5:15 PM - 7:15 PM
[U12-P09] Theoretical understanding of electroreduction of carbon dioxide on partially reduced nickel sulfides
Keywords:First-principles calculation, electrochemical reduction, Surface structure
It is still ambiguous how the chemical reaction proceeded before emergence of life. Among various possible environments, we focus on deep-sea hydrothermal vent, which consists of a chimney made from sulfide minerals and hot water that passes through it. The hot water contains hydrogen and other gases, which is oxidized in the inner wall of the chimney to generate electrons. The electrons are transferred through the conductive sulfides to the outer wall, where electroreduction of the sulfide minerals and/or molecules in seawater. In laboratory experiments, we revealed that heazlewoodite (Hzl, Ni3S2) can be partially electroreduced to metal (PERM), and the Hzl_PERM acts as an electrocatalyst to reduce carbon dioxide and to synthesize thioacetate ester [1,2]. Similarly, FeS_PERM acts as ammonia storage in deep-sea environment [3]. However, it is generally difficult to infer the reaction kinetics and the required conditions in ancient environments from experimental facts because of the limitation in experimental duration and the detection efficiency. Here we performed first-principles calculations of Hzl_PERM to elucidate the possible structure of PERM in atomic level and the energetics of CO2 electroreduction to CO. Since the reaction depends on co-existing metal species, one Ni was substituted to V to Zn and the adsorption energy was discussed.
We used Vienna ab-initio simulation package (VASP) to simulate the structure using Perdew-Bruke-Ernzerhof (PBE) density functional with Grimme’s dispersion correction (D3) and projector augmented wave method. Electroreduction of Hzl starts from hydrogen chemisorption of S terminals. The reduction was simulated as removal of a hydrogen sulfide from the H-capped Hzl, which required 2.1 eV energy. On the other hand, removal of second hydrogen sulfide proceeded with less energy of 1.4 eV. This result suggests that the reduction preferentially proceeds from surface defects or mineral edges, and that the reduction is accelerated to form partially metallic domain, which corresponds to the induction period of reduction and the appearance of metallic Ni in X-ray diffraction. The Ni-Ni distance of Hzl_PERM was 2.3 Å, which was smaller than that in crystal (2.5 Å). The adsorption of CO and CO2 was the most stable at the reduced Ni sites. Similarly, the reactivity of Ni was investigated when the second- to third-layer Ni in Hzl_PERM was substituted to V–Zn. It is known that Co-Ni sulfide had the highest electroreduction efficiency among pairs of Fe–Ni. The most stable adsorption was achieved when Ni in the second layer was substituted to Co, or when Ni in the third layer was substituted to V. The substitution by Cr or Zn suppressed CO adsorption on doubly reduced PERM than on PERM with one sulfide removed. This result qualitatively matched with the experimental results, and suggests other possibilities of mineral pair.
This study was supported by JSPS KAKENHI JP21H04527, and JP22H05153. All the theoretical calculations were performed on Earth Simulator 4 in JAMSTEC.
[1] Kitadai, N. et al. Metals likely promoted protometabolism in early ocean alkaline hydrothermal systems. Sci. Adv. 5, (2019).
[2] Kitadai, N. et al. Thioester synthesis through geoelectrochemical CO 2 fixation on Ni sulfides. Commun Chem 4, 37 (2021).
[3] Takahagi, W. et al. Extreme accumulation of ammonia on electroreduced mackinawite: An abiotic ammonia storage mechanism in early ocean hydrothermal systems. Proc. Natl. Acad. Sci. 120, e2303302120 (2023).
We used Vienna ab-initio simulation package (VASP) to simulate the structure using Perdew-Bruke-Ernzerhof (PBE) density functional with Grimme’s dispersion correction (D3) and projector augmented wave method. Electroreduction of Hzl starts from hydrogen chemisorption of S terminals. The reduction was simulated as removal of a hydrogen sulfide from the H-capped Hzl, which required 2.1 eV energy. On the other hand, removal of second hydrogen sulfide proceeded with less energy of 1.4 eV. This result suggests that the reduction preferentially proceeds from surface defects or mineral edges, and that the reduction is accelerated to form partially metallic domain, which corresponds to the induction period of reduction and the appearance of metallic Ni in X-ray diffraction. The Ni-Ni distance of Hzl_PERM was 2.3 Å, which was smaller than that in crystal (2.5 Å). The adsorption of CO and CO2 was the most stable at the reduced Ni sites. Similarly, the reactivity of Ni was investigated when the second- to third-layer Ni in Hzl_PERM was substituted to V–Zn. It is known that Co-Ni sulfide had the highest electroreduction efficiency among pairs of Fe–Ni. The most stable adsorption was achieved when Ni in the second layer was substituted to Co, or when Ni in the third layer was substituted to V. The substitution by Cr or Zn suppressed CO adsorption on doubly reduced PERM than on PERM with one sulfide removed. This result qualitatively matched with the experimental results, and suggests other possibilities of mineral pair.
This study was supported by JSPS KAKENHI JP21H04527, and JP22H05153. All the theoretical calculations were performed on Earth Simulator 4 in JAMSTEC.
[1] Kitadai, N. et al. Metals likely promoted protometabolism in early ocean alkaline hydrothermal systems. Sci. Adv. 5, (2019).
[2] Kitadai, N. et al. Thioester synthesis through geoelectrochemical CO 2 fixation on Ni sulfides. Commun Chem 4, 37 (2021).
[3] Takahagi, W. et al. Extreme accumulation of ammonia on electroreduced mackinawite: An abiotic ammonia storage mechanism in early ocean hydrothermal systems. Proc. Natl. Acad. Sci. 120, e2303302120 (2023).