Coverage-driven selectivity switch from ethylene to acetate in high-rate CO2/CO electrolysis

Tuning catalyst microenvironments by electrolytes and organic modifications is effective in improving CO2 electrolysis performance. An alternative way is to use mixed CO/CO2 feeds from

incomplete industrial combustion of fossil fuels, but its effect on catalyst microenvironments has been poorly understood. Here we investigate CO/CO2 co-electrolysis over CuO nanosheets in

an alkaline membrane electrode assembly electrolyser. With increasing CO pressure in the feed, the major product gradually switches from ethylene to acetate, attributed to the increased CO

coverage and local pH. Under optimized conditions, the Faradaic efficiency and partial current density of multicarbon products reach 90.0% and 3.1 A cm−2, corresponding to a carbon

selectivity of 100.0% and yield of 75.0%, outperforming thermocatalytic CO hydrogenation. The scale-up demonstration using an electrolyser stack achieves the highest ethylene formation rate

of 457.5 ml min–1 at 150 A and acetate formation rate of 2.97 g min–1 at 250 A.

The data that support the findings of this study are available within the paper and the Supplementary Information. Other relevant data are available from the corresponding authors on

reasonable request. Source data are provided with this paper.

This work was supported by the National Key R&D Program of China (2021YFA1501503), the National Natural Science Foundation of China (22125205, 92045302, 22002155), Dalian National Laboratory

for Clean Energy (DNL201924, DNL202007), the ‘Transformational Technologies for Clean Energy and Demonstration’ Strategic Priority Research Program of the Chinese Academy of Sciences

(XDA21070613), the CAS Youth Innovation Promotion (Y201938), the Natural Science Foundation of Liaoning Province (2021-MS-022), the High-Level Talents Innovation Project of Dalian City

(2020RQ038) and the Photon Science Center for Carbon Neutrality. We thank J. Xiao at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, for fruitful discussion on the DFT

calculations.

These authors contributed equally: Pengfei Wei, Dunfeng Gao, Tianfu Liu.

State Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China

Pengfei Wei, Dunfeng Gao, Tianfu Liu, Hefei Li, Jiaqi Sang, Chao Wang, Rui Cai, Guoxiong Wang & Xinhe Bao

Conceptualization, G.W., X.B. Methodology, P.W., D.G., T.L., H.L., J.S., C.W., R.C. Investigation, P.W., H.L. Visualization, P.W., D.G., T.L. Funding acquisition, D.G., G.W., X.B.

Supervision, G.W., X.B. Writing (original draft), D.G., P.W., T.L. Writing (review and editing), D.G., P.W., T.L., G.W., X.B.

Nature Nanotechnology thanks Thomas Burdyny and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Molar percentage of (a) n-propanol, (b) ethanol and (c) acetate collected from cathode exhaust using cold trap in these liquid products (cathode/(cathode+anode)*100%), after galvanostatic

measurements over Cu nanoparticle catalyst in 0.1 M KOH under CO feed at 0.5, 1 and 1.5 A cm−2 for 4 h. Error bars represent the standard deviation from two independent measurements.

1H-NMR spectra (a–c) and concentrations (d–f) of n-propanol (a, d), ethanol (b, e) and acetate (c, f) of the anolyte after electro-oxidation control experiments conducted under reaction

conditions similar to that for CO2/CO electrolysis. The cathode and anode catalysts are Cu nanoparticle and Ir black, respectively. The anode electrolyte is 0.1 M KOH containing ethanol,

n-propanol and acetate with concentrations similar to the actual values at 1 A cm−2 (11 mM ethanol, 7.5 mM n-propanol and 54 mM acetate), 2 A cm−2 (23.5 mM ethanol, 9.2 mM n-propanol and 115

 mM acetate) and 3 A cm−2 (15 mM ethanol, 6 mM n-propanol and 186 mM acetate). The cathode is fed with Ar at a flow rate of 30 mL min−1. Only peaks assigned n-propanol, ethanol and acetate

as well as DSS internal standard are observed from the 1H-NMR spectra, indicating the absence of any liquid products from the electro-oxidation of n-propanol, ethanol and acetate. Error bars

represent the standard deviation from two independent measurements. The concentrations before and after electro-oxidation control measurements are the same at all applied current densities,

also indicating that n-propanol, ethanol and acetate would not be electrochemically oxidized under reaction conditions.

