Developing a high-efficiency and stable anode catalyst layer (CL) is crucial for promoting the practical applications of anion exchange membrane (AEM) water electrolyzers. Herein, a hierarchical nanosheet array composed of oxygen vacancy-enriched CoCrOx nanosheets and dispersed FeNi layered double hydroxide (LDH) is proposed to regulate the electronic structure and increase the electrical conductivity for improving the intrinsic activity of the oxygen evolution reaction (OER). The CoCrOx/NiFe LDH electrodes require an overpotential of 205 mV to achieve a current density of 100 mA cm-2, and they exhibit long-term stability at 1000 mA cm-2 over 7000 h. Notably, a breakthrough strategy is introduced in membrane electrode assembly (MEA) fabrication by transferring CoCrOx/NiFe LDH to the surface of an AEM, forming a 3D-interlocked anode CL, significantly reducing the overall cell resistance and enhancing the liquid/gas mass transfer. In AEM water electrolysis, it exhibits an ultralow cell voltage of 1.55 Vcell to achieve a current density of 1.0 A cm-2 in 1 M KOH, outperforming the state-of-the-art Pt/C//IrO2. This work provides a valuable approach to designing high-efficiency electrocatalysts at the single-cell level for advanced alkaline water electrolysis technologies.

Herein, a new heterogeneous CoSe2-x@NC material with abundant selenium vacancies is synthesized via an in-situ carbonization-selenization process from cobaltic metal organic framework (Co-MOF). The obtained CoSe2-x@NC has a unique electronic structure and rich active sites, which can activate peroxymonosulfate (PMS) to degrade carbamazepine (CBZ) with superior catalytic performance and stability. The quenchingexperiments and EPR test show that SO4•- is the dominant reactive oxidation species (ROSs) for CBZ degradation. Significantly, systemic electrochemical tests and theoretical calculations illustrated that the dominant role of SO4•- is attributed to the existence of abundant selenium vacancies in CoSe2-x@NC, which can adjust the density of electron cloud of the Co atoms in CoSe2-x@NC to improve the PMS adsorption and promoting the conversion of transition metallic redox pairs (Co3+/Co2+). This work provides a facile way to improve the activity and stability of CoSe2 by defect engineering in the PMS based advanced oxidation process (AOPs).

The development of the proton exchange membrane water electrolyzer (PEMWE) is still limited by the prohibitive cost and scarcity of iridium (Ir)-based oxygen evolution reaction (OER) catalyst. This work presents a novel catalyst synthesized by precursor-atomization and rapid joule-heating method, successfully doping iridium atoms into polyvalent tungsten blends (W0, W5+, W6+) based on titanium substrate. The vacancy engineering of unsaturated tungsten oxide (W5+, W6+) reconstructs the electronic structure of the catalyst surface, which resulting in the low-valence state iridium species, avoiding excessive oxidation of iridium and accelerating the catalytic kinetics. Meanwhile, metallic tungsten (W0) improves the conductivity of catalyst and guarantees the stable existence of oxygen vacancy. The TiIrWOx possesses excellent performance in acidic OER catalysis, requiring overpotential of only 181 mV to drive 10.0 mA cm-2, and exhibiting a high mass activity of 753 A gIr -1 at an overpotential of 300 mV. The membrane electrode assembly (MEA) with TiIrWOx as anode electrocatalyst can reduce the Ir consumption amount by >60% compared to commercial IrO2, and it can operated over 120 h at a current density of 1.0 A cm-2.

