Electrolyte Diffusion Research Articles

Fe−Ni with Chitosan via Microwave and Carboxymethyl as Electrode Materials for Supercapacitor

AbstractIron‐nickel double hydroxides (Fe−Ni) have been broadly synthesized for supercapacitors (SC). However, the influence of precipitant quantity on SC performance is one of the present challenges. Herein, we found that Fe0.64Ni0.36@ graphite electrodes, the open and interconnected 3D graded conductive network of carboxymethyl chitosan‐derived porous carbon (C), have achieved effective surface contact. In addition, iron and nickel reinforced redox active materials on porous carbon will undergo more redox reactions for rapid diffusion of electrolyte ions/electrons. Due to the special construction and the synergistic effect of multiple oxidation transformations, the prepared Fe0.64Ni0.36@graphite composite material exhibits a maximum capacitance of 1232 F g−1 at a current density of 1 A g−1. The prepared Fe0.64Ni0.36@graphite//Fe0.64Ni0.36@graphite symmetric supercapacitors exhibit a high energy density of 22.9 Wh kg−1 at a power density of 771 W kg−1. Particularly, the sample exhibits excellent cycling stability, retaining approximately 95.8 % capacitance after 5000 cycles.

Metal-organic framework/layered double hydroxide (MOF/LDH) hetero-nanosheet array for capacitive deionization

Achieving rational and precise tuning of the structure and composition of electrode materials represents a promising strategy for enhancing the performance of capacitive deionization (CDI). However, this endeavor encounters significant challenges. Herein, we present an elaborately designed hierarchical porous MOF/LDH Hetero-Nanosheet array (NiCoMn-HNA) which could be used as anode for the efficient Cl− capture. The unique hierarchical and permeable configuration of NiCoMn-HNA offers extensive accessibility to active sites and facilitates rapid electrolyte diffusion, thereby establishing a convenient pathway for efficient charge and ion transfer. Consequently, this enhances both the overall efficiency and respective rates. Furthermore, the synergistic effect between NiCo-ZIF-L and NiCoMn-LDH hollow pseudocapacitive materials significantly contributes to the enhancement of both electrochemical performance and desalination capabilities in NiCoMn-HNA. Accordingly, the NiCoMn-HNA electrode demonstrated larger electrochemical capacitym outstanding salt adsorption capacity (103.1 mg g−1), and remarkable cyclic desalination stability (90.47 % retention rate). Density functional theory (DFT) calculations confirmed that the hollow structure of NiCoMn-HNA promotes efficient the interfacial charge transfer from NiCo-ZIF-L and NiCoMn-LDH, leading to enhanced ion transfer rate and decreased energy required for ion migration. This research introduces a novel strategy for the purposeful design of high-performance electrode materials to advance CDI technology.

Biomimetic Stylophora pistillata-like NiMoO4/NiFeS crystalline–amorphous phase boundary activated lattice oxygen mechanism for efficient electrochemical water oxidation

Leveraging the synergistic advantages of crystalline-amorphous interfaces to balance the stability and activity of catalysts has proven to be a promising strategy. Inspired by the structure of Stylophora pistillata, a biomimetic strategy to construct crystalline-amorphous structure is proposed, showcasing high-performance OER catalysts that mimic marine biological mechanisms for water splitting. In this strategy, NiMoO4 prepared acts as the coral structure, facilitating electron transfer, while NiFeS prepared serves as the calyx, increasing the number of catalytic active sites, promoting electrolyte diffusion, and enhancing OH– ion capture. Additionally, the crystalline-amorphous synergistic effect strengthens the metal–oxygen covalent bonds, activating lattice oxygen. In situ Raman reveals that the catalyst surface undergoes a reconstruction process similar to the formation of coral exoskeletons. Notably, NiMoO4/NiFeS exhibits an overpotential of only 155 mV at 10 mA cm−2, the best among various benchmark materials. This study establishes the groundwork for the development of efficient electrocatalysts through biomimetic strategies.

