Regulating the Coordination Geometry and Oxidation State of Single-Atom Fe Sites for Enhanced Oxygen Reduction Electrocatalysis.

FeNC catalysts demonstrate remarkable activity and stability for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells and Zn-air batteries (ZABs). The local coordination of Fe single atoms in FeNC catalysts strongly impacts ORR activity. Herein, FeNC catalysts containing Fe single atoms sites with FeN3 , FeN4 , and FeN5 coordinations are synthesized by carbonization of Fe-rich polypyrrole precursors. The FeN5 sites possess a higher Fe oxidation state (+2.62) than the FeN3 (+2.23) and FeN4 (+2.47) sites, and higher ORR activity. Density functional theory calculations verify that the FeN5 coordination optimizes the adsorption and desorption of ORR intermediates, dramatically lowering the energy barrier for OH- desorption in the rate-limiting ORR step. A primary ZAB constructed using the FeNC catalyst with FeN5 sites demonstrates state-of-the-art performance (an open circuit potential of 1.629 V, power density of 159 mW cm-2 ). Results confirm an intimate structure-activity relationship between Fe coordination, Fe oxidation state, and ORR activity in FeNC catalysts.

Recent Advances in Self-Supported Semiconductor Heterojunction Nanoarrays as Efficient Photoanodes for Photoelectrochemical Water Splitting.

Growth of semiconductor heterojunction nanoarrays directly on conductive substrates represents a promising strategy toward high-performance photoelectrodes for photoelectrochemical (PEC) water splitting. By controlling the growth conditions, heterojunction nanoarrays with different morphologies and semiconductor components can be fabricated, resulting in greatly enhanced light-absorption properties, stabilities, and PEC activities. Herein, recent progress in the development of self-supported heterostructured semiconductor nanoarrays as efficient photoanode catalysts for water oxidation is reviewed. Synthetic methods for the fabrication of heterojunction nanoarrays with specific compositions and structures are first discussed, including templating methods, wet chemical syntheses, electrochemical approaches and chemical vapor deposition (CVD) methods. Then, various heterojunction nanoarrays that have been reported in recent years based on particular core semiconductor scaffolds (e.g., TiO2 , ZnO, WO3 , Fe2 O3 , etc.) are summarized, placing strong emphasis on the synergies generated at the interface between the semiconductor components that can favorably boost PEC water oxidation. Whilst strong progress has been made in recent years to enhance the visible-light responsiveness, photon-to-O2 conversion efficiency and stability of photoanodes based on heterojunction nanoarrays, further advancements in all these areas are needed for PEC water splitting to gain any traction alongside photovoltaic-electrochemical (PV-EC) systems as a viable and cost-effective route toward the hydrogen economy.

Liver Fibrosis in the Natural Course of Chronic Hepatitis B Viral Infection: A Systematic Review with Meta-Analysis.

BACKGROUND: Quantitative data are limited on the natural course of liver fibrosis in patients with chronic HBV infection (CHB). AIMS: To estimate the prevalence of fibrosis status including non-fibrosis, significant fibrosis, advanced fibrosis, and cirrhosis throughout the natural course of CHB. METHODS: We searched Cochrane library, EMBASE, PubMed, SCOPUS, Web of Science, and ScienceDirect from January 1993 to November 2019 for studies with histologic data on liver fibrosis in CHB natural course. CHB course was defined based on current criteria for identifying infection phases as recommended by international clinical practice guidelines, including the HBeAg-positive immune-tolerant, HBeAg-positive immune-active, HBeAg-negative immune-inactive, HBeAg-negative immune-reactive, and HBsAg-negative phases. Pooled prevalence rate of fibrosis status at each phase was obtained from random-effect meta-analyses. RESULTS: Thirty-three studies with 9,377 adult participants (23.8-49.0 age years; 45.5-88.6% males) were eligible and finally included. The estimated prevalence of non-fibrosis, significant fibrosis, advanced fibrosis, and cirrhosis was, for HBeAg-positive immune-tolerant phase: 31.2% (95%CI 15.6-46.7), 16.9% (95%CI 7.8-26.1), 5.4% (95%CI 0.0-11.2), and 0.0% (95%CI 0.0-1.5); HBeAg-positive immune-active phase: 6.9% (95%CI 3.6-10.2), 50.6% (95%CI 39.2-61.9), 32.1% (95%CI 24.2-40.0), and 12.8% (95%CI 8.6-17.0); HBeAg-negative immune-inactive phase: 32.4% (95%CI 0.0-100.0), 24.8% (95%CI 4.5-45.1), 3.0% (95%CI 0.0-8.3), and 0.0% (95%CI 0.0-1.0); and HBeAg-negative immune-reactive phase: 6.3% (95%CI 3.5-9.2), 50.3% (95%CI 38.9-61.7), 30.3% (95%CI 20.9-39.6), and 10.0% (95%CI 6.6-13.5), respectively. There was only one study for HBsAg-negative phase, thus not allowing further meta-analyses. CONCLUSIONS: Fibrosis risk persists through CHB natural course. These data can support risk estimation in clinical practice and provide reference for noninvasive investigation.

