Slow Reaction Kinetics Research Articles

Built-in electric field control of electron redistribution (NiFe-based electrocatalyst) with efficient overall water splitting at industrial temperature

Nickel-iron layered double hydroxide (NiFe-LDH) is hindered in its further development in water splitting due to its slow kinetics of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). In this study, the synthesis of OER (FeO(OH)/NiFe-LDH) and HER (Fe7S8(NiS)/NiFe-LDH) catalysts endowed with inherent electric fields exhibited exceptional electrocatalytic properties. The presence of the built-in electric field modulated the redistribution of electrons within the catalyst, while the formation of a heterostructure preserved the intrinsic characteristics of the catalyst. Moreover, this electron redistribution optimized the catalyst’s adsorption of reaction intermediates (O*, OH*, OOH*, and H*) during the catalytic process, thereby enhancing the performance of both OER and HER. The electrolytic cell, equipped with these catalysts, achieved the current density of 10 mA cm−2 at a remarkably low potential of 1.409 V under industrial temperature conditions and demonstrated an ultra-long-term stability of 200 h.

Chitin-Derived Hierarchical Meso- and Microporous Carbon Enables High-Rate Sulfur Cathode of Sodium-Sulfur Batteries.

Room temperature Na-S batteries are considered as a promising alternative energy storage system because of their abundant material resources and high theoretical energy density. However, the severe polysulfide shuttle effect and slow reaction kinetics hinder their practical application. Herein, a hierarchical meso- and microporous carbon with nitrogen self-doping (NSPC) is prepared using chitin as the carbon precursor and serves as a novel host to confine the sulfur (S⊂NSPC). An optimized structure of NSPC, including abundant graphite nanocrystals, large pore volume of 1.76 cm3 g-1, and large specific surface area of 2073 m2 g-1 is obtained at the carbonization temperature of 1000 °C. These merits contribute to significantly enhanced charge transfer and ion diffusion of the as-prepared S⊂NSPC-1000 cathode, which exhibits the outstanding sodium storage performance, including high reversible capacities of 1207 mAh g-1 at 0.1 C and 891 mAh g-1 at 2 C and stable cycling with a low capacity decay for 400 cycles at 1 C, among other S⊂NSPC cathodes and previously reported cathodes for Na-S batteries. This cathode can also afford stable cycling at a high sulfur loading.

Ultrafast and stable molten salt aluminum organic batteries

Aluminum-organic batteries (AIBs) have gained significant popularity for large-scale energy storage due to their abundance of aluminum reserves, cost-effectiveness, and environmental friendliness. However, the current aluminum-organic batteries primarily relied on ionic liquid electrolytes suffer from slow reaction kinetics and limited cycle life. Herein, we report a novel and efficient aluminum-organic battery that addresses these limitations by utilizing a molten salt electrolyte and designing a strongly interacting organic cathode. By enhancing π-π stacking interactions, we induced a transition in commercial PTCDA (Perylene-3,4,9,10-tetracarboxylic dianhydride) molecules from the β-phase to the highly interactive α-phase, known as PA450. This transformation not only stabilizes the structure of the PA450 electrode, preventing dissolution in the molten salt electrolyte, but also significantly improves electron conductivity. The Al||PA450 molten salt battery demonstrates exceptional electrochemical performance, exhibiting a high reversible capacity of 135 mAh g–1 and outstanding cyclability for up to 2000 cycles at 10 A g−1. Additionally, the structural rearrangement and ion transport properties induced by the co-intercalation of Al3+ and AlCl2+ were studied are investigated. This work provides deep insights into the unique characteristics of organic materials for ultrafast energy storage in molten salt electrolytes.