(Invited) Understanding the Degradation of Oxide Ion Diffusivity in YSZ Electrolyte for Practical SOC

Yttria-stabilized zirconia (YSZ) is the most common and the most reliable electrolyte material for solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs), collectively referred to as solid oxide cells (SOCs). Typical SOCs for practical applications are of the fuel-electrode-supported cell variety because these type of cells could be operated under high current densities. Here, the YSZ electrolyte is co-sintered with porous NiO-YSZ support at temperatures as high as 1400 °C to obtain dense electrolyte layer on the anode. In this process, NiO is expected to diffuse into the YSZ electrolyte. The influence of dissolved NiO into YSZ electrolyte has been investigated in AIST [1-3]. For the YSZ electrolyte with intentionally dissolved NiO, the phase transformation from cubic phase to tetragonal phase is accelerated in the lower oxygen potential range where NiO is reduced to Ni metal in the YSZ electrolyte, consequently, degradation in the conductivity of YSZ electrolyte occurs. In this study, the influence of co-sintering process of YSZ electrolyte with the NiO-YSZ support, i.e. NiO diffusion into YSZ electrolyte under co-sintering process, and its influence on the oxide ion diffusivity of YSZ electrolyte are examined.YSZ electrolyte layers were prepared on the NiO-YSZ substrates by screen-printing method or dip-coating method, and then co-sintered at high temperatures between 1370 °C to 1550 °C. The co-sintered YSZ/NiO-YSZ half-cells were reduced under dry H2 flow for 5 to 300 hours. The crystal structure and Ni distribution of the YSZ electrolyte layer were analyzed using Raman spectroscopy and high-spatial-resolution SIMS (secondary ion mass spectrometry), respectively. Lastly, the oxide ion diffusivity of the YSZ electrolyte layer was obtained using the oxygen isotope exchange method and high-spatial-resolution SIMS technique.By co-sintering of YSZ electrolyte and NiO-YSZ support, NiO uniformly diffused into YSZ electrolyte layer, and the amount of dissolved Ni (NiO) increased with increasing sintering temperature. When the half-cell was reduced at 900 °C, a phase transformation of the YSZ electrolyte was clearly observed, moreover, the oxide ion diffusivity of the YSZ electrolyte also decreased. By reduction of the half-cell at 700 °C, such phase transformation could not be observed, however, the oxide ion diffusivity is slightly but clearly decreased. In the presentation, the mechanisms of phase transformation and conductivity degradation will be discussed. H. Yokokawa et. al., Fuel Cells, 19 (2019) 311–339.T. Ishiyama, H. Kishimoto, K. D. Bagarinao, K. Yamaji, T. Horita, H. Yokokawa, ECS Transactions, 78 (2017) 321–326.T. Shimonosono, H. Kishimoto, M.E. Brito, K. Yamaji, T. Horita, H. Yokokawa, Solid State Ionics,225, 69 (2012).

Saturation-Based Transport Limitation in Thick Electrodes with Conventional Carbonate Electrolytes

In electric vehicles, stationary grid storage, and low-power lithium-ion battery (LIB) applications, thick electrodes can minimize inactive material use to increase energy density and decrease costs but face challenges in performance and manufacturability. In thick electrodes, large concentration gradients form across the electrode to push lithium ions through the thickness of the electrode, resulting in large concentration overpotentials that limit capacity utilization at higher rates. It is well understood that lithium-ion depletion at one side of this concentration gradient results in a limiting current for the cell; our models show that for high-power thick electrode systems, salt accumulation at the other side of the concentration gradient exceeds the solubility of conventional carbonate electrolytes used in LIBs. In this study, ~1mm thick dry-pressed lithium iron phosphate (LFP) electrodes were cycled at various current densities to explore precipitation conditions. Thick electrodes become rate-limited in a hexafluorophosphate (PF6)-based carbonate electrolyte; they are able to maintain high capacity utilization (~98% at C/10, ~95% at C/5, ~76% at C/2) in a bis(fluorosulfonyl)imide (FSI)-based electrolyte, which has both higher solubility and diffusivity. Operando acoustics and ex-situ imaging techniques are used to observe the effects and reversibility of precipitation in the PF6 electrolyte system. Lastly, a physics-based model is employed to define saturation-based limiting conditions given the physical electrode thickness, tortuosity, porosity, and electrolyte diffusivity. Figure 1

