it is required to ensure the pathways of gaseous reactants by preventing the GDL getting wet.
We carried out the electrolysis using tinned mesh, CP with 0% wp, 40% wp, and hydrophobic microporous layer.
This result shows that the hydrophobicity of GDL has a great influence on the electrolysis performance.

15. This shows the FE and formate CD with different CO2 partial pressures.
The CF-CO2R exhibits high FE about 80% even at a low CO2 partial pressure of 30 kPa.
Although the formate current density decreased by the partial pressure,
this result shows the possibility of direct conversion of CO2 to formate from emission sources without co2 capture.

16. As I mentioned in the introduction, securing the durable performance is also very important issue.
(A few result has been reported for the degradation of performances.)
(In which the electrochemical damages result in the pulverization of Sn particles.)
(And the physical damages due to the liquid flow & HER result in loss of catalyst.)
After electrolysis during 48h, a high FE of 91.2% was stably maintained in the CF system, but the FE was decreased from 68% to 32% for the conventional system.
This stable performance of the CF system is due to the low cell potential and the absence of liquid flow. (which reduce the EC & PHY damages on the catalyst layer)

17. Today I introduced the CF method for formate production.
I think this will be very useful for the synthesis of other liquid products also as well as formate.

19. Although an aqueous solution of KHCO3 is the most commonly used catholyte for CO2R, the aqueous bicarbonate ions (HCO3-) are not stable and the decomposition of bicarbonate occurs at about 373 K by following reaction.
2 KHCO3 → K2CO3 + CO2 + H2O
It is considered that the use of KHCO3 solution is not suitable for the experiment investigating reaction temperature effects.
In addition, comparable performances have been reported for the aqueous solution of KCl as a catholyte in the literature.