To develop graphene-based nanomaterials as reliable catalysts for electrochemical energy conversion and storage systems (e.g. PEM fuel cells, metal–air batteries, etc.), it is imperative to critically understand their performance changes and correlated material degradation processes under different operational conditions. In these systems, hydrogen peroxide (H2O2) is often an inevitable byproduct of the catalytic oxygen reduction reaction, which can be detrimental to the catalysts, electrodes, and electrolyte materials. Here, we studied how the electrocatalytic performance changes for a heterogeneous nanocatalyst named nitrogen-doped graphene integrated with a metal–organic framework (N-G/MOF) by the effect of H2O2, and correlated the degradation process of the catalyst in terms of the changes in elemental compositions, chemical bonds, crystal structures, and morphology. The catalyst samples were treated with five different concentrations of H2O2 to emulate the operational conditions and examined to quantify the changes in electrocatalytic performances in an alkaline medium, elemental composition and chemical bonds, crystal structure, and morphology. The electrocatalytic performance considerably declined as the H2O2 concentration reached above 0.1 M. The XPS analyses suggest the formation of different oxygen functional groups on the material surface, the breakdown of the material's C–C bonds, and a sharp decline in pyridinic-N functional groups due to gradually harsher H2O2 treatments. In higher concentrations, the H2O2-derived radicals altered the crystalline and morphological features of the catalyst. Keywords: Nitrogen-doped graphene-based electrocatalyst; Metal–organic framework; Hydrogen peroxide effect on catalyst; Electrocatalytic performance; Material degradation.

The first page of this article is displayed as the abstract.

The first page of this article is displayed as the abstract.

Supercapacitors are highly valued energy storage devices with high power density, fast charging ability, and exceptional cycling stability. A profound understanding of their charging mechanisms is crucial for continuous performance enhancement. Electrochemical quartz crystal microbalance (EQCM), a detection means that provides in situ mass change information during charging–discharging processes at the nanogram level, has received greatly significant attention during the past decade due to its high sensitivity, non-destructiveness and low cost. Since being used to track ionic fluxes in porous carbons in 2009, EQCM has played a pivotal role in understanding the charging mechanisms of supercapacitors. Herein, we review the critical progress of EQCM hitherto, including theory fundamentals and applications in supercapacitors. Finally, we discuss the fundamental effects of ion desolvation and transport on the performance of supercapacitors. The advantages and defects of applying EQCM in supercapacitors are thoroughly examined, and future directions are proposed. Keywords: EQCM; Supercapacitors; Charging mechanisms; Quantitative characterization.

Efficient utilization of lignocellulosic biomass to substitute for fossil resources is an effective way to promote the sustainable development of current society. Numerous lignocellulose valorization routes for the production of value-added chemicals and fuels have been explored. Herein, we overview the catalytic reaction routes, reaction types and key steps involved in the selective preparation of various important products from lignocellulose. The information can facilitate the development of robust and selective catalytic systems to address the challenges in the major reaction steps. We present four catalytic conversion route maps starting from cellulose (including 5-hydroxylfurfural, HMF), hemicellulose and lignin, respectively. The reaction route for the important platform molecules of HMF and furfural, passing through critical intermediates to value-added chemicals and aviation fuels, is also highlighted. It provides a clear and concise panorama for people interested in this field and facilitates identifying the products or processes of interest with up-to-date research developments. We also put forward the current issues for the large-scale valorization of lignocellulose and the possible resolution strategies, focusing on the rational design of active and robust heterogeneous catalysts. Keywords: Biomass; Lignocellulose valorization; Catalytic conversion network; Reaction routes; Renewable chemicals.

Single-atom catalysts (SACs) attract significant attention owing to their high catalytic activity, high metal atom utilization efficiency, and well-defined and configurable active sites. However, achieving single-atom dispersion of active metals at high metal loadings remains challenging, limiting the performance of SACs in many practical applications. Herein, we provide a comprehensive review of recent methods developed for synthesizing high-loading SACs, critically exploring their advantages, limitations, and wider applicability. Additionally, we showcase the benefits of high-loading SACs in the oxygen reduction reaction (ORR), water electrolysis, photocatalytic hydrogen production and CO oxidation. Although great recent progress has been made in the synthesis of high loading SACs, simple and universal routes that allowed the pre-programmed preparation of single metal and multi-metal SACs with specific metal coordination need to be discovered. Keywords: Single atom catalyst; High-loading; Synthesis methods; ORR; Water electrolysis; CO oxidation.

