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Increased levels of oxidative stress are major factors that drive the process of post-ovulatory oocyte aging. Epigallocatechin-3-gallate (EGCG), which accounts for up to 50% of the catechins, possesses versatile biological functions, including preventing or treating diabetes, cancer, and heart diseases. The aim of this study was to explore whether EGCG can delay porcine oocyte aging by preventing oxidative stress. Metaphase II (MII) oocytes were cultured for 48 h with different concentrations of EGCG (0-100 μM)

The introduction of unnatural chemical moieties into glycosaminoglycans (GAGs) has enormous potential to facilitate studies of the mechanism and application of these critical, widespread molecules. Unnatural N -acetylhexosamine analogs were metabolically incorporated into the capsule polysaccharides of Escherichia coli and Bacillus subtilis via bacterial metabolism. Targeted metabolic labeled hyaluronan and the precursors of heparin and chondroitin sulfate were obtained. The azido-labeled polysaccharides (purified or in capsules) were reacted with dyes, via bioorthogonal chemistry, to enable detection and imaging. Site-specific introduction of fluorophores directly onto cell surfaces affords another choice for observing and quantifying bacteria in vivo and in vitro. Furthermore, azido-polysaccharides retain similar biological properties to their natural analogs, and reliable and predictable introduction of functionalities, such as fluorophores, onto azido- N -hexosamines in the disaccharide repeat units provides chemical tools for imaging and metabolic analysis of GAGs in vivo and in vitro.

A 24-fold increase in GlcNAc-transferase ability through KfiA screening and engineering. An approach for heparosan oligosaccharide synthesis relying on single-function glycosyltransferases.

Activating transcription factor 7 (ATF7) is a member of the ATF/cAMP response element (CRE) B superfamily. ATF2, ATF7, and CRE-BPa are present in vertebrates. Drosophila and fission yeast have only one homologue: dATF2 and Atf1, respectively. Under normal conditions, ATF7 promotes heterochromatin formation by recruiting histone H3K9 di- and tri-methyltransferases. Once the situation changes, all members are phosphorylated by the stress-activated kinase P38 in response to various stressors. However, the role of ATF7 in early porcine embryonic development remains unclear.In this study, we found that ATF7 gradually accumulated in the nucleus and then localized on the pericentric heterochromatin after the late 4-cell stage, while being co-localized with heterochromatin protein 1 (HP1). Knockdown of ATF7 resulted in decreases in the blastocyst rate and blastocyst cell number. ATF7 depletion resulted in downregulation of HP1 and histone 3 lysine 9 dimethylation (H3K9me2) expression. These effects were alleviated when P38 activity was inhibited. High temperatures increased the expression level of pP38, while reducing the quality of porcine embryos, and led to ATF7 phosphorylation. The expression level of H3K9me2 and HP1 was decreased and regulated by P38 activity.Stress-induced ATF7-dependent epigenetic changes play important roles in early porcine embryonic development.

There remains a challenge in designing electrocatalysts for water oxidation to create highly efficient catalytic sites for the oxygen evolution reaction (OER) while maintaining their robustness at large outputs. Herein, an etching-assisted synthesis approach was developed to integrate highly active NiFe2O4 nanoparticles with a robust and active NiOOH scaffold directly on commercial stainless steel. A precise selenization strategy was then introduced to achieve selective Se doping of NiFe2O4 to further enhance its intrinsic OER activity while maintaining a three-dimensional NiOOH nanosheet array as a robust scaffold for prompt mass transfer and gas evolution. The resulting NiFe2O4−xSex/NiOOH electrode exhibited superior electrocatalytic activity with low overpotentials of 153 and 259 mV to deliver benchmark current densities of 10 and 500 mA cm−2, respectively. More importantly, the catalyst exhibited remarkable durability at a stable current output of 100 mA cm−2 for hundreds of hours. These findings may open up opportunities for exploring efficient and robust electrocatalysts for scalable hydrogen production with practical materials.