The combination of hetero-elemental doping and vacancy engineering will be developed as one of the most efficient strategies to design excellent electrocatalysts for hydrogen evolution reaction (HER). Herein, a novel strategy for N-doping coupled with Co-vacancies is demonstrated to precisely activate inert S atoms adjacent to Co-vacancies and significantly improve charge transfer for CoS toward accelerating HER. In this strategy, N-doping favors the presence of Co-vacancies, due to greatly decreasing their formation energy. The as-developed strategy realizes the upshift of S 3p orbitals followed by more overlapping between S 3py and H 1s orbitals, which results in the favorable hydrogen atom adsorption free energy change (ΔGH ) to activate inert S atoms as newborn catalytical sites. Besides, this strategy synergistically decreases the bandgap of CoS, thereby achieving satisfactory electrical conductivity and low charge-transfer resistance for the as-obtained electrocatalysts. With an excellent HER activity of -89.0 mV at 10.0 mA cm-2 in alkaline environments, this work provides a new approach to unlocking inert sites and significantly improving charge transfer toward cobalt-based materials for highly efficient HER.

Cu9S5 possesses high hole concentration and potential superior electrical conductivity as a novel p-type semiconductor, whose biological applications remain largely unexploited. Encouraged by our recent work that Cu9S5 has enzyme-like antibacterial activity in the absence of light, which may further enhance the near infrared (NIR) antibacterial performance. Moreover, vacancy engineering can modulate the electronic structure of the nanomaterials and thus optimize their photocatalytic antibacterial activities. Here, we designed two different atomic arrangements with same VCuSCu vacancies of Cu9S5 nanomaterials (CSC-4 and CSC-3) determined by positron annihilation lifetime spectroscopy (PALS). Aiming at CSC-4 and CSC-3 as a model system, for the first time, we investigated the key role of different copper (Cu) vacancies positions in vacancy engineering toward optimizing the photocatalytic antibacterial properties of the nanomaterials. Combined with the experimental and theoretical approach, CSC-3 exhibited stronger absorption energy of surface adsorbate (LPS and H2O), longer lifetime of photogenerated charge carriers (4.29 ns), and lower reaction active energy (0.76 eV) than those of CSC-4, leading to the generation of abundant ·OH for attaining rapid drug-resistant bacteria killed and wound healed under NIR light irradiation. This work provided a novel insight for the effective inhibition of drug-resistant bacteria infection via vacancy engineering at the atomic-level modulation.

The vacancy defects in heterogeneous catalysts have received extensive attention for persulfate (PS) activation. Vacancy defects can tune the electronic structure of metal oxides and generate unsaturated coordination sites. Meanwhile, the adsorption energy of reactants on catalyst surface is optimized. Thereby, the reaction energy barrier between catalysts and PS decreases, which could promote catalytic activation and accelerate pollutants degradation. Nowadays, oxygen vacancy (OV), nitrogen vacancy (NV), sulfur vacancy (SV), selenium vacancy (SeV) and titanium vacancy (TiV) have been widely studied with great potential for water remediation. So far, no review was reported regarding the vacancy activated persulfate systems. This paper summarized the types, preparation, mechanism and applications of vacancy in PS systems systematically. In addition, we put forward possible development of vacancy engineering in PS activation systems. It is expected that this review will contribute to the controllable synthesis and applications of vacancies in catalysts for PS activation and contaminants removal.

The design of electrocatalysts with enhanced adsorption and activation of nitrogen (N2) is critical for boosting the electrochemical N2 reduction (ENR). Herein, we developed an efficient strategy to facilitate N2 adsorption and activation for N2 electroreduction into ammonia (NH3) by vacancy engineering of core@shell structured Au@SnO2 nanoparticles (NPs). We found that the ultrathin amorphous SnO2 shell with enriched oxygen vacancies was conducive to adsorb N2 as well as promoted the N2 activation, meanwhile the metallic Au core ensured the good electrical conductivity for accelerating electrons transport during the electrochemical N2 reduction reaction, synergistically boosting the N2 electroreduction catalysis. As confirmed by the 15N-labeling and controlled experiments, the core@shell Au@amorphous SnO2 NPs with abundant oxygen vacancies show the best performance for N2 electroreduction with the NH3 yield rate of 21.9 μg h-1 mg-1cat and faradaic efficiency of 15.2% at -0.2 VRHE, which surpass the Au@crystalline SnO2 NPs, individual Au NPs and all reported Au-based catalysts for ENR.

