Selective CO₂ Reduction to CO in Water using Earth-Abundant Metal and Nitrogen-Doped Carbon Electrocatalysts

TY - JOUR

T1 - Selective CO2 Reduction to CO in Water using Earth-Abundant Metal and Nitrogen-Doped Carbon Electrocatalysts

AU - Hu, Xin-Ming

AU - Hval, Halvor Hoen

AU - Bjerglund, Emil Tveden

AU - Dalgaard, Kirstine Junker

AU - Madsen, Monica Rohde

AU - Pohl, Marga-Martina

AU - Welter, Edmund

AU - Lamagni, Paolo

AU - Buhl, Kristian Birk

AU - Bremholm, Martin

AU - Beller, Matthias

AU - Pedersen, Steen Uttrup

AU - Skrydstrup, Troels

AU - Daasbjerg, Kim

PY - 2018/7/6

Y1 - 2018/7/6

N2 - Earth-abundant transition metal (Fe, Co, or Ni) and nitrogen-doped porous carbon electrocatalysts (M-N-C, where M denotes the metal) were synthesized from cheap precursors via silica-templated pyrolysis. The effect of the material composition and structure (i.e., porosity, nitrogen doping, metal identity, and oxygen functionalization) on the activity for the electrochemical CO 2 reduction reaction (CO 2RR) was investigated. The metal-free N-C exhibits a high selectivity but low activity for CO 2RR. Incorporation of the Fe and Ni, but not Co, sites in the N-C material is able to significantly enhance the activity. The general selectivity order for CO 2-to-CO conversion in water is found to be Ni > Fe ≥ Co with respect to the metal in M-N-C, while the activity follows Ni, Fe ≥ Co. Notably, the Ni-doped carbon exhibits a high selectivity with a faradaic efficiency of 93% for CO production. Tafel analysis shows a change of the rate-determining step as the metal overtakes the role of the nitrogen as the most active site. Recording the X-ray photoelectron spectra and extended X-ray absorption fine structure demonstrates that the metals are atomically dispersed in the carbon matrix, most likely coordinated to four nitrogen atoms and with carbon atoms serving as a second coordination shell. Presumably, the carbon atoms in the second coordination shell of the metal sites in M-N-C significantly affect the CO 2RR activity because the opposite reactivity order is found for carbon supported metal meso-tetraphenylporphyrin complexes. From a better understanding of the relationship between the CO 2RR activity and the material structure, it becomes possible to rationally design high-performance porous carbon electrocatalysts involving earth-abundant metals for CO 2 valorization.

AB - Earth-abundant transition metal (Fe, Co, or Ni) and nitrogen-doped porous carbon electrocatalysts (M-N-C, where M denotes the metal) were synthesized from cheap precursors via silica-templated pyrolysis. The effect of the material composition and structure (i.e., porosity, nitrogen doping, metal identity, and oxygen functionalization) on the activity for the electrochemical CO 2 reduction reaction (CO 2RR) was investigated. The metal-free N-C exhibits a high selectivity but low activity for CO 2RR. Incorporation of the Fe and Ni, but not Co, sites in the N-C material is able to significantly enhance the activity. The general selectivity order for CO 2-to-CO conversion in water is found to be Ni > Fe ≥ Co with respect to the metal in M-N-C, while the activity follows Ni, Fe ≥ Co. Notably, the Ni-doped carbon exhibits a high selectivity with a faradaic efficiency of 93% for CO production. Tafel analysis shows a change of the rate-determining step as the metal overtakes the role of the nitrogen as the most active site. Recording the X-ray photoelectron spectra and extended X-ray absorption fine structure demonstrates that the metals are atomically dispersed in the carbon matrix, most likely coordinated to four nitrogen atoms and with carbon atoms serving as a second coordination shell. Presumably, the carbon atoms in the second coordination shell of the metal sites in M-N-C significantly affect the CO 2RR activity because the opposite reactivity order is found for carbon supported metal meso-tetraphenylporphyrin complexes. From a better understanding of the relationship between the CO 2RR activity and the material structure, it becomes possible to rationally design high-performance porous carbon electrocatalysts involving earth-abundant metals for CO 2 valorization.

KW - CO2 reduction

KW - CO2-TO-CO CONVERSION

KW - DIOXIDE

KW - ELECTROCHEMICAL REDUCTION

KW - ELECTROREDUCTION

KW - HIGHLY EFFICIENT

KW - IMMOBILIZATION

KW - IRON

KW - ORGANIC FRAMEWORKS

KW - OXYGEN REDUCTION

KW - SITES

KW - carbon

KW - electrocatalysis

KW - iron/cobalt/nickel doping

KW - structure-activity relationship

UR - https://www.scopus.com/pages/publications/85049743689

U2 - 10.1021/acscatal.8b01022

DO - 10.1021/acscatal.8b01022

M3 - Journal article

SN - 2155-5435

VL - 8

SP - 6255

EP - 6264

JO - ACS Catalysis

JF - ACS Catalysis

IS - 7

ER -