This study aimed to compare the efficacy and safety of laparoscopic cholecystectomy combined with intraoperative endoscopic retrograde cholangiopancreatography (LC-IntraERCP) and laparoscopic cholecystectomy combined with laparoscopic common bile duct exploration (LC-LCBDE) to determine which one-stage therapeutic strategy provides better outcomes for patients with gallstones and common bile duct stones. Cochrane Library, EMBASE, PubMed, and Web of Science databases were searched to identify eligible articles from the database inception to September 2020. The revised Cochrane risk of bias tools for randomized trials (RoB-2) and non-randomized interventions (ROBINS-I) was used to assess the quality of the included studies. The overall quality of evidence was assessed through the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) tool. The primary outcomes consisted of surgical success, retained stones, and overall postoperative complications, while secondary outcomes included postoperative bleeding, postoperative pancreatitis, postoperative bile leakage, conversion to laparotomy, and operative time. Eight studies (four RCTs and four Non-RCTs with high quality) with 2948 patients were included. No significant difference was seen between the two groups regarding surgical success, overall postoperative complications, conversion to laparotomy, and operative time. The meta-analysis demonstrated that in the LC-IntraERCP group, the rate of retained stones (OR 0.51, 95% CI 0.28–0.91) and postoperative bile leakage were lower (OR 0.25, 95% CI 0.09–0.69), while in the LC-LCBDE group, postoperative bleeding (OR 5.24, 95% CI 1.65–16.65) and postoperative pancreatitis (OR 4.80, 95% CI 2.35–9.78) decreased. LC-IntraERCP and LC-LCBDE exhibited similar efficacies when surgical success rate, overall postoperative complications, conversion to laparotomy, and operative time were compared. However, LC-IntraERCP is probably to be more effective in terms of lowering the rate of retained stones.

In mammals, E2 factor (E2F) acts as a cell cycle regulator. E2F transcription factor 4 (E2F4) is a member of the E2F family of transcription factors and usually represents predominant E2F activity in cells. The E2F4 gene has been extensively studied in animals and is associated with multiple functions, such as cell cycle regulation and apoptosis; however, little is known about its role during embryonic development. In this study, we investigated the function of E2F4 and its mechanism of action in porcine embryo development. For this purpose, we knocked down E2F4 by microinjecting double-stranded RNA of E2F4 at the 1-cell stage. The results showed that E2F4 knockdown in porcine embryos led to a significant decrease in the blastocyst rate and total cell number. Defective E2F4 expression reduced the level of G1/S checkpoints (cyclin E-cyclin-dependent kinase 2) and cell cycle-related gene expression at the 4-cell embryo stage and blastocyst. Moreover, a decrease in E2F4 expression increased phosphorylated H2A.X variant histones and activated ataxia telangiectasia mutated (ATM) and p53-p21 pathway. In addition, E2F4 depletion caused a significant decrease in histone acetylation. Taken together, E2F4 plays a critical role as a transcriptional activator in the development of porcine embryos, an observation that contradicts its well-established role as a transcription repressor.

Background: Rotenone is a commonly used insecticidal chemical in agriculture and it is an inhibitor of mitochondrial complex 1. Previous studies have found that rotenone induces the production of reactive oxygen species (ROS) by inhibiting electron transport in the mitochondria of somatic and germ cells. However, there is little precise information on the effects of rotenone exposure in porcine oocytes during in vitro maturation, and the mechanisms underlying these effects have not been determined.Results: First, we found that the maturation rate and expansion of cumulus cells was significantly reduced in the 3 and 5 μM rotenone-treated groups. Further experiments showed that rotenone treatment induced mitochondrial dysfunction and failure of mitochondrial biogenesis by repressing the levels of PGC1-α and SIRT1 during in vitro maturation of porcine oocytes. In addition, rotenone treatment reduced the ratio of active mitochondria to total mitochondria, increased ROS production, and decreased ATP production. The levels of LC3 and active-caspase 3 were significantly increased by rotenone treatment, indicating that mitochondrial dysfunction induced by rotenone increased mitophagy but eventually led to apoptosis.Conclusions: Collectively, these results suggest that rotenone interferes with porcine oocyte maturation by inhibiting mitochondrial function.

