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Compared with most cathodes for lithium-ion batteries (LIBs), α-MoO3exhibits high specific capacity and therefore receives widespread attention. However, due to its irreversible structural transformation, the capacity of α-MoO3declines rapidly upon discharge-charge process. Herein, via H2plasma etching, oxygen-deficient α-MoO3-xwith improved electrochemical performance is prepared on the basis of pristine α-MoO3(MoO3(I)). The obtained MoO3(II) (10 min etching) and MoO3(III) (20 min etching) have reduced bandgap and expanded van der Waals gap (vdW gap). Electrochemical test results demonstrate MoO3(II) obtains the largest Li+diffusion coefficient, the lowest charge transfer resistance and the slightest polarization. In situ X-ray diffraction characterization further reveals that during cycling, vdW gap of MoO3(II) changes periodically within a small range, indicating a stabilized crystal structure. This work shows that moderate oxygen vacancies can enhance the capacity and stabilize the structure of molybdenum trioxide cathode for LIBs, which has great potential in other cathode materials.

Transition metal phosphides or partially phosphatized oxides usually suffer from surface reconstruction during oxygen evolution reaction (OER), but still possess enhanced catalytic activity than directly synthesized oxides, which has aroused great interest in exploring the causes of such high catalytic activity. To monitor electronic property of catalyst during the OER can provide crucial insights into catalytic ability. Here we design a planar electrochemical microdevice based on individual thin-film catalyst, and for the first time explore the continuous electric conductance evolution of lattice P-doped oxides during the electrochemical activation process. Moreover, combining on-chip electrochemical impedance spectra measurements, in situ I-Vmeasurements, and theoretical simulations of reconstructed lattice P-doped oxides, the effect of P–O groups on new-formed oxides is clarified. The induced electronic coupling between new-formed oxides and P-O groups has been studied and demonstrated. The coupled P–O groups effectively promote the metal–oxygen covalency of new-formed oxides, which accelerates electron transfer between active metallic center and oxygen adsorbates, thus leading to the enhanced electrocatalytic activity. Our study highlights the role of surface P–O groups in Co3O4during the OER, and such unique on-chip electrochemical microdevice platform can also be applied in other related fields to understand the dynamic behavior of energy materials at nanoscale.