Atomic Cation-Vacancy Engineering of NiFe-Layered Double Hydroxides for Improved Activity and Stability towards the Oxygen Evolution Reaction.

NiFe-layered double hydroxides (NiFe-LDH) are among the most active catalysts developed to date for the oxygen evolution reaction (OER) in alkaline media, though their long-term OER stability remains unsatisfactory. Herein, we reveal that the stability degradation of NiFe-LDH catalysts during alkaline OER results from a decreased number of active sites and undesirable phase segregation to form NiOOH and FeOOH, with metal dissolution underpinning both of these deactivation mechanisms. Further, we demonstrate that the introduction of cation-vacancies in the basal plane of NiFe LDH is an effective approach for achieving both high catalyst activity and stability during OER. The strengthened binding energy between the metals and oxygen in the LDH sheets, together with reduced lattice distortions, both realized by the rational introduction of cation vacancies, drastically mitigate metal dissolution from NiFe-LDH under high oxidation potentials, resulting in the improved long-term OER stability. In addition, the cation vacancies (especially M3+ vacancies) accelerate the evolution of surface γ-(NiFe)OOH phases, thereby boosting the OER activity. The present study highlights that tailoring atomic cation-vacancies is an important strategy for the development of active and stable OER electrocatalysts.

Tuning Interfacial Structures for Better Catalysis of Water Electrolysis.

Interface modulation, as an old concept of heterogeneous catalysis, represents an emerging, fast-growing and exciting direction in the field of water electrolysis. Over the past five years, diverse hetero-nanostructures have been synthesised as water electrolysis catalysts by taking advantage of interface modulation. However, it seems that the performance (i.e., efficiency and durability) of these materials needs to be further improved. Therefore, a comprehensive summary of recent achievements and the challenging issues concerning the regulation of material functionalities through interface modulation is necessary and helpful. Herein, firstly, the fundamentals of water electrolysis are outlined, and then the delicate design and fine control of well-defined interfaces, as well as related mechanisms for performance improvement are discussed. Finally, future opportunities and challenges in the everlasting pursuit of highly efficient and robust water electrolysis catalysts are highlighted.

Preparation of Hollow Nitrogen Doped Carbon via Stresses Induced Orientation Contraction.

Hollow structured materials are widely applicable in various fields. Although many routes have been explored for getting such materials, a strategy mainly based on physical effect is still deficient. Herein, a "stresses induced orientation contraction" mechanism for preparation of hollow structures is reported. The composites constructed by zeolite imidazolate framework-8 (ZIF8) cores and polymerized dopamine (PDA) shells, upon annealing, form intensive interfacial interactions, which drag the ZIF8 cores outward to restrain their shrinkage. The gradually accumulated stresses in the central position of ZIF8 dodecahedron nanoparticles, then destroy the ZIF8 crystalline cores to form the hollow structures. In this stress-based route for creating hollow interiors with core-shell composites as the starting materials, three critical factors are necessary: 1) an intensive core-shell interfacial interaction; 2) the distinctly higher shrinkage degree of the cores than the shells; and 3) the relatively loose core structures. In oxygen reduction reaction (ORR) tested with three-electrode solution system and Zn-O2 battery, the achieved hollow nitrogen doped carbon (NC) demonstrates ultrahigh catalytic activities. This work gives an absolutely novel strategy for preparation of hollow structures, which may afford the exploration of a wider range of materials system with hollow interiors.