Pairing the positive and negative electrodes with their individual dynamic characteristics properly matched is essential to the optimal design of electrochemical energy storage devices. However, the complex relationship between the performance data measured for individual electrodes and the two-electrode cells used in practice often makes an optimal pairing experimentally challenging. In this work, taking graphene-based supercapacitors as an example, we combine experiments with machine learning to generate a large pool of capacitance data for graphene-based electrode materials with varied slit pore sizes and thicknesses, and numerically pair them into different combinations for two-electrode cells. The as-achieved pairing results allow us to conduct a comprehensive analysis of the correlations between the key electrode structural features of individual electrodes and volumetric capacitance of the resultant two-electrode cells. The results show that the optimal pairing parameters are varied considerably with the operation rate of the cells and are even influenced by the thickness of the inactive components. The best-performing individual electrode does not necessarily result in optimal cell-level performance. The machine learning-assisted pairing approach presents much higher efficiency compared with the traditional trial-and-error approach for the optimal design of supercapacitors and provides an additional effective avenue for further improving the performance of supercapacitors and is expected to play an enabling role in the future on-demand design of energy storage devices. The results observed in this work also indicate the call for comprehensive performance data reporting in the electrochemical energy storage field to enable the adoption of artificial intelligence techniques to accelerate the translation of academic research in this rapidly growing field.

Strong metal-support interaction (SMSI), commonly happening between metal and metal oxide support, has drawn significant attention in heterogeneous catalysis due to its capability of enhancing the activity and stability of catalysts. Herein, the strong interaction between metal oxide and carbon supports is discovered to significantly boost the performance for electrocatalytic CO2 reduction reaction (CO2RR). A molecular engineering strategy is designed to develop undoped, N-doped, S-doped, and N,S-codoped porous carbon supports with similar physical properties (denoted as C, NC, SC, and NSC, respectively). These supports can host high-density SnO2 nanoparticles (over 60 wt. %) in a small size of ∼3.5 nm and good distribution, providing an excellent platform to understand the strong metal oxide-support interaction (SMOSI) and their influence on electrocatalytic performance. Systematic experimental and theoretical investigations discover the SMOSI between SnO2 nanoparticles and carbon supports in an order of SnO2/NSC > SnO2/NC > SnO2/SC > SnO2/C. Such SMOSI enables the effective electron transfer from carbon support to SnO2 nanoparticles, strengthening the adsorption of key reaction intermediate of CO2- and thus promoting CO2RR. With the strongest SMOSI, SnO2/NSC exhibits significantly enhanced selectivity and activity for CO2 reduction to HCOOH with a high faradaic efficiency of 94.4% and an extraordinary partial current density of 56.0 mA·cm-2 in an H-cell, outperforming the majority of Sn-based catalysts. Notably, SMOSI can simultaneously secure the active sites and thus remarkably enhance their catalytic durability, making it a promising strategy for exploring efficient and stable catalysts for diverse applications.

Modal properties are recognized as indicators reflecting structural condition in structural health monitoring (SHM). However, changing environmental and operational variables (EOVs) cause variability in the identified modal parameters and subsequently obscure damage effects. To address the issue caused by EOV-related variability, this study investigated the variability of modal frequencies in long-term SHM of a steel plate-girder bridge. A Bayesian fast Fourier transform (FFT) method was used for operational modal analysis in a probabilistic viewpoint. Bayesian linear regression (BLR) and Gaussian process regression (GPR) models were utilized to capture the variability in the identified most probable values (MPVs) of modal frequencies as temperature-driven models, and the limitation of these models for data normalization with latent EOVs is discussed. To overcome the interference of latent EOVs indirectly, a long short-term memory (LSTM) network was established to trace the variability as an autocorrelated process, with a traditional seasonal autoregressive integrated moving average (SARIMA) model as a benchmark. Finally, an anomaly detection method based on residuals of one-step-ahead predictions by LSTM was proposed associating with the Mann-Whitney U-test.

