Recent Achievements in Heterogeneous Bimetallic Atomically Dispersed Catalysts for Zn-Air Batteries: A Minireview.

Rechargeable Zn-air batteries (ZABs) hold promise as the next-generation energy-storage devices owing to their affordability, environmental friendliness, and safety. However, cathodic catalysts are easily inactivated in prolonged redox potential environments, resulting in inadequate energy efficiency and poor cycle stability. To address these challenges, anodic active sites require multiple-atom combinations, that is, ensembles of metals. Heterogeneous bimetallic atomically dispersed catalysts (HBADCs), consisting of heterogeneous isolated single atoms and atomic pairs, are expected to synergistically boost the cyclic oxygen reduction and evolution reactions of ZABs owing to their tuneable microenvironments. This minireview revisits recent achievements in HBADCs for ZABs. Coordination environment engineering and catalytic substrate structure optimization strategies are summarized to predict the innovation direction for HBADCs in ZAB performance enhancement. These HBADCs are divided into ferrous and nonferrous dual sites with unique microenvironments, including synergistic effects, ion modulation, electronic coupling, and catalytic activity. Finally, conclusions and perspectives relating to future challenges and potential opportunities are provided to optimise the performance of ZABs.

Self-supported iron-doped cobalt-copper oxide heterostructures for efficient electrocatalytic denitrification.

The electrocatalytic reduction of nitrate ions (NO3-) to nitrogen gas (N2) has emerged as an effective approach for mitigating nitrate pollution in water bodies. However, the development of efficient and highly selective cathode materials remains challenging. Conventional copper-based catalysts often exhibit low selectivity because they strongly adsorb oxygen. In this study, a straightforward solvothermal and pyrolysis method was used to grow iron-doped cobalt-copper oxide heterogeneous structures on copper foam surfaces (Fe-CoO/CuO@CF). Then, the effects of the applied potential, initial NO3- concentration, Cl- concentration, electrolyte pH, and different catalysts on the catalyst performance were investigated. Compared with recently reported congeners, Fe-CoO/CuO@CF is less expensive and exhibits outstanding activity for NO3- reduction. Meanwhile, under a cathode potential of - 1.31 V vs. Ag/AgCl, Fe-CoO/CuO@CF degrades 98.6 % of NO3- in 200 min. In addition, when employing a method inspired by NH4+ removal by breakpoint chlorination, N2 selectivity over Fe-CoO/CuO@CF was raised from 10 % without Cl- to 99.7 % when supplemented with Cl-. The catalyst demonstrated excellent cyclic stability, maintaining a high electrocatalytic activity for the conversion of NO3- to N2 gas over eleven cycles. Moreover, Fe-CoO/CuO@CF enabled 63.7 % removal of NO3- from wastewater (50 mg/L NO3--N) prepared from natural water, with 100 % conversion to N2. Computational studies showed that iron doping decreased the free energy change of the intermediate of NO3- reduction reaction. This study provides an effective strategy for the electrochemical reduction of nitrate to nitrogen gas and offers good prospects for addressing nitrate pollution.

Recent Advances in Catalyst Design and Performance Optimization of Nanostructured Cathode Materials in Zinc-Air Batteries.

This review focuses on the advanced design and optimization of nanostructured zinc-air batteries (ZABs), with the aim of boosting their energy storage and conversion capabilities. The findings show that ZABs favor porous nanostructures owing to their large surface area, and this enhances the battery capacity, catalytic activity, and life cycle. In addition, the nanomaterials improve the electrical conductivity, ion transport, and overall battery stability, which crucially reduces dendrite growth on the zinc anodes and improves cycle life and energy efficiency. To obtain a superior performance, the importance of controlling the operational conditions and using custom nanostructural designs, optimal electrode materials, and carefully adjusted electrolytes is highlighted. In conclusion, porous nanostructures and nanoscale materials significantly boost the energy density, longevity, and efficiency of Zn-air batteries. It is suggested that future research should focus on the fundamental design principles of these materials to further enhance the battery performance and drive sustainable energy solutions.

Recent advances in alginate-based composite gel spheres for removal of heavy metals.

The discharge of heavy metal ions from industrial wastewater into natural water bodies is a consequence of global industrialisation. Due to their high toxicity and resistance to degradation, these heavy metal ions pose a substantial threat to human health as they accumulate and amplify. Alginate-based composite gels exhibit good adsorption and mechanical properties, excellent biodegradability, and non-toxicity, making them environmentally friendly heavy metal ion adsorbents for water with promising development prospects. This paper introduces the basic properties, cross-linking methods, synthetic approaches, modification methods, and manufacturing techniques of alginate-based composite gels. The adsorption properties and mechanical strength of these gels can be enhanced through surface modification, multi-component mixing, and embedding. The main production processes involved are sol-gel and cross-linking methods. Additionally, this paper reviews various applications of alginate composite gels for common heavy metals, rare earth elements, and radionuclides and elucidates the adsorption mechanism of alginate composite gels. This study aimed to provide a reference for synthesising new, efficient, and environmentally friendly alginate-based adsorbents and to contribute new ideas and directions for addressing the issue of heavy metal pollution.

