Advanced opportunities and insights on the influence of nitrogen incorporation on the physico-/electro-chemical properties of robust electrocatalysts for electrocatalytic energy conversion

Promoting Electrocatalytic Oxygen Reactions Using Advanced Heterostructures for Rechargeable Zinc-Air Battery Applications

In order to facilitate electrochemical oxygen reactions in electrically rechargeable zinc-air batteries (ZABs), there is a need to develop innovative approaches for efficient oxygen electrocatalysts. Due to their reliability, high energy density, material abundance, and ecofriendliness, rechargeable ZABs hold promise as next-generation energy storage and conversion devices. However, the large-scale application of ZABs is currently hindered by the slow kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). However, the development of heterostructure-based electrocatalysts has the potential to surpass the limitations imposed by the intrinsic properties of a single material. This Account begins with an explanation of the configurations of ZABs and the fundamentals of the oxygen electrochemistry of the air electrode. Then, we summarize recent progress with respect to the variety of heterostructures that exploit bifunctional electrocatalytic reactions and overview their impact on ZAB performance. The range of heterointerfacial engineering strategies for improving the ORR/OER and ZAB performance includes tailoring the surface chemistry, dimensionality of catalysts, interfacial charge transfer, mass and charge transport, and morphology. We highlight the multicomponent design approaches that take these features into account to create advanced highly active bifunctional catalysts. Finally, we discuss the challenges and future perspectives on this important topic that aim to enhance the bifunctional activity and performance of zinc-air batteries.

Electrospinning-derived transition metal/carbon nanofiber composites as electrocatalysts for Zn-air batteries

The sluggish kinetics of the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) significantly impede the broader implementation of Zn-air batteries (ZABs), underscoring the necessity for advanced high-efficiency materials to catalyze these electrochemical processes. Recent advancements have highlighted the potential of transition metal/carbon nanofiber (TM/CNF) composite materials, synthesized via electrospinning technology, due to their expansive surface area, profusion of active sites, and elevated catalytic efficacy. This review comprehensively examines the structural characteristics of TM/CNFs, with a particular emphasis on the pivotal role of electrospinning technology in fabricating diverse structural configurations. Additionally, it delves into the mechanistic underpinnings of various strategies aimed at augmenting the catalytic activity of TM/CNFs. A meticulous discourse is also presented on the application scope of TM/CNFs in the realm of electrocatalysis, with a special focus on their impact on the performance of assembled ZABs. Lastly, this review encapsulates the challenges and future prospects in the development of TM/CNF composite materials via electrospinning, aiming to provide an exhaustive understanding of the current state of research in this domain and to foster further advancements in the commercialization of ZABs.

Recent advances in the role of MXene based hybrid architectures as electrocatalysts for water splitting

The development of non-noble metal based and cost-effective electrocatalysts for water splitting has attracted significant attention due to their potential in production of clean and green hydrogen fuel. Discovered in 2011, a family of two-dimensional transition metal carbides, nitrides, and carbonitrides, have demonstrated promising performance as electro catalysts in the water splitting process due to their high electrical conductivity, very large surface area and abundant catalytic active sites. However, their-long term stability and recyclability are limited due to restacking and agglomeration of MXene flakes. This problem can be solved by combining MXene with other materials to create their hybrid architectures which have demonstrated higher electrocatalytic performance than pristine MXenes. Electrolysis of water encompasses two half-cell reactions, hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode. Firstly, this concise review explains the mechanism of water splitting. Then it provides an overview of the recent advances about applications of MXenes and their hybrid architectures as HER, OER and bifunctional electrocatalysts for overall water splitting. Finally, the recent challenges and potential outlook in the field have been presented. This concise review may provide further understanding about the role of MXene-based hybrid architectures to develop efficient electrocatalysts for water splitting.