(a, c) Faradaic efficiency (left Y axis) and cell voltage (right Y axis) and (b, d) Full cell energy efficiency as a function of applied current density over CuO nanosheet catalyst measured

in (a, b) 0.1 M KOH under 0.6 MPa pure CO feed with a flow rate of 30 mL min−1 and (c, d) 1 M KOH under 0.6 MPa pure CO feed with a flow rate of 60 mL min−1. Error bars represent the

standard deviation from three independent measurements.

Product selectivity (left Y axis) and CO/CO2 conversion (right Y axis) as a function of applied current density over CuO nanosheet catalyst measured in 0.1 M KOH under (a) pure CO2 feed, (b)

CO/CO2 (1:3) co-feed, (c) CO/CO2 (1:1) co-feed, (d) CO/CO2 (3:1) co-feed, (e) pure CO feed, and (f) 0.6 MPa pure CO with a flow rate of 30 mL min−1, as well as 1 M KOH under 0.6 MPa pure CO

with a flow rate of 30 (g) and 60 (h) mL min−1. For pure CO2 electrolysis in (a), only C2+ products were accounted for the carbon selectivity. Error bars represent the standard deviation

from three independent measurements.

Stability test of CuO nanosheet catalyst at 1 A cm−2 measured in 1 M KOH under pure CO feed with a flow rate of 30 mL min−1.

CO2 distribution over CuO nanosheet catalyst measured in 0.1 M KOH under CO/CO2 (3:1) co-feed. CO2, CO32–, HCO3– in anode outlet solution were adsorbed and quantified by saturated Ba(OH)2

solution. CO2 in cathode outlet was quantified by on line GC. Most of CO2 is transferred to anode through carbonate crossover.

(a) Molar percentage of 12C–12C, 12C–13C and 13C–13C in the produced acetate over CuO nanosheet catalyst measured in 0.1 M KOH under different 13CO/CO2 co-feeds at 0.6 A cm−2. (b) Molar

percentage of CH3C16O16O−, CH3C16O18O− and CH3C18O18O− in the produced acetate over CuO nanosheet catalyst measured in 0.1 M KOH under pure C18O feed at 0.6 A cm−2.

(a) TEM image and (b) XRD pattern of Cu nanoparticles. (c–e) Faradaic efficiency (left Y axis) and cell voltage (right Y axis) as a function of applied current density over Cu nanoparticle

catalyst measured in 0.1 M KOH under (c) pure CO2 feed (30 mL min–1), (d) pure CO feed (60 mL min–1) and (e) 0.6 MPa CO feed (60 mL min–1). Error bars represent the standard deviation from

two independent measurements.

Photographs of (a) 100-cm2 gas diffusion electrode and (b) integrated electrolysis system used in this work. FE and cell voltage as a function of applied current density over CuO nanosheet

catalyst measured in (c, d) 0.1 M KOH under (c) pure CO2 feed and (d) CO/CO2 (3:1) co-feed as well as (e) 1 M KOH under pure CO feed. The KOH flow rate is 120 mL min–1, and the gas flow rate

is 750 mL min–1.

Single cell voltage (a, c) and ethylene Faradaic efficiency (b, d) for 4-cm2 and 100-cm2 electrolysers as well as an electrolyser stack with four 100-cm2 MEAs for (a, b) CO2 electrolysis

measured in 0.1 M KOH under pure CO2 feed and (c, d) CO electrolysis measured in 1 M KOH under pure CO feed, over CuO nanosheet catalyst.

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