Fast Charge Transfer Research Articles

Pd-substitution impact in nickel–cobalt spinel oxide grown on Ni foam as very effectual electrocatalyst for green hydrogen production supported by DFT study

The hydrothermal preparation of catalytic NiPdxCo2-xO4 (x ≦ 0.08) nano-electrocatalysts on Ni foam (NF) was successfully accomplished. The morphology and chemical composition of the catalysts are confirmed by advanced analytical techniques XRD, SEM, EDX, TEM, HR-TEM, and XPS. The NiPdxCo2-xO4 (x = 0.06) NF nano-electrocatalyst demonstrated remarkable performance in the HER, with an overpotential of 191.6 mV, a Tafel slope of 84.7 mV/dec, and extraordinary stability over 24 h using chronopotentiometry methods. The surface and electrochemical analyses demonstrated that the sample, doping with a 6.0% Pd2+ concentration, had appreciably enhanced performance in the HER. The improvement may be attributed to a much larger electrochemical surface area and fast charge transfer kinetics at the semiconductor and electrolyte interface. The influence of Pd dopants on the HER performance of CNs is studied with the help of density functional theory. It elucidates the way in which hydrogen and water molecules bind to the surface of PCN slabs. The theoretical results suggest that the incorporation of Pd dopants enhances the electrocatalytic process and boosts the HER activity as the concentration of Pd increases. The density of state spectra reveals their effect on spin-dependent electronic structure characteristics. Our findings point to a practical path for creating distinctive electrocatalysts that will serve as better electrodes for a variety of forthcoming hydrogen fuel cell applications.

Interfacially Ordered NiCoMoS Nanosheets Arrays on Hierarchical Ti3C2Tx MXene for High-Energy-Density Fiber-Shaped Supercapacitors with Accelerated Pseudocapacitive Kinetics.

Balancing electrochemical activity and structural reversibility of fibrous electrodes with accelerated Faradaic charge transfer kinetics and pseudocapacitive storage are highly crucial for fiber-shaped supercapacitors (FSCs). Herein, we report novel core-shell hierarchical fibers for high-performance FSCs, in which the ordered NiCoMoS nanosheets arrays are chemically anchored on Ti3C2Tx fibers. Beneficial from architecting stable polymetallic sulfide arrays and conductive networks, the NiCoMoS-Ti3C2Tx fiber maintains fast charge transfer, low diffusion and OH- adsorption barrier, and stabilized multi-electronic reaction kinetics of polymetallic sulfide. Consequently, the NiCoMoS-Ti3C2Tx fiber exhibits a large volumetric capacitance (2472.3 F cm-3) and reversible cycling performance (20,000 cycles). In addition, the solid-state symmetric FSCs deliver a high energy density of 50.6 mWh cm-3 and bending stability, which can significantly power electronic devices and offer sensitive detection for dopamine.

Pt-decorated spinel MnCo2O4 nanosheets enable ampere-level hydrazine assisted water electrolysis

Coupling hydrazine oxidation reaction (HzOR) with hydrogen evolution reaction (HER) has been widely concerned for high efficiency of green hydrogen preparation with low energy consumption. However, the lacking of bifunctional electrodes with ampere-level performance severely limits its industrialization. Herein, we put forward an efficient active site anchored strategy for MnCo2O4 nanosheet arrays on nickel foam (NF) by introducing Pt species (denoted as Pt-MnCo2O4/NF), which is standing for excellent bifunctional electrodes. The Pt-MnCo2O4/NF delivers ultralow potentials of −195 mV and 350 mV at 1000 mA cm−2 as well as robust stability for HzOR and HER, respectively. The study of in-situ Raman and reaction kinetics reveal that the formation of key adsorbed *NH2 and *N2H4 intermediates and the rapidly oxidization of intermediates with a fast interfacial charge transfer on Pt-MnCo2O4/NF. Remarkably, the Pt-MnCo2O4/NF assembled two-electrode hydrazine assisted water electrolyzer realizes current density of 100 mA cm−2 and 1000 mA cm−2 at 0.16 V and 0.62 V with over 80 h stability. This work provides a promising way to design efficient electrodes for energy-saving H2 generation under ampere-level current density.

