Single-Atoms Synthesized Via a Novel Method As the Active Site with Highly Selectivity Electrocatalytic Conversion of CO2 to Ethanol
Authors: Xu Haiping , Liu Di-Jia , Xu Tao 
Published: February 2020

Abstract

Single-atom catalysts (SACs) are recently emerging as a new frontier in heterogenous catalysis for their effectiveness in promoting catalytic reactions. We report herein the study of carbon-supported single-atom catalysts synthesized by a novelty method exhibit distinctive selectivity for some special electrochemical reactions during the electrolysis process. The aberration-corrected HAADF-STEM images combined with X-ray absorption spectroscopy identified the presence of single atoms. Theoretical density functional theory simulations of the best performing catalytic activity and selectivity could be attributed to the existence of single atoms in the catalysts.

Introduction

CO2 is a cheap resource of carbon that can be used as raw materials for fuel synthesis using renewable energy In 2005, 36.2 billion metric tons of CO2 was emitted to the atmosphere from anthropogenic sources, [1] which is corresponding to an increase in global mean temperature of around 0.1oC. New carbon capture, sequestration and conversion technologies are widely pursued as potential solutions to mitigate the concerns. The electrochemical CO2 reduction reaction (CO2RR) can combine carbon capture storage with renewable energy to convert CO2 into fuels and chemical feedstocks. Which is extraordinary significance for industry and is highly competitive with water electrolysis. Therefore, efficient electrocatalysts are required to reduce the reaction overpotential and improve the faradaic efficiency and selectivity for high value chemical products further. [2] The earth-rare, high price and low selectivity of precious metals prevent further large-scale commercial applications. Furthermore, these precious metal catalysts exhibit desirable products at highly cathodic potential window with high overpotential, which causes lot of energy consuming problem in application. Recently, single-atom catalysts (SACs) are emerging as a new frontier in heterogenous catalysis for their effectiveness in promoting catalytic reactions. [3] The unique electronic structure and unsaturated coordination environments in single atom catalysts (SACs) have been proven to enhance catalytic activity and excellent selectivity in a variety of reactions. In this work, the catalyst was prepared by a proprietary method currently under patent examination.

Results and Discussion

We report herein the study of carbon-supported SACs synthesized by a novel method that exhibit distinctive selectivity in electrochemical synthesis. The aberration-corrected HAADF-STEM images combined with X-ray absorption spectroscopy identified the presence of single atoms. Theoretical density functional theory simulations of the best performing catalytic activity and selectivity could be attributed to the existence of single atoms in the catalysts.
The prepared metal single atoms dispersed on substrate catalysts showed high faradaic efficiency and selectivity of CO2 to C2 products conversion with low onset potential. Fig. 1a shows linear sweep voltammetry (LSVs) over M/C-0.1 before and after chronoamperometry measurements at different potentials. CV curves (Figure 1b) also displayed obvious activity toward CO2RR in the potential range from 0.5 V to -1.5 V vs RHE, and the current density remained stable with no apparent decay before and after electrolysis in CO2 saturated KHCO3 solution. The FE reached to as high as ~91.8% for ethanol at a low potential of -0.6 V when the metal loading is 0.1 wt% on carbon support.

Figure 1.
Electrochemical CO2RR over M/C-0.1.

(a) LSV in a potential range of 0 to -1.5 V vs RHE in Ar and CO2 saturated 0.1 M KHCO3. (Scan rate: 50 mV s-1). (b) CV in a potential range of 0.5 to -1.5 V vs RHE in Ar and CO2 saturated 0.1 M KHCO3. (Scan rate: 50 mV s-1, (c) FEs of key byproduct as the function of potential over the catalysts of M/C-0.1

Significance

Understanding the role of metal single atoms on the CO2 electrochemical reduction reaction is fundamental for design of an appropriated catalyst for the large-scale application of CO2 RR that aims the production of high energy liquid chemicals.

References

[1] Chen, C., Khosrowabadi Kotyk, J. F., Sheehan, S. W., Chem. 4, 2571-2586, (2018).
[2] Zheng, X. L., Ji, Y. F., Tang, J., Wang, J. Y., Liu, B. F., Steinruck, H. G., Lim, K., Li, Y. Z., Toney, M. F., Chan, K. and Cui. Y. Nature Catalysis. 2, 55-61 (2019)
[3] Wang, A. Q., Li, J., Zhang, T. Nature Reviews. 2, 65-81 (2018)

Figure 1