Exploring Fe-Nx for Peroxide Reduction: Template-Free Synthesis of Fe-Nx Traumatized Mesoporous Carbon Nanotubes as an ORR Catalyst in Acidic and Alkaline Solutions.

Fe-based electrocatalysts are elegant due to their better performance towards the oxygen reduction reaction. Nevertheless, they commonly contain different moieties, for example Fe-Nx , Fe, Fe3 C and N-doped carbon, primarily the debatable assistance of these components towards ORR electrocatalysis, specifically for intermediate peroxide reduction reactions (PRR). In this paper, to explore the role of Fe-Nx centres for PRR, a Fe-N-C electrocatalyst rooted in nitrogen-doped carbon nanotubes with mesoporous structures was synthesized from a Fe/Zn-dicyanoimidazolate framework. The use of dicyanoimidazole coordinated with iron can introduce the Fe-Nx active sites as well as directional N-doped carbon nanotubes, which is good for enhancing electronic conductance of the catalyst. The attained electrocatalyst shows tremendous enactment to ORR, being comparable to the activity of Pt/C in acidic and better in alkaline electrolytes. This study also reveals that Fe-Nx active centres are responsible for less H2 O2 production. Though the Fe-Nx moieties and Fe3 C/Fe particles encapsulated N-doped carbon, both are active centres for ORR, however, Fe-Nx sites are more active than others for peroxide reduction reaction. These perceptions suggest rational methodologies for more active and consequently further durable Fe-N-C catalysts.

Recent Progress on Copper-Based Bimetallic Heterojunction Catalysts for CO2 Electrocatalysis: Unlocking the Mystery of Product Selectivity.

Copper-based bimetallic heterojunction catalysts facilitate the deep electrochemical reduction of CO2 (eCO2RR) to produce high-value-added organic compounds, which hold significant promise. Understanding the influence of copper interactions with other metals on the adsorption strength of various intermediates is crucial as it directly impacts the reaction selectivity. In this review, an overview of the formation mechanism of various catalytic products in eCO2RR is provided and highlight the uniqueness of copper-based catalysts. By considering the different metals' adsorption tendencies toward various reaction intermediates, metals are classified, including copper, into four categories. The significance and advantages of constructing bimetallic heterojunction catalysts are then discussed and delve into the research findings and current development status of different types of copper-based bimetallic heterojunction catalysts. Finally, insights are offered into the design strategies for future high-performance electrocatalysts, aiming to contribute to the development of eCO2RR to multi-carbon fuels with high selectivity.

Dopant-Induced Charge Redistribution on the 3D Sponge-like Hierarchical Structure of Quaternary Metal Phosphides Nanosheet Arrays Derived from Metal-Organic Frameworks for Natural Seawater Splitting.

Dopant-induced electron redistribution on transition metal-based materials has long been considered an emerging new electrocatalyst that is expected to replace noble-metal-based electrocatalysts in natural seawater electrolysis; however, their practical applications remain extremely daunting due to their sluggish kinetics in natural seawater. In this work, we developed a facile strategy to synthesize the 3D sponge-like hierarchical structure of Ru-doped NiCoFeP nanosheet arrays derived from metal-organic frameworks with remarkable hydrogen evolution reaction (HER) performance in natural seawater. Based on experimental results and density functional theory calculations, Ru-doping-induced charge redistribution on the surface of metal active sites has been found, which can significantly enhance the HER activity. As a result, the 3D sponge-like hierarchical structure of Ru-NiCoFeP nanosheet arrays achieves low overpotentials of 52, 149, and 216 mV at 10, 100, and 500 mA cm-2 in freshwater alkaline, respectively. Notably, the electrocatalytic activity of the Ru-NiCoFeP electrocatalyst in simulated alkaline seawater and natural alkaline seawater is nearly the same as that in freshwater alkaline. This electrocatalyst exhibits superior catalytic properties with outstanding stability under a high current density of 85 mA cm-2 for more than 100 h in natural seawater, which outperforms state-of-the-art 20% Pt/C at high current density. Our work provides valuable guidelines for developing a low-cost and high-efficiency electrocatalyst for natural seawater splitting.

