Strategic catalyst modification for boosting CO2 concentration at electrode surface and easing selective CO2 reduction at higher potential

Abstract

Electrochemical CO₂ reduction offers an efficient route to store renewable energy in the form of carbon-based fuels via hydrogenation, and thus ensures a net-zero carbon emission energy cycle. However, the search for highly stable and selective catalyst material with an acceptable current density for the CO₂ reduction reaction (CO₂RR) is ongoing. Therefore, the synthesis of novel materials or modifications of existing materials is one of the most pursued research subjects. Earth-abundant and environment-friendly low-cost 2D bismuth (Bi) with long-term stability casts a bright possibility in this regard with its high formate selectivity. Here, first, we demonstrated a controlled synthesis of (012) faceted 2D Bi flakes with uniform height via a chemical reduction of 2D BiOCl sacrificial template in a facile ambient atmosphere. These 2D Bi flakes were then deposited on carbon paper for electrochemical CO₂RR, which manifested the partial formate current density of 18.7 mA cm⁻² at −1.14 V_RHE, while chronoamperometry was performed in CO₂-saturated 0.5 M KHCO₃ electrolyte; a peak formate faradaic efficiency (FE) of ∼90% was observed at −0.84 V_RHE. Furthermore, we have demonstrated how the redox-active conducting polymer, polyaniline (PANI), which alone is not even active for CO₂RR, can significantly slow down the sharp drop in formate selectivity at higher potentials as compared to Bi flakes. When the 2D Bi flakes are soaked in PANI, the formate partial current density in chronoamperometry enhances to 35.5 mA cm⁻² at −1.14 V_RHE. Furthermore, we also correlated these phenomena in terms of different feasible mechanistic paths.