Designing Undercoordinated Ni–N<sub><i>x</i></sub> and Fe–N<sub><i>x</i></sub> on Holey Graphene for Electrochemical CO<sub>2</sub> Conversion to Syngas
Josh Leverett, Rahman Daiyan, Lele Gong, Kevin Iputera, Zizheng Tong, Jiangtao Qu, Zhipeng Ma, Qingran Zhang, Soshan Cheong, Julie M. Cairney, Ru‐Shi Liu, Xunyu Lu, Zhenhai Xia, Liming Dai, Rose Amal
Abstract
In this study, we propose a top-down approach for the controlled preparation of undercoordinated Ni–Nx (Ni-hG) and Fe–Nx (Fe-hG) catalysts within a holey graphene framework, for the electrochemical CO2 reduction reaction (CO2RR) to synthesis gas (syngas). Through the heat treatment of commercial-grade nitrogen-doped graphene, we prepared a defective holey graphene, which was then used as a platform to incorporate undercoordinated single atoms via carbon defect restoration, confirmed by a range of characterization techniques. We reveal that these Ni-hG and Fe-hG catalysts can be combined in any proportion to produce a desired syngas ratio (1–10) across a wide potential range (−0.6 to −1.1 V vs RHE), required commercially for the Fischer–Tropsch (F–T) synthesis of liquid fuels and chemicals. These findings are in agreement with our density functional theory calculations, which reveal that CO selectivity increases with a reduction in N coordination with Ni, while unsaturated Fe–Nx sites favor the hydrogen evolution reaction (HER). The potential of these catalysts for scale up is further demonstrated by the unchanged selectivity at elevated temperature and stability in a high-throughput gas diffusion electrolyzer, displaying a high-mass-normalized activity of 275 mA mg–1 at a cell voltage of 2.5 V. Our results provide valuable insights into the implementation of a simple top-down approach for fabricating active undercoordinated single atom catalysts for decarbonized syngas generation.