Defect engineering serves as a pivotal strategy for improving the performance of CO₂ electrocatalytic reduction (CO₂RR). However, understanding the structure-activity relationship between defect configurations and catalytic activity at the atomic level remains a significant challenge. This study utilized a series of structurally well-defined Au₁Ag_24+2n(SR)_18+n (where n = 0, 1, 2; SR = adamantanethiol) nanoclusters as model catalysts to systematically explore the impact of defect engineering on CO₂RR. In the Au₁Ag₂₆ nanocluster, rearrangement of the peripheral ligands creates structural defects, which increases the exposure of the active surface area. This defect engineering leads to optimal catalytic performance, achieving a Faradaic efficiency (FE) for CO of 63% at −1.0 V (vs. RHE)—nearly double that of Au₁Ag₂₄, which has an FE of 32%. In contrast, due to the surface units of Au₁Ag₂₈ being fully covered, its catalytic activity is negligible (FE_CO < 5%). By integrating comprehensive structural characterization with electrocatalytic performance analysis, we have demonstrated at the atomic level that the Ag₁S₃ motif acts as the possible catalytic active center, with catalytic performance exhibiting a direct correlation with the degree of active site exposure. This research uncovers the fundamental mechanism by which defect engineering enhances CO₂RR catalyst performance by reconstructing the coordination environment and strategically exposing active sites of cluster-based catalysts.

Catalytic reactions play a key role in energy production, green chemistry, and chemical synthesis, and are the cornerstone for addressing global challenges such as environmental pollution and energy crisis. The design and performance optimization of efficient catalysts rely on a deep understanding of their structural characteristics, electronic states, and kinetic behaviors during reactions, and advanced characterization techniques provide key technical support. This review summarizes the applications, advantages, and limitations of spectroscopic techniques (X-ray absorption spectroscopy, nuclear magnetic resonance, Raman spectroscopy, infrared spectroscopy, and electron paramagnetic resonance), microscopic imaging techniques (transmission electron microscopy, scanning electron microscopy, and atomic force microscopy), and component analysis techniques (X-ray photoelectron spectroscopy, X-ray diffraction, and inductively coupled plasma mass spectrometry) in catalytic research. These techniques can provide multi-dimensional insights into the microstructure of catalysts, the properties of active sites, and their evolution during reactions, laying a solid foundation for elucidating catalytic mechanisms and optimizing catalyst performance. Although current characterization methods still face challenges in spatial resolution, compatibility with extreme reaction conditions, and data processing complexity, significant progress is expected through emerging strategies such as multi-technique integration and artificial intelligence-assisted analysis. This review aims to provide a reference for researchers in the field of catalysis and a forward-looking perspective for the development of characterization techniques.

Propane dehydrogenation using CO₂ as a mild oxidizer (CO₂-ODP) is a promising technology for high propylene production and CO₂ reduction utilization. Among them, the reverse water gas shift reaction (RWGS) can change the reaction equilibrium to increase the propylene yield, and the Boudouard reaction can assist in the carbon accumulation elimination. However, the efficiency of the catalysts developed so far is limited, we introduced the Cr active component during the synthesis of porous silica spheres to form a CO₂-ODP catalyst, with a uniform distribution of active sites via (NH₄)₃[CrMo₆O₂₄H₆]·7H₂O produce a derivative. As an α-type Anderson series of polyoxometalates (POMs), this six octahedral structure formed by Mo participation surrounds the central atom Cr, which is more stable in structure by electrostatic effect, its derivatives generated after calcination are stably bound to the silica-based carrier, which reduces the formation of inert α-Cr₂O₃ by CrO_x aggregation during the catalytic process. Meanwhile, the oxygen atoms rich in polyoxometalates are more likely to form Si–O bonds with the carrier, which makes the active sites evenly and stably branched in the inner wall of the pores of mesoporous silica spheres, reduces the influence of carbon accumulation, and facilitates the activation and regeneration. The CO₂ conversion of the catalyst CrMoO_x@ mesoporous silica spheres (MSS) is typically greater than 20% under selected ideal conditions. This synthesis method of assembling POMs with mesoporous materials opens a new pathway for developing propane dehydrogenation catalysts. Compared to traditional impregnation synthesis, this catalyst contains a lower Cr content while achieving higher CO₂ consumption efficiency.