Co–FeOOH thin nanosheets derived from 2D ZIF-L for efficient oxygen evolution reaction

The complicated reaction pathway and slow electron-transfer kinetics of the oxygen evolution reaction (OER) have been identified as a critical bottleneck that restricts the overall performance of electrochemical water splitting. Metal oxyhydroxides have emerged as viable alternative catalysts as compared to the precious metal-based commercial benchmarks. Yet, the activity may be compromised by the instability of the layered structures. Herein, a simple two-step method is developed for the synthesis of Co–FeOOH electrocatalysts by thermal treatment of cobalt-containing zeolitic imidazolate framework (ZIF-L) deposited on the skeleton of NF (nickel foam) in the presence of FeSO4 and urea. Co–FeOOH/NF, the thin nanosheet arrays exhibit a high specific surface area and high hydrophobicity. The addition of Co regulates the electronic environment around the Fe center, which optimizes the adsorption energy of intermediates and enhances the inherent OER activity of active sites. The Co–FeOOH nanoarrays show excellent OER performance and 99.7% Faradaic efficiency (FE). At current densities of 10 and 100 mA cm−2, there is a low overpotential of 208 and 249 mV, respectively at 1 M KOH. This kind of synthesis method will provide a promising approach for the construction of catalysts featuring stable structures for alkaline water oxidation.

Pt nanoclusters confined in the pores of hollow carbon spheres boost adsorption and electrochemical redox reaction for lithium-sulfur batteries

Sulfur (S) cathode is considered an ideal energy storage material for secondary batteries due to the high specific capacity and energy density. However, the insulating nature of S and lithium sulfide and slow electrochemical reaction kinetics, among many other issues, limit its power and energy output. Precious metals are vigorous catalytic materials and have been applied in various fields. However, the investigation of small-sized precious metal nanoclusters as the catalytic for polysulfide conversion in lithium-sulfur (Li-S) batteries has yet to be deepened. Herein, small-sized Pt nanoclusters are successfully synthesized and confined in the pores of hollow carbon spheres as the host for Li-S batteries cathode. The resultant PtNC@HCS provides the space for storing S and the electron transport network. Meanwhile, the Pt nanoclusters in the pores serve as catalytic sites for adsorbing and accelerating polysulfide conversion, thus effectively suppressing the shuttle effect. As a result, PtNC@HCS exhibits an initial capacity of 1460 mAh g−1 and a reversible capacity of 1316 mAh g−1 at 0.2C, with outstanding capacity retention, which confirms that such precious metal nanocluster catalytic material design effectively can optimize the electrochemical performance of Li-S batteries.

A Nitrogen/Oxygen Dual-Doped Porous Carbon with High Catalytic Conversion Ability toward Polysulfides for Advanced Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) have attracted widespread attention due to their high theoretical energy density and low cost. However, their development has been constrained by the shuttle effect of lithium polysulfides and their slow reaction kinetics. In this work, a nitrogen/oxygen dual-doped porous carbon (N/O-PC) was synthesized by annealing the precursor of zeolitic imidazolate framework-8 grown in situ on MWCNTs (ZIF-8/MWCNTs). Then, the N/O-PC composite served as an efficient host for LSBs through chemical adsorption and providing catalytic conversion sites of polysulfides. Moreover, the interconnected porous carbon-based structure facilitates electron and ion transfer. Thus, the S/N/O-PC cathode exhibits high cycling stability (a stable capacity of 685.9 mA h g−1 at 0.2 C after 100 cycles). It also demonstrates excellent rate performance with discharge capacities of 1018.2, 890.2, 775.1, 722.7, 640.4, and 579.6 mAh g−1 at 0.2, 0.5, 1.0, 2.0, 3.0, and 5.0 C, respectively. This work provides an effective strategy for designing and developing high energy density, long cycle life LSBs.

An Electron-Coupled Co-ZrO2 Nanodot Heterojunction Electrocatalyst with Lewis Acid-Base Site Pairs Enables High Redox Reaction Kinetics of Li-S Batteries.

Using electrocatalysts is effective in solving the slow reaction kinetics of polysulfides in Li-S batteries, but designing stable electrocatalysts with an integrated adsorption-catalysis-desorption system is challenging. Here, we report a stable metal-semiconductor (Co-ZrO2) heterojunction electrocatalyst fabricated by assembling electron-coupled Co-ZrO2 nanodots into macroporous carbon nanofibers. The Co-ZrO2 contact causes interfacial electron enrichment and electron transfer from Co to ZrO2, which creates abundant Lewis-acid sites on Co that can adsorb polysulfides. Simultaneously, the enriched interfacial electrons can activate the S-S bond and boost the catalytic conversion of long-chain polysulfides, while the ZrO2 with Lewis-base sites facilitate the desorption of short-chain polysulfides from the electrocatalyst. Moreover, the nanodot heterojunctions show great chemical stability and high redox reaction kinetics of polysulfides. Li-S batteries show high discharge capacities of 954.5 mA h·g-1 at 0.5 C with a retention of 84.9% over 200 cycles, and 710.2 mA hg-1 at 1 C with a retention of 98.6% over 200 cycles. This study provides an effective strategy for developing active and durable electrocatalysts for Li-S batteries.

