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High-entropy oxide (HEO) nanoparticles have been regarded as a promising catalytic material system for oxygen evolution reaction in recent years. However, their traditional physical and chemical synthesis remains challenges due to the limitation of fabricating controllable small size HEO nanoparticles. Herein, a general and novel method of low-energy-recoil ion implantation and subsequent annealing is successfully developed to synthesize high-entropy oxide nanoparticles catalysts. By controlling the fluence of irradiation Ar+ ions, the size and the load of HEO nanoparticles can be accurately controlled. The obtained (FeCoNiCrAl)O HEO nanoparticles exhibit an overpotential of 295 mV at 10 mA cm−2, a small Tafel slope of 39 mV dec−1 and good stability in 1 M KOH, which is much better than the properties of binary and medium entropy oxide counterparts prepared by the same method, showing the good application prospect of low-energy-recoil ion implantation in the preparation of complicated multi-element-metal oxide nanoparticles. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fabrication of TiO2 films by ion implantation and annealing strongly depends on ion energy. [•] Best photocatalytic activity is achieved in the TiO2 nanofilm annealed at 1000°C. [•] Phase transformation of TiO2 appears under annealing temperature of 900°C. [ABSTRACT FROM AUTHOR]

Hematite is a prospective semiconductor in photoelectrochemical (PEC) water oxidation field due to its suitable bandgap for the solar spectrum absorption. Nevertheless, the low transfer and separation efficiency of the charge carriers are restricted by its diffusion length of hole which is 2–4 nm and further reduce the PEC performance. Here, we report an innovative method, by introducing nanocavities into the α-Fe 2 O 3 nanorod arrays photoanodes through helium ions implantation, to improve the charge carriers' transfer and separation efficiency and further to enhance water oxidation performance. The result indicates that, the photocurrent density of nanocavities embedded α-Fe 2 O 3 photoanode (S2-A sample) reaches 1.270 mA/cm2 at 1.6 V vs. RHE which is 1-fold higher than that of the pristine α-Fe 2 O 3 (0.688 mA/cm2) and the photocurrent density of S2-A sample reaches 0.652 mA/cm2 at 1.23 V vs. RHE. In this work, the ion implantation combined with post annealing method is found to be a valid method to improve the photoelectrochemical performance, and it also can be further used to modify the other semiconductor photoelectrodes materials. • The photoelectrochemical performance of α-Fe 2 O 3 photoanode was enhanced through controlled He+ ion implantation. • The size and density of nanocavities in the α-Fe 2 O 3 nanorods can be tailored by controlling the ion fluences. • Nanocavities can increase the separation efficiency of electron-hole pairs. [ABSTRACT FROM AUTHOR]

In this work, V ions were doped into ZnO nanorod arrays via an advanced ion implantation method for photoelectrochemical water splitting under visible light. It was indicated that the V dopants were incorporated into ZnO lattice as V 4+ and V 5+ ions. V ion doping expanded the optical absorption of ZnO nanorod arrays into visible light region and led to considerable photoelectrochemical performance under visible light illumination ( λ > 420 nm). The photocurrent density of V ions doped ZnO nanorod arrays could achieve 10.5 μA/cm 2 at 0.8 V (vs. Ag/AgCl), which was about 4 times higher than that of the pure ZnO nanorod arrays. The enhancement in photoelectrochemical performances for V ions doped ZnO nanorod arrays should be attributed to the improved visible light absorption ability and the increased charge carrier density induced by V ion doping. [ABSTRACT FROM AUTHOR]