Due to the high structural flexibility and controllable thermal expansion, cubic double ReO₃-type negative thermal expansion (NTE) fluorides provide a solution for solving the prominent phenomenon of thermal expansion mismatch between materials. However, the expensive raw materials and complex synthesis steps limit its practical application. In this work, we have designed a more advantageous method for the synthesis of NTE material CaZrF₆, and it is expected to be generalized to the synthesis of other double ReO₃-fluorides. Intriguingly, a new orthorhombic phase CaZrF₆ has been synthesized via this method in a lower temperature. Unlike the strong isotropic NTE of the cubic phase CaZrF₆, the orthorhombic phase shows the strong anisotropic positive thermal expansion (PTE). The combined analysis of temperature-dependent X-ray diffraction (XRD), Raman spectra, and first-principles calculations shows that the low frequency phonon vibration mode with negative Grüneisen parameter in cubic CaZrF₆ are strongly correlated with the transverse thermal vibration of F atoms and dominates the NTE of the material.

Herein, a unique mesoporous heterostructure (average pore size: 15 nm) cobalt disulfide/carbon nanofibers (CoS₂/PCNFs) composite with excellent hydrophilicity (contact angle: 23.5°) is prepared using polyethylene glycol (PEG) as a pore-forming agent. The CoS₂/PCNF electrode exhibits excellent cycle stability (95.2% of initial specific capacitance at 10 A∙g⁻¹ after 8000 cycles), good rate performance (46.5% at 10 A∙g⁻¹), and high specific capacity (86.1 mAh∙g⁻¹ at 1 A∙g⁻¹, about 688.8 F∙g⁻¹ at 1 A∙g⁻¹). Density functional theory (DFT) simulation elucidates that CoS₂ tends to transfer substantial charges to CNF. As the center of positive charge, CoS₂ is more likely to capture negative ions in the electrolyte, thus accelerating the ion diffusion process. The excellent properties of the electrode material can not only accelerate the electrochemical reaction kinetics, but also provide abundant redox-active sites and a high Faradaic capacity for the entire electrode due to the synergistic contributions of CoS₂ nanoparticles, mesoporous heterostructure of PCNF, and admirable hydrophilicity of the composite material. A CoS₂/PCNF-0.25//AC (AC: activated carbon) asymmetric supercapacitor is assembled using CoS₂/PCNF-0.25 as the positive electrode and AC as the negative electrode, which possesses a high energy density (35.5 Wh∙kg⁻¹ at a power density of 824 W∙kg⁻¹) and superior cycling stability (maintaining over 98% of initial capacitance after 2000 cycles). In addition, the unique CoS₂/PCNF electrode is expected to be widely used in other electrochemical energy storage devices, such as lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, etc.

Herein, we prepare the unique hierarchical polypyrrole@cobalt sulfide (PPy-hs@CoS) hollow sphere-based nanofilms as interdigitated electrodes for flexible on-chip micro-supercapacitors (MSC). Benefiting from the excellent flexibility and high electrical conductivity of PPy-hs combined with the great electrochemical activity of CoS, such PPy-hs@CoS composite material can not only inhibit the volume expansion of PPy but also promote the diffusion of the electrolyte ions. The PPy-hs@CoS film-based electrode delivers a greatly improved specific capacitance and small resistance. Density functional theory calculations infer that OH⁻ prefers to bind to PPy on CoS@PPy and confirms the synergistic effect of each component for enhanced reaction kinetics. A quasi-solid-state on-chip flexible asymmetric MSC based on PPy-hs@CoS and activated carbon (AC) microelectrodes exhibits large areal-specific capacitance (131.9 mF/cm² at 0.3 mA/cm²), ultrahigh energy density (0.041 mWh/cm²@0.224 mW/cm² and 25.6 mWh/cm³@140.6 mW/cm³), and long cycle lifespan. We demonstrate the possibility to scale up the PPy-hs@CoS nanofilm microelectrode by arranging two of our asymmetric MSC in series and parallel connections, which respectively increase the output voltage and current. A self-charging system by connecting our asymmetric MSCs with a piece of commercial solar cells is developed as a potential possible mode for future highly durable and high-voltage integrated electronics.