Catalysis of Electrochemical Reactions by Surface-Active Sites: Analyzing the Occurrence and Significance of Volcano Plots by Cyclic Voltammetry

An Integrated Therapeutic and Preventive Nanozyme-Based Microneedle for Biofilm-Infected Diabetic Wound Healing

The healing of biofilm-infected diabetic wounds characterized by a deteriorative tissue microenvironment represents a substantial clinical challenge. Current treatments remain unsatisfactory due to the limited antibiofilm efficacy caused by weak tissue and biofilm permeability of drugs and the risk of reinfection during the healing process. To address these issues, an integrated therapeutic and preventive nanozyme-based microneedle (denoted as Fe2 C/GOx@MNs) is engineered. The dissolvable tips with enough mechanical strength can deliver and rapidly release Fe2 C nanoparticles (NPs)/glucose oxidase (GOx) in the biofilm active regions, enhancing tissue and biofilm permeability of Fe2 C NPs/GOx, ultimately achieving highly efficient biofilm elimination. Meanwhile, the chitosan backing layer can not only act as an excellent physical barrier between the wound bed and the external environment, but also prevent the bacterial reinvasion during wound healing with its superior antibacterial property. Significantly, the biofilm elimination and reinfection prevention abilities of Fe2 C/GOx@MNs on wound healing are proved on methicillin-resistant Staphylococcus aureus-biofilm-infected diabetic mouse model with full-thickness wound. Together, these results demonstrate the promising clinical application of Fe2 C/GOx@MNs in biofilm-infected wound healing.

Confinement Effects in Carbonized ZIF-Confined Hollow PtCo Nanospheres Enable the Methanol Oxidation Reaction

Confinement effects in highly porous nanostructures can effectively adjust the selectivity and kinetics of electrochemical reactions, which can boost the methanol oxidation reaction (MOR). In this work, carbonized ZIF-8-confined hollow PtCo nanospheres (PtCo@carbonized ZIF-8) were fabricated using a facile strategy. A monodisperse confined region was successfully prepared, and the dispersion of the PtCo nanoparticles (NPs) could be precisely regulated, allowing for the effective tuning of the confined region. Thus, the precise regulation of the catalytic reaction was achieved. Importantly, hollow PtCo NPs were prepared using a method based on the Kirkendall effect, and their forming mechanism was systematically investigated. Because of the confinement effects of carbonized zeolitic imidazolate framework-8 (ZIF-8), the crystal and electronic structures of the PtCo NPs were able to be effectively tuned. Our electrochemical results show that PtCo@carbonized ZIF-8 composites manifest a higher mass activity (1.4 A mgPt-1) and better stability compared to commercial Pt/C.

Simple Approach for Reconciling Cyclic Voltammetry with Hydrogen Adsorption Energy for Hydrogen Evolution Exchange Current

Cyclic voltammetry (CV) is a standard technique to analyze the current-potential characteristics of the hydrogen evolution reaction (HER). Herein, we develop a computational quantum-scaled CV model for the HER building on the Butler-Volmer relation for a one-step, one-charge transfer process. Owing to a universal and absolute rate constant verified by fitting to experimental cyclic voltammograms of elemental metals, we show that the model quantifies the exchange current─the main analytical descriptor for HER activity─solely using the hydrogen adsorption free energy obtained from density functional theory calculations. Furthermore, the model resolves controversies over analytical studies for HER kinetics.

Nanogap-Resolved Adsorption-Coupled Electron Transfer by Scanning Electrochemical Microscopy: Implications for Electrocatalysis

Here, we demonstrate for the first time that the mechanism of adsorption-coupled electron-transfer (ACET) reactions can be identified experimentally. The electron transfer (ET) and specific adsorption of redox-active molecules are coupled in many electrode reactions with practical importance and fundamental interest. ACET reactions are often represented by a concerted mechanism. In reductive adsorption, an oxidant is simultaneously reduced and adsorbed as a reductant on the electrode surface through the ACET step. Alternatively, the non-concerted mechanism mediates outer-sphere reduction and adsorption separately when the reductant adsorption is reversible. In electrocatalysis, reversibly adsorbed reductants are ubiquitous and crucial intermediates. Moreover, electrocatalysis is complicated by the mixed mechanism based on simultaneous ACET and outer-sphere ET steps. In this work, we reveal the non-concerted mechanism for ferrocene derivatives adsorbed at highly oriented pyrolytic graphite as simple models. We enable the transient voltammetric mode of nanoscale scanning electrochemical microscopy (SECM) to kinetically control the adsorption step, which is required for the discrimination of non-concerted, concerted, and mixed mechanisms. Experimental voltammograms are compared with each mechanism by employing finite element simulation. The non-concerted mechanism is supported to indicate that the ACET step is intrinsically slower than its outer-sphere counterpart by at least four orders of magnitude. This finding implies that an ACET step is facilitated thermodynamically but may not be necessarily accelerated or catalyzed by the adsorption of the reductant. SECM-based transient voltammetry will become a powerful tool to resolve and understand electrocatalytic ACET reactions at the elementary level.