Lithium-Ion Intercalation By Coupled Ion-Electron Transfer Mechanism

Ion intercalation in intercalation solids is crucial for energy storage device, including Li-ion batteries. Despite significant advancements in understanding Li-ion diffusion and discoveries of new electrodes and electrolytes, the molecular process of ion intercalation across electrode-electrolyte interfaces remains poorly understood. Li intercalation kinetics has been traditionally treated by the empirical Butler-Volmer kinetics, but remains poorly measured and understood. In this study, we developed experimental electrochemical methods to probe Li+ (de-)intercalation kinetics, and provided unique experimental evidence to support the microscopic mechanism of Li+ intercalation, described by the coupled ion-electron transfer mechanism. Current-voltage responses and reaction-limited capacities, indicative of small and large overpotentials, respectively, were measured across various electrode materials, including common LixCoO2 and NMCs, and were consistent with the proposed theory. A universal dependence of the intercalation rate on the lithium-ion filling fraction was revealed, as well as temperature and electrolyte effects, consistent with the theoretical description that classical ion transfer from the electrolyte is coupled with quantum-mechanical electron transfer from the electrode. Our findings suggest that the proposed mechanism applies to a variety of intercalation materials used in energy storage, and governs the power density at low and moderate applied current densities. The possibility of modifying the reaction-limited current with electrodes and electrolytes opens new directions for interfacial engineering of Li-ion batteries.

Exploring the Relationship between Ion Diffusion and Molecular Structure of Gel Polymer Electrolytes Using NMR Spectroscopy

Lithium rechargeable batteries are widely used as energy sources for portable electronic devices, automobile, and wearable electronics. However, concerns regarding fire hazards have prompted efforts to transition from liquid to solid electrolytes. Gel polymer electrolytes (GPEs) have emerged as promising alternatives for enhancing the safety of lithium batteries. The ion conduction mechanism in GPEs can be conceptualized in two distinct modes: a liquid-like mechanism and a solid-like mechanism. We focus on the investigation of the liquid-like mechanism, which relies on polymer segmental motion. Various factors can influence ionic conduction of gel polymer electrolytes such as the structure of the sidechain, interaction between sidechain and ionic species etc. We utilize PFG NMR and nuclear relaxation time measurements to explore the correlation between the ionic motion and the structure of polymers and ionic liquids. Chain length of polymer sidechain will be varied and structurally isomeric ionic liquids will be utilized. We will demonstrate that NMR spectroscopy is a good indicator to examine the dynamics of the gel polymer electrolyte. Understanding of the structure-dynamics relation from our study will serve as a design principle to develop new gel polymer electrolyte with desired properties.

Hidden Electronic Disorder behind Diffusion in Solid-State Electrolytes

Solid-state superionic conductors (SSICs) promise significant improvements over liquid electrolytes for energy storage technologies. The advancement and application of SSICs in battery technologies are currently constrained due to an insufficient comprehension of the mechanisms underlying their ion conduction. Conduction in molecular ionic solids is well understood, where conducting ions rapidly diffuse through the rigid lattice. The rotational motion of the lattice often facilitates the rapid ionic diffusion through the “paddle-wheel” motion. This paddle-wheel motion has since become a principle for designing molecular SSICs, but a similar explanation for ion conduction in SSICs composed of monatomic ions is still needed. We predict ion conduction in the SSICs composed of monatomic ions involves 'electronic paddle-wheels,' where the hidden disorder of lone pairs (rotational motion) couple to and facilitate ion diffusion. The electronic paddle-wheel mechanism creates a universal perspective for understanding ion conductivity in both monatomic and molecular SSICs that will create design principles for engineering solid-state electrolytes from the electronic level up to the macroscale. We expect that hidden rotational electronic disorder and the resulting electronic paddle wheels will be an important marker for designing electrolytes through tuning lone pair-mobile ion interactions.

All-Solid-State Rechargeable Air Batteries Using Redox Active Naphthoquinone in the Negative Electrode

