# Porous Electrodeposited Cu as a Potential Electrode for Electrochemical Reduction Reactions of CO2
## 3 Results and Discussions
### CO\({}_{2}\)RR Analysis
Considering the results in Figure 3, the chemical products and possible related cathodic reactions generated at the Cu electrodes under investigation include:  
\[\text{CO}_{2}+2\text{H}^{+}+2\text{e}^{-}\rightarrow\text{CO}_{\text{(g)}}+ \text{H}_{2}\text{O} \tag{4}\]  
\[2\text{CO}_{2}+10\text{H}^{+}+10\text{e}^{-}\rightarrow\text{CH}_{3}\text{CHO }_{\text{(aq)}}+3\text{H}_{2}\text{O} \tag{5}\]  
\[2\text{CO}_{2}+8\text{H}^{+}+8\text{e}^{-}\rightarrow\text{CH}_{3}\text{COOH }_{\text{(aq)}}+2\text{H}_{2}\text{O} \tag{6}\]  
\[3\text{CO}_{2}+16\text{H}^{+}+16\text{e}^{-}\rightarrow\text{CH}_{3}\text{ COCH}_{3\text{(aq)}}+5\text{H}_{2}\text{O} \tag{7}\]  
\[2\text{CO}_{2}+12\text{H}^{+}+12\text{e}^{-}\rightarrow\text{CH}_{5}\text{OH }_{\text{(aq)}}+3\text{H}_{2}\text{O} \tag{8}\]  
\[\text{CO}_{2}+2\text{H}^{+}+2\text{e}^{-}\rightarrow\text{HCOOH}_{\text{(aq)}} \tag{9}\]  
\[2\text{H}^{+}+2\text{e}^{-}\rightarrow\text{H}_{2\text{(g)}} \tag{10}\]  
It can be observed that all porous Cu specimens provided relatively high current density, signifying a faster rate of reduction reaction, as compared to the Cu foil. For all types of Cu electrodes under consideration, the products comprised those in gas and liquid forms. H2 was the major gas product found in all testing groups, whereas CO was detected only in the systems with porous Cu electrodes. The group C electrode in particular provided relatively high amounts of H2 and CO, approximately 3-4 times higher than that of other porous Cu groups. Furthermore, whereas the Cu foil electrode provided acetone, ethanol and formate, the use of electrocatalytic porous Cu resulted in additional chemical products not found from the Cu foil system, including acetaldehyde and acetate. The group B sample, specifically, provided the highest reduction current density, and gave both acetaldehyde and acetate, and relatively high selectivity of ethanol compared to other testing electrodes. The group A electrode also yielded comparatively high selectivity of ethanol, but acetaldehyde was not detected from this system. The group C electrode, on the other hand, is unique in its relatively high production rate of formate, compared to the other sample groups. From the results presented above, it is evidenced that the deposition of DHBT porous Cu influences both the electrochemical reduction rate of CO2 and selectivity of species of chemical products developed from the CO2 RR process. These improvements may stem from various factors related to the intricate structures of the porous Cu electrodes, as follows: (i) porous structures appear to promote the absorption of chemical species, including oxygen as noted previously. As demonstrated by [PERSON] et al. [2], [PERSON] et al. [12], and [PERSON] et al. [37], the surface of copper oxide thus formed can play a role in promoting the catalytic activity, owing to the development of a large number of active sites and roughening of the surface, following reduction of the oxide phase over the course of CO2 RR. Furthermore, the XPS analysis (Figure 5) signifies that porous Cu electrodes of different morphologies exhibit a variation of oxidation states of Cu on the surface (i.e., Cu\({}^{+}\)/Cu\({}^{2+}\)). The oxidation states of Cu are known to influence preferential formations of intermediates and hence affect the CO2 reduction pathways and promote selectivity [30; 34; 38]. In addition, (ii) the intricate structure of the porous Cu electrodes may enhance dynamic diffusion of the dissolved gas to provide increasing CO2 concentration at the catalytic electrode-electrolyte interface [12]. Temporal trapping of gaseous intermediates, e.g., CO,could also be induced inside the pores [2]. Furthermore, the high porosity of the porous Cu provides high surface areas and hence large active sites for the electrodes. Correspondingly, the retention time for CO2 RR could be effectively enlarged.