Recent progress in electrode materials for micro-supercapacitors.

Micro-supercapacitors (MSCs) stand out in the field of micro energy storage devices due to their high power density, long cycle life, and environmental friendliness. The key to improving the electrochemical performance of MSCs is the selection of appropriate electrode materials. To date, both the composition and structure of electrode materials in MSCs have become a hot research topic, and it is urgent to compose a review to highlight the most important research achievements, major challenges, opportunities, and encouraging perspectives in this field. In this review, research background of MSCs is first reviewed followed by their working principles, structural classifications, and physiochemical and electrochemical characterization techniques. Next, various materials and preparation methods are summarized, and the relationship between the MSC performance and structure and composition of materials are discussed in depth. Finally, this review provides a comprehensive suggestion on accelerating the development of electrode materials to facilitate the commercialization of MSCs.

MOF-Derived Nitrogen-Doped Porous Carbon Polyhedrons/Carbon Nanotubes Nanocomposite for High-Performance Lithium-Sulfur Batteries.

Nanocomposites that combine porous materials and a continuous conductive skeleton as a sulfur host can improve the performance of lithium-sulfur (Li-S) batteries. Herein, carbon nanotubes (CNTs) anchoring small-size (~40 nm) N-doped porous carbon polyhedrons (S-NCPs/CNTs) are designed and synthesized via annealing the precursor of zeolitic imidazolate framework-8 grown in situ on CNTs (ZIF-8/CNTs). In the nanocomposite, the S-NCPs serve as an efficient host for immobilizing polysulfides through physical adsorption and chemical bonding, while the interleaved CNT networks offer an efficient charge transport environment. Moreover, the S-NCP/CNT composite with great features of a large specific surface area, high pore volume, and short electronic/ion diffusion depth not only demonstrates a high trapping capacity for soluble lithium polysulfides but also offers an efficient charge/mass transport environment, and an effective buffering of volume changes during charge and discharge. As a result, the Li-S batteries based on a S/S-NCP/CNT cathode deliver a high initial capacity of 1213.8 mAh g-1 at a current rate of 0.2 C and a substantial capacity of 1114.2 mAh g-1 after 100 cycles, corresponding to a high-capacity retention of 91.7%. This approach provides a practical research direction for the design of MOF-derived carbon materials in the application of high-performance Li-S batteries.

Recent Advances in Porous Carbon Materials as Electrodes for Supercapacitors.

Porous carbon materials have demonstrated exceptional performance in various energy and environment-related applications. Recently, research on supercapacitors has been steadily increasing, and porous carbon materials have emerged as the most significant electrode material for supercapacitors. Nonetheless, the high cost and potential for environmental pollution associated with the preparation process of porous carbon materials remain significant issues. This paper presents an overview of common methods for preparing porous carbon materials, including the carbon-activation method, hard-templating method, soft-templating method, sacrificial-templating method, and self-templating method. Additionally, we also review several emerging methods for the preparation of porous carbon materials, such as copolymer pyrolysis, carbohydrate self-activation, and laser scribing. We then categorise porous carbons based on their pore sizes and the presence or absence of heteroatom doping. Finally, we provide an overview of recent applications of porous carbon materials as electrodes for supercapacitors.

Water Management Capacity of Metal Foam Flow Field for PEMFC under Flooding Situation.

Porous metal foam with complex opening geometry has been used as a flow field to enhance the distribution of reactant gas and the removal of water in polymer electrolyte membrane fuel cells. In this study, the water management capacity of a metal foam flow field is experimentally investigated by polarization curve tests and electrochemical impedance spectroscopy measurements. Additionally, the dynamic behavior of water at the cathode and anode under various flooding situations is examined. It is found that obvious flooding phenomena are observed after water addition both into the anode and cathode, which are alleviated during a constant-potential test at 0.6 V. Greater abilities of anti-flooding and mass transfer and higher current densities are found as the same amount of water is added at the anode. No diffusion loop is depicted in the impedance plots although a 58.3% flow volume is occupied by water. The maximum current density of 1.0 A cm-2 and the lowest Rct around 17 mΩ cm2 are obtained at the optimum state after 40 and 50 min of operation as 2.0 and 2.5 g of water are added, respectively. The porous metal pores store a certain amount of water to humidify the membrane and achieve an internal "self-humidification" function.