Typical air batteries are composed of metallic negative electrode, liquid electrolyte, and gas (oxygen) diffusion positive electrode. The use of metals often causes dendrite growth, which deteriorates the durability of the air batteries similar to the secondary batteries. The liquid electrolyte poses the risk of leakage, limiting application of air batteries to small devices. Recently, air batteries that use organic redox molecules as the negative electrode have been explored. This type of emerging air batteries can be charged/discharged by the redox reactions of the organic molecules associated with protons. We have recently succeeded in developing an all-solid-state rechargeable air batteries (SSAB) combining a redox-active organic molecule as negative electrodes and a proton-conductive polymer membrane as solid electrolyte. We initially focused on 2,5-dihydroxy-1,4-benzoquinone (DHBQ) as the redox-active molecule and commercial Nafion as the solid electrolyte1 (Fig. 1a and b) to fabricate an SSAB. For improving the capacity and cyclability, polymeric DHBQ was also used. In the present study, the principle of SSAB was further verified with other redox-active organic molecules. 1,4-Naphthoquinone (NQ) was used for the negative electrode, which is known to undergo reversible redox reaction via two electrons / two protons transfer process (Fig. 2a). Nafion or a hydrocarbon-based polymer electrolyte membrane (SPP-QP)2 developed at the University of Yamanashi was used as the solid electrolyte (Fig. 2b). Pt/CB (TEC10E50E, Tanaka Kikinzoku) or Pt/GCB catalyst (TEC10EA50E, Tanaka Kikinzoku) was used for the oxygen electrode. NQ, carbon powder (Ketjen black, Tanaka Kikinzoku) and Nafion were used for the inks to be used for the negative electrode. The ink was sprayed onto one side of the electrolyte membrane. The ink for the oxygen electrode composed of Pt/CB or Pt/GCB and Nafion. was similarly sprayed onto the other side of the membrame to obtain catalyst-coated membrane (CCM). SSAB was tested at a cell temperature of 40 °C and 100% RH. Cyclic voltammograms (CV) were obtained at a scan rate of 20 mV s-1 and all charge-discharge cycling tests were performed at 15 C rate. The redox potential of the negative electrode observed in the CV measurements was 0.47 V (vs RHE) for DHBQ and 0.34 V (vs RHE) for NQ, indicating that NQ with a lower redox potential could provide higher electromotive force. Fig. 3 shows the charge-discharge curves of SSABs, in which DHBQ or NQ was used as the negative electrode. The SSAB-DHBQ had an open circuit voltage of 0.80 V, a discharge capacity of 73 mAh g-1, and a Coulomb efficiency of 58%, while the SSAB-NQ had an open circuit voltage of 0.88 V, a discharge capacity of 78 mAh g-1, and a Coulomb efficiency of 85%. Replacing Nafion with the SPP-QP membrane resulted in improved Coulomb efficiency (98%) since SPP-QP was much less permeable than Nafion and thus suppressed oxygen permeation to the negative electrode. Acknowledgement This work was partly supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, through Grants-in-Aid for Scientific Research (KAKENHI 23H02058). References 1) M. Yonenaga, Y. Kaiwa, K. Oka, K. Oyaizu, K. Miyatake, Angew. Chem. Int. Ed., 62, e202304366(2023).2) J. Miyake, R. Taki, T. Mochizuki, R. Shimizu, R. Akiyama, M. Uchida, K. Miyatake, Sci. Adv., 3, eaao0476 (2017). Figure 1

A Low Self-Discharge Lithium−Sulfur Cell for the Evaluation of the Long Battery Shelf Life