C3N5-based nanomaterials and their applications in heterogeneous catalysts, energy harvesting, and environmental remediation.

Over the past few decades, the global reliance on fossil fuels and the exponential growth of human population have escalated global energy consumption and environmental issues. To tackle these dual challenges, metal catalysts, in particular precious metal ones, have emerged as pivotal players in the fields of environment and energy. Among the numerous metal-free and organic catalyst materials, C3N5-based materials have a major advantage over their carbon nitride (CxNy) counterparts owing to the abundant availability of raw materials, non-toxicity, non-hazardous nature, and exceptional performance. Although significant efforts have been dedicated to synthesising and optimising the applicable properties of C3N5-based materials in recent years, a comprehensive summary of the immediate parameters of this promising material is still lacking. Given the rapid development of C3N5-based materials, a timely review is essential for staying updated on their strengths and weaknesses across various applications, as well as providing guidance for designing efficient catalysts. In this study, we present an extensive overview of recent advancements in C3N5-based materials, encompassing their physicochemical properties, major synthetic methods, and applications in photocatalysis, electrocatalysis, and adsorption, among others. This systematic review effectively summarises both the advantages and shortcomings associated with C3N5-based materials for energy and environmental applications, thus offering researchers focussed on CxNy-materials an in-depth understanding of those based on C3N5. Finally, considering the limitations and deficiencies of C3N5-based materials, we have proposed enhancement schemes and strategies, while presenting personal perspectives on the challenges and future directions for C3N5. Our ultimate aim is to provide valuable insights for the research community in this field.

Co Nanoparticles Confined in Mesoporous Mo/N Co-Doped Polyhedral Carbon Frameworks towards High-Efficiency Oxygen Reduction.

Exploiting effective non-noble metal electrocatalysts for oxygen reduction reaction (ORR) is crucial for fuel cells and metal-air batteries. Herein, we designed and fabricated Co nanoparticles confined in Mo/N co-doped polyhedral carbon frameworks (Co-NP/MNCF) derived from polyoxometalate-encapsuled metal-organic framework, which showed comparable ORR performance with commercial Pt/C and a larger diffusion-limited current density. Moreover, the Co-NP/MNCF also exhibited excellent ORR stability and methanol tolerance. These appealing performances can be attributed to the porosity regulation and heteroatom doping of metal-organic framework derived polyhedral carbon frameworks, which could be beneficial for the exposure of more active sites, the optimization of electronic structure and the mass transfer of electrolyte/electron/ion.

Nitrogen-Doped Carbon Polyhedrons Confined Fe-P Nanocrystals as High-Efficiency Bifunctional Catalysts for Aqueous Zn-CO2 Batteries.

Emerging Fe bonded with heteroatom P in carbon matrix (FePC) holds great promise for electrochemical catalysis, but the design of highly active and cost-efficient FePC structure for the electrocatalytic CO2 reduction reaction (CO2 RR) and aqueous ZnCO2 batteries (ZCBs) is still challenging. Herein, polyhedron-shaped bifunctional electrocatalysts, FeP nanocrystals anchored in N-doped carbon polyhedrons (Fe-P@NCPs), toward a reversible aqueous ZnCO2 battery, are reported. The Fe-P@NCPs are synthesized through a facile strategy by using self-templated zeolitic imidazolate frameworks (ZIFs), followed by an in situ high-temperature calcination. The resultant catalysts exhibit aqueous CO2 RR activity with a CO Faradaic efficiency up to 95% at -0.55 V versus reversible hydrogen electrode (RHE), comparable to the previously best-reported values of FeNC structure. The as-constructed ZCBs with designed Fe-P@NCPs cathode, show the peak power density of 0.85 mW cm-2 and energy density of 231.8 Wh kg-1 with a cycling durability over 500 cycles, and outstanding stability in terms of discharge voltage for 7 days. The high selectivity and efficiency of the battery are attributed to the presence of highly catalytic FeP nanocrystals in N-doped carbon matrix, which can effectively increase the number of catalytically active sites and interfacial charge-transfer conductivity, thereby improving the CO2 RR activity.

Metal-Free Bifunctional Ordered Mesoporous Carbon for Reversible Zn-CO2 Batteries.

The fabrication of Zn-CO2 batteries is a promising technique for CO2 fixation and energy storage. Herein, nitrogen-doped ordered mesoporous carbon (NOMC) is adopted as a bifunctional metal-free electrocatalyst for CO2 reduction and oxygen evolution reaction in the near-neutral electrolyte. The ordered mesoporous structures and abundant N-dopings of NOMC facilitate the accessibility and utilization of the active sites, which endow NOMC with excellent electrocatalysis performance and outstanding stability. Especially, a nearly 100% CO Faradaic efficiency is achieved at an ultralow overpotential of 360 mV for CO2 reduction. When constructed as an aqueous rechargeable Zn-CO2 battery using NOMC as the cathode, it yields a high peak power density of 0.71 mW cm-2 , a good cyclability of 300 cycles, and excellent energy efficiency of 52.8% at 1.0 mA cm-2 .