Boosting Urea-Assisted Natural Seawater Electrolysis in 3D Leaf-Like Metal-Organic Framework Nanosheet Arrays Using Metal Node Engineering.

Metal node engineering, which can optimize the electronic structure and modulate the composition of poor electrically conductive metal-organic frameworks, is of great interest for electrochemical natural seawater splitting. However, the mechanism underlying the influence of mixed-metal nodes on electrocatalytic activities is still ambiguous. Herein, a strategic design is comprehensively demonstrated in which mixed Ni and Co metal redox-active centers are uniformly distributed within NH2-Fe-MIL-101 to obtain a synergistic effect for the overall enhancement of electrocatalytic activities. Three-dimensional mixed metallic MOF nanosheet arrays, consisting of three different metal nodes, were in situ grown on Ni foam as a highly active and stable bifunctional catalyst for urea-assisted natural seawater splitting. A well-defined NH2-NiCoFe-MIL-101 reaches 1.5 A cm-2 at 360 mV for the oxygen evolution reaction (OER) and 0.6 A cm-2 at 295 mV for the hydrogen evolution reaction (HER) in freshwater, substantially higher than its bimetallic and monometallic counterparts. Moreover, the bifunctional NH2-NiCoFe-MIL-101 electrode exhibits eminent catalytic activity and stability in natural seawater-based electrolytes. Impressively, the two-electrode urea-assisted alkaline natural seawater electrolysis cell based on NH2-NiCoFe-MIL-101 needs only 1.56 mV to yield 100 mA cm-2, much lower than 1.78 V for alkaline natural seawater electrolysis cells and exhibits superior long-term stability at a current density of 80 mA cm-2 for 80 h.

Neoadjuvant sintilimab plus chemotherapy in EGFR-mutant NSCLC: Phase 2 trial interim results (NEOTIDE/CTONG2104).

The clinical efficacy of neoadjuvant immunotherapy plus chemotherapy remains elusive in localized epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer (NSCLC). Here, we report interim results of a Simon's two-stage design, phase 2 trial using neoadjuvant sintilimab with carboplatin and nab-paclitaxel in resectable EGFR-mutant NSCLC. All 18 patients undergo radical surgery, with one patient experiencing surgery delay. Fourteen patients exhibit confirmed radiological response, with 44% achieving major pathological response (MPR) and no pathological complete response (pCR). Similar genomic alterations are observed before and after treatment without influencing the efficacy of subsequent EGFR-tyrosine kinase inhibitors (TKIs) in vitro. Infiltration and T cell receptor (TCR) clonal expansion of CCR8+ regulatory T (Treg)hi/CXCL13+ exhausted T (Tex)lo cells define a subtype of EGFR-mutant NSCLC highly resistant to immunotherapy, with the phenotype potentially serving as a promising signature to predict immunotherapy efficacy. Informed circulating tumor DNA (ctDNA) detection in EGFR-mutant NSCLC could help identify patients nonresponsive to neoadjuvant immunochemotherapy. These findings provide supportive data for the utilization of neoadjuvant immunochemotherapy and insight into immune resistance in EGFR-mutant NSCLC.

Exhaustion of CD8+ T Cells in HBV Infection: Searching for Serological Markers.

