[M-IS08] Astrobiology

[MIS08-P01] Nickel incorporation into fresh iron sulfide precipitates modulates selectivity in nitrite and carbon dioxide reduction

*Felipe Garibello¹, Shawn E McGlynn¹ (1.Institute of science tokyo)

Keywords:Mackinawite, Catalytst, Reductant

Nickel and iron sulfide minerals are abundant in natural systems and co-precipitate in various forms, making a significant contribution to Earths biogeochemical cycles. These metals also play crucial roles in the active centers of metalloenzymes, facilitating essential biochemical reactions, and have been proposed as potential reductants, catalysts and proto-enzymes in the emergence of life. Here, we examined differences in the capability of co-precipitated nickel and iron sulfides to both catalyse and directly reduce carbon dioxide, nitrite and protons. These differences were correlated to the structure of the sulfides, which was probed by X-ray absorption spectroscopy (XAS) at the Ni and Fe K-edges, as well as the composition of the sulfides. The materials were prepared using FeCl₂4H₂O (p.a., 98.0%) and NiCl₂ 6H₂O (p.a.,99.9%) solutions containing Ni²⁺ and Fe²⁺ precursor in different compositions. At low Ni²⁺:Fe²⁺ ratios, nickel substitutionally dopes the mackinawite (FeS_m) crystal structure forming [Ni_nFe_m]S_x materials, while high amounts of the Ni²⁺ precursor suppress the precipitation of iron sulfides and induce the formation of distinct NiS2-like materials. When compared to FeS_m, samples with a higher nickel content exhibit higher catalytic activity for both CO₂ reduction and proton reduction to H₂ by sulfide, as well as stronger reducing capability towards NO₂^-. In contrast, high iron content favoured the catalytic reduction of NO₂^- by Fe²⁺while suppressing the reduction of protons to hydrogen gas. This contrast in reactivity implies the involvement of distinct reaction mechanisms for these reduction processes. These reactions correlate with how biology uses the metals with nature using Ni for both H₂ evolution and CO₂ reduction.