The simultaneous introduction of shallow acceptors and elimination of donor compensation is the key issue toward achieving p-type ZnO. Herein, through accurate control of the Li dopant configuration and systematic spectroscopy characterization, we obtain direct evidence that Li doping creates isolated VZn in ZnO with a luminescence peak around 414 nm (∼3.0 eV), and at the same time, removes donors. Interestingly, the same defect emission is also created by simple H2O2 treatment and appeared in a ZnO single crystal with abundant metal vacancies, unambiguously demonstrating its shallow acceptor characteristic.
Photocatalytic carbon-carbon (C─C) coupling of benzyl alcohol is a promising means to coproduce the value-added chemicals with H 2 but is generally subject to low efficiency in terms of photon utilization. Here, efficient benzyl alcohol C─C coupling is achieved over Zn 2 In 2 S 5 containing a tunable content of Zn vacancies ( V Zn ). The V Zn tends to form shallow defect states below the conduction band that can expedite photocarrier separation by collecting the photo-generated electrons. The V Zn -collected electrons are essential for a high selectivity of the C─C coupling reactions because they enable a fast elimination of the byproduct benzaldehyde by catalyzing its reduction back to the ketyl radicals. Under simulated sunlight, the V Zn -containing Zn 2 In 2 S 5 accomplishes ≈100% conversion of benzyl alcohol for merely 1 h and attains ≈100% selectivity for the C─C coupling compounds for 2 h, delivering an apparent quantum yield as high as 7.7% at 420 ± 20 nm. The benefits of V Zn have also been verified by the theoretical calculations that indicate reduced energy barriers for various surface reactions in the presence of V Zn . This work brings fresh mechanistic insights into the role of V Zn and can serve as a useful guideline in the design of efficient photocatalysts.
Selective CO2 photoreduction to valuable chemicals is promising for a carbon-neutral future and still remains a challenge. Herein, Zn vacancy-rich ZnO (Zn1–xO) nanoparticles were used as cocatalyst to construct a Zn1–xO/TiO2 nanostructure via the self-assembly process. The existence of Zn vacancies triggered the intimate contact between Zn1–xO and TiO2 through the Ti–O–Zn bonds. Theoretical and experimental results show that the hybridization of Zn1–xO and TiO2 resulted in the formation of a p–n heterojunction, leading to the enhanced separation efficiency of photoinduced electron–hole pairs. As a result, the optimized Zn1–xO/TiO2 nanocomposite exhibited nearly 100% selectivity of CO2-to-CO photoreduction, and the productivity was 4.2 times higher than that of pristine TiO2. In situ Fourier transform infrared spectra along with theoretical calculations were also conducted to investigate the mechanism of the selective photocatalytic CO2-to-CO process. It is concluded that the charge depletion on the TiO2 surface induced by the charge transfer from Zn1–xO to TiO2 can lower the energy barrier of CO* desorption and convert the endothermic CO* desorption process into an exothermic reaction step, thus triggering selective CO production. This work provides a new perspective on the rational fabrication of nanostructures for efficient and selective photocatalytic CO2 conversion through intermediate modulation.
Co-Fe spinel oxides are attractive alternatives to noble metal-based electrocatalysts for water splitting due to their abundant reserves, unique electrochemical redox characteristics and inherent stability. However, their alkaline HER performance under high-current conditions remains limited by inefficient water adsorption/dissociation and suboptimal hydrogen adsorption balance. Herein, a 600-cm 2 amorphous Ce-doped Co 2 FeO 4 cathode with Zn vacancies (Ce, Zn v -Co 2 FeO 4 ) were synthesized by electrodeposition and alkaline etching method. It exhibits exceptional alkaline HER performance with low overpotentials of 47.5 and 247.5 mV at 10 and 1000 mA cm −2 , meanwhile maintaining high stability over 500 h at 1000 mA cm −2 with a potential retention rate of 96.5%. The resulting water electrolyzer with Ce, Zn v -Co 2 FeO 4 as cathode only needs a cell voltage of 1.90 V at 1000 mA cm −2 for overall water splitting. In-situ electrochemical tests and density functional theory (DFT) calculations demonstrate that the synergistic effect of Ce doping and Zn vacancies in Co 2 FeO 4 leads to a 50% reduction in bandgap, thereby enhancing conductivity. It also facilitates spontaneous water adsorption and dissociation, reduces the energy barrier by 46%, and optimizes the balance of hydrogen adsorption/desorption, thereby ultimately enhancing HER activity. This study presents a potential strategy to address the performance limitations of spinel-based HER catalysts.
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