Monitoring chalcogenide ions-guided in situ transform active sites of tailored bismuth electrocatalysts for CO2 reduction to formate

Abstract

Although bismuth catalysts enable accelerated electrochemical CO₂-to-formate conversion, the intrinsic active sites and forming mechanisms under operating conditions remain elusive. Herein, we prepared Bi₂O₂NCN, Bi₂O₃, and Bi₂O₂S as precatalysts. Among them, Bi₂O₂NCN-derived catalyst possesses optimum performance of electrochemical CO₂-to-formate, exhibiting an upsurge of Faradaic efficiency to 98.3% at -0.6 V vs. reversible hydrogen electrodes. In-situ infrared and electrochemical impedance spectra trace and interpret the superior performance. Multimodal structural analyses utilizing quasi-in-situ X-ray diffraction, in-situ X-ray absorption near edge structure and in-situ Raman spectra provide powerful support to monitoring the catalysts' in-situ transforms to metallic Bi, identifying the formation of the active sites influenced by the chalcogenide ions-guided: Carbodiimide promotes to form of the dominant Bi(003) facet exposure, which distinguishes from sulfide- and oxide-preferred dominant Bi(012) facets exposure. Concurrently, theoretical insights garnered from multiscale/multilevel computational analyses harmoniously corroborate the experimental findings. These findings show the pivotal role of chalcogenide in tailoring bismuth electrocatalysts for selective CO₂ reduction to formate, illuminating the significance of controlling structural chemistry in designing catalysts toward high-efficiency renewable energy conversion.

Keywords: CO2 reduction to formate; chalcogenide ions-guided; in-situ transform; tailored bismuth electrocatalysts.

Fig. 1.

Electrochemical performance of CO₂RR-to-formate and electrochemical analysis. (A) FE at –0.6 V vs. RHE of Bi(O), Bi(NCN), and Bi(S) in the flow-type cell. (B) ECSA of Bi(O), Bi(NCN), and Bi(S). (C) Nyquist plots at –0.6 V vs. RHE with the insert equivalent circuit and fitting data of Bi(O), Bi(NCN), and Bi(S). (D–F) Potential-dependent in-situ (D) Nyquist plots, (E) Bode phase plots, and (F) ATR-IR spectra of Bi(NCN).

Fig. 2.

Potential-dependent in-situ investigations on dynamic evolution of the catalysts. (A–C) Potential-dependent XRD patterns of Bi(O), Bi(NCN), and Bi(S). (D and E) TEM images with lattice planes of Bi(NCN) and Bi(S). (F and G) Potential-dependent in-situ XANES Bi L₃-edge spectra and the corresponding contour-map of the first derivative of Bi(NCN). (H and I) Potential-dependent in-situ Raman spectra and the corresponding contour-map of Bi(NCN).

Fig. 3.

Schematic illustration and characterization of structural transforms. (A) Schematic illustration of the chalcogenide ions-guided in-situ structural reconstructions of the tailored bismuth catalysts for electrochemical CO₂RR-to-formate. (B–D) Time-dependent XRD patterns of (B) Bi(NCN), (C) Bi(O), and (D) Bi(S).

Fig. 4.

Monitoring the operando transforming process. (A–G) In-situ XANES Bi L₃-edge spectra and the corresponding contour maps of the first derivative of Bi(NCN), Bi(O), and Bi(S). (G–L) In-situ Raman spectra and the corresponding contour maps of Bi(NCN), Bi(O), and Bi(S).

Fig. 5.

Theoretical insights garnered from multiscale/multilevel computational analyses. (A–C) Theoretical atomic models under various views, charge density difference plots for the interfaces and electron density distribution of (A) Bi₂O₂NCN, (B) *Bi₂O₂, and (C) Bi, in the rearrangement of the atoms during the reduction procedure, where the atom’s colors of black, blue, red, and light blue spheres represent C, N, O, and Bi, respectively. (D–F) The calculated PDOS of (D) Bi₂O₂NCN, (E) *Bi₂O₂ and (F) Bi with aligned Fermi level. (G–I) Plots of RDF and CN with aligned the distance between the atoms for (G) Bi₂O₂NCN, (H) *Bi₂O₂, and (I) Bi. (J–L) Variations of temperature and energy against the time for the AIMD simulations of (J) Bi₂O₂NCN, (K) *Bi₂O₂, and (L) Bi for structural stability analyses, the simulation was run under 500 K for 10 ps with a time step of 1 fs.