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Heterogeneous photocatalysis using photoexcited TiO2 substrates (either in dispersed suspensions or in thin film form) is shown to be a versatile method for preparing Se- or metal selenide (MSe)-modified TiO2 surfaces. The mechanistic aspects underlying this novel preparative route are addressed using chronopotentiometry and linear sweep photovoltammetry. The photovoltammograms of Se/TiO2 composite electrodes exhibit unusual “bipolar” behavior, i.e., both photocathodic and photoanodic enhancement of current flow on the same trace, depending on the imposed potential bias. This interesting photoelectrochemical behavior is rationalized on the basis of the electronic properties of the Se/TiO2 junction. Ex situ characterization of the composite semiconductor samples was also carried out. Finally, an application of CdSe/TiO2 samples for environmental remediation of CrVI is demonstrated.

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Injection of phase transition from a layered to rocksalt phase into the bulk lattice and side reactions on the interfacial usually causes structure degradation, quick capacity/voltage decay, and even thermal instability. Here, a self-formed interfacial protective layer coupled with lattice tuning was constructed for Ni-rich cathodes by simultaneous incorporation of Zr and Al in a one-step calcination. The migration energy between Zr and Al from the surface into the bulk lattice induces dual modifications from the surface into the bulk lattice, which effectively decrease the formation of cation mixing, the degree of anisotropic lattice change, and the generation of microcracks. With the stabilization role provided by the doped Zr-Al ions and protective function endowed by the surface layer, the modified cathode material exhibits significantly enhanced capacity and voltage retention. Specifically, the capacity retention for the modified cathode material reaches 99% after 100 cycles at 1 C and 25 °C in a voltage range of 3.0−4.3 V, which outperformed that for the pristine cathode (70%). The declination values of the average voltage for the modified cathode are only 0.025 and 0.097 V after 100 cycles at 1 C in voltage ranges of 3.0−4.3 and 2.8−4.5 V, respectively, which are much lower than those for the pristine cathode (0.230 and 0.405 V). The synchronous accomplishment of modification from the surface into the bulk lattice for Ni-rich materials with multiple elements in a one-step calcination process would provide some referenced value for the preparation of other cathode materials.

It is shown that titania-based heterogeneous photocatalysis can be combined with underpotential deposition for the preparation of composite or coupled semiconductors. Thus, ultraviolet (UV) irradiation of titania particles in an aqueous solution of Se(IV) is shown to result in the formation of Se/TiO2 composites. Subsequent UV irradiation of these composites in aqueous solutions containing M2+ ions (M = Cd, Pb) results in the underpotential deposition of the latter on the Se/TiO2 surface to afford MSe/TiO2 composites.