TY - JOUR
T1 - Efficient CO2 to CO electrolysis on solid Ni-N-C catalysts at industrial current densities
AU - Moeller, Tim
AU - Ju, Wen
AU - Bagger, Alexander
AU - Wang, Xingli
AU - Luo, Fang
AU - Trung Ngo Thanh, null
AU - Varela, Ana Sofia
AU - Rossmeisl, Jan
AU - Strasser, Peter
PY - 2019/2
Y1 - 2019/2
N2 - The electrochemical CO 2 reduction reaction (CO 2 RR) to pure CO streams in electrolyzer devices is poised to be the most likely process for near-term commercialization and deployment in the polymer industry. The reduction of CO 2 to CO is electrocatalyzed under alkaline conditions on precious group metal (PGM) catalysts, such as silver and gold, limiting widespread application due to high cost. Here, we report on an interesting alternative, a PGM-free nickel and nitrogen-doped porous carbon catalyst (Ni-N-C), the catalytic performance of which rivals or exceeds those of the state-of-the-art electrocatalysts under industrial electrolysis conditions. We started from small scale CO 2 -saturated liquid electrolyte H-cell screening tests and moved to larger-scale CO 2 electrolyzer cells, where the catalysts were deployed as Gas Diffusion Electrodes (GDEs) to create a reactive three-phase interface. We compared the faradaic CO yields and CO partial current densities of Ni-N-C catalysts to those of a Ag-based benchmark, and its Fe-functionalized Fe-N-C analogue under ambient pressures, temperatures and neutral pH bicarbonate flows. Prolonged electrolyzer tests were conducted at industrial current densities of up to 700 mA cm -2 . Ni-N-C electrodes are demonstrated to provide CO partial current densities above 200 mA cm -2 and stable faradaic CO efficiencies around 85% for up to 20 hours (at 200 mA cm -2 ), unlike their Ag benchmarks. Density functional theory-based calculations of catalytic reaction pathways help offer a molecular mechanistic basis of the observed selectivity trends on Ag and M-N-C catalysts. Computations lend much support to our experimental hypothesis as to the critical role of N-coordinated metal ion, Ni-N x , motifs as the catalytic active sites for CO formation. Apart from being cost effective, the Ni-N-C powder catalysts allow flexible operation under acidic, neutral, and alkaline conditions. This study demonstrates the potential of Ni-N-C and possibly other members of the M-N-C materials family to replace PGM catalysts in CO 2 -to-CO electrolyzers.
AB - The electrochemical CO 2 reduction reaction (CO 2 RR) to pure CO streams in electrolyzer devices is poised to be the most likely process for near-term commercialization and deployment in the polymer industry. The reduction of CO 2 to CO is electrocatalyzed under alkaline conditions on precious group metal (PGM) catalysts, such as silver and gold, limiting widespread application due to high cost. Here, we report on an interesting alternative, a PGM-free nickel and nitrogen-doped porous carbon catalyst (Ni-N-C), the catalytic performance of which rivals or exceeds those of the state-of-the-art electrocatalysts under industrial electrolysis conditions. We started from small scale CO 2 -saturated liquid electrolyte H-cell screening tests and moved to larger-scale CO 2 electrolyzer cells, where the catalysts were deployed as Gas Diffusion Electrodes (GDEs) to create a reactive three-phase interface. We compared the faradaic CO yields and CO partial current densities of Ni-N-C catalysts to those of a Ag-based benchmark, and its Fe-functionalized Fe-N-C analogue under ambient pressures, temperatures and neutral pH bicarbonate flows. Prolonged electrolyzer tests were conducted at industrial current densities of up to 700 mA cm -2 . Ni-N-C electrodes are demonstrated to provide CO partial current densities above 200 mA cm -2 and stable faradaic CO efficiencies around 85% for up to 20 hours (at 200 mA cm -2 ), unlike their Ag benchmarks. Density functional theory-based calculations of catalytic reaction pathways help offer a molecular mechanistic basis of the observed selectivity trends on Ag and M-N-C catalysts. Computations lend much support to our experimental hypothesis as to the critical role of N-coordinated metal ion, Ni-N x , motifs as the catalytic active sites for CO formation. Apart from being cost effective, the Ni-N-C powder catalysts allow flexible operation under acidic, neutral, and alkaline conditions. This study demonstrates the potential of Ni-N-C and possibly other members of the M-N-C materials family to replace PGM catalysts in CO 2 -to-CO electrolyzers.
U2 - 10.1039/c8ee02662a
DO - 10.1039/c8ee02662a
M3 - Journal article
SN - 1754-5692
VL - 12
SP - 640
EP - 647
JO - Energy & Environmental Science
JF - Energy & Environmental Science
IS - 2
ER -