The in-situ fabricated Bi nanoparticles on the BiOBr efficiently inhibit the production of toxic by-product NO2 during the photocatalytic NO oxidation

In this study, bismuth nanoparticles (NPs) are reduced in-situ on the BiOBr surface to enhance the electron transfer rate. The formation of Bi NPs is directly confirmed by characterizations such as XRD, TEM and XPS. Meanwhile, UV–Vis, PL characterization analysis and DFT theoretical calculation suggest that Bi NPs not only broaden the photoresponse range but also form a fast charge-transfer channel with the BiOBr. The results demonstrate that the NO removal rate of the optimal sample (BiOBr-1.5) is about 48.93%, which is 6.5 times that of the original BiOBr, and almost no toxic by-product NO2 is produced. This study provides a valuable strategy for designing photocatalysts that remove NO while effectively suppressing toxic by-products.

Engineering FeOOH/Fe2O3@Carbon Interfaces With Biomass-Derived Carbon Nanodot/Iron Colloids for Efficient Redox-Modulated Dopamine Voltammetric Detection.

The Fe2+/Fe3+ redox couple is effective for voltammetric detection of trace dopamine (DA). However, achieving adequate concentrations with high electroactive surface area (ECSA), DA affinity, and fast interfacial charge transfer is challenging. Consequently, most reported Fe-based sensors have a high nanomolar range detection limit (LOD). Herein, we address these limitations by manipulating the phase and morphology of FeOOH/Fe2O3 heterojunctions anchored on sp2-carbon. FeOOH/Fe2O3 is synthesized by variable temperature aging of unique Fe5H9O15/Fe2O3@sp2-carbon colloidal nanoparticles, which form via chelation between biomass-derived carbon nanodots (CNDs) and Fe2+ ions. At 27 °C and 120 °C, Fe5H9O15/Fe2O3@sp2-carbon transforms into β-FeOOH/Fe2O3 nanoparticles and α-FeOOH/Fe2O3 nanosheet, respectively. The β-FeOOH/Fe2O3 interface exhibits higher eg orbital electron occupancy than α-FeOOH/Fe2O3, thereby facilitating oxygen adsorption and the generation of Fe2+/Fe3+ sites near the polarization potential of DA. This facilitates interfacial electron transfer between Fe3+ and DA. Moreover, its nanoparticle morphology enhances ECSA and DA adsorption compared to α-FeOOH/Fe2O3 nanosheets. With a LOD of ~3.11 nM, β-FeOOH/Fe2O3 surpasses the lower threshold in humans (~10 nM) and matches noble-metal sensors. Furthermore, it exhibits selective detection of DA over 10 biochemicals in urine. Therefore, the β-FeOOH/Fe2O3@sp2-C platform holds promise as a low-cost, easy-to-synthesize, and practical voltammetric DA monitor.

In-situ synthesis of Fe3O4@Fe3C nanoparticles with heterostructures embedded in the N-doped porous carbon for high-performance lithium ion batteries

Metal oxides (Fe3O4) have attracted immense attention as high-capacity anode materials for high-performance electrochemical energy storage systems. However, the large structural change and sluggish reaction kinetics in the lithiation and delithiation reactions critically limit their practical development. Here, we design a novel composite consisting of Fe3O4@Fe3C nanoparticles embedded in N-doped porous carbon (Fe3O4@Fe3C-NPC) for lithium ion batteries. Benefiting from the synergistic effect of heterostructures, the Fe3O4@Fe3C-NPC delivers high reversible capacities (911.9 mAh g−1 at 0.2 A g−1, 319.6 mAh g−1 at 5.0 A g−1). The formed heterointerfaces can build an internal electric field, which help to improve reaction kinetics with fast ion diffusion kinetics and low charge transfer resistance. Furthermore, the Fe3O4@Fe3C-NPC//LiFePO4 full cell also displays great performance. The structural design concept and efficient synthesis method in the work can be extended to construct metal oxide/carbide heterostructures for anode materials.

Fast Outer-Sphere Electron Transfer and High Specific Capacitance at Covalently Modified Carbon Electrodes.