The rate-determining process for sodium storage in TiO2 is greatly depending on charge transfer happening in the electrode materials owing to its inferior diffusion coefficient and electronic conductivity. Apart from reducing the diffusion distance of ion/electron, the increasement of ionic/electronic mobility in the crystal lattice is also very important for charge transport. Here, an oxygen vacancy (OV) engineering assisted in high-content anion (S/Se/P) doping strategy to enhance charge transfer kinetics for ultrafast sodium-storage performance is proposed. Theoretical calculations indicate that OV-engineering evokes spontaneous S doping into the TiO2 phase and achieves high dopant concentration to bring about impurity state electron donor and electronic delocalization over S occupied sites, which can largely reduce the migration barrier of Na+. To realize the speculation, high-content anion doped anatase TiO2/C composites (9.82 at% for S in A-TiO2-x-S/C) are elaborately designed. The optimized A-TiO2-x-S/C anode exhibits extraordinarily high-rate capability with 209.6 mAh g-1 at 5000 mA g-1. The assembled sodium ion capacitors deliver an ultrahigh energy density of 150.1 Wh kg-1 at a power density of 150 W kg-1 when applied as anode materials. This work provides a new strategy to realize high content anion doping concentration, and enhances the charge transfer kinetics for TiO2, which delivers an efficient approach for the design of electrode materials with fast kinetic.

Reversible conversion over multimillion times in bond types between metavalent and covalent bonds becomes one of the most promising bases for universal memory. As the conversions have been found in metastable states, an extended category of crystal structures from stable states via redistribution of vacancies, research on kinetic behavior of the vacancies is highly in demand. However, it remains lacking due to difficulties with experimental analysis. Herein, the direct observation of the evolution of chemical states of vacancies clarifies the behavior by combining analysis on charge density distribution, electrical conductivity, and crystal structures. Site-switching of vacancies of Sb2Te3 gradually occurs with diverged energy barriers owing to their own activation code: the accumulation of vacancies triggers spontaneous gliding along atomic planes to relieve electrostatic repulsion. Studies on the behavior can be further applied to multiphase superlattices composed of Sb2Te3 (2D) and GeTe (3D) sublayers, which represent superior memory performances, but their operating mechanisms were still under debate due to their complexity. The site-switching is favorable (suppressed) when Te-Te bonds are formed as physisorption (chemisorption) over the interface between Sb2Te3 (2D) and GeTe (3D) sublayers driven by configurational entropic gain (electrostatic enthalpic loss). Depending on the type of interfaces between sublayers, phases of the superlattices are classified into metastable and stable states, where the conversion could only be achieved in the metastable state. From this comprehensive understanding on the operating mechanism via kinetic behaviors of vacancies and the metastability, further studies toward vacancy engineering are expected in versatile materials.

Cu-based nanomaterials have been developed to alleviate the problem of antibiotic resistance due to their superior properties and good biocompatibility. Defects in nanomaterials have a major role in improving photocatalytic performance. Herein, two CuS nanospheres with predominant VCuSCu and VCuSS vacancy (abbreviated as CuS and CuS-T150, respectively) characterized by positron annihilation spectra are synthesized. The combination of experimental and theoretical calculation results demonstrates that CuS-T150 exhibits excellent antibacterial, achieving bactericidal rates of 99.9% against to Escherichia coli (E. coli) under 808 nm laser irradiation. Compared with CuS, the superior antimicrobial activity of CuS-T150 is mainly attributed to its stronger ability to adsorb oxygen molecules, more easily bind with surface of E. coli, and higher photothermal conversion efficiency (PTCE). This work provides a deeper understanding of nanomaterials with vacancy modulated the antibacterial efficiency by synergistic effect of photodynamic and photothermal therapy.