Sequential co-reduction of nitrate and carbon dioxide enables selective urea electrosynthesis

Sequential co-reduction of nitrate and carbon dioxide enables selective urea electrosynthesis

02 January 2024 | Yang Li, Shisheng Zheng, Hao Liu, Qi Xiong, Haocong Yi, Haibin Yang, Zongwei Mei, Qinghe Zhao, Zu-Wei Yin, Ming Huang, Yuan Lin, Weihong Lai, Shi-Xue Dou, Feng Pan, Shunning Li
This study reports a novel catalyst design that enables high selectivity for urea electrosynthesis by sequentially reducing nitrate (NO3−) and carbon dioxide (CO2) at a dynamic catalytic center. The catalyst, a nitrogen-doped carbon (NC) material, facilitates the spontaneous switch between NO3− and CO2 reduction paths through reversible hydrogenation on nitrogen functional groups. This sequential reduction strategy significantly reduces competition between the two parallel reduction reactions, enhancing the formation of urea. The NC catalyst demonstrates a high urea yield rate of 596.1 μg mg−1 h−1 with a Faradaic efficiency of 62% under -0.5 V versus reversible hydrogen electrode (RHE). In situ spectroscopic techniques and theoretical calculations support the findings, revealing that the proton-involved dynamic catalyst evolution mitigates the reduction of reactants and minimizes side product formation. The sequential reduction mechanism is further elucidated through operando attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and in situ Raman characterization, confirming the role of C=N-H species in the catalytic process. This work provides a promising strategy for designing highly selective catalysts for urea electrosynthesis, offering a sustainable approach to energy conservation and CO2 fixation.This study reports a novel catalyst design that enables high selectivity for urea electrosynthesis by sequentially reducing nitrate (NO3−) and carbon dioxide (CO2) at a dynamic catalytic center. The catalyst, a nitrogen-doped carbon (NC) material, facilitates the spontaneous switch between NO3− and CO2 reduction paths through reversible hydrogenation on nitrogen functional groups. This sequential reduction strategy significantly reduces competition between the two parallel reduction reactions, enhancing the formation of urea. The NC catalyst demonstrates a high urea yield rate of 596.1 μg mg−1 h−1 with a Faradaic efficiency of 62% under -0.5 V versus reversible hydrogen electrode (RHE). In situ spectroscopic techniques and theoretical calculations support the findings, revealing that the proton-involved dynamic catalyst evolution mitigates the reduction of reactants and minimizes side product formation. The sequential reduction mechanism is further elucidated through operando attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and in situ Raman characterization, confirming the role of C=N-H species in the catalytic process. This work provides a promising strategy for designing highly selective catalysts for urea electrosynthesis, offering a sustainable approach to energy conservation and CO2 fixation.
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