Intrinsic DNA properties such as bending play a crucial role in diverse biological systems. A recent advantage in the high-throughput method called loop-seq makes it possible to determine bendability of hundred thousand 50-bp DNA duplexes in one experiment. However, it’s still infeasible to assess whole sequence bendability in large genomes such as human, which needs thousands of loop-seq experiments. Here we introduce ‘BendNet’ – a neural network to accurately predict the intrinsic DNA bending at base-resolution by only given DNA sequences. BendNet can increase the resolution of experimental results, and can predict DNA bendability for any new given sequences in high accuracy. We applied BendNet to the human genome and observed high-stiffness regions located at both transcriptional start sites and transcriptional end sites. Such stiffness patterns are different for coding and non-coding genes, which matches distinct nucleosome occupancy patterns. As expected, most transcription factors (TFs) bind in DNA of low bendability. In contrast, we observed an unusually high bendability within binding elements of specific TFs such as EBF1 and regulators of genome folding such as CTCF. These factors either co-bind or compete with nucleosomes to carry out their functions. More interestingly, CTCF binding regions exhibit the highest bendability than other DNA elements, implying their potential role in trapping and holding the CTCF in the exact locations to make sure CTCF as stable anchor in loop extrusion process. Our work provides a tool to assess DNA bendability for large-scale DNA sequences and expands our understanding on DNA mechanics in chromatin regulation and genome folding.

Tumor-associated macrophages (TAMs) constitute a large population of glioblastoma and facilitate tumor growth and invasion of tumor cells, but the underlying mechanism remains undefined. In this study, we demonstrate that chemokine (C-C motif) ligand 8 (CCL8) is highly expressed by TAMs and contributes to pseudopodia formation by GBM cells. The presence of CCL8 in the glioma microenvironment promotes progression of tumor cells. Moreover, CCL8 induces invasion and stem-like traits of GBM cells, and CCR1 and CCR5 are the main receptors that mediate CCL8-induced biological behavior. Finally, CCL8 dramatically activates ERK1/2 phosphorylation in GBM cells, and blocking TAM-secreted CCL8 by neutralized antibody significantly decreases invasion of glioma cells. Taken together, our data reveal that CCL8 is a TAM-associated factor to mediate invasion and stemness of GBM, and targeting CCL8 may provide an insight strategy for GBM treatment.

Despite the fact that thyroid surgery has evolved towards minimal incisions and endoscopic approaches, the role of total endoscopic thyroidectomy (TET) in thyroid cancer has been highly disputed. We performed a systematic review and meta-analyses of peer reviewed studies in order to evaluate the safety and effectiveness of TET compared with conventional open thyroidectomy (COT) in papillary thyroid cancer (PTC). Medical literature databases such as PubMed, Embase, the Cochrane Library, and Web of science were systematically searched for articles that compared TET and COT in PTC treatment from database inception until March 2019. The quality of the studies included in the review was evaluated using the Downs and Black scale using Review Manager software Stata V.13.0 for the meta-analysis. The systematic review and meta-analysis were based on 5664 cases selected from twenty publications. Criteria used to determine surgical completeness included postoperative thyroglobulin (TG) levels, recurrence of the tumor after long-term follow-up. Adverse event and complication rate scores included transient recurrent laryngeal nerve (RLN) palsy, permanent RLN palsy, transient hypocalcaemia, permanent hypocalcaemia, operative time, number of removed lymph nodes, length of hospital stay and patient cosmetic satisfaction. TET was found to be generally equivalent to COT in terms of surgical completeness and adverse event rate, although TET resulted in lower levels of transient hypocalcemia (OR 1.66; p

