FeS_(2)/MoS_(2)纳米花异质结室温电催化固氮

FeS_(2)/MoS_(2) nano-flower heterojunction for electrocatalytic nitrogen fixation under environmental conditions

氨及其产物在储氢、农业和工业上都不可或缺,与此同时环境问题日益受到关注,二氧化碳零排放、低电能消耗的电催化固氮已经成为世界各国能源发展的重要战略目标.本工作中,从生物固氮酶中的Fe-Mo-S辅助因子获得灵感,一锅法合成了FeS_(2)/MoS_(2)双金属硫化物催化剂,用于电化学氮还原(NRR).FeS_(2)/MoS_(2)催化剂由纳米片构筑形成的纳米花形貌,增大了催化剂的活性表面积.并且FeS_(2)/MoS_(2)双金属硫化物之间的协同作用和异质界面有助于界面间电子转移,提高催化剂的活性.对FeS_(2)/MoS_(2)催化剂在0.1mol·L^(-1)HCl电解质中进行电化学氮还原测试,-0.2V(νs.RHE)下氨产率最高可达(11.3±0.18)μg·h^(-1)·mg^(-1),法拉第效率为(5.29±0.12)%.在酸性介质中既表现出良好的NRR活性也展示出极好的稳定性.这为进一步探索具有异质界面的双金属催化剂用于电化学氮还原反应提供了开阔的前景.

The industrial ammonia production method is generally the traditional Haber-Bosch process,but the high temperature and high pressure conditions have high requirements on equipment and process,and will cause a large number of carbon dioxide emissions,making the greenhouse effect more serious.Compared with traditional Haber-Bosch process,electrocatalytic nitrogen fixation(NRR reaction)has been widely concerned and studied for its low consumption and no pollution.However,N_(2) is not easy to be activated due to the low solubility of N_(2) and the fact that N≡N is relatively firm and not easy to be broken.In addition,both electrochemical nitrogen reduction reaction(NRR)and hydrogen evolution reaction(HER)are competitive reactions of electrode cathodes,so inhibition of HER competition is also the bottleneck.Ammonia yield and low Faraday efficiency are also problems existing in the research progress of NRR catalysts.In recent years,there are few studies on sulfide as NRR catalyst.Inspired by nitrogenase,MoS_(2)has been widely explored and studied in nitrogen reduction reaction.The theoretical and experimental results confirm that MoS_(2) has good NRR catalytic activity.In this work,FeS_(2)/MoS_(2) bimetallic sulfide catalyst was synthesized by one-pot method,mimicking Fe-Mo-S cofactor in biological nitrogenase,for NRR.The materials are characterized by X-ray powder diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).The structure of nano-flower and the construction of heterogeneous interfaces are proved by SEM and TEM.The highest ammonia yield is(11.3±0.18)μg·h^(-1)·mg^(-1)and the Faraday efficiency is(5.29±0.12)% at-0.2 V(νs.RHE).Different comparisons and control experiments are carried out to verify that the measured ammonia production is converted from FeS_(2)/MoS_(2) nitrogen to ammonia.N_(2)H_4 is the main by-product of NRR reaction.The yield of N_(2)H_4 measured by Watt and Chrisp methods is almost negligible compared with that of ammonia.Excellent stability is demonstrated by cyclic test and long time stability test in acidic medium.By comparing the SEM of FeS_(2) and MoS_(2),it is shown that FeS_(2)/MoS_(2) has better morphology of nano-flower.The large specific surface area can expose more active sites and the heterogeneous interface accelerates electron transport,which are conducive to improving the activity of the catalyst.We also compare the ammonia yield of FeS_(2),MoS_(2) and FeS_(2)/MoS_(2),which also confirmed this view.Nyquist diagram shows that FeS_(2)/MoS_(2) has low impedance and superior electrochemical kinetics.We synthesize FeS_(2)/MoS_(2) by one-step hydrothermal method,which provides a new idea for the exploration and development of NRR catalyst in the future.