Nickel vanadate nitrogen-doped carbon nanocomposites for high-performance supercapacitor electrode

A nickel-vanadium-based bimetallic precursor was produced using the polymerization process by urea-formaldehyde copolymers. The precursor was then calcined at 800 °C in an argon ambiance to form a Ni3V2O8-NC magnetic nanocomposite. Powerful techniques were used to study the physical characteristics and chemical composition of the fabricated Ni3V2O8-NC electrode. PXRD, Raman, and FTIR analyses proved that the crystal structure of Ni3V2O8-NC included N-doped graphitic carbon. FESEM and TEM analyses imaging showed the distribution of the Ni3V2O8 nanoparticles on the layered graphitic carbon structure. TEM images showed the prepared sample has a particle size of around 10-15 nm with an enhanced active site area of 146 m2/g, as demonstrated by BET analysis. Ni3V2O8-NC nanocomposite exhibits magnetic behaviors and a magnetization saturation value of 35.99 emu/g. The electrochemical (EC) studies of the synthesized Ni3V2O8-NC electrode proceeded in an EC workstation of three-electrode. In a 5 M potassium hydroxide as an electrolyte, the cyclic voltmeter exhibited an enhanced capacitance (CS) of 915 F/g at 50 mV/s. Galvanic charge-discharge (GCD) study also exhibited a superior capacitive improvement of 1045 F/g at a current density (It) of 10 A/g. Moreover, the fabricated Ni3V2O8-NC nanocomposite displays a good power density (Pt) of 356.67 W/kg, improved ion accessibility, and substantial charge storage. At the high energy density (Et) of 67.34 W h/kg, the obtained Pt was 285.17 W/kg. The enhanced GCD rate, cycle stability, and Et of the Ni3V2O8-NC magnetic nanocomposite nominate the sample as an excellent supercapacitor electrode. This study paves the way for developing effective, efficient, affordable, and ecologically friendly electrode materials.

Magnesium Bismuth Ferrite Nitrogen-Doped Carbon Nanomagnetic Perovskite: Synthesis and Characterization as a High-Performance Electrode in a Supercapacitor for Energy Storage

Bismuth ferrite (BiFeO₃) is regarded as an important ABO₃ perovskite in the areas of energy storage and electronics. A high-performance novel MgBiFeO₃-NC nanomagnetic composite (MBFO-NC) electrode was prepared using a perovskite ABO₃-inspired method as a supercapacitor for energy storage. The electrochemical behavior of the perovskite BiFeO₃ has been enhanced by magnesium ion doping in the basic aquatic electrolyte as the A-site. H₂-TPR revealed that the doping of Mg²⁺ ions at the Bi³⁺ sites minimizes the oxygen vacancy content and improves the electrochemical characteristics of MgBiFeO₃-NC. Various techniques were used to confirm the phase, structure, surface, and magnetic properties of the MBFO-NC electrode. The prepared sample showed an enhanced mantic performance and specific area with an average nanoparticle size of ∼15 nm. The electrochemical behavior of the three-electrode system was shown by cyclic voltammetry to have a significant specific capacity of 2079.44 F/g at 30 mV/s in 5 M KOH electrolyte. GCD analysis at a 5 A/g current density also showed an enhanced capacity improvement of 2159.88 F/g, which is 3.4× higher than that of pristine BiFeO₃. At the power density of 5284.83 W/kg, the constructed MBFO-NC//MBFO-NC symmetric cell showed an exceptional energy density of 730.04 W h/kg. The MBFO-NC//MBFO-NC symmetric cell was employed as a direct practical application of the electrode material to entirely brighten the laboratory panel, which had 31 LEDs. This work proposes the utilization of duplicate cell electrodes made of MBFO-NC//MBFO-NC in portable devices for daily use.

Mutual Self-Regulation of d-Electrons of Single Atoms and Adjacent Nanoparticles for Bifunctional Oxygen Electrocatalysis and Rechargeable Zinc-Air Batteries