The pursuit of high-energy-density charge storage has driven significant research into next-generation energy-storage systems, with lithium–sulfur cells emerging as a promising candidate. Lithium–sulfur batteries, with the high theoretical capacity of sulfur (1,675 mA·h g–1), coupled with its abundance and eco-friendly nature, are potential post-lithium-ion battery system for commercialization in energy-storage technology. However, the polysulfide diffusion during cell cycling and resting is still the major and remained challenge hindered the development of lithium–sulfur batteries. To address this problem, many studies have introduced novel electrode designs, polysulfide adsorbents, and electrolyte additives to hinder the polysulfide diffusion while enhancing the lithium–sulfur cell performances for the accomplishment of high energy density rechargeable battery systems.However, although great improvements in the dynamic electrochemistry, cycling performance, and energy densities of the batteries have been shown in recent studies, the measurements of the static electrochemistry of the self-discharge behavior and battery shelf life of the lithium–sulfur cells have rarely been discussed. Moreover, the discussion of long-term effect of the extreme self-discharge of lithium–sulfur cell is even less. The self-discharge caused by the reaction between active material and liquid electrolyte and polysulfide diffusion is more serious when raising the active-material loading to achieve high energy density. The severe self-discharge effect reduces the battery charge-storage performance and may further causes cell heating and thermal runaways due the non-electrochemical reactions during long-term storage.To understand and subsequently resolve the self-discharge effect of the lithium–sulfur cell, in this study, we present an evaluation method to measure both electrochemistry of long-term static storage and dynamic cycling of self-discharge effect of the lithium–sulfur cells. Through cell measurements and quantitative analyses, the comprehensive study and analysis reveal the self-discharge behavior in the lithium–sulfur battery chemistry. Furthermore, to address the critical issue of self-discharge of lithium–sulfur cells to achieve long shelf life, a low-self-discharge lithium–sulfur cell is introduced. The low-self-discharge lithium–sulfur cell, having a cathode combining polysulfide active material and carbonized electrospun nanofiber, can achieve a high sulfur content (66.7 wt%) and a high sulfur loading (4.03 mg cm– 2). With strong hindrance of the polysulfide diffusion and great stability as a conductive network, the designed cell can maintain low time-dependent capacity-fade rate of 0.26 % per day while reaching a long shelf life of 90 days. The low-self-discharge lithium–sulfur cells also retain high lithium-ion diffusion rate with both freshly made and cycled conditions after long resting periods (7–28 days). This study has demonstrated a comprehensive study into the self-discharge behavior of the lithium–sulfur batteries and introduced a well-designed cell with low-self discharge and stable electrochemistry (Figure).

Localized corrosion behavior on a heterogeneous surface involving multicomponent reactive transport and morphology evolution

AbstractLocalized corrosion sometimes brings about unanticipated and catastrophic damages in petrochemical pipelines and pressure vessels. For localized corrosion modeling, multicomponent reactive transport and corrosion morphology evolution are two arduous problems that involve multi–physical‐(electro) chemical processes along with multi–temporal and spatial scales. In this study, the lattice Boltzmann method (LBM) is employed to shed some light on the evolution of localized corrosion on a heterogeneous surface focusing on the effects of electrolyte ohmic resistance and diffusion. The corrosion pit is always initiated at the junction of anode and cathode sites; however, quite different morphologies are prompted under ohmic control or ohmic‐diffusion control. Under ohmic control, the pit propagates along the interface of the anode and cathode. Under ohmic‐diffusion control, the pathway of reactive species is broadened, and the corrosion morphology is developed into a more regular shape, like a flattened semicircle in 2‐D modeling. This work presents the huge potential of LBM in long‐term corrosion modeling.

High-energy density asymmetric supercapacitors with bimetallic Mo-Ni sulfides anchored on boron carbon nitride matrix

One of the current challenges in energy storage applications is the development of electrode materials that can generate high specific capacitance with considerable energy and power density. Here, our work demonstrates the fabrication of hierarchical MoNiS (Molybdenum Nickel Sulfide) anchored BCN (Boron Carbon Nitride) nanosheets as an anode electrode material for the production of asymmetric supercapacitor (ASSC) device. The facile in-situ hydrothermal reactions are utilized for the synthesis of MoNiS and MoNiS/BCN nanostructures used as electrocatalysts in supercapacitor applications. The morphological and structural analysis confirmed the successful integration of MoNiS flowers anchored on the BCN hybrid matrix. As an electroactive material, MoNiS/BCN nanostructures with the optimized mass have exhibited outstanding electrochemical activity with a specific capacitance of 1157 Fg−1 at 1 A g−1 current density, 96 % of its initial retention after 10,000 consecutive GCD cycles in 1 M of KOH electrolyte. The MoNiS/BCN/AC asymmetric device comprises an anode (MoNiS/BCN) and cathode (AC) with an excellent specific capacitance of 56.2 F g−1 at 1 Ag−1 with a high energy density of 70 Whkg−1 at power density 1200 Wkg−1. The combination of MoNiS and BCN is favoured by the exposure of several electrochemical active sites for rapid transportation of electron and electrolyte diffusion, resulting in better cycling retention.