Surface and Interface Engineering: Molybdenum Carbide-Based Nanomaterials for Electrochemical Energy Conversion

Molybdenum carbide (Mo_x C)-based nanomaterials have shown competitive performances for energy conversion applications based on their unique physicochemical properties. A large surface area and proper surface atomic configuration are essential to explore potentiality of Mo_x C in electrochemical applications. Although considerable efforts are made on the development of advanced Mo_x C-based catalysts for energy conversion with high efficiency and stability, some urgent issues, such as low electronic conductivity, low catalytic efficiency, and structural instability, have to be resolved in accordance with their application environments. Surface and interface engineering have shown bright prospects to construct highly efficient Mo_x C-based electrocatalysts for energy conversion including the hydrogen evolution reaction, oxygen evolution reaction, nitrogen reduction reaction, and carbon dioxide reduction reaction. In this Review, the recent progresses in terms of surface and interface engineering of Mo_x C-based electrocatalytic materials are summarized, including the increased number of active sites by decreasing the particle size or introducing porous or hierarchical structures and surface modification by introducing heteroatom(s), defects, carbon materials, and others electronic conductive species. Finally, the challenges and prospects for energy conversion on Mo_x C-based nanomaterials are discussed in terms of key performance parameters for the catalytic performance.

Electroactive and Sustainable Cu-MOF/PEDOT Composite Electrocatalysts for Multiple Redox Mediators and for High-Performance Dye-Sensitized Solar Cells

An electrically conductive Cu-MOF, {[Cu₂(6-mercaptonicotinic acid)(6-mercaptonicotinate)]·NH₄}_n, was successfully electrodeposited on the conductive substrates via using poly(3,4-ethylenedioxythiophene) (PEDOT) as the binder. Multiple functionalities of the Cu-MOF microparticle within the Cu-MOF/PEDOT composite electrode were systematically vindicated as (1) releasing the cohesive strength among the PEDOT matrix, thus enhancing the film adhesion to substrate, (2) providing excellent intrinsic heterogeneous rate constant via lowering the reaction active energy, (3) supplying numerous active sites at the center or edges on its (-Cu-S-)_n honeycomb-like planes, (4) facilitating the electron transfer through its two-dimensional (-Cu-S-)_n plains, and (5) benefiting the penetration of the redox mediators through its porous frameworks. In multiple redox mediators (i.e., I^-/I₃^-, cobalt(II/III)-complex, and copper(I/II)-complex), the composite Cu-MOF/PEDOT electrode exhibited superior electrocatalyst activity and kept almost 100% of its initial redox peak currents after continuous cyclic voltammetric scanning for 300 cycles. As a high-performance electrocatalyst for the counter electrode in dye-sensitized solar cells (DSSCs), the composite Cu-MOF/PEDOT electrode rendered its cell a decent solar-to-electricity conversion efficiency of up to 9.45% at 1 sun and 22.80% at room light illumination. Compared to the traditional platinum electrode (7.67%), the low-cost Cu-MOF/PEDOT composite electrode has great possibility to be used for various electrochemical devices and the Internet-of-things applications.

Electrochemical determination of T2 toxin by graphite/polyacrylonitrile nanofiber electrode

Fabricating graphite electrode corrected with nanofiber by electrospinning as a considerable procedure for utilization in the fluid materials, milk, and syrup for detection of T2 mycotoxin is a significant technique. The modern biosensor was fabricated at normal degrees of room and utilized via buffer Britton-Robinson (B-R) in pH = 5 to refine the chemico-mechanical specifications. The electrochemical manner of the modified surface was surveyed using the scanning electron microscopy (SEM), cyclic voltammetry (CV), square wave voltammetry (SQWV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). The corrected electrode displayed a linear reply to T2 toxin in two distinct concentration ranges of 30-100 nM with correlation coefficients of 0.99. The greatest signals in the square wave spectrums for the B-R buffer created on the uttermost signals of the obtained streams were pH = 5 and 0.5 M of KNO3 for T2 toxin. The modified electrode has a big signal, broad dynamic concentration and high sensitivity and selectivity.

Nanohole-boosted electron transport between nanomaterials and bacteria as a concept for nano-bio interactions

Biofilms contribute to bacterial infection and drug resistance and are a serious threat to global human health. Antibacterial nanomaterials have attracted considerable attention, but the inhibition of biofilms remains a major challenge. Herein, we propose a nanohole-boosted electron transport (NBET) antibiofilm concept. Unlike known antibacterial mechanisms (e.g., reactive oxygen species production and cell membrane damage), nanoholes with atomic vacancies and biofilms serve as electronic donors and receptors, respectively, and thus boost the high electron transport capacity between nanomaterials and biofilms. Electron transport effectively destroys the critical components (proteins, intercellularly adhered polysaccharides and extracellular DNA) of biofilms, and the nanoholes also significantly downregulate the expression of genes related to biofilm formation. The anti-infection capacity is thoroughly verified both in vitro (human cells) and in vivo (rat ocular and mouse intestinal infection models), and the nanohole-enabled nanomaterials are found to be highly biocompatible. Importantly, compared with typical antibiotics, nanomaterials are nonresistant and thereby exhibit high potential for use in various applications. As a proof-of-principle demonstration, these findings hold promise for the use of NBET in treatments for pathogenic bacterial infection and antibiotic drug resistance.