OBJECTIVE: Chronic infection of the hepatitis B virus (HBV) is associated with the dysfunction and exhaustion of CD8+ T cells, which are crucial in controlling HBV. While clinical parameters provide insight into the state of HBV infection, the relationship between HBV biochemical parameters and CD8+ T cell exhaustion remains poorly understood. This study aimed to evaluate the expression of activation, exhaustion, and function-related markers in CD8+ T cells of HBV carriers, and to determine the potential of HBV clinical parameters as biomarkers for CD8+ T cell exhaustion. METHODS: We enrolled 93 patients with HBV and measured the expression levels of CD160, T cell Ig and mucin-domain containing-3 (Tim-3), programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte antigen 4 (CTLA-4), CD28, CD137, granzyme B, and perforin in CD8+ T cells using flow cytometry. HBV clinical parameters including, HBsAg, HBsAb, HBeAg, HBeAb, HBcAb, HBV DNA load, ALT, AST, ABil, and ALB, were measured in the blood samples. RESULTS: Patients were divided into two groups, HBV DNA+, and HBV DNA-, based on whether their HBV DNA load was below the test baseline; ALT, AST, and CD160+CD8+ T cell percentages were significantly higher in the HBV DNA+ group than in the HBV DNA- group (P=0.0323; P=0.0072; P=0.0458). However, the granzyme B-expressing CD8+ T cell percentage in the HBV DNA-group was higher than the HBV DNA+ group (P=0.0497). In the HBV DNA+ group, CD160, Tim-3, CD28, and perforin were significantly correlated with ALT, granzyme B was significantly correlated with AST; however, there was no correlation with HBV DNA load. CONCLUSION: It is possible to infer the level of CD8+ T cell exhaustion in patients with an HBV DNA load >102 copies/mL based on clinical parameters (such as ALT, AST, and ABIL).

Recent advances in bifunctional dual-sites single-atom catalysts for oxygen electrocatalysis toward rechargeable zinc-air batteries.

Rechargeable zinc-air batteries (ZABs) with high energy density and low pollutant emissions are regarded as the promising energy storage and conversion devices. However, the sluggish kinetics and complex four-electron processes of oxygen reduction reaction and oxygen evolution reaction occurring at air electrodes in rechargeable ZABs pose significant challenges for their large-scale application. Carbon-supported single-atom catalysts (SACs) exhibit great potential in oxygen electrocatalysis, but needs to further improve their bifunctional electrocatalytic performance, which is highly related to the coordination environment of the active sites. As an extension of SACs, dual-sites SACs with wide combination of two active sites provide limitless opportunities to tailor coordination environment at the atomic level and improve catalytic performance. The review systematically summarizes recent achievements in the fabrication of dual-site SACs as bifunctional oxygen electrocatalysts, starting by illustrating the design fundament of the electrocatalysts according to their catalytic mechanisms. Subsequently, metal-nonmetal-atom synergies and dual-metal-atom synergies to synthesize dual-sites SACs toward enhancing rechargeable ZABs performance are overviewed. Finally, the perspectives and challenges for the development of dual-sites SACs are proposed, shedding light on the rational design of efficient bifunctional oxygen electrocatalysts for practical rechargeable ZABs.

Neoadjuvant immunotherapy in patients with pulmonary lymphoepithelioma-like carcinoma.

OBJECTIVES: Neoadjuvant immunotherapy can be used to treat early-stage non-small-cell lung cancer; however, their effects on pulmonary lymphoepithelioma-like carcinomas (LELC) remain unclear. MATERIALS AND METHODS: Thirty-nine patients with stages I-III LELC were treated with chemotherapy (Chemo) or neoadjuvant immune-checkpoint inhibitors (ICIs) with or without chemo (IO) before radical-intent surgery. Short-term outcomes included objective response rate (ORR), major pathologic response (MPR), pathologic complete response (PCR), and event-free survival. For comparison, we used IO to treat 63 patients with pulmonary squamous cell carcinomas (SQC) and 47 with adenocarcinomas (ADC). Propensity score matching was analyzed to minimize bias. RESULTS: ORRs of the LELC-IO and LELC-Chemo groups were 62.5% and 42.9%, respectively (odds ratio, 2.2, 95% confidence interval, 0.423-11.678, p = 0.346). Seven (21.9%) and zero patients in LELC-IO and LELC-Chemo groups, respectively, reached PCR. MPR was identified in five (15.6%) of the 32 patients with LELC-IO. The 1-year progression-free survival rates were 96.9% and 71.4% in IO and Chemo groups, respectively (p > 0.05). However, no difference was observed in ORR, PCR, and MPR between LELC and SQC groups (ORR, 63.2% vs. 68.4%, p > 0.05; PCR, 21.1% vs. 47.4, p > 0.05; MPR, 42.1% vs. 57.9%, p > 0.05) and LELC and ADC groups (ORR, 58.8% vs. 41.2%, p > 0.05; PCR, 17.6% vs. 23.5%, p = 0.672; MPR, 29.4% vs. 47.1%, p > 0.05). The plasma Epstein-Barr virus (EBV) DNA level in a patient was altered posttreatment. CONCLUSION: Patients with LELC could be benefit from neoadjuvant immunotherapy. Distinct histological subtypes demonstrated comparable efficacy with respect to neoadjuvant immunotherapy.