Single-unit-cell-thick layered electrocatalysts: from synthesis to application.

Electrocatalysts are critical for water splitting, carbon dioxide reduction, and zinc-air battery. However, the low-exposed surface areas of bulk electrocatalysts usually limit the complete utilization of active sites. Ultrathin electrocatalysts have noteworthy advantages in maximizing the use of active sites. Among the pioneering works on such performing catalysts, the development of single-unit-cell-thick layered electrocatalysts (STLEs) has attracted extensive attention owing to their superior specific surface area and large number of vacancies, which can provide abundant available surface active sites. Therefore, this minireview provides recent advances in STLE synthesis and applications, which are helpful for electrocatalysis-oriented researchers. Finally, the future perspectives and challenges for developing high-performance STLEs are proposed.

A Facile Electrochemical Sensor Based on PyTS⁻CNTs for Simultaneous Determination of Cadmium and Lead Ions.

A simple and easy method was implemented for the contemporary detection of cadmium (Cd2+) and lead (Pb2+) ions using 1,3,6,8-pyrenetetrasulfonic acid sodium salt-functionalized carbon nanotubes nanocomposites (PyTS⁻CNTs). The morphology and composition of the obtained PyTS⁻CNTs were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). The experimental results confirmed that the fabricated PyTS⁻CNTs exhibited good selectivity and sensitivity for metal ion-sensing owing to the insertion of sulfonic acid groups. For Cd2+ and Pb2+, some of the electrochemical sensing parameters were evaluated by varying data such as the PyTS⁻CNT quantity loaded on the pyrolytic graphite electrode (PGE), pH of the acetate buffer, deposition time, and deposition potential. These parameters were optimized with differential pulse anodic sweeping voltammetry (DPASV). Under the optimal condition, the stripping peak current of the PyTS⁻CNTs/Nafion/PGE varies linearly with the heavy metal ion concentration, ranging from 1.0 µg L-1 to 90 µg L-1 for Cd2+ and from 1.0 µg L-1 to 110 µg L-1 for Pb2+. The limits of detection were estimated to be approximately 0.8 µg L-1 for Cd2+ and 0.02 µg L-1 for Pb2+. The proposed PyTS⁻CNTs/Nafion/PGE can be used as a rapid, simple, and controllable electrochemical sensor for the determination of toxic Cd2+ and Pb2+.

Selective voltammetric determination of Cd(II) by using N,S-codoped porous carbon nanofibers.

Porous carbon nanofibers codoped with nitrogen and sulfur (NFs) were prepared by pyrolysis of trithiocyanuric acid, silica nanospheres and polyacrylonitrile (PAN) followed by electrospinning. The NFs were used to modify a glassy carbon electrode (GCE) which then displayed highly sensitive response to traces of Cd(II). Compared to a bare GCE and a Nafion modified GCE, the GCE modified with codoped NFs shows improved sensitivity for Cd(II) in differential pulse anodic sweep voltammetry. The stripping peak current (typically measured at 0.81 V vs. Ag/AgCl) increases linearly in the 2.0-500 µg·L-1 Cd(II) concentration range. This is attributed to the large surface area (109 m2·g-1), porous structure, and high fraction of heteroatoms (19 at.% of N and 0.75 at.% of S). The method was applied to the determination of Cd(II) in (spiked) tap water where it gave recoveries that ranged between 96% and 103%. Graphical abstract Schematic of a glassy carbon electrode (GCE) modified with N- and S-codoped porous carbon nanofibers (N,S-PCNFs). This GCE has good selectivity for cadmium ion (Cd2+) which can be determined by differential pulse anodic sweeping voltammetry (DPASV) with a detection limit as low as 0.7 ng·mL-1.

Synergistic Effects between Atomically Dispersed Fe-N-C and C-S-C for the Oxygen Reduction Reaction in Acidic Media.

Various advanced catalysts based on sulfur-doped Fe/N/C materials have recently been designed for the oxygen reduction reaction (ORR); however, the enhanced activity is still controversial and usually attributed to differences in the surface area, improved conductivity, or uncertain synergistic effects. Herein, a sulfur-doped Fe/N/C catalyst (denoted as Fe/SNC) was obtained by a template-sacrificing method. The incorporated sulfur gives a thiophene-like structure (C-S-C), reduces the electron localization around the Fe centers, improves the interaction with oxygenated species, and therefore facilitates the complete 4 e- ORR in acidic solution. Owing to these synergistic effects, the Fe/SNC catalyst exhibits much better ORR activity than the sulfur-free variant (Fe/NC) in 0.5 m H2 SO4 .