Understanding the synergistic geopolymerization mechanism of multiple solid wastes in ternary geopolymers

The use of ground granulated blast furnace slag (GBFS), fly ash (FA) and steel slag (SS) to form ternary geopolymers consumes several industrial solid wastes and produces high-performance construction materials. However, the unexplored synergistic geopolymerization mechanism of multiple solid wastes limits the design of high-performance ternary geopolymers. This study investigated the synergistic mechanism through testing the macroscopic performances such as unconfined compressive strength (UCS), final setting time (FST) and fluidity, and characterizing the microscopic structure of ternary geopolymers with different mixture proportions. In addition, the influence of variables on strength development of ternary geopolymers is analyzed by developing machine learning models. Results reveal that the highest strength of ternary geopolymers was achieved at a ratio of FA to GBFS to SS of 3:5:2, and alkali activator to precursor materials of 0.08. Addition of 20 % SS refines the pore network, reducing cumulative and detrimental pore volumes, thus enhancing compressive strength. In addition, the SS addition extends the heat generation peak during geopolymerization due to its slower reaction kinetics. Material components (Na/Al, Si/Al, Ca/Si) have a significant influence on UCS, with Na/Al ratio being the most sensitive variable. The study provides a new approach for utilization of bulk industrial wastes.

Novel coal-based carbon encapsulating Co-N-C derived from ZIF-67 composite as an efficient chainmail electrocatalyst for zinc-air batteries

Energy shortages and the global climate crisis have led researchers to develop renewable clean energy sources. Zinc-air batteries have attracted much attention due to their high theoretical energy density, safety, and conversion efficiency. However, the cathodic oxygen reduction reaction (ORR) exhibits slow reaction kinetics and high reaction energy barriers, which require catalysts with high activity, selectivity, and stability to improve the reaction rate. Chainmail catalysts have attracted attention in the field of energy conversion and storage due to their structural stability. In this paper, coal-based carbon encapsulating Co-N-C chainmail electrocatalysts are designed and constructed, which can effectively reduce the thermal crumpling phenomenon of the framework structure, enhance the defect content and provide active sites for ORR. The results show that G/Co-N-C-0.025 exhibits a higher half-wave potential than that of Pt/C, with a high ultimate current density of 4.6 mA cm−2, good cycling stability, and high methanol resistance. A primary zinc-air battery is assembled, with an open-circuit voltage of 1.417 V and a maximum power density of 82 mW cm−2. The specific capacity is 789.2 mAh g−1 at a current of 20 mA cm−2. This work provides new ideas for the design and application of high-performance chainmail electrocatalysts.

Advanced Separator Materials for Enhanced Electrochemical Performance of Lithium-Sulfur Batteries: Progress and Prospects.

Lithium-sulfur (Li-S) batteries are promising energy storage devices owing to their high theoretical specific capacity and energy density. However, several challenges, including volume expansion, slow reaction kinetics, polysulfide shuttle effect and lithium dendrite formation, hinder their commercialization. Separators are a key component of Li-S batteries. Traditional separators, made of polypropylene and polyethylene, have certain limitations that should be addressed. Therefore, this review discusses the basic properties and mechanisms of Li-S battery separators, focuses on preparing different functionalized separators to mitigate the shuttle effect of polysulfides. This review also introduces future research trends, emphasizing the potential of separator functionalization in advancing the Li-S battery technology.

Constructing Built-in-Electric Field for Boosting Electrocatalytic Water Splitting.