Electrolytic ion diffusion properties and their effects on charge storage potentials of pseudocapacitive Co3O4 electrode film

Electrolytic ion diffusion properties and their effects on charge storage potentials of pseudocapacitive Co3O4 electrode film

Fast kinetics for lithium storage rendered by Li3VO4 nanoparticles/porous N-doped carbon nanofibers

Li3VO4 (LVO) has been recognized as an alternative anode material for lithium-ion batteries (LIBs) because of its appropriate lithium storage potential and capacity merits. However, its practical application is seriously hindered by slow reaction kinetics stemming from poor electronic conductivity. Herein, Li3VO4/porous N-doped carbon nanofibers (LVO/PNC NFs) are firstly designed and fabricated via an electrospinning method, utilizing the thermal decomposition characteristics of polylactic acid (PLA). The porous N-doped carbon nanofibers provide efficient electrolyte diffusion paths and facilitate ion transport. In addition, LVO nanoparticles are uniformly dispersed along the nanofibers to effectively inhibit particle aggregation. The obtained LVO/PNC NFs are evaluated as anodes for LIBs and deliver high reversible capacity of 768 mAh g−1 after 300 cycles at 0.2 A g−1, along with excellent rate capability (average capacity of 355 mAh g−1 at 8 A g−1 after 6 periodic rate testing) and long cycling life (286 mAh g−1 after 2000 cycles at 4 A g−1). The special porous nanofiber represents an effective strategy for improving the electronic conductivity, inhibiting particle aggregation, and ensuring rapid ion/charge transport towards advanced energy storage technologies.

Introducing a new model for solid-state batteries: Parameter estimation and sensitivity analysis on diffusion, concentration, and electrochemical kinetics

Despite their potential, solid-state batteries (SSBs) are challenging to optimize due to the complexity of their materials and the early stage of their modeling, especially compared to liquid-electrolyte technologies. Many existing models rely on empirical equations that cannot represent internal mass-transport and kinetic phenomena. Even studies based on mechanistic models often focus on theoretical explanations of experimental phenomena or generating hard-to-obtain experimental data. In this work, a simple yet versatile mechanistic model – able to simulate any battery composed of a metallic anode, solid electrolyte and intercalation cathode – is proposed and used in a parameter estimation routine to identify the material properties of a Li/LiPON/LiCoO2 battery. After validation, a parametric study is made to address how each material property impacts concentration profiles, discharge curves, overpotentials, and core key-performance indexes (KPIs) related to energy efficiency and battery capacity. Findings reveal that cathode diffusion is critical to enhancing Extraction Efficiency, in some cases reaching 98.9% of the theoretical capacity without enhancing any other parameter. In the case of Energy Efficiency being a priority over capacity, electrolyte diffusion and concentration showed a pivotal role, in the range of parameters studied, to increase Voltaic Efficiency up to 97.8%. Despite not directly affecting the Extraction Efficiency, it is discussed how high overpotentials caused by Electrolyte Concentration and Kinetic Constants still can harm battery capacity, for charge–discharge cycles limited by boundaries in electrical potential. Finally, studies simultaneously varying two or more parameters show that, despite extreme property enhancements (up to ca 500x higher than the standard case) indeed lead to exceptional results (up to 96.4% for Voltaic Efficiency and 98.9% for Extraction Efficiency), to use such materials at its full potential will result in other zones of the device usually neglected – such as the overpotentials from the metal anode or even the current collector – may become the new stumbling block, underscoring the significance of considering the battery as a holistic system that will inherently exhibit bottlenecks. This also implies, however, in the perpetual potential for enhancement across its components.

Two-Phase Fluid Dynamics in Proton Exchange Membrane Fuel Cells: Counter-Flow Liquid Inlets and Gas Outlets at the Electrolyte-Cathode Interface

Understanding the counter-flow of liquid inlet and gas outlet at the interface between the electrolyte and cathode gas diffusion layer (GDL) is crucial for water management in proton exchange membrane fuel cells. Existing studies typically overlook air outlets and assume a fixed liquid inlet direction. This study uses a volume of fluid method to model two-phase interactions in a T-shaped GDL and gas channel (GC) assembly, with GDL geometry derived from nano-computer tomography. Considering potential electrode deformations, such as local cracks and blockages, this research investigates the impact of the size and shape of liquid invasion on the liquid-gas behavior in the cathode GDL and GC using five liquid injection configurations. Simulations also incorporate GDL gas outlets, integrating them with a tailored liquid inlet setup. Results show that the injection site and configuration significantly affect water behavior in the GDL, affecting saturation, stabilization, and breakthrough, followed by drainage in the GCs. Comparisons of simulations with and without air outflow show distinct counter-flow interactions, highlighting variations in water distribution and discrepancies in two-phase transport across the GCs.