Metric Learning for High-Throughput Combinatorial Data Sets

Materials design and discovery through the high-throughput exploration of materials space has been recognized as a new paradigm in materials science. However, typical high-throughput exploration methods deliver high-dimensional and very diverse data sets that pose the challenge of extracting the key features and patterns that could guide the discovery process. Unraveling patterns is a nontrivial task as quite often the underlying physical phenomena are uncertain and latent variables governing the performance are mainly unknown. In this paper, we discuss challenges related to designing a data analytics tool for clustering high-throughput measurements performed on the compositional library of materials. The critical aspects of our methodology are (i) learning the similarity measures, as opposed to using fixed similarity measures (e.g., Euclidean distance, dynamic time warping), while (ii) imposing the similarity in the composition space. Our methodology is based on the multitask learning approach that is formulated to account for the composition neighborhoods that are specific to the compositional libraries. We demonstrate the advantages of our methodology for the library of cyclic voltammetry curves generated for model multimetal catalysts, as well as X-ray diffraction patterns from experimental studies. We also compare our approach with the current state-of-the-art methods used in similar problems. This work has important implications for designing high-throughput exploration including catalysts for electrochemical systems, such as fuel cells and metal-air batteries.

Interplay of Homogeneous Reactions, Mass Transport, and Kinetics in Determining Selectivity of the Reduction of CO2 on Gold Electrodes

Gold electrocatalysts have been a research focus due to their ability to reduce CO₂ into CO, a feedstock for further conversion. Many methods have been employed to modulate CO₂ reduction (CDR) vs hydrogen evolution reaction (HER) selectivity on gold electrodes such as nano-/mesostructuring and crystal faceting control. Herein we show that gold surfaces with very different morphologies (planar, leaves, and wires) lead to similar bell-shaped CO faradaic efficiency as a function of applied potential. At low overpotential (E > -0.85 V vs standard hydrogen electrode (SHE)), HER is dominant via a potential quasi-independent rate that we attribute to a rate limiting process of surface dissociation of competent proton donors. As overpotential is increased, CO faradaic efficiency reaches a maximal value (near 90%) because CO production is controlled by an electron transfer rate that increases with potential, whereas HER remains almost potential independent. At high overpotential (E < -1.2 V vs SHE), CO faradaic efficiency decreases due to the concurrent rise of HER via bicarbonate direct reduction and leveling off of CDR as CO₂ replenishment at the catalyst surface is limited by mass transport and homogeneous coupled reactions. Importantly, the analysis shows that recent attempts to overcome mass transport limitations with gas diffusion electrodes confront low carbon mass balance owing to the prominence of homogeneous reactions coupled to CDR. The comprehensive kinetics analysis of the factors defining CDR vs HER on gold electrodes developed here provides an activation-driving force relationship over a large potential window and informs on the design of conditions to achieve desirable high current densities for CO₂ to CO conversion while maintaining high selectivity.

Metal Organic Framework Derived Materials: Progress and Prospects for the Energy Conversion and Storage

Exploring new materials with high efficiency and durability is the major requirement in the field of sustainable energy conversion and storage systems. Numerous techniques have been developed in last three decades to enhance the efficiency of the catalyst systems, control over the composition, structure, surface area, pore size, and moreover morphology of the particles. In this respect, metal organic framework (MOF) derived catalysts are emerged as the finest materials with tunable properties and activities for the energy conversion and storage. Recently, several nano- or microstructures of metal oxides, chalcogenides, phosphides, nitrides, carbides, alloys, carbon materials, or their hybrids are explored for the electrochemical energy conversion like oxygen evolution, hydrogen evolution, oxygen reduction, or battery materials. Interest on the efficient energy storage system is also growing looking at the practical applications. Though, several reviews are available on the synthesis and application of MOF and MOF derived materials, their applications for the electrochemical energy conversion and storage is totally a new field of research and developed recently. This review focuses on the systematic design of the materials from MOF and control over their inherent properties to enhance the electrochemical performances.

Modular O2 electroreduction activity in triphenylene-based metal-organic frameworks

Electrically conductive layered metal–organic frameworks, regardless of the metal or chelating atom identity, exhibit phase-dependent catalytic activity for O₂ electroreduction.

Triphenylene ligands hexasubstituted with amino or phenol groups afford two phases of electrically conductive layered two-dimensional metal–organic frameworks upon reaction with various metals. Regardless of the identity of the metal or chelating atom, π-stacking within the MOF layers is essential to achieve high electrical conductivity, redox activity, and catalytic activity.