Podophyllotoxin (PPT) is a lignan extracted from podophyllum genera and it shows potent antitumor activity since it could effectively inhibit the assembly of microtubule in tumor cells. However, the effects of podophyllotoxin exposure on porcine oocyte quality is still unclear. In present study we tried to examine whether podophyllotoxin exposure was toxic to porcine oocyte maturation. Our results showed that podophyllotoxin exposure inhibited porcine oocyte maturation, showing with the failure of polar body extrusion, and the inhibitory effects of podophyllotoxin on porcine oocytes was dose-depended. Moreover, the meiotic spindle formation was disturbed and the chromosomes were misaligned in the podophyllotoxin-treated porcine oocytes. However, there was no different expression for p-MAPK and ace-tubulin between the control and podophyllotoxin treatment group. In addition, after 0.01 μM podophyllotoxin treatment, the intracellular reactive oxygen species (ROS) levels and the Annexin-V signal at MI stage significantly increased compared to the control group, indicating the occurrence of oxidative stress and early apoptosis. Taken together, our results suggested that the toxic effects of podophyllotoxin exposure on porcine oocyte maturation might be through its effects on spindle formation and the induction of oxidative stress-mediated early apoptosis.

Aging oocytes undergo various molecular, cellular, and biochemical changes. Aging of oocytes results in reduced embryo developmental capacity and blastocyst quality, which is thought to be caused partly by the accumulation of reactive oxygen species (ROS). This study aimed to determine the effect of l -carnitine (LC) on the development of embryos formed from aged oocytes in vitro. The development and quality of the blastocysts in the LC-treated group were significantly higher than those in the untreated aged group after in vitro fertilization (IVF). In addition, after LC treatment, the level of intracellular ROS in aged group significantly decreased, and glutathione (GSH) levels significantly increased compared with those in the untreated aged group. There was no significant difference in the mitochondrial membrane potential among the three groups. Moreover, ROS could induce autophagy and LC3 antibody was widely used as a marker for detecting autophagy. The fluorescence intensity of LC3 in the aged group was significantly higher than that of LC3 in the LC-treated group. Furthermore, Real-time reverse transcriptase-polymerase chain reaction showed that the mRNA levels of antioxidation genes GPX4 and SOD1 were significantly higher in embryos from LC-treated group than in those from the untreated aged group. In summary, our results indicated that LC can improve the developmental capacity of embryos from aging oocytes in vitro by reducing oxidative stress.

The electrochemical nitrogen reduction reaction (NRR) as an energy-efficient approach for ammonia synthesis is hampered by the low ammonia yield and ambiguous reaction mechanism. Herein, phosphorus-doped carbon nanotube (P-CNTs) is developed as an efficient metal-free electrocatalyst for NRR with a remarkable NH3 yield of 24.4 μg·h−1·mg−1cat. and partial current density of 0.61 mA·cm−2. Such superior activity is found to be from P doping and highly conjugated CNTs substrate. Experimental and theoretical investigations discover that the electron-deficient phosphorus sites with Lewis acidity should be genuine active sites and NRR on P-CNTs follows the distal pathway. These findings provide insightful understanding on NRR processes on P-CNTs, opening up opportunities for the rational design of highly-active cost-effective metal-free catalysts for electrochemical ammonia synthesis.

Fe-doped Co3O4 polycrystalline nanosheets vertically grown on carbon cloth were developed as self-standing efficient bifunctional electrocatalysts for oxygen reduction and evolution, enabling high-performance Zn–air batteries with a power density of 268.6 mW cm−2 and superior cycling stability.

Exploring advanced electrocatalysts for the sluggish oxygen reduction reaction is extremely important for fuel cell commercialization but still remains a great challenge, especially the durability issue that gains increasing attention. Herein, we demonstrate an extremely durable catalyst prototype that combines structurally ordered intermetallic nanoparticles (NPs) with mesoporous carbon. With ZIF-8 derived mesoporous carbon supported Pt3Co intermetallic NPs (Pt3Co/DMC-F) as an example, we illustrate its synthetic details, electrocatalytic performance and durability enhancement mechanism. The Pt3Co/DMC-F catalyst exhibited significant enhancement in activity and durability. More importantly, its extraordinary performance was observed/verified in a H2/air PEM single cell test. The confinement of mesoporous carbon not only efficiently controls the particle size of Pt3Co and hampers their aggregation during thermal annealing and electrochemical reactions, but also significantly suppresses detachment. Beyond offering an advanced electrocatalyst, this study provides a solution to the durability issue of cathodes that has prevented practical application of proton exchange membrane fuel cells.

