Techniques for anionic defect engineering in transition metal oxides and mechanisms of how anion defects affect their oxygen reaction activities.

Transition metal dichalcogenides (TMDs) have attracted much attention due to their promising optical, electronic, magnetic, and catalytic properties. Engineering the defects in TMDs represents an effective way to achieve novel functionalities and superior performance of TMDs devices. However, it remains a significant challenge to create defects in TMDs in a controllable manner or to correlate the nature of defects with their functionalities. In this work, taking single-layer MoS 2 as a model system, defects with controlled densities are generated by 500 keV Au irradiation with different ion fluences, and the generated defects are mostly S vacancies. We further show that the defects introduced by ion irradiation can significantly affect the properties of the single-layer MoS 2 , leading to considerable changes in its photoluminescence characteristics and electrocatalytic behavior. As the defect density increases, the characteristic photoluminescence peak of MoS 2 first blueshifts and then redshifts, which is likely due to the electron transfer from MoS 2 to the adsorbed O 2 at the defect sites. The generation of the defects can also strongly improve the hydrogen evolution reaction activity of MoS 2 , attributed to the modified adsorption of atomic hydrogen at the defects.

Developing low-cost, high-performance electro-catalysts is essential for large-scale application of electrochemical energy devices. In this article, reported are the findings in understanding and controlling oxygen defects in PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+δ (PBSCF) for significantly enhancing the rate of oxygen evolution reaction (OER) are reported. Utilizing surface-sensitive characterization techniques and first-principle calculations, it is found that excessive oxygen vacancies promote OH − affiliation and lower the theoretical energy for the formation of O* on the surface, thus greatly facilitating the OER kinetics. On the other hand, however, oxygen vacancies also increase the energy band gap and lower the O 2p band center of PBSCF, which may hinder OER kinetics. Still, careful tuning of these competing effects has resulted in enhanced OER activity for PBSCF with oxygen defects. This work also demonstrates that oxygen defects generated by different techniques have very different characteristics, resulting in different impacts on the activity of electrodes. In particular, PBSCF nanotubes after electrochemical reduction exhibit outstanding OER activity compared with the recently reported perovskite-based catalysts.

Developing cost effective electrocatalysts with high oxygen evolution reaction (OER) activity is essential for large‐scale application of many electrochemical energy systems. Although the impacts of either lattice strain or oxygen defects on the OER performance of oxide catalysts have been extensively investigated, the effects of both factors are normally treated separately. In this work, the coupled effects of both strain and oxygen deficiency on the electrocatalytic activity of La 0.7 Sr 0.3 CoO 3−δ (LSC) thin films grown on single crystal substrates (LaAlO3 (LAO) and SrTiO3 (STO)) are investigated. Electrochemical tests show that the OER activities of LSC films are higher under compression than under tension, and are diminished as oxygen vacancies are introduced by vacuum annealing. Both experimental and computational results indicate that the LSC films under tension (e.g., LSC/STO) have larger oxygen deficiency than the films under compression (e.g., LSC/LAO), which attribute to smaller oxygen vacancy formation energy. Such strain‐induced excessive oxygen vacancies in the LSC/STO increases the e g state occupancy and enlarges the energy gap between the O 2p and Co 3d band, resulting in lower OER activity. Understanding the critical role of strain–defect coupling is important for achieving the rational design of highly active and durable catalysts for energy devices.