Carbon electrodes typically display sluggish electron transfer kinetics due to the adsorption of adventitious molecules that effectively insulate the surface. Here, we describe a method for rendering graphitic carbon electrodes permanently hydrophilic by functionalization with 4-(diazonium)benzenesulfonic acid. In aqueous electrolytes, these hydrophilic carbon electrodes exhibit metal-like specific capacitance (∼40 μF/cm2) as measured by cyclic voltammetry, suggesting a change in the double-layer structure at the carbon surface. Additionally, the modified electrodes show fast charge transfer kinetics to outer-sphere one-electron redox couples such as ferro-/ferricyanide as well as improved electron transfer kinetics in alkaline aqueous redox flow batteries.

Control of Photoinduced Charge Transfer Through Selective Cyanation of Spirofluorene‐Bridged N‐Heterotriangulenes

AbstractA series of selectively cyanated spirofluorene‐bridged N‐heterotriangulenes (N‐HTAs) with three to nine cyano groups are synthesized via a newly developed synthetic strategy. X‐ray crystallographic analysis of the compounds revealed a tripod‐like molecular shape with the fluorenyl moieties arranged in a perpendicular fashion around the nitrogen‐centered N‐HTA core. The solid state packing is found to be strongly influenced by the dipolar cyano functions. Under electrochemical conditions, the N‐HTA core is prone to undergo a reversible one‐electron oxidation toward the nitrogen‐centered radical cation, which becomes increasingly difficult as the number of the cyano acceptors, and consequently the ionization potential, increases. While a clear bathochromic shift is observed in the steady‐state UV–vis absorption spectra, the fluorescence behavior is complex and strongly dependent on the position and number of the cyano groups. The compound with six cyano functions at the fluorenyl flanks is unique within the series and shows a broad emission maximum at 499 nm and an unusually large Stokes shift of 10 171 cm−1. Time‐resolved absorption and fluorescence measurements, supported by quantum chemical calculations, identified this spectroscopic signature to originate from fast and robust photoinduced intramolecular charge transfer.

Metal-Organic Framework-Derived Co9S8 Nanowall Array Embellished Polypropylene Separator for Dendrite-Free Lithium Metal Anodes.

Developing a reasonable design of a lithiophilic artificial solid electrolyte interphase (SEI) to induce the uniform deposition of Li+ ions and improve the Coulombic efficiency and energy density of batteries is a key task for the development of high-performance lithium metal anodes. Herein, a high-performance separator for lithium metal anodes was designed by the in situ growth of a metal-organic framework (MOF)-derived transition metal sulfide array as an artificial SEI on polypropylene separators (denoted as Co9S8-PP). The high ionic conductivity and excellent morphology provided a convenient transport path and fast charge transfer kinetics for lithium ions. The experimental data illustrate that, compared with commercial polypropylene separators, the Li//Cu half-cell with a Co9S8-PP separator can be cycled stably for 2000 h at 1 mA cm-2 and 1 mAh cm-2. Meanwhile, a Li//LiFePO4 full cell with a Co9S8-PP separator exhibits ultra-long cycle stability at 0.2 C with an initial capacity of 148 mAh g-1 and maintains 74% capacity after 1000 cycles. This work provides some new strategies for using transition metal sulfides to induce the uniform deposition of lithium ions to create high-performance lithium metal batteries.

Vacancy‐Rich Ternary Iron Phosphoselenide Multicavity Nanorods: A Highly Reversible and Fast Anode for Sodium‐Ion Batteries

AbstractThe significance of exploring optimal electrode materials cannot be overstated, particularly in mitigating the critical issues posed by sluggish redox kinetics, significant volume variations, and severe structural collapse resulting from the insertion and extraction of sodium ions. These efforts are crucial for enhancing the longevity and rapid charging capabilities of sodium‐ion batteries (SIBs). Herein, a defect engineering strategy for the in situ encapsulation of single‐phase ternary iron phosphoselenide into porous carbon by robust chemical bonds with the formation of rod‐like multicavity nanohybrids (FePSe3@C) is presented. The incorporation of Se atom not only modulates the electronic structure of the central metal Fe atom and enhances the intrinsic electrical conductivity, but also generates numerous additional reaction sites and accelerates the reaction kinetics of FePSe3@C, as corroborated by theoretical calculations and kinetic analysis. Notably, the FePSe3@C demonstrates an outstanding rate capability of 321.7 mAh g−1 even at 20 A g−1 and long cycling stability over 1000 cycles. The sodium‐ion full cell, pairing the FePSe3@C anode with the Na3V2(PO4)3@C cathode, exhibits a remarkable energy density of 202 Wh kg−1, demonstrating its practical applicability. This work provides a controllable defect and morphology engineering strategy to construct advanced materials with fast charge transfer for high‐power/energy SIBs.

