Fig. 2.

Electrochemical carbon dioxide reduction measurements in the H-type cell. a Polarization curves of nanotube-derived Bi (NTD-Bi) in CO₂ or N₂-saturated electrolytes. b Chronoamperometric responses in CO₂-saturated electrolyte at different potentials as indicated. c Potential-dependent Faradaic efficiencies of HCOO⁻, CO, and H₂. d Formate partial current density derived from (b) and (c). e Long-term amperometric stability and corresponding selectivity change at −0.82 V. f Operando Bi L-edge XANES spectra of Bi₂O₃ nanotubes (NTs) at OCV and NTD-Bi at −0.24 V in comparison with Bi or Bi₂O₃ standards; inset plot is the partially enlarged spectra. g, h Fitting results of the operando EXAFS spectra to (g) R space and (h) K space