High temperature proton exchange membrane fuel cells (HT-PEMFCs) operating at elevated temperatures above 120 °C take advantage of feasible anode fuels and simplified water/heat management. A high temperature polymer electrolyte membrane (HT-PEM) is the core material for HT-PEMFCs. In this work, a series of phosphoric acid (PA) doped HT-PEMs based on poly(terphenyl piperidine) (PTP) tailored with alkyl groups are synthesized. Five different pendant alkyl groups (including methyl, propyl, pentyl, heptyl and decyl) are grafted onto the piperidine group through the Menshutkin reaction between PTP and alkyl halides. Compared with PTP and methyl grafted PTP (PTP-C1) membranes, the PTP-Cx membranes with long alkyl side chains exhibit improved PA doping contents and conductivities. The optimized pentyl-substituted PTP membrane (PTP-C5) possessed a reasonable PA doping content (202% after immersing in 85 wt% PA at 60 °C), high proton conductivity (96 mS cm−1 at 180 °C) and good tensile strength (4.6 MPa at room temperature). A H2–air single cell equipped with PTP-C5/PA consequently achieved a high peak power density of 676 mW cm−2 at 210 °C without any humidification or backpressure. Thus, this work provides a simple method for preparing high-performance HT-PEMs. Keywords: High temperature polymer electrolyte membrane; Fuel cell; Grafted membrane.

Carbazole and anthracene, two aromatic hydrocarbon components contained in coal tar, are used as essential organic intermediates to synthesize various carbazole derivatives and anthraquinones. N,N-Dimethylformamide (DMF) is a commonly used solvent to extract carbazole from crude mixtures of carbazole and anthracene. However, the interaction between carbazole/anthracene and DMF in the extraction process is still to be fully understood at the molecular level. In this work, the intermolecular interaction of carbazole/anthracene with DMF was investigated using various NMR techniques, including 1H NMR titration, variable temperature NMR spectroscopy (VT-NMR), Nuclear Overhauser Effect Spectroscopy (NOESY), and diffusion-ordered spectroscopy (DOSY). The observed 1H chemical shift changes of carbazole indicated strong intermolecular hydrogen bonds between carbazole and DMF, which was further supported by the decrease in the molecular self-diffusion coefficients (D) of both carbazole and DMF according to DOSY measurements. Moreover, NOESY experiments revealed that the distance between the aldehydic hydrogen of DMF and the N–H of carbazole was smaller than 5 Å. Accordingly, an intermolecular hydrogen bond between carbazole and DMF in the form of CO⋯H–N was proposed. This research increases our knowledge about the separation process of carbazole and anthracene and hence helps improve the methods. Keywords: NMR; Carbazole; Separation; Intermolecular hydrogen bonds.

