A bifunctional electrocatalyst with high efficiency and low costs for overall water splitting is critical to achieving a green hydrogen economy and coping with the energy crisis. However, developing robust electrocatalysts still faces huge challenges, owing to unsatisfactory electron transfer and inherent activity. Herein, NiFe LDH/NiS₂/VS₂ heterojunctions have been designed as freestanding bifunctional electrocatalysts to split water, exhibiting enhanced electron transfer and abundant catalytic sites. The optimum NiFe LDH/NiS₂/VS₂ electrocatalyst exhibits a small overpotential of 380 mV at 10 mA cm⁻² for overall water splitting and superior electrocatalytic performance in both hydrogen and oxygen evolution reactions (HER/OER). Specifically, the electrocatalyst requires overpotentials of 76 and 286 mV at 10 mA cm⁻² for HER and OER, respectively, in alkaline electrolytes, which originate from the synergistic interaction among the facilitated electron transfer and increasingly exposed active sites due to the modulation of interfaces and construction of heterojunctions.

Novel BiOI–multi-walled carbon nanotube (MWCNT) composite photocatalysts have been prepared by one-step microwave hydrothermal method. The structures, morphology, optical properties and photocatalytic were studied by X-ray diffraction, scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), diffuse reflection spectroscopy (UV–vis DRS), Brunauer–Emmett–Teller and photoluminescence methods etc. The results show that the BiOI–MWCNT composite exhibits increased photocatalytic than pure BiOI for decomposition of methyl orange (MO) and antibiotics agent levofloxacin (LEV). Meanwhile, the BiOI–MWCNT-1% composites showed highest photoactivity, the degradation rate constant is 2.4 times and 3.5 times higher than that of pure BiOI under the same conditions for degradation MO and LEV, respectively. The hole (h⁺) and superoxide radical ( $\cdot {\mathrm{O}}_2^{-}$) were identified to be the dominant active species in the photocatalytic reaction.

A Pr-doped p-Cu₂O thin film was prepared on indium tin oxide conductive glass by electrochemical deposition; the effect of Pr doping on the structure, morphology, and physicochemical properties of p-Cu₂O was investigated. The results show that with the increase in Pr doping amount, the particle size of p-Cu₂O increases, the absorption boundary redshifts, and the band-gap width decreases. Pr doping increases the flat band potential and carrier concentration of p-Cu₂O; when the doping amount is 1.2 mM, the carrier concentration reaches 1.14 × 1024 cm⁻³. Compared with pure p-Cu₂O, the charge transfer resistance of Pr-doped p-Cu₂O decreases and the photocurrent and open circuit voltage increase, indicating that the carrier transfer rate is accelerated, and the separation efficiency of photogenerated electrons and holes is effectively improved. The result of a norfloxacin photocatalytic degradation experiment showed that the degradation rate of norfloxacin increased from 52.3% to 76.2% and Pr doping effectively improved the photocatalytic performance of p-Cu₂O. The main reasons for enhancing the photocatalytic performance are that the band gap of Pr-doped p-Cu₂O decreases, the Fermi level of Cu₂O is closer to the valence band position, the hole concentration near the valence band, and the oxidation capacity increases, and more h⁺ oxidize norfloxacin molecules. In addition, the Pr in Pr-Cu₂O acts as a conductor to guide electrons on the guide band to the crystal surface, which increases the contact between photogenerated electrons and dissolved oxygen, which is conducive to the formation of the active species ·O₂⁻ and can effectively reduce the recombination of photogenerated carriers. In the process of photocatalytic degradation of norfloxacin, the main active species are ·O₂⁻, ·OH, and h⁺, which play auxiliary roles. TOC tests show that the norfloxacin molecules can be effectively degraded into small molecule organic matter, CO₂, and H₂O in the presence of Pr-doped p-Cu₂O.