Figure 1

Left: Simplified crystal structure of MoO₃ and hydrogen bronze(s). Chains of MoO₆ octahedrons are fused together by edge sharing to form corrugated layers. The intercalation of hydrogen into MoO₃ does not markedly modify the structural motif apart from slight increase of the cell volume, lattice distortion and hydrogen ordering^12,13,14. As already suggested by the vicinity of hydrogens to oxygen, water is formed at higher concentrations. In this case, the metal/oxygen ratio is modified leading to MoO₂. The changes of the electronic structure by hydrogen intercalation are depicted in the right panel. Hydrogen forms band gap states (red) and “valence band-like Mo⁵⁺ states” (green-rimmed boxes: grey: occupied, white: empty), as depicted by the width of electronic states. The loss of oxygen at higher hydrogen concentrations is depicted by the smaller width of the blue rimmed boxes, simultaneously, more Mo bands are filled.