Rechargeable zinc-air batteries (ZABs) are a promising energy conversion device, which rely critically on electrocatalysts to accelerate their rate-determining reactions such as oxygen reduction (ORR) and oxygen evolution reactions (OER). Herein, we fabricate a range of bifunctional M-N-C (metal-nitrogen-carbon) catalysts containing M-Nx coordination sites and M/MxC nanoparticles (M = Co, Fe, and Cu) using a new class of γ-cyclodextrin (CD) based metal-organic framework as the precursor. With the two types of active sites interacting with each other in the catalysts, the obtained Fe@C-FeNC and Co@C-CoNC display superior alkaline ORR activity in terms of low half-wave (E1/2) potential (~ 0.917 and 0.906 V, respectively), which are higher than Cu@C-CuNC (~ 0.829 V) and the commercial Pt/C (~ 0.861 V). As a bifunctional electrocatalyst, the Co@C-CoNC exhibits the best performance, showing a bifunctional ORR/OER overpotential (ΔE) of ~ 0.732 V, which is much lower than that of Fe@C-FeNC (~ 0.831 V) and Cu@C-CuNC (~ 1.411 V), as well as most of the robust bifunctional electrocatalysts reported to date. Synchrotron X-ray absorption spectroscopy and density functional theory simulations reveal that the strong electronic correlation between metallic Co nanoparticles and the atomic Co-N4 sites in the Co@C-CoNC catalyst can increase the d-electron density near the Fermi level and thus effectively optimize the adsorption/desorption of intermediates in ORR/OER, resulting in an enhanced bifunctional electrocatalytic performance. The Co@C-CoNC-based rechargeable ZAB exhibited a maximum power density of 162.80 mW cm-2 at 270.30 mA cm-2, higher than the combination of commercial Pt/C + RuO2 (~ 158.90 mW cm-2 at 265.80 mA cm-2) catalysts. During the galvanostatic discharge at 10 mA cm-2, the ZAB delivered an almost stable discharge voltage of 1.2 V for ~ 140 h, signifying the virtue of excellent bifunctional ORR/OER electrocatalytic activity.

A Rising 2D Star: Novel MBenes with Excellent Performance in Energy Conversion and Storage

As a flourishing member of the two-dimensional (2D) nanomaterial family, MXenes have shown great potential in various research areas. In recent years, the continued growth of interest in MXene derivatives, 2D transition metal borides (MBenes), has contributed to the emergence of this 2D material as a latecomer. Due to the excellent electrical conductivity, mechanical properties and electrical properties, thus MBenes attract more researchers' interest. Extensive experimental and theoretical studies have shown that they have exciting energy conversion and electrochemical storage potential. However, a comprehensive and systematic review of MBenes applications has not been available so far. For this reason, we present a comprehensive summary of recent advances in MBenes research. We started by summarizing the latest fabrication routes and excellent properties of MBenes. The focus will then turn to their exciting potential for energy storage and conversion. Finally, a brief summary of the challenges and opportunities for MBenes in future practical applications is presented.

Facile synthesis of novel molybdenum disulfide decorated banana peel porous carbon electrode for hydrogen evolution reaction

Hydrogen is one of the cleanest renewable and environmentally friendly energy resource that can be generated through water splitting. However, hydrogen evolution occurs at high overpotential, and efficient hydrogen evolution catalysts are desired to replace state-of-the-art catalysts such as platinum. In the present work, a novel molybdenum disulfide decorated banana peel porous carbon (MoS₂@BPPC) catalyst has been developed using banana peel carbon and molybdenum disulfide (MoS₂) for hydrogen evolution reaction (HER). Banana peel porous carbon (BPPC) was initially synthesized from the banana peel (biowaste) by a simple carbonization method. Subsequently, 20 wt% of bare MoS₂ was distributed on the pristine BPPC matrix using the dry-impregnation method. The resulting MoS₂@BPPC composites were systematically investigated to determine the morphology and structure. Finally, using a three-electrode cell system, pristine BPPC, bare MoS₂, and MoS₂@BPPC composite were used as HER electrocatalysts. The developed MoS₂@BPPC composite showed greater HER activity and possessed excellent stability in the acid solution, including an overpotential of 150 mV at a current density of -10 mA cm^-2, and a Tafel slope of 51 mV dec^-1. This Tafel study suggests that the HER takes place by Volmer-Heyrovsky mechanism with a rate-determining Heyrovsky step. The excellent electrochemical performance of MoS₂@BPPC composite for HER can be ascribed to its unique porous nanoarchitecture. Further, due to the synergetic effect between MoS₂ and porous carbon. The HER activity using the MoS₂@BPPC electrode advises that the prepared catalyst may hold great promise for practical applications.

