Defective Metal Oxides: Lessons from CO₂RR and Applications in NO_xRR

Abstract

Sluggish reaction kinetics and the undesired side reactions (hydrogen evolution reaction and self‐reduction) are the main bottlenecks of electrochemical conversion reactions, such as the carbon dioxide and nitrate reduction reactions (CO2RR and NO3RR). To date, conventional strategies to overcome these challenges involve electronic structure modification and modulation of the charge‐transfer behavior. Nonetheless, key aspects of surface modification, focused on boosting the intrinsic activity of active sites on the catalyst surface, are yet to be fully understood. Engingeering of oxygen vacancies (OVs) can tune surface/bulk electronic structure and improve surface active sites of electrocatalysts. The continuous breakthroughs and significant progress in the last decade position engineering of OVs as a potential technique for advancing electrocatalysis. Motivated by this, the state‐of‐the‐art findings of the roles of OVs in both the CO2RR and the NO3RR are presented. The review starts with a description of approaches to constructing and techniques for characterizing OVs. This is followed by an overview of the mechanistic understanding of the CO2RR and a detailed discussion on the roles of OVs in the CO2RR. Then, insights into the NO3RR mechanism and the potential of OVs on NO3RR based on early findings are highlighted. Finally, the challenges in designing CO2RR/NO3RR electrocatalysts and perspectives in studying OV engineering are provided.

Defect-Rich CoFe-Layered Double Hydroxides as Superior Peroxidase-like Nanozymes for the Detection of Ascorbic Acid

“…Compared with lattice oxygen (O L ) at 531.1 eV and adsorbed oxygen (O s ) at 532.7 eV in b-CoFe-LDHs, the peak at 531.5 eV in d-CoFe-LDHs can prove the existence of V O . In addition, the EPR test shows that d-CoFe-LDHs has a stronger signal peak than b-CoFe-LDHs at g = 2.4, which also proves that there are defects in d-CoFe-LDHs (Figure S5). In conclusion, d-CoFe-LDHs are rich in defects, which may enhance the catalytic performance.…”

Electronic Structure Design of Transition Metal-Based Catalysts for Electrochemical Carbon Dioxide Reduction

“…Anion Vacancies. At present, oxygen vacancies 162,185,281,282 are the most common vacancies in catalysts, and S 161, 283 and Se 174 in the same main group are also relatively prone to form vacancies. Since transition metal atoms in oxides are always stable and inactive, the presence of anion vacancies can reduce them to a more excited intermediate valence state.…”

The Synergistic Effect between Metal and Sulfur Vacancy to Boost CO2 Reduction Efficiency: A Study on Descriptor Transferability and Activity Prediction

“…The widely used metal–supported catalysts are composed of active metal atoms anchored on supports. Excellent catalytic performance is achieved through the interaction between the metal and support, which affects the electronic structure and morphology of the catalyst. − Surface vacancies are unavoidably introduced during the preparation of the surface-supported catalysts, tuning the electrical, magnetic, and optical properties. − For instance, metal–supported catalysts enriched with anion vacancies (oxide, sulfide, and nitride vacancies) effectively promoted charge separation, enhanced oxygen adsorption, and stabilized interfacial structures, thus improving the activity and selectively for surface reactions. − The vacancies on metal–supported catalysts are also able to promote light absorption, charge separation, and CO 2 conversion. − The essential role of vacancies, including vacancy type and location, vacancy concentration, and doped metal-based motifs, has been revealed in CO 2 reduction reactions (CO 2 RR). − The oxygen-vacancy-rich MoO 2– x nanosea-urchins can promote CO 2 adsorption and activation, displaying extremely strong CO 2 photoreduction ability . In the NiCo 2 O 4 system, the synergistic effect between oxygen vacancies and Ni facilitates CH 4 generation and vacancy regeneration, showing an attempt at precise control of photocatalytic selectivity and stability .…”