Pumpkin shell-derived activated carbon-supported S-incorporated transition metal oxide electrocatalyst for hydrogen evolution reaction

In the pursuit of a more sustainable future and to combat the environmental impact of fossil fuels, green hydrogen production through water electrolysis is gaining traction. While noble metals currently dominate electrocatalyst design, their expense limits widespread adoption. This study proposes a solution by outlining a method for designing efficient and affordable electrocatalysts based on non-precious metals. Herein, we introduce a novel S-incorporated Ni2O3 supported on biowaste-derived activated carbon (S-Ni2O3@AC) synthesized from pumpkin shells. This facile and sustainable approach utilizes readily available resources. The S-Ni2O3@AC nanocomposite demonstrates excellent HER performance with low overpotential and high durability. This is attributed to a high surface area of the composite, fast charge transfer, optimal hydrogen adsorption, and lowered energy barrier for water dissociation facilitated by sulfur incorporation, which is demonstrated by density functional theory (DFT) calculations. This research paves the way for cost-effective and sustainable hydrogen evolution electrocatalysts.

Enhanced photodetection in organic semiconductor single crystal sensitized by a tailored synergistic absorption of capsule-shaped chlorophyll derived CQDs

Organic single-crystal phototransistors have emerged as one of the most promising light signal detectors for their minimal defects, high mobility and light sensitivity. However, fully exploiting their advantages in advanced flexible optoelectronic applications remains great difficulty and challenging due to the lack of efficient methods for upgrading the photoresponse of delicate organic crystalline materials. Herein, we developed a capsule-shaped chlorophyll derived carbon quantum dots (Chl-CQDs) to enhance the single-crystal photodetection. Through a multi-site carbonization of chlorophyll peripheral substituents, the CQDs were produced around the chlorophyll tetrapyrrole macrocyclicvia. It makes Chl-CQDs combine the light absorption advantages of chlorophyll and CQDs, and exhibit an amazing synergistic absorption behavior. Compared to pristine devices of 2,6-diphenyl anthracene (DPA), the key figures of merit such as P, R, and D* of the Chl-CQDs/DPA heterophototransistors are improved by over 6000 times, 5 times, and 200 times, respectively. Additionally, an ultra fast charge transfer dynamics (τrise = 35 ms and τdecay = 45 ms) is observed at such unique type II heterointerface. These results not only offer a new approach for improving the photoresponse of single crystal organic phototransistors, but also make it possible to be superior to that of silicon-based devices.

Huge Electron Sponge of Polyoxometalate toward Advanced Lithium-Ion Storage.

The huge polyoxometalate, ({Mo368}), which can be prepared by a facile solution process and can be applied in lithium-ion storage applications as the anode. The large and open hollow nanostructure is promising to store a larger number of lithium ions and expedite the diffusion of lithium ions. A single {Mo368} nanocluster can transfer 624 electrons, referred to as a "huge electron sponge". Pure {Mo368} without any support materials exhibits very high capacities of 964 mA h g-1 with hardly any decay for 100 cycles at 0.1 A g-1 and still maintains 761 mA h g-1 after 180 cycles at 0.5 A g-1, indicating great cycling stability. The {Mo368} anode provides excellent rate performance and reversibility during the lithiation/delithiation processes, which are contributed by both the diffusion-controlled process and the capacitive process. The capacitive contribution can reach 71.7% at a scan rate of 2 mV s-1. The high DLi+ value measured by GITT confirms the fast reaction kinetics of the {Mo368} electrode. The {Mo368}//NCM111-A full cell is practically applied to light LED lamps. These investigations indicate that {Mo368} nanoclusters are advanced energy storage materials with high capacities, fast charge transfer, and low-cost mass production for lithium-ion storage. Moreover, {Mo368} should be considered a clean energy material because there is no production of environmental pollution during the charge/discharge processes.