Although the significance of charge diffusion has been recognized in many high-performance energy devices, it has received very less attention in the design of electrocatalysts for the oxygen evolution reaction (OER), which is particularly crucial for highly active but less conductive OER electrocatalysts, such as two-dimensional metal hydroxides (MHs) with anisotropic conductivity. Herein, we report the elaborate design of a series of CoFe hydroxide nanosheets on graphene (CFH@G) composites to demonstrate the importance of charge diffusion regulation in improving the OER activity of MHs. It was discovered that the few-layer-thick CFH nanosheets lying on the graphene substrate provided an effective in-plane charge diffusion pathway, while keeping the substrate surface entirely covered by the laid nanosheets is necessary for providing sufficient active sites. The overly thick or stacked nanosheets are not favourable for charge diffusion, especially at large current outputs. By regulating the charge diffusion properties, the best-performing CFH@G-based material can deliver a steady OER current density of 2000 mA cm−2 at a cost of only 1.507 V under near-industrial conditions (6 M KOH and 60 °C). A practical water electrolyzer also demonstrated an impressive current output of 400 mA cm−2 at 1.694 V as well as a steady solar-to-hydrogen efficiency of 17.41%. These findings provide new insights into the role of charge diffusion in water oxidation and may open up an avenue for developing low-cost, stable and efficient electrocatalysts for practical water electrolysis and diverse energy devices.

Developing efficient, durable, and economical electro-catalysts for large-scale commercialization of hydrogen evolution (HER) is still challenging. Herein, we report for the first time, to the best of our knowledge, a Pd-based ternary metal phosphide as an active and stable HER catalyst. The face-centered-cubic Pd–Ni–P nanoparticles (NPs) annealed at 400 °C show the best HER activity with a low overpotential of 32 mV to realize a current density of 10 mA cm−2 and a high mass activity of 1.23 mA μg−1Pd, superior to Pd NPs, Pd–P NPs, Pd–Ni NPs, and Pd–Ni–P NPs annealed under different temperatures. Moreover, this catalyst is also highly stable during 20 h of continuous electrolysis. Notably, the easily fabricated Pd–Ni–P NPs are among the most active Pd-based HER catalysts. This work indicates that Pd-based metal phosphides could be potentially applied as a type of practical HER catalyst and might inform the fabrication of analogous materials for hydrogen-related applications.

Heat stress (HS) has been known to cause reproductive failure in animals, especially in summer. HS severely affects the developmental potential of oocytes and leads to low fertility rates. Previous studies have reported that HS compromises embryo development in bovine oocytes, and reduces ovarian development in mice, thereby impairing reproductive function in animals. However, the effect of high temperature (HT) on the organelles of porcine oocytes is unknown. In this study, we reported that exposure to HT for 24 h (41°C) significantly decreased meiotic maturation in porcine oocytes (p < 0.05). Further experiments on organelles found that HT induced mitochondrial dysfunction, increased abnormal mitochondrial distribution, and decreased mitochondrial membrane potential (MMP). We also found that HT induced abnormal endoplasmic reticulum (ER) distribution and higher expression of glucose regulatory protein 78 (GRP78), suggesting that HT exposure induces ER stress. Our results also indicated that exposure to HT induced abnormal distribution and dysfunction of the Golgi apparatus, which resulted from a decrease in the expression of the vesicle transporter, Ras-related protein Rab-11A (RAB11A). In addition, we found that HT exposure led to lysosomal damage by increasing the expression of lysosome-associated membrane protein 2 (LAMP2) and microtubule-associated protein 1A/1B-light chain 3 (LC3). In summary, our study revealed that HT exposure disrupts organelle dynamics, which further leads to the failure of meiotic maturation in porcine oocytes.