Theoretical design and synthesis of Co30Ni60/CC for high selective methanol oxidation assisted energy-saving hydrogen production

The integration of methanol oxidation reaction (MOR) with hydrogen evolution reaction (HER) represents an advanced approach to hydrogen production technology. Nonetheless, the rational design and synthesis of bifunctional catalysts for both MOR and HER with exceptional activity, stability and selectivity present formidable challenges. In this work, firstly, density functional theory (DFT) was utilized to design and evaluate material models with high performance for both MOR and HER. Secondly, guided by DFT, Co30Ni60/CC (CC, carbon cloth) composites with a leaf-like nanosheet structure were successfully fabricated via electrodeposition. In the MOR process, Ni acts as the predominant active center, while Co amplifies the electrochemically active surface area (ECSA) and enhances the selectivity of methanol oxidation. Conversely, in the HER process, Co serves as the primary active center, with Ni augmenting the charge transfer rate. The electrochemical results demonstrate that Co30Ni60/CC exhibits exceptional performance in both MOR and HER at a current density (j) of 10 mA cm−2, with peak potentials of 1.323 V and −95 mV, respectively. Additionally, it shows remarkable selectivity for the oxidiation of methanol to high value-added formic acid. Thirdly, following a 100 h chronopotentiometry (CP) test, the required potential demonstrates an increase of 4.9 % (MOR) and 8.1 % (HER), signifying the superior stability of Co30Ni60/CC compared to those reported in the literature. The exceptional performance of Co30Ni60/CC can be primarily attributed to that the leaf-like nanosheets structure not only exposes a plethora of active sites but also facilitates electrolyte diffusion, the monolithic structure prepared by electrodeposition enhances its stability, and the transfer of electrons from Co to Ni regulates its electronic structure, as corroborated by X-ray photoelectron spectroscopy (XPS) and density of states (DOS) analyses. Finally, at the same j, the voltage required by the Co30Ni60/CC||Co30Ni60/CC electrolytic cell, powered by an electrochemical workstation, is 198 mV lower than that required for alkaline water-splitting. Meanwhile, at higher j (100 mA cm−2), the electrolytic cell exhibits sustained and stable operation for 150 h, enabling high-efficiency hydrogen production and the synthesis of high value-added formic acid.

Effect of Ce-doping on the structural, morphological, and electrochemical features of Co3O4 nanoparticles synthesized by solution combustion method for battery-type supercapacitors

This study investigates the potential of cerium (Ce) doping to improve the performance of cobalt oxide (Co₃O₄) nanoparticles as battery-type supercapacitor electrodes. Pure Co₃O₄ nanoparticles were synthesized via a solution combustion method and then doped with 2.5 % (Ce-Co3O4) and 5 % Ce (CeO2-Co3O4). Comprehensive characterization, including X-ray diffraction (XRD), Raman spectroscopy, and field emission scanning electron microscopy (FESEM), was used to analyze the impact of Ce doping on the material properties. XRD analysis confirmed the successful incorporation of Ce into the Co₃O₄ structure, with distinct CeO2 phases forming at higher doping levels. Ce doping resulted in decreased crystallite size and peak intensity, indicating reduced crystallinity and increased defect concentration. Raman spectroscopy corroborated these findings, showing a redshift that suggests weakened metal-oxygen bonds and smaller grain sizes due to Ce³⁺ incorporation. FESEM images demonstrated that Ce doping effectively reduced nanoparticle agglomeration, with 2.5 % doping leading to smaller particles and 5 % doping promoting a 2D flake-like morphology with increased porosity. Nitrogen adsorption-desorption measurements revealed a significant increase in surface area and pore volume for CeO2-Co₃O₄, facilitating improved electrolyte diffusion and reduced resistance, thereby enhancing electrochemical performance. Evaluation of the electrochemical properties of undoped and Ce-doped Co₃O₄ materials revealed a battery-like response in a three-electrode configuration. Notably, the CeO2-Co3O4 exhibited a superior specific capacity of 603.3 C g−1 at a current density of 1 A g−1, significantly exceeding the values of 368.5 C g−1 and 127.1 C g−1 achieved by Ce-Co3O4 and undoped Co3O4, respectively. Furthermore, the CeO2-doped Co3O4 demonstrated exceptional cyclic stability, retaining 87 % of its initial capacity after undergoing 5000 charge-discharge cycles at a high current density of 10 A g−1. These results suggest that Ce doping is a promising strategy for optimizing Co₃O₄-based battery-type electrode materials, potentially leading to the development of high-performance and cost-effective energy storage systems.