Amorphous/crystalline NiFe LDH hierarchical nanostructure for large-current-density electrocatalytic water oxidation

Amorphous structure shows more catalytic active sites but poor conductivity towards oxygen evolution reaction (OER). Herein, we fabricated a novel three-dimensional (3D) self-supported NiFe layered double hydroxides (LDH) catalytic material with amorphous/ crystalline interface, aiming to obtain both excellent catalytic activity and conductivity. This homogeneous hierarchical structure exhibits a high catalytic activity and robustness, giving the industrially required current density of 1000 mA cm−2 at an ultralow overpotential of 359.8 mV with 240-hour stability in 1 M KOH. In-situ electrochemical tests reveal that the amorphous/crystalline interface boosts the intermediates evolution and OER kinetics, which might be ascribed to considerable active sites and fast charge transfer. Moreover, the 3D structure has unique superhydrophilicity and superaerophobicity, which can further accelerate the electrolyte penetration, facilitate the bubbles desorption from the electrode, enhance mass transport, and thus improve OER performance at large current densities. This work provides a feasible way to develop high-performance electrocatalytic material via constructing homogeneous amorphous/crystalline interface.

Real direct urea fuel Fell operation using standalone Ni-based metal-organic framework prepared by ball mill at room temperature

Climate change and health issues are exacerbated by fossil fuel use. Efficient environmental energy conversion devices can reduce these effects. For the first time, we used a simple ball milling approach to manufacture a Nickel-based metal-organic framework (Ni-MOF) at ambient temperature directly onto a carbon cloth surface (Ni-MOF/CC) for a direct urea fuel cell (DUFC) anode. The prepared materials' crystaline structure, surface topography, and elemental content were studied using X-Ray diffraction and a scanning electron microscope with an EDS analyzer. Cyclic voltammetry, impedance electrochemical spectroscopy, and chronoamperometry were used in a three-electrode cell configuration to evaluate the material's electrochemical oxidation efficiency, particularly toward urea. In-Situ, under real fuel cell operation circumstances, we tested the electrodes in a two-electrode cell configuration. The Ni-MOF/CC exhibited a 0.35 V onset potential owed to Ni(OH)2 (Ni+2)/Ni+3 NiOOH active site. The electrode was stable for urea oxidation and operated well under real fuel cell conditions, producing 5 mW/cm2 using 1 M urea. The Ni-based MOF's fast charge and mass transfer capabilities, which was directly synthesized onto the carbon cloth surface, make the produced electrode operate well compared with bare carbon cloth. The results of the current work allow for more efficient environmental energy conversion devices that will reduce global warming.

Effect of carbon fiber structure of Marimo carbon on polymer electrolyte fuel cell performance

Fibrous carbon has attracted attention for use as a carbon support of polymer electrolyte fuel cells (PEFC). In this study, Marimo carbon (MC), a fibrous carbon, was used as the carbon support. The MC has a higher order structure in which many carbon nanofilaments (CNFs) are grown on the surface of diamond particles (dia.). The MC was synthesized by the contact reaction between a Ni supported oxidized diamond (Ni/O-dia.) and CH4 gas, the carbon source of the CNFs. The flow rate of the CH4 gas during the MC synthesis altered the structure of the CNFs. A thick CNFs was observed in the MC with a low CH4 gas flow rate, which was not observed in the MC with a high CH4 gas flow rate. The MC with the thicker CNFs had wider interspaces between the CNFs and higher Pt supporting amounts. Electrochemical measurements of the Pt support MC (Pt/MC) were evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and current–voltage (I–V) measurements. The lower CH4 gas flow rate of the MC indicated faster charge transfer. The MC structural and charge transfer changed with the flow rate of the CH4 gas altered the electrochemical active surface area (ECSA), the oxygen reduction reaction (ORR) catalytic activity and the I–V performance of the Pt/MC.