Citrinin (CTN) is a polyketide mycotoxin produced by several strains of Penicillium, Monascus, and Aspergillus. While CTN poses various toxic effects on the female reproductive system in animals, its direct effects on germ cell development are unclear. This study aimed to evaluate the effects of increasing concentrations of CTN (0,20,40,80,100 μM) on porcine oocyte in vitro maturation. Our results indicate that CTN supplementation inhibited polar body extrusion in a dose-dependent manner. Actin and spindle assembly were also disrupted after treatment, indicating that CTN affects the cytoskeleton of porcine oocytes. Oxidative stress and apoptosis were observed under CTN treatment to explore the cause of meiotic maturation failure in porcine oocytes. The results showed that reactive oxygen species levels, cathepsin B activity, and caspase-3 activity were increased in the treated group, indicating that CTN induced oxidative stress and apoptosis. In conclusion, CTN exposure could reduce porcine oocyte maturation by affecting cytoskeletal dynamics, oxidative stress, and apoptosis.

The recent emergence of electrically conductive nanoporous membranes based on graphene and other 2D materials opens up new opportunities to revisit some longstanding nanoconfined ion transport problems under electrification. This work probes the ionic resistance in electrified multilayered graphene membranes with electrochemical impedance spectroscopy. This study demonstrates that the combination of additive-free feature and tunable slit pore sizes in the sub-10 nm range in graphene-based membranes has made it possible to deconvolute the different ionic processes from the impedance obtained and examine the exclusive influence of pore size on the ionic resistance in a quantitative manner. The trends revealed for the ionic resistance at the pore entrance and inside the pores under severe nanoconfinement (2 nm) are found to be generally consistent with the microscale theoretical simulations previously reported. It also allows a quantitative analysis of the relative effects of the external polarization potential and ion identity under nanoconfinement. The results suggest that the classic electrochemical impedance spectroscopy technique, when applied to appropriate nanoporous electrode materials, can provide rich information about nanoconfined ion transport phenomena under electrification for fundamental understanding and application development.

Single-atom catalysts (SACs) have been at the frontier of research field in catalysis owing to the maximized atomic utilization, unique structures and properties. The atomically dispersed and catalytically active metal atoms are necessarily anchored by surrounding atoms. As such, the structure and composition of anchoring sites significantly influence the catalytic performance of SACs even with the same metal element. Significant progress has been made to understand structure-activity relationships at an atomic level, but in-depth understanding in precisely designing highly efficient SACs for the targeted reactions is still required. In this review, various anchoring sites in SACs are summarized and classified into five different types (doped heteroatoms, defect sites, surface atoms, metal sites, and cavity sites). Then, their impacts on catalytic performance are elucidated for electrochemical reactions based on their distance from the metal center (first coordination shell and beyond). Further, SACs anchored on two typical types of hosts, carbon- and metal-based materials, are highlighted, and the effects of anchoring points on achieving the desirable atomic structure, catalytic performance, and reaction pathways are elaborated. At last, insights and outlook to the SAC field based on current achievements and challenges are presented.

Fe-N-C materials with Fe-Nx coordination sites are promising to replace the state-of-the-art Pt-based electrocatalysts for oxygen reduction reaction (ORR) due to high activity and low cost although there is still debate on its activity origin. Herein, we develop a strategy to investigate the role of iron species in Fe-N-C nanohybrids for catalysing ORR by delicately tuning the iron chemical state. By engineering peripheral substituents of iron porphyrin precursors, two Fe-N-C nanohybrids with metallic or oxidized iron species inside are achieved while holding the similar catalyst structure. Systematic experiments and theoretical analysis discover that metallic iron species promote the electrocatalytic activity of Fe-Nx sites for ORR, while oxidative ones inhibit O2 adsorption on Fe-Nx sites, decreasing their ORR activity. This finding sheds light on unravelling the activity origin in Fe-N-C electrocatalysts for ORR towards their applications in energy devices.