Recent Insight in Transition Metal Anchored on Nitrogen-Doped Carbon Catalysts: Preparation and Catalysis Application

The design and preparation of novel, high-efficiency, and low-cost heterogeneous catalysts are important topics in academic and industry research. In the past, inorganic materials, metal oxide, and carbon materials were used as supports for the development of heterogeneous catalysts due to their excellent properties, such as high specific surface areas and tunable porous structures. However, the properties of traditional pristine carbon materials cannot keep up with the sustained growth and requirements of industry and scientific research, since the introduction of nitrogen atoms into carbon materials may significantly enhance a variety of their physicochemical characteristics, which gradually become appropriate support for synthesizing supported transition metal catalysts. In the past several decades, the transition metal anchored on nitrogen-doped carbon catalysts has attracted a tremendous amount of interest as potentially useful catalysts for diverse chemical reactions. Compared with original carbon support, the doping of nitrogen atoms can significantly regulate the physicochemical properties of carbon materials and allow active metal species uniformly dispersed on the support. The various N species in support also play a critical role in accelerating the catalytic performance in some reactions. Besides, the interaction between support and transition metal active sites can offer an anchor site to stabilize metal species during the preparation process and then improve reaction performance, atomic utilization, and stability. In this review, we highlight the recent advances and the remaining challenges in the preparation and application of transition metal anchored on nitrogen-doped carbon catalysts.

ZnO-ZnCr2O4 composite prepared by a glycine nitrate process method and applied for hydrogen production by steam reforming of methanol

To address climate change, the energy crisis, and global warming, hydrogen (H₂) can be used as a potential energy carrier because it is clean, non-toxic and efficient. Today, the mainstream industrial method of H₂ generation is steam reforming of methanol (SRM). In this process, a zinc-based commercial catalyst is usually used. In this work, a ZnO–ZnCr₂O₄ catalyst was successfully synthesised by the glycine nitrate process (GNP) and developed for use in H₂ production by SRM. The specific surface area, porous structure and reaction sites of the zinc-based catalyst were effectively increased by the preparation method. The as-combusted ZnO–ZnCr₂O₄ composite catalyst had a highly porous structure due to the gas released during the GNP reaction process. Moreover, according to the ZnO distribution and different G/N ratios, the specific surface area (S_BET) of the as-combusted ZnO–ZnCr₂O₄ catalyst varied from 29 m² g⁻¹ to 46 m² g⁻¹. The ZnO–ZnCr₂O₄ composite catalyst (G/N 1.7) exhibited the highest hydrogen production, 4814 ml STP min⁻¹ g-cat⁻¹, at a reaction temperature of 450 °C without activation treatment. After activation, the ZnO–ZnCr₂O₄ composite catalyst achieved hydrogen production of 6299 ml STP min⁻¹ g-cat⁻¹ at a reaction temperature of 500 °C. The hydrogen production performance of the ZnO–ZnCr₂O₄ composite powder was improved by the uniform addition of ZnO to ZnCr₂O₄. Based on the performance, this ZnO–ZnCr₂O₄ composite catalyst has great potential to have industrial and economic impact due to its high efficiency in hydrogen production.

ZnO–ZnCr₂O₄ composite for hydrogen production by steam reforming of methanol.

Insights into the Effect of Sulfur Incorporation into Tungsten Diphosphide for Improved Hydrogen Evolution Reaction

Exploring the highly active and stable nonprecious metal electrocatalysts is particularly important for the advancement of water electrolysis, whereas it remains a challenge to efficiently improve the intrinsic electrocatalytic activity. Herein, we reasonably constructed a self-supporting nanosheet array material with sulfur incorporated into WP₂. Because of the tunability of electronic configuration and the formation of partial metal phase sulfides, the optimized catalyst exhibits a low overpotential of 115 mV at 10 mA cm^-2, along with superb durability over 24 h in acidic media. Furthermore, theoretical calculations reveal that sulfur substitution effectively manipulates the local electronic configuration of WP₂, which reduces the interaction between the catalyst surface and hydrogen atoms, thus improving the intrinsic activity of the hydrogen evolution reaction. This work provides valuable insight into the rational fabrication of highly efficient flexible electrode materials based on resourceful electrocatalysts for electrochemical water splitting.