Synthesis and application of petal-shaped bismuth subcarbonate (Bi2O2CO3) by the immersion method

Abstract

Bismuth catalyst is a good candidate for producing formate (formic acid) via electro-chemical reduction of CO2. Also, it has known that various bismuth oxide derivatives are used to improve catalytic performance such as Bi2O3, BiOX (X is Cl, Br, I) and Bi2O2CO3. Among them, Bi2O2CO3 has a crystal structure of (Bi2O2)2+ layers interleaved by slabs comprising CO32- groups, and has various two-dimensional structures such as nanosheets or nanoflowers. In general, many studies have been performed as photocatalys ts for removing environmental pollutants, and recently, catalyst studies for generating for-mate by electrochemically reducing CO2 have been conducted. Thus the research on Bi2O2CO3 catalyst has become attractive because of these excel-lent catalytic properties. The fabrication method of Bi2O2CO3 materials is known to be in various ways: hydrothermal synthesis, Low temperature solution synthesis and electro-chemical exfoliation. However, all of these methods have additional post-processing steps to the formation of Bi2O2CO3. In addition, in the case of hydrothermal and electrochemi-cal exfoliation methods to use electrodes, since the catalyst is in powder form, a binder is also required, which is not advantageous for industrial use. In this work, we could confirm spontaneously formed petal-shaped Bi2O2CO3 by using the immersion method in CO2 saturated KHCO3 electrolyte at room temperature and we studied the formation mechanism of Bi2O2CO3. Bismuth was known to be easily oxidized in acidic solution environment. However, anyone never reported what is happening in CO2 saturated the KHCO3 electrolyte (pH: 6.77) used as CO2 reduction electrolyte at room temperature. We confirmed that redox reactions, such as corrosion, occurred simul-taneously on the surface of bismuth in CO2 saturated the KHCO3 electrolyte. Bismuth atoms were oxidized to form BiO+ ions and electrons and simultaneously oxygen dis-solved in the electrolyte is reduced to from OH- ions. Subsequently BiO+ react with CO32- dissolved in the electrolyte to form Bi2O2CO3. We used these principles and we have suc-cessfully fabricated petal-shaped Bi2O2CO3 (named petal-BOC) on various substrates us-ing the immersion method in CO2 saturated 0.1M KHCO3 electrolyte at room temperature without some post-processing step. To confirm the possibility of use as electrochemical catalysis and photoelectrochem-cal catalysis, the EC CO2RR and the PEC CO2RR measurements were conducted in H-type two compartment electrochemical cell using petal-shaped BOC and bismuth thin film cathode as the working electrode, applying a constant potential in the specific ranges. In particular, it can be used as an electrochemical CO¬2 reduction catalyst for the production of formate by growing petal-shaped bismuth carbonate on a conductive Cu substrate. Compared with the bismuth thin film, the electrochemical active area increased by about 6.45 times, and the formate faradaic efficiency of 95.9% at -0.8 VRHE showed a result of 4.8 mA/cm2. In addition, it was confirmed that the light transmittance of bismuth subcarbonate grown on the TiO2/p-Si substrate by the same immersion method increased with longer immersion time of the bismuth thin film. Compared with the bismuth thin film, it exhibited high photoelectrochemical CO¬2reduction characteristics due to increased surface area and increased light transmittance. At -0.5VRHE, the formate faradaic efficiency was about 95.12% and the current density was 4.54 mA/cm2.