A paper led by Masahiro Takano, investigating the reaction between high-pressure phases of FeS and hydrogen, has been published in ACS Earth and Space Chemistry.
Iron monosulfide (FeS) has long been considered a candidate host for hydrogen in planetary interiors. Using synchrotron X-ray diffraction, X-ray absorption spectroscopy, neutron diffraction, and first-principles calculations, we reassessed hydrogen incorporation into FeS. Our results demonstrate that the volume expansion observed under high-pressure, hydrogen-saturated conditions is attributable to Fe³⁺→Fe²⁺ reduction and changes in Fe deficiency, rather than hydrogen uptake into the FeS lattice. The upper limit of hydrogen incorporation in FeS is estimated to be ~200 ppm up to 30 GPa, suggesting that hydrogen is preferentially partitioned into the metallic phase in planetary cores.