Harvesting, Storing and Utilising Solar Energy using MoO 3 : Modulating Structural Distortion through pH Adjustment

Nanostructured molybdenum oxide (α‐MoO 3 ) thin film photoelectrodes were synthesised by anodisation. Upon band gap‐excitation by light illumination, α‐MoO 3 is able to store a portion of the excited charges in its layered structure with the simultaneous intercalation of alkali cations. The stored electrons can be discharged from α‐MoO 3 for utilisation under dark conditions, and α‐MoO 3 is able to recharge itself with successive illuminations to behave as a ‘self‐photo‐rechargeable’ alkali‐ion battery. The alteration of the anodisation pH allowed the crystal structure and oxygen vacancy concentrations of α‐MoO 3 to be modulated to achieve (i) a distorted MoO 6 octahedra for enhanced charge separation and storage, (ii) a layered structure with a greater exposed (010) crystal face for rich and reversible ion intercalation and (iii) a highly crystalline thin film that suppresses electron–hole pair recombination. Overall, the larger MoO 6 octahedral distortion in α‐MoO 3 at a higher pH favours charge storage, whereas smaller octahedral distortion at a lower pH leads to anodic photocurrent enhancement.