Morphology and Strain Engineering of Cu-based Materials by Chemical Dealloying for Electrochemical CO Reduction

TL;DR

This study investigates how tuning the morphology and chemistry of nanoporous copper via chemical dealloying affects its efficiency in electrochemical CO reduction, using advanced in situ characterization techniques.

Contribution

It introduces a novel in situ method to analyze nano-ligament chemistry and strain, revealing the relationship between surface strain and catalytic performance.

Findings

Optimal ligament surface strain enhances CO reduction efficiency.

In situ synchrotron XRD and cryo-APT reveal phase transformations during dealloying.

Nanoporous Cu outperforms polycrystalline Cu in electrochemical CO reduction.

Abstract

Nanoporous Cu (NPC), synthesized by chemical dealloying of brass, holds significant potential for catalysis of electrochemical CO2 and CO reduction, owing to the optimal binding energy of Cu with *CO and *H intermediates, and the abundance of surface under-coordinated atoms inherent to the nanoporous structure. However, further optimization of NPC morphology and chemistry for CO reduction can only be made possible by understanding the dealloying process. Hence overcoming challenges concerning the direct measurement of atomic scale chemistry and under-coordinated atoms in NPC nano-ligaments is vital. In this study, NPC with tunable ligament sizes between nanometer and micrometer range were synthesized by varying the temperature of Cu20Zn80 (atomic ratio) chemical dealloying in concentrated phosphoric acid. The evolution of chemistry and structure of nano-ligaments during dealloying were probed for the first time using in situ synchrotron X-ray diffraction (XRD) and cryo-atom probe tomography (APT) revealing the phase transformations and complex chemistry in nano-ligaments. A method based on the asymmetricity of synchrotron XRD peaks of NPC samples was also proposed to estimate the quantity of under-coordinated atoms on nano-ligaments, as ligament surface strain. Finally, CO reduction using electrochemistry mass spectrometry (EC-MS) demonstrated the promising performance of NPC compared to polycrystalline Cu. An optimal ligament surface strain value was also observed for the CO reduction on NPC, which provides more mechanistic insights into the complicated CO reduction process and an alternative strategy for Cu-based catalysts engineering. This work also shows how the application of synchrotron X-ray diffraction and EC-MS facilitates more efficient and accurate optimization of copper-based catalysts for electrochemical CO reduction.