17:15 〜 19:15
[U12-P07] Elucidating key parameter of electrochemical N2 reduction on metal sulfide to ammonia
The chemical evolution hypothesis for the origin of life requires that compounds important for life’s metabolism be synthesized from simple molecules. Among those molecules, ammonia, NH3/NH4+, is one of the important molecules as a building block of nitrogen-containing biomolecules like nucleic acid. Because metal sulfide minerals are widely distributed at the deep-sea floors, they could have worked as reaction sites/catalysts for nitrogen conversion, which contributed to the emergence of life. Especially, based on the knowledge that electrical power is generated at the hydrothermal vent (R. Nakamura et al., Angew. Chem., 2010, 122, 7858), it is important to investigate electrochemical nitrogen conversion activity of metal sulfide minerals to get insight about how chemical evolution has been proceeded.
Here in this work, we examined electrochemical N2 reduction activity of metal sulfide minerals for NH3 synthesis. Furthermore, we adapted machine-learning technique to clarify which physicochemical properties of metal sulfides are key parameter to achieve high NH3 synthesis activity.
We synthesized 18 kinds of metal sulfides (Ag2S, CdS, CoS2, CuS, Cu2S, FeS2 (Marcasite and Pyrite), In2S3, MnS, MoS2, NiS2, NiS, PbS, SnS, SnS2, WS2, and ZnS (Sphalerite and Wurtzite)) using hydrothermal method and characterized them with X-ray diffraction, Scanning Electron Microscopy observation, and elemental analysis. The characterization results indicated that all the samples were single phase. Those samples were subjected to electrochemical test using flow reactor under N2 flow.
As for the NH3 generation activity, metal sulfide with layered structure such as SnS2 and WS2 demonstrated higher activity, while other layered metal sulfides like SnS and MoS2 exhibited lower activity.
To clarify the relationship between physicochemical properties of metal sulfides and observed NH3 generation rate, multi-regression analysis was conducted using Gradient-Boosted Decision Tree model. Among 15 parameters considered, it revealed that absolute electron negativity and maximum metal-sulfur-metal bonding angle largely affected the NH3 generation rate. Namely, to achieve high NH3 generation rate, larger absolute electron negativity and smaller maximum meta-sulfur-metal bonding angle are necessary.
In summary, higher electrochemical N2 reduction activity to NH3 was observed on SnS2 and WS2. Machine learning technique revealed that absolute electron negativity and maximum metal-sulfur-metal bonding angle were key parameters to achieve higher NH3 generation rate. Results in this work show the possibility that N2 was electrochemically reduced to ammonia on metal sulfide minerals and it contributed to the emergence of life.
Here in this work, we examined electrochemical N2 reduction activity of metal sulfide minerals for NH3 synthesis. Furthermore, we adapted machine-learning technique to clarify which physicochemical properties of metal sulfides are key parameter to achieve high NH3 synthesis activity.
We synthesized 18 kinds of metal sulfides (Ag2S, CdS, CoS2, CuS, Cu2S, FeS2 (Marcasite and Pyrite), In2S3, MnS, MoS2, NiS2, NiS, PbS, SnS, SnS2, WS2, and ZnS (Sphalerite and Wurtzite)) using hydrothermal method and characterized them with X-ray diffraction, Scanning Electron Microscopy observation, and elemental analysis. The characterization results indicated that all the samples were single phase. Those samples were subjected to electrochemical test using flow reactor under N2 flow.
As for the NH3 generation activity, metal sulfide with layered structure such as SnS2 and WS2 demonstrated higher activity, while other layered metal sulfides like SnS and MoS2 exhibited lower activity.
To clarify the relationship between physicochemical properties of metal sulfides and observed NH3 generation rate, multi-regression analysis was conducted using Gradient-Boosted Decision Tree model. Among 15 parameters considered, it revealed that absolute electron negativity and maximum metal-sulfur-metal bonding angle largely affected the NH3 generation rate. Namely, to achieve high NH3 generation rate, larger absolute electron negativity and smaller maximum meta-sulfur-metal bonding angle are necessary.
In summary, higher electrochemical N2 reduction activity to NH3 was observed on SnS2 and WS2. Machine learning technique revealed that absolute electron negativity and maximum metal-sulfur-metal bonding angle were key parameters to achieve higher NH3 generation rate. Results in this work show the possibility that N2 was electrochemically reduced to ammonia on metal sulfide minerals and it contributed to the emergence of life.