Interfacial effect investigation of lithium perchlorate-interacted oxygen-containing carbon paper

The lithium perchlorate-interacted oxygen-containing carbon paper (LiClO4-OCP) is designed to act as electroactive supercapacitor electrode substrates for the energy storage application. The OCP is fabricated through hydrothermal activation treatment of carbon paper in H2O2 reaction medium. The OCP is composed of graphite pitches with ultra-thin graphene structure of top layer, showing the improved graphitization degree. The LiClO4-OCP with the polarized electrostatic force-induced interfacial adsorption reveals much more intensive interaction than LiClO4-CP with van der Waals force-induced interfacial adsorption, contributing to promoting interfacial charge transfer of LiClO4-OCP. LiClO4-OCP reveals more effective interface charge transfer and more feasible electrolyte diffusion than LiClO4-CP, contributing to higher electrochemical double-layer capacitance. LiClO4-OCP with oxygen-containing groups conducts reversible redox process to supply additional Faradaic capacitance. Mean response current is increased from 0.10 ∼ 1.34 mA cm-2 for LiClO4-CP to 0.19 ∼ 2.31 mA cm-2 for LiClO4-OCP at scan rates of 5∼100 mV s-1, indicating the improved electrochemical activity of LiClO4-OCP. The cyclic voltammetry-based capacitance increases from 19.91 ∼ 13.01 mF cm-2 mF g-1 for LiClO4-CP to 37.76 ∼ 23.06 mF cm-2 for LiClO4-OCP. The galvanostatic charge/discharge-based capacitance decreases from 13.84 ∼ 3.97 mF cm-2 for LiClO4-CP to 29.71 ∼ 12.92 mF cm-2 for LiClO4-OCP. Density-functional theory-based simulation calculation proves LiClO4-OCP with such a short molecular distance is allowed to occur strong electrostatic interaction which is caused by the perchlorate ion-induced polarization of oxygen-containing groups. The LiClO4-OCP has lower interfacial energy, lower band gap and higher density of states at Fermi energy level than LiClO4-CP, indicating the improved interfacial interaction and electrical conductivity of LiClO4-OCP. The experimental measurement and theoretical calculation achieve the consistent results of higher electrochemical activity of LiClO4-OCP electrode substrate to present its superior capacitance performance.

Bio-derived mesoporous carbon confinement synthesis of ultra-small α-Fe2O3 nanoparticles as electrocatalysts for overall water splitting

The use of high-surface-area materials in loading α-Fe2O3 nanoparticles presents an intriguing approach to improve the electrocatalytic efficiency of overall water splitting. Nevertheless, the effective management of α-Fe2O3 nanoparticle size to prevent their agglomeration continues to pose a significant challenge. This study used bio-based porous carbon with a specific surface area of 2876 m2/g and a mesoporous ratio of 95 % as a carrier to effectively disperse and inhibit the growth of α-Fe2O3 nanoparticles. The Fe2O3/NSC-30 was synthesized using urea as a precipitant through an ethylene glycol-assisted hydrothermal method accompanied by high-temperature calcination, with the α-Fe2O3 nanoparticle size being approximately 5.5 nm. The synergistic effect between the ultra-small nanoparticles and the mesoporous structure facilitates the effective diffusion of electrolyte and exposes more catalytic active sites. The Fe2O3/NSC-30 exhibited remarkable catalytic performance in the OER and HER, as evidenced by the respective low overpotentials of 270 mV and 250 mV at 20 mA cm−2. Furthermore, when Fe2O3/NSC-30 was utilized in the overall water-splitting reaction, a low cell voltage of 1.70 V was sufficient to achieve a current density of 20 mA cm−2. In this study, a new method was proposed for loading ultra-small nanoparticles onto bio-derived mesoporous carbon for promoting overall water splitting with remarkable efficiency.