(337c) Importance of Substrate Metals in Cu-Based Catalysts for Electroreduction of CO2

Importance of Substrate Metals in
Cu-based Catalysts for Electroreduction of CO₂

Alexandros
N. Karaiskakis,
Sujan Shrestha and Elizabeth J. Biddinger^*

Department
of Chemical Engineering, City College of New York, New York 10031(USA)

^*ebiddinger@che.ccny.cuny.edu

The utilization of carbon dioxide
to valuable carbon based fuels and chemicals through electrochemical reduction
combined with renewable resources could contribute to the achievement of a
carbon-neutral cycle. The biggest hindrances of CO₂ electrochemical
reduction are related with the characteristics of the electrocatalysts due to
their low performance¹
(catalyst activity, the product selectivity, the catalyst stability and
faradaic efficiency). Copper (Cu) is the only metal, until now, that was proven
to effectively yield hydrocarbons and alcohols².
Surface morphology³
attracts the efforts of recent research activity as a solution to the
aforementioned obstacles and in particular the switch from Cu foil to the
construction of Cu particle-based catalysts with higher surface area.

One way to change the morphology
of Cu particles is by changing the substrate they grow on. The electrochemical
techniques used for the growth of Cu particles use Cu as substrate.  In this
report, the Cu-based catalysts were constructed with electrodeposition on
different substrates metals (Cu, Ni, Ti), and their reduction efficiency of CO₂
and products selectivity were investigated. Two main deposition parameters were
evaluated: the charge (Q) of the Cu deposited on the substrate metals and the
potential during the deposition. A range of charge (1.5C to 15C) was used
representing the film thickness of Cu deposited and a potential range (-0.6V to
-1V), which influences the size of the Cu particles⁴.

The evaluation of each catalyst
involved the examination of surface morphology, the efficiency during the CO₂
reduction, and the products selectivity evaluation. For that purpose, scanning
electron microscopy (SEM), X-ray diffraction (XRD) and capacitance measurements with cyclic voltammetry were used. The products analysis was conducted with micro gas spectrometry
(microGS) for gas products and with high pressure liquid chromatography (HPLC)
for liquid products.

The results of the optimal experimental
conditions regarding the performance of the catalysts are presented under the
use of cyclic voltammograms in CO₂-saturated electrolyte. The
following order of overpotential reduction occurred: Cu/Ni> Cu/Cu> Cu/Ti
> Cu foil based on the observed potentials for specific current density. Surface
evaluation experiments gave the following roughness factor order: Cu/Ni> Cu/Cu
> Cu/Ti> Cu foil.  From XRD experiments performed for copper characterization
under same deposition conditions (-1V and Q= 15C), the results illustrate that
Cu crystal orientation is dependent upon the electrodeposition substrate; Cu/Cu
gave Cu (111) and Cu (200), whereas Cu/Ti and Cu/Ni gave Cu (111) and Cu (220). 
The impact of the changes in substrate material on CO₂
electroreduction performance and suggestions for further modifications to the
Cu electrocatalyst will be presented.

(1)          Qiao, J.; Liu, Y.; Hong, F.; Zhang, J. Chemical
Society Reviews 2014, 43, 631.

(2)          Hori, Y. In Modern Aspects of Electrochemistry;
Vayenas, C. G., White, R. E., Gamboa-Aldeco, M. E., Eds.; Springer: New York,
2008; Vol. 42.

(3)          Tang, W.; Peterson, A. A.; Varela, A. S.; Jovanov,
Z. P.; Bech, L.; Durand, W. J.; Dahl, S.; Norskov, J. K.; Chorkendorff, I. Physical
Chemistry Chemical Physics 2012, 14, 76.

(4)          Zhang, Q. B.; Hua, Y. X. Physical Chemistry
Chemical Physics 2014, 16, 27088.