A high throughput optical method for studying compositional effects in electrocatalysts for CO2 reduction

Jeremy L Hitt,Thomas E Mallouk,Yuguang C Li,Songsheng Tao,Simon J L Billinge,Yue Gao,Zhifei Yan

doi:10.1038/s41467-021-21342-w

Abstract

In the problem of electrochemical CO2 reduction, the discovery of earth-abundant, efficient, and selective catalysts is essential to enabling technology that can contribute to a carbon-neutral energy cycle. In this study, we adapt an optical high throughput screening method to study multi-metallic catalysts for CO2 electroreduction. We demonstrate the utility of the method by constructing catalytic activity maps of different alloyed elements and use X-ray scattering analysis by the atomic pair distribution function (PDF) method to gain insight into the structures of the most active compositions. Among combinations of four elements (Au, Ag, Cu, Zn), Au6Ag2Cu2 and Au4Zn3Cu3 were identified as the most active compositions in their respective ternaries. These ternary electrocatalysts were more active than any binary combination, and a ca. 5-fold increase in current density at potentials of −0.4 to −0.8 V vs. RHE was obtained for the best ternary catalysts relative to Au prepared by the same method. Tafel plots of electrochemical data for CO2 reduction and hydrogen evolution indicate that the ternary catalysts, despite their higher surface area, are poorer catalysts for the hydrogen evolution reaction than pure Au. This results in high Faradaic efficiency for CO2 reduction to CO.

Highlights

In the problem of electrochemical CO2 reduction, the discovery of earth-abundant, efficient, and selective catalysts is essential to enabling technology that can contribute to a carbonneutral energy cycle
For the best ternary catalysts, we evaluated the alloying of elements by X-ray diffraction and pair distribution function (PDF) analysis to understand the relationship between alloy structure and catalytic activity
Arrays of multimetallic catalysts were robotically deposited onto Toray carbon paper to make an array working electrode, and the working electrode was assembled into a gas-fed, threeelectrode electrochemical cell that was fabricated by 3D printing

Summary

Introduction

In the problem of electrochemical CO2 reduction, the discovery of earth-abundant, efficient, and selective catalysts is essential to enabling technology that can contribute to a carbonneutral energy cycle. Because there are multiple reaction intermediates in the multi-electron, multiproton CO2 reduction reaction (CO2RR), and because their adsorption energies are linearly related, tuning a catalyst surface to optimize one reaction step simultaneously affects the other steps[6] Breaking this scaling relationship is one of the grand challenges in the development of better CO2RR catalysts. In exploring complex catalyst composition spaces that may include both alloying elements and surface-modifying molecules, high-throughput experimentation can often accelerate the process of catalyst discovery The utility of these methods has been demonstrated for several other problems in electrocatalysis, including methanol oxidation in direct methanol fuel cells[19,20], the oxygen reduction reaction[21], the oxygen evolution reaction[22,23,24], the hydrogen evolution reaction (HER)[25], and methane reforming[26]. For the best ternary catalysts, we evaluated the alloying of elements by X-ray diffraction and pair distribution function (PDF) analysis to understand the relationship between alloy structure and catalytic activity

Methods

Results

Conclusion