Electrocatalytic water splitting shows great potential for producing clean and green hydrogen, but it is hindered by slow reaction kinetics. Advanced electrocatalysts are needed to lower the energy barriers. The establishment of built-in electric fields (BIEF) in heterointerfaces has been found to be beneficial for speeding up electron transfer, increasing electrical conductivity, adjusting the local reaction environment, and optimizing the chemisorption energy with intermediates. Engineering and modifying the BIEF in heterojunctions offer significant opportunities to enhance the electronic properties of catalysts, thus improving the reaction kinetics. This comprehensive review focuses on the latest advances in BIEF engineering in heterojunction catalysts for efficient water electrolysis. It highlights the fundamentals, engineering, modification, characterization, and application of BIEF in electrocatalytic water splitting. The review also discusses the challenges and future prospects of BIEF engineering. Overall, this review provides a thorough examination of BIEF engineering for the next generation of water electrolysis devices.

Multicomponent hierarchical Ni-MOFs/MWCNTs@Ni/Co-LDH nanohybrid as advanced electrode material for supercapacitor

Layer double hydroxide (LDH) is a metal hydroxide with two or more metal components. It has promising prospects in supercapacitors (SCs) as electrode material due to the chemical composition adjustability, excellent ion exchangeability, good redox activity and high specific capacity. However, the further application of LDH is limited to the inferior electrochemical conductivity and slow reaction kinetics. Multiwalled carbon nanotubes (MWCNTs) as electrode materials possess excellent conductivity and distinctive hollow structure but the specific capacities are low. Metal-organic frameworks (MOFs) have abundant electrochemical active sites, multifunctionality and tunable porosity, which could accelerate the process of transporting and diffusing electrolyte ions, enhancing the specific capacitance as electrode material. Hence, in this work, MWCNTs decorated with Ni-MOFs were introduced into Ni/Co-LDH to fabricate multicomponent heterostructure Ni-MOFs/MWCNTs@Ni/Co-LDH nanohybrid by in situ chemical reaction. The specific capacity of Ni-MOFs/MWCNTs@Ni/Co-LDH was 1032.0 C g−1 at a current density of 1.0 A g−1 and retained 66.0 % initial capacity following 5000 cycles at 5 A g−1. A power density of 850.0 W kg−1 and an energy density of 28.9 Wh kg−1 were obtained for the assembled asymmetric supercapacitor.

Improving Zn2+ migration via designing multiple zincophilic polymer electrolyte for advanced aqueous zinc ion batteries

Aqueous zinc ion batteries (AZIBs)-based on Zn metal anode face serious issues of hydrogen evolution, corrosion, and zinc dendrite growth, limiting their practical applications. Polymer-based electrolytes can effectively inhibit the above issue, but usually bring additional interfacial resistance, resulting in slow reaction kinetics. Herein, we report a poly(4-acryloylmorpholine) electrolyte with multiple zincophilic primitives for fast zinc ion transport at bulk and interface of Zn metal anode (zinc ion transfer number of 0.77) via a facile one-pot polymerization. The special electrolyte structure with multiple zincophilic primitives can adhere tightly to the Zn metal anode and induce uniform Zn deposition, resulting in low interface resistance and enhanced cycling life of batteries. Therefore, the symmetric Zn||Zn batteries assembled based on the designed and synthesized polymer electrolyte can be stably cycled for 1400 with low overpotential (∼220 mV) at 0.5 mA cm−2 with a capacity of 0.5 mAh cm−2, and the corresponding V2O5||Zn full batteries exhibit attractive reversibility, rate performance, and cycling stability. The electrolyte engineering in this work paves a new path for the construction of polymer-based electrolytes for safe and stable AZIBs.

Construction of an Ohmic Contact Cathode by Two Metal Sulfides for efficient Capture and Catalysis of Polysulfide.

