Electrochemical CO2 Reduction Activity of Reduced Copper Oxide Derived from Layered Copper Hydroxide with Different Interlayer Distance and Anion Species
Authors: Suda Yuya , Takimoto Daisuke , Hideshima Sho , Sugimoto Wataru 
Published: December 2020

Electrochemically reduced copper oxide (EC-CuOx) has attracted attention as an electrocatalyst to obtain C2 products with high selectivity via electroreduction of CO2. EC-CuOx is typically formed by chemically induce dissolution of copper oxide and subsequent electororeduction to metalic copper during the electrochemical CO2 reduction reaction (CO2RR). It is well known that the electronic state and morphology of electrocatalysts have a strong correlation to the catalytic activity. Although the effects of electronic state for the electrocatalyst for CO2RR have been studied, the morphological effects of EC-CuOx during and after CO2RR have not been discussed sufficiently.
In this study, we focused on layered copper hydroxides as a model electrocatalyst precursor to clarify the morphological effects. The interlayer distance of the layered copper hydroxide can be controlled through ion-exchange reactions while maintaining the morphology, crystallinity and crystal size in the lateral direction. The dissolution rate of copper ion from the host layer of layered copper hydroxide anticipated to differ due to the different interlayer distance of layered structures, leading to a difference in the accessibility of electrolyte. Based on the above hypothesis, three types of layered copper hydroxides with different interlayer distance were used as a model precursor for EC-CuOx.
The layered acetate copper hydroxide (AcO-Cu2(OH)3) intercalation compound was synthesized according to a previously-reported procedure1. In order to prepare the layered structure with different interlayer distances and anion species, AcO-Cu2(OH)3 was dispersed in an aqueous solution of sodium dodecyl sulfate or nitric acid, and consequently the layered dodecyl sulfate copper hydroxide (DS-Cu2(OH)3) and layered nitrate copper hydroxide (NO3-Cu2(OH)3) intercalation compounds were obtained. CO2RR measurements were conducted in a two-compartment electrochemical cell separated by a Nafion® N117 membrane. The gaseous products were quantified by gas chromatography (GC; Shimadzu Corporation, Nexis GC-2030).
SEM images show that after CO2RR, AcO-Cu2(OH)3 had needle-like morphology, while DS-Cu2(OH)3 and NO3-Cu2(OH)3 had dendritic and whisker-like morphology, respectively (Figure 1). The morphological changes during CO2RR were observed owing to the dissolution and electrodeposition of Cu-based compounds. The difference in morphology after CO2RR could be attributed to the difference of interlayer distances and anion species i.e. difference in accessibility of the inter layer. The Faradaic efficiency for ethylene production with DS-Cu2(OH)3 was ~60% at -1.4 V vs. RHE (Figure 2), which was twice higher than that for Cu(OH)2 particles (~30%). The results indicate that DS-Cu2(OH)3 with dendritic molphology possesses high selectivity for ethylene production.

Acknowledgement

DT thanks the partial support by The Public Foundation of Chubu Science and Technology Center.

References

S. Švarcová, M. Klementová, P. Bezdička, W. Śasocha, M. Dušek and D. Hradil, Cryst. Res. Technol., 46, 1051 (2011).

Figure 1