Search

The electrochemical CO2 reduction reaction (CO2RR) to controllable chemicals is considered as a promising pathway to store intermittent renewable energy. Herein, a set of catalysts based on copper-nitrogen-doped carbon xerogel (Cu-N-C) are successfully developed varying the copper amount and the nature of the copper precursor, for the efficient CO2RR. The electrocatalytic performance of Cu-N-C materials is assessed by a rotating ring-disc electrode (RRDE), technique still rarely explored for CO2RR. For comparison, products are also characterized by online gas chromatography in a H-cell. The as-synthesized Cu-N-C catalysts are found to be active and highly CO selective at low overpotentials (from −0.6 to −0.8 V vs. RHE) in 0.1 M KHCO3, while H2 from the competitive water reduction appears at larger overpotentials (−0.9 V vs. RHE). The optimum copper acetate-derived catalyst containing Cu-N4 moieties exhibits a CO2-to-CO turnover frequency of 997 h−1 at −0.9 V vs. RHE with a H2/CO ratio of 1.8. These results demonstrate that RRDE configuration can be used as a feasible approach for identifying electrolysis products from CO2RR.

Fig. S1. STEM (left) and TEM (right) images of Cu-N-C-Ac2 acquired using a Tecnay F30 microscope (300 kV). Fig. S2. XRD pattern of Cu-N-C-Ac2-3h obtained using the same experimental details than for Cu-N-CAc2 but with a lixiviation treatment of 3 hours. Fig. S3. N1s XPS spectra of the Cu-N-C. The material Cu-N-C-Ac1-BPT before the two-step post-treatment (acid leaching and 2nd carbonization) is also included for comparison purposes. Fig. S4. Effect of the two-step post-treatment (acid leaching and 2nd carbonization) on the nitrogen adsorption-desorption isotherms for Cu-N-C-Ac1. Fig. S5. Correlation between the Cu oxidation state and the energy position of the XANES spectrum, determined as the first maximum of the first derivative spectrum of Cu-N-C-Ac0.5 (red circle) and different copper reference compounds (black circles).Fig. S6. Variation with time of pH of the electrolyte (0.1 M KHCO3 aqueous solution) as a function of CO2 partial pressure. Balance with an inert gas for the equilibrium CO2 (aq) + H2O ↔ HCO3– + H+, pKa = 6.4, room temperature, 1 atm total pressure. Fig. S7. Oxidation of formic acid and methanol at the Pt ring of an RRDE, disc turned off, 1600 rpm. Fig. S8. Comparison of the CV in 0.1 M KHCO3 saturated with N2 (blue curve), methane oxidation voltammogram after saturation of the electrolyte with CH4 at the open circuit potential (red curve) and CH4 stripping voltammogram (Ead = 0.4 V vs. RHE, green curve) at the Pt ring of an RRDE, disc turned off, 1600 rpm. CV conditions from 0.05 to 1.6 V vs. RHE, 50 mV s-1. Room temperature. Fig. S9. CVs of the disc at 50 mV s-1 and 1600 rpm in CO2-saturated 0.1 M KHCO3 of Cu-N-C catalysts. Fig. S10. Chronoamperometric experiments at the disc for the Cu-N-C catalysts. Electrolyte: Fig. S11. CVs at the platinum ring for disc potentials reported in the legend. Table S1. Bulk chemical composition (wt. %) from EA and ICP of Cu-N-C electrocatalysts before and after the two-step post-treatment (acid leaching and 2nd