Developing non-precious metal-based inexpensive and highly active electrocatalysts for the oxygen reduction reaction (ORR) in alkaline media is important for fuel cell applications. Herein, we report a simple and effective synthesis of transition-metal-doped zeolitic imidazolate framework-8 (ZIF-8) and carbon nanotube (CNT) composite catalysts (ZIF-8@CNT) prepared via high-temperature pyrolysis at 900 °C. The catalysts were characterized using different physicochemical techniques and employed as cathode materials in anion exchange membrane fuel cells (AEMFC). The prepared metal-free (ZNT-900), single-metal-doped (Fe-ZNT-900, Co-ZNT-900) and binary-metal-doped (Fe1Co1-ZNT-900, Fe1Co2-ZNT-900) catalysts had a sufficient amount of N-doping with the presence of FeCo moieties in the carbon skeleton of the latter two materials. N2 adsorption–desorption isotherms showed that all the prepared catalysts possess a sufficient Brunauer–Emmett–Teller surface area with more micropores present in ZNT-900, while a combined micro–mesoporous structure was obtained for transition-metal-doped catalysts. Binary-metal-doped catalysts showed the highest number of ORR-active sites (pyridinic-N, pyrrolic-N, graphitic-N, M–Nx) and exhibited a half-wave potential (E1/2) of 0.846 and 0.847 V vs. RHE for Fe1Co1-ZNT-900 and Fe1Co2-ZNT-900, respectively, which surpassed that of the commercial Pt/C catalyst (E1/2 = 0.834 V). In H2–O2 AEMFCs, the Fe1Co2-ZNT-900 catalyst delivered a maximum power density (Pmax) of 0.171 W cm−2 and current density at 0.5 V (j0.5) of 0.326 A cm−2, which is very close to that of the Pt/C catalyst (Pmax = 0.215 W cm−2 and j0.5 = 0.359 A cm−2). The prepared ZIF-8@CNT catalysts showed remarkable electrocatalytic ORR activity in 0.1 M KOH solution and fuel cell performance comparable to that of the benchmark Pt/C catalyst. Keywords: Rotating disk electrode; Anion exchange membrane fuel cell; Zeolitic imidazolate framework; Non-precious metal catalyst; Oxygen reduction reaction.

Direct regeneration is a low-cost and environmentally friendly way of recycling spent Li-ion batteries. In this study, a new method is adopted to regenerate spent LiFePO4. First, the spent LiFePO4 powder is homogenized, and then, small amounts of a lithium source and a carbon source are thoroughly mixed by spray drying. After that, a high-temperature solid-phase method is used to regenerate the carbon-coated lithium iron phosphate. Compared with traditional regeneration methods, the proposed method significantly improves the universality of spent LiFePO4 having different degrees of damage. The regenerated LiFePO4 is characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and electrochemical measurements. The results show that the regenerated sample has a stable morphology, structure, and electrochemical performance. Under the conditions of 0.1C, the initial capacity exceeds 160 mA h g−1. After 800 cycles under the conditions of 1C, the capacity retention is 80%, which satisfies the requirements for regenerated LiFePO4 batteries. Keywords: LiFePO4; Direct regeneration; Homogenization; Spray drying; Electrochemical performance.

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A graphical abstract is available for this content

Organic materials with room-temperature phosphorescence (RTP) emission have attracted extensive attention owing to their extraordinary properties, including long lifetime, large Stokes shift, and stimuli-responsiveness, and show bright prospects in broad fields. Numerous design strategies, such as creating a rigid environment through crystallization and supramolecular assembly, can be employed to improve the luminescent characteristics of RTP materials by restricting nonradiative transition, enhancing intersystem crossing, and so forth. This review summarizes recent progress with organic room-temperature phosphorescent materials from the perspective of practical applications, including luminescence and display, environmental detection, and bioimaging, and the challenges and prospects will be discussed at the end, which should assist with future research on the application of RTP materials. Keywords: Room-temperature phosphorescence; OLEDs; Anti-counterfeiting; Environmental detection; Bioimaging.

Correction for ‘Hierarchically ordered porous carbon with atomically dispersed cobalt for oxidative esterification of furfural’ by Wen Yao et al., Ind. Chem. Mater., 2023, 1, 106–116, http://doi.org/10.1039/D2IM00045H.

Electroreduction of small molecules such as CO2, N2, and NO3− is one of the promising routes to produce sustainable chemicals and fuels and store renewable energy, which could contribute to our carbon neutrality goal. Emerging multicomponent electrocatalysts, integrating the advantages of individual components of catalysts, are of great importance to achieve efficient electroreduction of small molecules via activation of inert bonds and multistep transformation. In this review, some basic issues in the electroreduction of small molecules including CO2, N2, and NO3− are briefly introduced. We then discuss our fundamental understanding of the rule of interaction in multicomponent electrocatalysts, and summarize three models for multicomponent catalysts, including type I, “a non-catalytically active component can activate or protect another catalytic component”; type II, “all catalytic components provide active intermediates for electrochemical conversion”; and type III, “one component provides the substrate for the other through conversion or adsorption”. Additionally, an outlook was considered to highlight the future directions of multicomponent electrocatalysts toward industrial applications. Keywords: Green chemistry; Green carbon science; Electrocatalysis; Synergetic effect.

