Spontaneous hydrogen gas evolution from in-situ iron-nickel sulfides (FexNi(1−x)S) under ambient alkaline conditions

Abstract The Iron-Sulfur World Hypothesis, a hypothesis for the origin of life on early Earth, posits that hydrogen generation from sulfide minerals such as iron sulfide was the first step in the origin of life. This study investigated whether hydrogen evolution from sulfide minerals is possible at room temperature and atmospheric pressure, without application of any external potential. The spontaneous hydrogen evolution reaction by iron-nickel sulfide Fe x Ni (1− x ) S, which is instantaneously generated by injecting a precursor of iron-nickel sulfide into a batch reactor under alkaline anoxic conditions at room temperature and atmospheric pressure, was confirmed by analyzing the composition of the reactor headspace gas. Gas evolution analysis showed that a significant amount of H 2 was produced, which was influenced by the Fe content, with the maximum level observed in FeS without the injection of Ni-containing precursors. Structural characterization using X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) confirmed the presence of amorphous and nanocrystalline phases, highlighting the influence of composition and synthesis conditions on the reactivity of the material. These findings provide insight into the H 2 evolution from iron-nickel sulfides under anoxic, alkaline conditions and represent an important experimental demonstration of spontaneous abiotic H 2 generation under geochemically relevant ambient conditions.