Modulating the Cu (111) facet for selective CO2 electroreduction via tuning the oxidation state of polyaniline

Abstract

Polyaniline (PANI) can molecularly modify metallic copper to enhance CO₂ electrochemical reduction (CO₂ECR) performance by interacting with CO₂ molecules and intermediates and optimizing the catalyst structure. Here, we report a new role of PANI, where its oxidation state, tuned by electrodeposition conditions, influences the growth of nanocrystals of Cu (111) facets by Cu²⁺ adsorption on –N sites in the quinoid structure, thereby affecting the CH₄ selectivity during CO₂ECR. This Cu-PANI catalyst is prepared by sequentially electrodepositing PANI and Cu on carbon paper. X-ray absorption spectroscopy confirms that all catalysts contain metallic Cu⁰ with similar coordination environments. The CH₄ selectivity correlates with the Cu (111) facet exposure, which is influenced by the oxidation degree of PANI as well as the size of the deposited Cu. In situ Raman spectroscopy reveals that the sample with an optimal PANI oxidation state (Cu-PANI-48) exhibits the strongest *CO and *COH signals, matching its highest CH₄ selectivity. This work introduces a facile approach for tuning the oxidation degree of a conducting polymer to modulate Cu facet growth, which offers a new platform to achieve synergetic CO₂ adsorption and design selective CO₂ECR catalysts.