Hydrogen holds the advantages of high gravimetric energy density and zero emission. Effective storage and transportation of hydrogen constitute a critical and intermediate link for the advent of widespread applications of hydrogen energy. Magnesium hydride (MgH2) has been considered as one of the most promising hydrogen storage materials because of its high hydrogen storage capacity, excellent reversibility, sufficient magnesium reserves, and low cost. However, great barriers both in the thermodynamic and the kinetic properties of MgH2 limit its practical application. Doping catalysts and nanostructuring are two facile but efficient methods to prepare high-performance magnesium (Mg)-based hydrogen storage materials. Core–shell nanostructured Mg-based hydrogen storage materials synergize the strengths of the above two modification methods. This review summarizes the preparation methods and expounds the thermodynamic and kinetic properties, microstructure and phase changes during hydrogen absorption and desorption processes of core–shell nanostructured Mg-based hydrogen storage materials. We also elaborate the mechanistic effects of core–shell nanostructures on the hydrogen storage performance of Mg-based hydrogen storage materials. The goal of this review is to point out the design principles and future research trends of Mg-based hydrogen storage materials for industrial applications. Keywords: Hydrogen storage; Mg/MgH2; Core–shell nanostructure; Thermodynamics and kinetics.

The widespread application of polymer electrolyte membrane water electrolyzers (PEMWEs) remains a tough challenge to date, as they rely on the use of highly scarce iridium (Ir) with insufficient catalytic performance for the oxygen evolution reaction (OER). Therefore, exploring the degradation and activation mechanism of Ir-based catalysts during the OER and searching for highly efficient Ir-based catalysts are essential to achieve large-scale hydrogen production with PEMWEs. This minireview briefly describes the adsorbate evolution mechanism and lattice oxygen oxidation mechanism for Ir-based catalysts to complete the OER process. Then, the valence change of Ir during the OER is discussed to illustrate the origin of the favorable stability of Ir-based catalysts. After that, different modification strategies for IrO2, such as elemental doping, surface engineering, atom utilization enhancing, and support engineering, are summarized in the hopes of finding some commonalities for improving performance. Finally, the perspectives for the development of Ir-based OER catalysts in PEMWEs are presented. Keywords: Polymer electrolyte membrane water electrolyzers; Oxygen evolution reaction; Iridium catalysts; Degradation mechanism; Hydrogen production.

The oxygen evolution reaction (OER) represents an anodic reaction for a variety of sustainable energy conversion and storage technologies, such as hydrogen production, CO2 reduction, etc. To realize the large-scale implementation of these technologies, the sluggish kinetics of the OER resulting from multi-step proton/electron transfer and occurring at the gas–liquid–solid triple-phase boundary needs to be accelerated. Manganese oxide-based (MnOx) materials, especially MnO2, have become promising non-precious metal electrocatalysts for the OER under acidic conditions due to the good trade-off between catalytic activity and stability. This paper reviews the recent progress of MnO2-based materials to catalyze the OER through either the traditional adsorbent formation mechanism (AEM) or the emerging lattice-oxygen-mediated mechanism (LOM). Pure manganese dioxide OER catalysts with different crystalline structures and morphologies are summarized, while MnO2-based composite structures are also discussed, and the application of MnO2-based catalysts in PEMWEs is summarized. Critical challenges and future research directions are presented to hopefully help future research. Keywords: Manganese dioxides; Electrocatalysts; Oxygen evolution reaction; Adsorbate evolution mechanism; Lattice-oxygen-mediated mechanism.

Correction for ‘Lithium-mediated electrochemical dinitrogen reduction reaction’ by Muhammad Saqlain Iqbal et al., Ind. Chem. Mater., 2023, DOI: http://doi.org/10.1039/D3IM00006K.