Ion-irradiation induced structural, electronic, and optical properties modification in a few layered MoS2

Two-dimensional MoS2 is a promising candidate due to its layered structure, high conductivity, and fast charge transfer kinetics. In this work,the structural, electronic, and optical properties of pristine MoS2 have to be done by the ion irradiation technique with different ion fluences.The structural quality of the film has been confirmed by Raman spectroscopy, with peak positions of A1g and E12g indicating a few MoS2 layers. Fourier-transform infrared (FTIR) spectroscopy revealed the conformal fabrication of MoS2 nanosheets. Defect engineering by ion irradiation is an effective approach to tuning the intrinsic properties of Layered MoS2, as analyzed by photoluminescence spectroscopy.

High performance hydrovoltaic devices based on asymmetrical electrode design

As a promising method for energy harvesting, water evaporation can generate electrical energy without additional mechanical energy input. In the evaporation power generation unit based on the principle of flow potential, the low charge collection efficiency is the key factor limiting the energy output, which limits the practical application of water evaporation equipment. Based on the principle of evaporation potential, an asymmetric sandwiched hydrovoltaic device based on metallic aluminum plate and carbon cloth electrodes is designed, which not only matches the electrode, but also reduces the carrier migration route and realizes fast charge transfer and collection. The device achieves an open-circuit voltage (Voc) of 730 mV and a short-circuit current density (Jsc) of 558 μA cm−2, capable of producing output power density exceeding 61.7 μW cm−2. Micro-nano electronic devices with low power consumption can be powered by integration of multiple devices. This study proposes a strategy for clean energy collection based on water evaporation.

In Situ Interphasial Engineering Enabling High‐Rate and Long‐Cycling Li Metal Batteries

AbstractThe practical implementation of Li metal anode has long been hindered by the significant challenges of notorious dendritic Li growth and severe interphase instability during repeated cycling. Herein, a highly lithiophilic NiSe‐modified host has rationally been constructed to stabilize Li metal by the facile mechanical rolling strategy. The in situ configurated high‐flux Li2Se‐enriched interphase layer can facilitate the fast interfacial charge transfer, high Li plating/stripping reversibility and homogeneous Li nucleation/growth. Consequently, the achieved modified Li metal demonstrates ultrahigh rate capability (10 mA cm−2) and ultralong‐term cycling stability (6600 cycles) with dendrite‐free Li deposition. The Li|LiFePO4 (LFP) cell exhibits an extraordinarily long lifespan cycling stability over 500 cycles with an ultra‐low decay rate of only ≈0.0092% per cycle at 1 C. Furthermore, the 4.5 V high‐voltage Li|LiCoO2 pouch cell with a high areal capacity (≈1.9 mAh cm−2) still reveals an impressively prolonged cyclability over 200 cycles even under the harsh test condition of low negative‐to‐positive‐capacity (N/P) ratio of ≈3.4 and lean electrolyte of ≈5.5 µL mAh−1. This work provides a facile and scalable strategy toward a highly stable Li metal anode for reliable practical usage.

Interlayer Structure Manipulation of FeOCl/MXene with Soft/Hard Interface Design for Safe Water Production Using Dechlorination Battery Deionization

AbstractSuffering from the susceptibility to decomposition, the potential electrochemical application of FeOCl has greatly been hindered. The rational design of the soft‐hard material interface can effectively address the challenge of stress concentration and thus decomposition that may occur in the electrodes during charging and discharging. Herein, interlayer structure manipulation of FeOCl/MXene using soft‐hard interface design method were conducted for electrochemical dechlorination. FeOCl was encapsulated in Ti3C2Tx MXene nanosheets by electrostatic self‐assembly layer by layer to form a soft‐hard mechanical hierarchical structure, in which Ti3C2Tx was used as flexible buffer layers to relieve the huge volume change of FeOCl during Cl− intercalation/deintercalation and constructed a conductive network for fast charge transfer. The CDI dechlorination system of FeOCl/Ti3C2Tx delivered outstanding Cl− adsorption capacity (158.47 ± 6.98 mg g−1), rate (6.07 ± 0.35 mg g−1 min−1), and stability (over 94.49 % in 30 cycles), and achieved considerable energy recovery (21.14 ± 0.25 %). The superior dechlorination performance was proved to originate from the Fe2+/Fe3+ topochemical transformation and the deformation constraint effect of Ti3C2Tx on FeOCl. Our interfacial design strategy enables a hard‐to‐soft integration capacity, which can serve as a universal technology for solving the traditional problem of electrode volume expansion.