Challenging the Surge of Inflammatory Bowel Disease: The Role of the China Crohn's and Colitis Foundation in the Healthcare Landscape of Inflammatory Bowel Disease.

Inflammatory bowel disease (IBD) is a chronic and lifelong disease, and patients must ultimately learn to live with and manage the condition. With advances in diagnostics and treatment in IBD, healthcare professionals (HCPs) and patients are now concerned with both quality of care (QOC) and quality of life (QOL). The China Crohn's and Colitis Foundation (CCCF) is committed to improving the QOC and QOL for IBD patients by garnering social resources. This paper details how CCCF has worked for better IBD management over the past 5 years. The foundation has 4 main projects: education programs for IBD HCPs and patients, support activities, public awareness and advocacy, and research programs. CCCF is an increasingly influential public welfare organization providing advocacy for IBD patients in China. The foundation is now entering the next stage of its development in pursuing professional operations and helping to solve the social problems experienced by IBD patients. The CCCF ultimately plans to pioneer reforms in China's medical system and hopefully provide a successful example of IBD advocacy for developing countries to emulate.

Constructing Ni-VN interfaces with superior electrocatalytic activity for alkaline hydrogen evolution reaction.

The promotional effects of inert nitrides for metal catalysts in the electrolysis are rarely reported. Recently, we reported an efficient Ni-VN/NF (that NF represents Ni foam) composite by nitriding treatment of NiV-layered double hydroxides (NiV-LDH) precursor that was in-situ hydrothermal growth on nickel foam. The optimal Ni-VN/NF exhibited outstanding electrocatalytic performance for hydrogen evolution reaction (HER) with a small overpotential of 39 mV at 10 mA cm-2 and strong durability for 100 h without degradation. The optimized electronic structure and local charge density at the hetero-interface of Ni-VN, evidenced by both experiment and DFT results, were significantly modulated by the electron transfer from Ni to V-N bond at the interfaces, leading to moderate H* adsorption energy and diminished barrier for H2O dissociation, synergistically promoted basic HER. This work highlights the design principle of strong metal-nitride interactions for advanced HER catalysts.

Electronic Tuning of Core-Shell CoNi Nanoalloy/N-Doped Few-Layer Graphene for Efficient Oxygen Electrocatalysis in Rechargeable Zinc-Air Batteries.

The discovery of highly efficient, durable, and affordable bifunctional ORR/OER electrocatalysts is of great significance for the commercialization of rechargeable metal-air batteries. Herein, we synthesized uniformly sized CoNi alloy nanoparticles encapsulated with N-doped few-layer graphene (N-FLG) sheets via pyrolysis of a CoNi dual metal-organic framework precursor. The developed CoNi/N-FLG catalyst exhibited excellent oxygen reduction activity (comparable to a commercial 20 wt % Pt/C catalyst) and outstanding oxygen evolution activity (superior to a commercial 20 wt % IrO2/C catalyst), thus enabling efficient bifunctional oxygen electrocatalysis and stability when applied in prototype rechargeable zinc-air batteries. The remarkable electrochemical properties of CoNi/N-FLG originate from its unique core-shell structure and favorable electron penetration effects, thereby optimizing the adsorption/desorption strengths of intermediates formed during the oxygen reduction and oxygen evolution reactions.

Mesopore-Rich Fe-N-C Catalyst with FeN4 -O-NC Single-Atom Sites Delivers Remarkable Oxygen Reduction Reaction Performance in Alkaline Media.

