Bismuthene for highly efficient carbon dioxide electroreduction reaction

Abstract

Bismuth (Bi) has been known as a highly efficient electrocatalyst for CO₂ reduction reaction. Stable free-standing two-dimensional Bi monolayer (Bismuthene) structures have been predicted theoretically, but never realized experimentally. Here, we show the first simple large-scale synthesis of free-standing Bismuthene, to our knowledge, and demonstrate its high electrocatalytic efficiency for formate (HCOO^-) formation from CO₂ reduction reaction. The catalytic performance is evident by the high Faradaic efficiency (99% at -580 mV vs. Reversible Hydrogen Electrode (RHE)), small onset overpotential (<90 mV) and high durability (no performance decay after 75 h and annealing at 400 °C). Density functional theory calculations show the structure-sensitivity of the CO₂ reduction reaction over Bismuthene and thicker nanosheets, suggesting that selective formation of HCOO^- indeed can proceed easily on Bismuthene (111) facet due to the unique compressive strain. This work paves the way for the extensive experimental investigation of Bismuthene in many different fields.

Fig. 1. Characterization of monolayer Bi nanosheets (Bismuthene).

a−c Typical TEM images. Scale bar in (a): 500 nm; scale bar in (b): 200 nm; scale bar in (c): 50 nm. d Typical HRTEM image; scale bar: 2 nm. e FFT of (d). f Typical atomic force microscopy (AFM) image. g The corresponding height profiles for three Bismuthene nanosheets marked in (f). h Typical lateral HAADF-STEM image of a Bismuthene nanosheet, directly showing the single-atom thickness of the layer with zig-zag structure.

Fig. 2. Physical characterization of Bismuthene.

a High-resolution Bi 4f XPS spectra before and after 75-h CO2RR process at −0.58 V. b Raman spectrum of fresh metallic Bismuthene nanosheets.

Fig. 3. Electroreduction of CO₂ to formic acid on BiNSs.

a pH-corrected linear sweep voltammetric curves (LSV) in the CO₂ saturated (solid line pH 7.2) and N₂ saturated (dash line pH 8.8) 0.5 M KHCO₃ aqueous solution with the same Bi loading of 0.39 mg/cm² on glassy carbon electrode. b Comparison of Faradaic efficiencies for formate at each applied potential for BiNSs with different thicknesses. c Charging current density differences Δj plotted against scan rates on BiNSs with different thickness for the calculation of ECSA. d Tafel plots of the partial HCOO⁻ current density for BiNSs with different thicknesses. e Nyquist plots for BiNSs with different thicknesses. The dotted curves are the fittings. f Long-term stability of Bismuthene nanosheets (0.65 nm) at a potential of −0.58 V and the corresponding FEs for HCOO⁻ and H₂. All the error bars in (b, c) represent the standard error of the mean.

Fig. 4. BP-induced enhancement of CO2RR performance on Bismuthene.

a SEM image of the transect to show the compact catalyst layer of Bismuthene nanosheets on carbon paper electrode. b Partial current density for HCOO⁻ (j_HCOO-) versus potential on Bismuthene and Bismuthene@BP (with BP 3 wt.% optimally). c SEM image of the transect to show the noncompact catalyst layer of Bismuthene@BP on carbon paper electrode. The arrows in (a, c) indicate the thickness difference of the catalyst layers with the same mass loading, scale bars in (a, c): 1.0 μm. d ECSA measurement for both pure Bismuthene and Bismuthene@BP. All the error bars in (d) represent the standard error of the mean.

Fig. 5. DFT calculations.

a, b Calculated free energy diagrams for CO2RR and HER on (111) single-atom-thick Bismuthene (a) and (011) thick Bi nanosheets (b) at 0.0 V. HER is represented in green, and CO2RR through OCHO* and COOH* are represented in blue and orange, respectively. The state of CO* + OH* is represented in red. The insets below the diagrams depict the adsorption structures of OCHO* and H*. Violet, red, gray, and white spheres in the insets represent Bi, O, C, and H atoms, respectively.