Some oxides have the ability to trap excess electrons in the form of small polarons. Here, using first-principles techniques, we investigate the interaction of excess electrons with α-MoO3. Polarons are found to be about 0.6 eV more stable than delocalized electrons. They can propagate with a high degree of anisotropicity along different crystallographic directions with the lowest barrier found to be about 0.08 eV. In addition to the band gap photoexcited charge carriers that can populate such polaron states, we investigate the role of oxygen vacancies as an intrinsic source of electrons. We also investigate intercalated alkali ions that can form complexes with the created polarons in the lattice. The alkali-polaron complex (AxMoO6, A = alkali ion) binding energies are relatively low, making it easy for the complex to dissociate. This, coupled with the low polaron migration energies, can generate a non-negligible contribution to electronic conductivity even in the absence of illumination, which is experimentally verified. Combined, this light-induced intercalation of alkali ion in MoO3 and its subsequent deintercalation (complex dissociation) processes lead to a novel self-photocharghing phenomenon.

Nanocrystalline molybdenum oxide (α-MoO3) thin films with iso-oriented crystalline layers were synthesised by the anodisation of Mo foils. Upon band-gap excitation using light illumination, α-MoO3 generates excited electrons for reductive reactions and stores some of the excited electrons in its layered crystalline structure via alkali cation intercalation. These stored electrons can be subsequently discharged from α-MoO3 to allow reductive reactions to continue to occur under non-illuminated conditions. The modulation of water concentrations in the organic/aqueous anodisation electrolytes readily produces α-MoO3 crystals with high degree of (kk0) crystallographic orientation. Moreover, these (kk0)-oriented MoO3 crystals exhibit well-developed {hk0} and {0k0} crystal facets. In this paper, we show the benefits of producing α-MoO3 thin films with defined crystal facets and an iso-oriented layered structure for in situ storing of excited charges. α-MoO3 crystals with dominant (kk0) planes can achieve fast charging and a strong balance between charge release for immediate exploitation under illuminated conditions and charge storage for subsequent utilisation in dark. In comparison, α-MoO3 crystals with dominant (0k0) planes show a preference for excited charge storage.

Nanostructured molybdenum oxide (α‐MoO3) thin film photoelectrodes were synthesised by anodisation. Upon band gap‐excitation by light illumination, α‐MoO3 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‐MoO3 for utilisation under dark conditions, and α‐MoO3 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‐MoO3 to be modulated to achieve (i) a distorted MoO6 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 MoO6 octahedral distortion in α‐MoO3 at a higher pH favours charge storage, whereas smaller octahedral distortion at a lower pH leads to anodic photocurrent enhancement.

A photoactive Bi2MoO6/MoO3 heterojunction electrode derived from a direct thin-film-route showed close to 100% faradic photocurrent-to-O2 conversion efficiency.

The rational design of previously unidentified materials that could realize excellent electrochemical-controlled optical and charge storage properties simultaneously, are especially desirable and useful for fabricating smart multifunctional devices. Here, a facile synthesis of a 1D-d conjugated coordination polymer (Ni-BTA) is reported, consisting of metal (Ni)-containing nodes and organic linkers (1,2,4,5-benzenetetramine), which could be easily grown on various substrates via a scalable chemical bath deposition method. The resulting Ni-BTA film exhibits superior performances for both electrochromic and energy storage functions, such as large optical modulation (61.3%), high coloration efficiency (223.6 cm 2 C −1), and high gravimetric capacity (168.1 mAh g −1). In particular, the Ni-BTA film can maintain its electrochemical recharge-ability and electrochromic properties even after 10 000 electrochemical cycles demonstrating excellent durability. Moreover, a smart energy storage indicator is demonstrated in which the energy storage states can be visually recognized in real time. The excellent electrochromic and charge storage performances of Ni-BTA films present a great promise for Ni-BTA nanowires to be used as practical electrode materials in various applications such as electrochromic devices, energy storage cells, and multifunctional smart windows.