The slow reaction kinetics and severe shuttle effect of lithium polysulfide make Li-S battery electrochemical performance difficult to meet the demands of large electronic devices such as electric vehicles. Based on this, an electrocatalyst constructed by metal phase material (MoS2) and semiconductor phase material (SnS2) with ohmic contact is designed for inhibiting the dissolution of lithium polysulfide with improving the reaction kinetics. According to the density-functional theory calculations, it is found that the heterostructured samples with ohmic contacts can effectively reduce the reaction-free energy of lithium polysulfide to accelerate the sulfur redox reaction, in addition to the excellent electron conduction to reduce the overall activation energy. The metallic sulfide can add more sulfophilic sites to promote the capture of polysulfide. Thanks to the ohmic contact design, the carbon nanotube-MoS2-SnS2 achieved a specific capacity of 1437.2 mAhg-1 at 0.1 C current density and 805.5 mAhg-1 after 500 cycles at 1 C current density and is also tested as a pouch cell, which proves to be valuable for practical applications. This work provides a new idea for designing an advanced and efficient polysulfide catalyst based on ohmic contact.

Syngas production through CO2-assisted catalytic pyrolysis of ethylene vinyl acetate (EVA) with a cobalt-based catalyst

Ethylene vinyl acetate (EVA) is a representative copolymer widely adopted across various sectors owing to its superior physiochemical properties; however, an environmentally benign protocol for the disposal of EVA waste has not yet been established owing to the various ratios of acetate to polyethylene. Therefore, in this study, we proposed an innovative thermochemical technique for converting EVA waste into energy resources, specifically syngas. CO2 was used to enhance the environmental sustainability of pyrolysis. Thermogravimetric analysis revealed that most of the EVA (approximately 99 wt%) was converted into pyrolytic oil and gases. However, the mechanistic features of CO2 in the pyrolysis of EVA could not be fully elucidated through single- or double-stage pyrolysis owing to the slow kinetics of the homogeneous reaction between CO2 and volatiles. To expedite the reaction kinetics, we used a cobalt (Co)-based catalyst (Co/SiO2). In the presence of Co/SiO2, the concentration of CO produced under CO2 was approximately 30-fold higher than that under N2. Furthermore, the homogeneous reactions resulted in fewer benzene derivatives and polycyclic aromatic hydrocarbons (PAHs) in the pyrolytic oil under CO2 conditions. These experimental findings suggest that CO2 and EVA could serve as valuable feedstocks for the production of energy.

Boron-Doped Dinickel Phosphide to Enhance Polysulfide Conversion and Suppress Shuttling in Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are promising for next-generation high-energy energy storage systems. However, the slow reaction kinetics render mobile polysulfides hardly controlled, yielding shuttling effects and eventually damaging Li metal anodes. To improve the cyclability of Li-S batteries, high-efficiency catalysts are desired to accelerate polysulfide conversion and suppress the shuttling effect. Herein, we studied a doping system with Ni2P and Ni2B as the end members and found a B-doped Ni2P catalyst that demonstrates high activity for Li-S batteries. As anionic dopants, B demonstrates an interesting reverse electron transfer to P and tunes the electronic structure of Ni2P dramatically. The resultant B-doped Ni2P exhibits short Ni-B bonds and strong Ni-S interaction, and the electron donation of B to P further enhances the adsorption of polysulfide on catalysts. The S-S bonds of polysulfides were activated appropriately, therefore decreasing a low energy barrier for conversion reactions.

Boosting nitrate electroreduction to ammonia on atomic Ru-Co pair sites in hollow spinels

Electrocatalytic nitrate reduction reaction (NO3RR) to ammonia (NH3) provides a promising way to simultaneously remove widespread nitrogen pollution and electrify NH3 manufacturing. However, developing suitable electrocatalysts to efficiently convert NO3--to-NH3 remains a great challenge because of the slow kinetics of NO3RR and competitive hydrogen evolution reaction (HER). Herein, we reported a novel method to incorporating Ru single atom into hollow Co3O4 to construct atomically dispersed Ru-Co pair sites (Ru1-Co/HCO) for efficient NO3- electroreduction to NH3, with a maximal NH3 Faradaic efficiency of ∼100 % and a yield rate as high as 7.02 mg h−1 cm−2 (11.0 mg h−1 mgcat−1). The NO3RR activity can be explained by the synergistic tandem effect of Ru1-Co pair sites, where Ru sites are responsible for activating NO3- and stabilizing the intermediates, and neighboring Co site promotes water dissociation to generate active hydrogen (*H) for accelerating intermediate hydrogenation on Ru sites, alleviating the site competition between NO3RR and HER. A Zn–NO3- battery coupled with in-situ NH3 recovery device was also assembled to achieve the co-generation of high-purity NH4Cl fertilizer and electricity. Our work paves a new way for boosting NO3RR activity via constructing dual active sites.

