Periodic Reporting for period 1 - GDYNRR (Site-Specific Heteroatoms Doped Graphdiyne as Metal-Free Electrocatalysts for Nitrogen Reduction)
Okres sprawozdawczy: 2021-08-01 do 2023-07-31
Ammonia is an important energy carrier and fertilizer feedstock for many industries and household chemicals. Currently, the large-scale production of ammonia is predominantly achieved by the energy- and capital-intensive Haber−Bosch process, which consumes 1% of the total energy production and results in 1.4% of the global CO2 emissions. Electrocatalytic ammonia production by using N-containing species has recently attracted great interests owing to the mild conditions and high compatibility with renewable electricity.[3] Compared to N2 with high dissociation energy (945 kJ mol-1) and low water solubility (Henry’s constant 0.62 mM bar-1 at 25 °C), nitrate (NO3-) is considered an attractive nitrogen precursor for NH3 electrosynthesis because of its low dissociation energy of the N=O bond (204 kJ mol-1), high water solubility (3.8 M at 25 °C as KNO3) and wide distribution as pollutant in wastewater.
As the conversion of NO3−-to-NH3 involves a complex nine-proton coupled eight-electron transfer and multiple reaction pathways, the precise design of selective catalysts towards NH3 is considerably challenging. Noble-metal based catalysts especially ruthenium oxides/alloys have shown great promise in nitrate reduction (NO3RR), but the low abundance and high price severely restrict their large-scale application. Copper-based materials have recently appeared at the forefront of NO3RR due to the high abundance, strong adsorption of NO3− and favorable conversion from NO3−-to-NO2−.Nevertheless, the sequential hydrogenation process of NO2- under the assistance of Cu is poor due to the weak adsorption of active atom hydrogen (H*), which leads to a low selectivity and activity towards NH3. Therefore, developing novel Cu-based catalysts which couple the favorable conversion of nitrate to nitrite and the facilitation of subsequent hydrogenation is highly necessary.
The overall objective of this project is to develop novel Cu-based catalysts which couple the favorable conversion of nitrate to nitrite and the facilitation of subsequent hydrogenation for high activity and selectivity towards NH3.In addition, the catalysts will be integrated in a functional device to test the performance under industrial relevant conditions.
As the conversion of NO3−-to-NH3 involves a complex nine-proton coupled eight-electron transfer and multiple reaction pathways, the precise design of selective catalysts towards NH3 is considerably challenging. Noble-metal based catalysts especially ruthenium oxides/alloys have shown great promise in nitrate reduction (NO3RR), but the low abundance and high price severely restrict their large-scale application. Copper-based materials have recently appeared at the forefront of NO3RR due to the high abundance, strong adsorption of NO3− and favorable conversion from NO3−-to-NO2−.Nevertheless, the sequential hydrogenation process of NO2- under the assistance of Cu is poor due to the weak adsorption of active atom hydrogen (H*), which leads to a low selectivity and activity towards NH3. Therefore, developing novel Cu-based catalysts which couple the favorable conversion of nitrate to nitrite and the facilitation of subsequent hydrogenation is highly necessary.
The overall objective of this project is to develop novel Cu-based catalysts which couple the favorable conversion of nitrate to nitrite and the facilitation of subsequent hydrogenation for high activity and selectivity towards NH3.In addition, the catalysts will be integrated in a functional device to test the performance under industrial relevant conditions.
In this project, we prepared CuxO/N-doped graphdiyne (CuxO/N-GDY) with pyridine N configuration in one pot. Benefiting from the synergistic effect of pyridinic N in GDY and CuxO, the prepared CuxO/N-GDY tested in commercial H cell achieved a faradaic efficiency of ~85.0% towards NH3 at -0.5 V vs RHE with a production rate of ~342 μmol h-1 mgcat-1 in 0.1 M KNO3. The CuxO/NGDY was then integrated in an anion exchange membrane flow electrolyzer. A maximum Faradaic efficiency of ~89% was achieved at a voltage of 2.3 V and the production rate was ~1700 umol h-1 mgcat-1 at 3.3 V in 0.1 M KNO3 at ambient temperature. Operation at higher temperature improved the overall reaction kinetics of NO3- reduction but lowered the maximum faradaic efficiency to 66.7% towards NH3. This work has been submitted to Anew. chem. int.Ed.
This work provides a straightforward method for the synthesis of hybrid catalysts on the basis of pyridine N-doped carbon materials, paving the way for new designs of cheap and efficient NO3RR catalysts, which thus has a very strong potential to positively impact the development of ammonia production. In addition, the high selectivity and production rate in the device configuration demonstrates its great potential towards industrial application, which is a big step towards the industrialization for the production of NH3.