Fe-N-C catalysts offer excellent performance for the oxygen reduction reaction (ORR) in alkaline media. With a view toward boosting the intrinsic ORR activity of Fe single-atom sites in Fe-N-C catalysts, fine-tuning the local coordination of the Fe sites to optimize the binding energies of ORR intermediates is imperative. Herein, a porous FeN4 -O-NCR electrocatalyst rich in catalytically accessible FeN4 -O sites (wherein the Fe single atoms are coordinated to four in-plane nitrogen atoms and one subsurface axial oxygen atom) supported on N-doped carbon nanorods (NCR) is reported. Fe K-edge X-ray absorption spectroscopy (XAS) verifies the presence of FeN4 -O active sites in FeN4 -O-NCR, while density functional theory calculations reveal that the FeN4 -O coordination offers a lower energy and more selective 4-electron/4-proton ORR pathway compared to traditional FeN4 sites. Electrochemical tests validate the outstanding intrinsic activity of FeN4 -O-NCR for alkaline ORR, outperforming Pt/C and almost all other M-N-C catalysts reported to date. A primary zinc-air battery constructed using FeN4 -O-NCR delivers a peak power density of 214.2 mW cm-2 at a current density of 334.1 mA cm-2 , highlighting the benefits of optimizing the local coordination of iron single atoms.

Tailoring the microenvironment in Fe-N-C electrocatalysts for optimal oxygen reduction reaction performance.

Fe-N-C electrocatalysts, comprising FeN4 single atom sites immobilized on N-doped carbon supports, offer excellent activity in the oxygen reduction reaction (ORR), especially in alkaline solution. Herein, we report a simple synthetic strategy for improving the accessibility of FeN4 sites during ORR and simultaneously fine-tuning the microenvironment of FeN4 sites, thus enhancing the ORR activity. Our approach involved a simple one-step pyrolysis of a Fe-containing zeolitic imidazolate framework in the presence of NaCl, yielding a hierarchically porous Fe-N-C electrocatalyst containing tailored FeN4 sites with slightly elongated Fe-N bond distances and reduced Fe charge. The porous carbon structure improved mass transport during ORR, whilst the microenvironment optimized FeN4 sites benefitted the adsorption/desorption of ORR intermediates. Accordingly, the developed electrocatalyst, possessing a high FeN4 site density (9.9 × 1019 sites g-1) and turnover frequency (2.26 s-1), delivered remarkable ORR performance with a low overpotential (a half-wave potential of 0.90 V vs. reversible hydrogen electrode) in 0.1 mol L-1 KOH.

MIL-101-Derived Mesoporous Carbon Supporting Highly Exposed Fe Single-Atom Sites as Efficient Oxygen Reduction Reaction Catalysts.

Fe single-atom catalysts (Fe SACs) with atomic FeNx active sites are very promising alternatives to platinum-based catalysts for the oxygen reduction reaction (ORR). The pyrolysis of metal-organic frameworks (MOFs) is a common approach for preparing Fe SACs, though most MOF-derived catalysts reported to date are microporous and thus suffer from poor mass transfer and a high proportion of catalytically inaccessible FeNx active sites. Herein, NH2 -MIL-101(Al), a MOF possessing a mesoporous cage architecture, is used as the precursor to prepare a series of N-doped carbon supports (denoted herein as NC-MIL101-T) with a well-defined mesoporous structure at different pyrolysis temperatures. The NC-MIL101-T supports are then impregnated with a Fe(II)-phenanthroline complex, and heated again to yield Fe SAC-MIL101-T catalysts rich in accessible FeNx single atom sites. The best performing Fe SAC-MIL101-1000 catalyst offers outstanding ORR activity in alkaline media, evidenced by an ORR half-wave potential of 0.94 V (vs RHE) in 0.1 m KOH, as well as excellent performance in both aqueous primary zinc-air batteries (a near maximum theoretical energy density of 984.2 Wh kgZn -1 ) and solid-state zinc-air batteries (a peak power density of 50.6 mW cm-2 and a specific capacity of 724.0 mAh kgZn -1 ).