Improving the Oxygen Evolution Reaction Kinetics in Zn-Air Battery by Iodide Oxidation Reaction.

Zinc-air batteries (ZABs) have garnered considerable attention as a highly promising contender in the field of energy storage and conversion. Nevertheless, their performance is considerably impeded by the proliferation of dendrites on the Zinc anode and the slow kinetics of the redox reaction on the air cathode. Herein, taking Ag30%@LaCoO3 (Ag30%@LCO) heterojunction catalyst as the cathode, it is demonstrated that adding KI additives to the alkaline electrolyte can not only enhance the oxygen electrocatalytic reaction but also inhibit the formation of zinc anode dendrites, thereby achieving a comprehensive improvement in the performance of ZABs. Under the action of the KI additive, the optimized Ag30%@LCO catalyst shows a decreased overpotential from 460 to 220mV at j = 10mA cm-2, while the assembled ZAB shows reduced charging potential (1.8V), and long cycle stability (180h). Furthermore, the morphology characterization results indicate a reduction in dendrites on the Zn anode. Both experimental and calculated results indicate that the presence of I- as a reaction modifier alters the trajectory of the conventional oxygen evolution reaction, resulting in a more thermodynamically favorable pathway. The introduction of KI additives as electrolytes provides a straightforward approach to developing comprehensively improved ZABs.

Construct heterostructures of MoO3 nanorods modified with Fe2O3 rice grains to improve the performance of light-involved Li-O2 battery

Light-involved Li-O2 batteries have received widespread attention in recent years. However, slow reaction kinetics and high charge/discharge overpotentials at high current densities, as well as rapid recombination of photogenerated holes and electrons have hindered their further development. In this study, we propose a design strategy to grow Fe2O3 rice grains in situ on α-MoO3 nanorods to fabricate heterostructures for Li-O2 batteries at high current densities. The heterostructure α-MoO3@Fe2O3 serves as dual-function cathode catalysts for light-involved Li-O2 batteries by facilitating oxygen reduction/oxidation reactions and enhancing the separation of photogenerated charges, thereby effectively improving photoelectrocatalytic performance. Under light irradiation conditions, the heterostructure α-MoO3@Fe2O3 exhibits low charge/discharge overpotential (0.99 V) while demonstrating good cycling stability (stable cycling for 120 cycles at a high current density of 0.5 mA cm−2 with a fixed capacity of 0.5 mAh cm−2) and good rate performance, which significantly better than that was reported the currently popular light-involved Li-O2 batteries under a high current density.

Bimetallic Fe/Ni-BTC MOF decorated MXene hybrid for improved oxidation of water

Electrochemical production of green hydrogen via water-splitting is an emerging technology to generate a substitute source of energy. However, due to the slow kinetics of oxygen evolution reaction (OER), high cost, lesser availability and easy oxidation of noble metal-based electrocatalysts led the explorers to find an efficient and low-cost electrocatalysts. In the current communication, we have developed a synthesis strategy for the preparation of hybrid electrocatalyst composed of bimetallic (iron, nickel) based metal organic framework (FeNiBTC MOF) and MXene (Ti3C2Tx) via solvothermal reaction. Thanks to the ultrathin heterostructure with high electrical conductivity of MXene, with abundant active sites of FeNiBTC MOF, the as-prepared hybrid electrocatalyst FeNiBTC@MXene, leads the high efficiency OER in an alkaline environment. FeNiBTC MOF was impeccably decorated on the surfaces of MXene nanosheets with different FeNiBTC to MXene ratios and was characterized via pXRD, FESEM/EDS, XPS and BET. The optimized hybrid structured catalyst (FeNiBTC@Mx-3) revealed the best performance for OER with a low overpotential of 210 mV vs. RHE at a current density of 10 mA/cm2 and a Tafel plot value of 38.4 mV/dec and stable up to 1000th CV cycles.