Unlocking the Potential of Bi2S3-Derived Bi Nanoplates: Enhanced Catalytic Activity and Selectivity in Electrochemical and Photoelectrochemical CO2 Reduction to Formate

Abstract

Various electrocatalysts are extensively examined for their ability to selectively produce desired products by electrochemical CO₂ reduction reaction (CO₂RR). However, an efficient CO₂RR electrocatalyst doesn't ensure an effective co-catalyst on the semiconductor surface for photoelectrochemical CO₂RR. Herein, Bi₂S₃ nanorods are synthesized and electrochemically reduced to Bi nanoplates that adhere to the substrates for application in the electrochemical and photoelectrochemical CO₂RR. Compared with commercial-Bi, the Bi₂S₃-derived Bi (S-Bi) nanoplates on carbon paper exhibit superior electrocatalytic activity and selectivity for formate (HCOO^-) in the electrochemical CO₂RR, achieving a Faradaic efficiency exceeding 93%, with minimal H₂ production over a wide potential range. This highly selective S-Bi catalyst is being employed on the Si photocathode to investigate the behavior of electrocatalysts during photoelectrochemical CO₂RR. The strong adhesion of the S-Bi nanoplates to the Si nanowire substrate and their unique catalytic properties afford exceptional activity and selectivity for HCOO^- under simulated solar irradiation. The selectivity observed in electrochemical CO₂RR using the S-Bi catalyst correlates with that seen in the photoelectrochemical CO₂RR system. Combined pulsed potential methods and theoretical analyses reveal stabilization of the OCHO* intermediate on the S-Bi catalyst under specific conditions, which is critical for developing efficient catalysts for CO₂-to-HCOO^- conversion.

Keywords: Bi nanoplates; CO2 reduction; formate production; photoelectrochemical reaction; silicon nanowires.

Figure 1

a) SEM and b) TEM image of Bi₂S₃ nanorods. c) TEM‐EDS elemental distributions of Bi₂S₃ and corresponding distributions of Bi (green) and S (red). XRD patterns of d) Bi₂S₃ and e) S‐Bi/CP. f) SEM and g) TEM images of S‐Bi nanoplates. h) TEM‐EDS elemental distributions of S‐Bi and corresponding distributions of Bi (green) and S (red). i) In situ Raman spectra of Bi₂S₃/CP as a function of the applied potentials in the CO₂‐saturated 0.1 m KHCO₃ electrolyte.

Figure 2

E‐CO₂RR efficiency of S‐Bi/CP and commercial‐Bi/CP in 0.1 m KHCO₃. a) CVs of S‐Bi/CP (red) and commercial‐Bi/CP (black) in CO₂‐saturated electrolyte (scan rate: 10 mV s⁻¹). b) Faradaic efficiency of S‐Bi/CP (blue: HCOO⁻, red: CO, green: H₂) depending on applied potentials. c) Faradaic efficiency and d) partial current density of HCOO⁻ using S‐Bi/CP (red) and commercial‐Bi/CP (black). e) Chronoamperometric measurement and Faradaic efficiency of S‐Bi/CP at an applied potential of −1.4 V versus RHE over 20 h.

Figure 3

DFT‐optimized structures of a) pristine Bi surface, and defective Bi surfaces with b) mono‐vacancy and c) di‐vacancy. The Bi vacancy site (V_Bi) is highlighted by a blue dashed circle. d) Free‐energy diagrams for CO₂RR to generate formate and HER on the pristine Bi surface (pink line) and the defective surfaces (green line for mono‐vacancy surface and blue line for di‐vacancy surface). OCHO adsorption structures of e) pristine Bi surface, and defective Bi surfaces with f) mono‐vacancy and g) di‐vacancy. The green, red, gray, and white balls represent Bi, O, C, and H, respectively.

Figure 4

Electronic structure and bonding analysis. a) Density of states (DOS) for pristine Bi surface (top), mono‐vacancy Bi surface (middle), and di‐vacancy Bi surface (bottom). b) Projected crystal orbital Hamilton population (pCOHP) analysis depicting the bonding characteristics of OCHO when adsorbed on each Bi surface.

Figure 5

a) Schematic of the fabrication of the S‐Bi/SiNWs photocathode. b) XRD pattern and c) cross‐sectional SEM image of S‐Bi/SiNWs at low and (inset) high magnifications.

Figure 6

PEC‐CO₂RR efficiency of S‐Bi/SiNWs and SiNWs in 0.1 m KHCO₃ under light irradiation (light intensity: 100 mW cm⁻²). a) LSVs in CO₂‐saturated electrolyte (scan rate: 10 mV s⁻¹). b) Faradaic efficiency (blue: HCOO⁻, red: CO, green: H₂) of S‐Bi/SiNWs depending on applied potentials. c) Comparison of the partial current density of HCOO⁻ for S‐Bi/CP (black) and S‐Bi/SiNWs (red). d) Stability of S‐Bi/SiNWs at −0.8 V versus RHE and the corresponding Faradaic efficiency. e) Schematic of applied constant potential (blue) and pulsed potential (yellow). f) Consecutive Faradaic efficiency (blue: HCOO⁻, red: CO, green: H₂) of S‐Bi/SiNWs during alternating pulsed potential cycles (E _−1.4 V = 3 s, E_{0 .1 V} = 1 s) and constant potential (E _−1.4 V) measurements. g) Schematic of the proposed CO₂ reduction mechanism during the pulsed potential and constant potential electrolysis.