Robust Porous TiN Layer for Improved Oxygen Evolution Reaction Performance.

The poor reversibility and slow reaction kinetics of catalytic materials seriously hinder the industrialization process of proton exchange membrane (PEM) water electrolysis. It is necessary to develop high-performance and low-cost electrocatalysts to reduce the loss of reaction kinetics. In this study, a novel catalyst support featured with porous surface structure and good electronic conductivity was successfully prepared by surface modification via a thermal nitriding method under ammonia atmosphere. The morphology and composition characterization-confirmed that a TiN layer with granular porous structure and internal pore-like defects was established on the Ti sheet. Meanwhile, the conductivity measurements showed that the in-plane electronic conductivity of the as-developed material increased significantly to 120.8 S cm−1. After IrOx was loaded on the prepared TiN-Ti support, better dispersion of the active phase IrOx, lower ohmic resistance, and faster charge transfer resistance were verified, and accordingly, more accessible catalytic active sites on the catalytic interface were developed as revealed by the electrochemical characterizations. Compared with the IrOx/Ti, the as-obtained IrOx/TiN-Ti catalyst demonstrated remarkable electrocatalytic activity (η10 mA cm−2 = 302 mV) and superior stability (overpotential degradation rate: 0.067 mV h−1) probably due to the enhanced mass adsorption and transport, good dispersion of the supported active phase IrOx, increased electronic conductivity and improved corrosion resistance provided by the TiN-Ti support.

Enhanced Ageing Performance of Sulfonic Acid-Grafted Pt/C Catalysts.

Chemical functionalization of carbon support for Pt catalysts is a promising way to enhance the performance of catalysts. In this study, Pt/C catalysts grafted with various amounts of phenylsulfonic acid groups were prepared under mild conditions. The influence of sulfonic acid groups on the physiochemical characteristics and electrochemical activities of the modified catalysts were studied using X-ray diffraction, X-ray photoelectron spectroscopy, a transmission electron microscope, and cyclic voltammetry (CV). The presence of the chemical groups enhanced the hydrogen adsorption onto/desorption off the Pt surface during the CV cycling. In contrast, the hydrogen peaks of the grafted catalysts increased after 500 CV cycles, especially for Pt (111) facets. The highest electrochemical surface area (ECSA) after the aging test was obtained for the catalyst with 18.0 wt.% graft, which was ca. 87.3% higher than that of the non-functionalized Pt catalyst. In the density functional theory (DFT) calculation, it was proven that SO3H adsorption on the crystalline was beneficial for Pt stability. The adsorption energy and bond distance of the adsorbed SO3H on Pt (110), (100), and (111) surfaces were calculated. All the stable configurations were obtained when O from S-O single bond or S was bound to the Pt surface, with the adsorption energy following the trend of (111)F > (100)H > (110)H. This result was consistent with the ECSA experiment, which explained the high electrochemical stability of the sulfonic acid groups-grafted Pt/C catalyst.

Au-TiO2/Ti Hybrid Coating as a Liquid and Gas Diffusion Layer with Improved Performance and Stability in Proton Exchange Membrane Water Electrolyzer.

The liquid and gas diffusion layer is a key component of proton exchange membrane water electrolyzer (PEMWE), and its interfacial contact resistance (ICR) and corrosion resistance have a great impact on the performance and durability of PEMWE. In this work, a novel hybrid coating with Au contacts discontinuously embedded in a titanium oxidized layer was constructed on a Ti felt via facile electrochemical metallizing and followed by a pre-oxidization process. The physicochemical characterizations, such as scanning electron microscopy, energy dispersive spectrometer, and X-ray diffraction results confirmed that the distribution and morphology of the Au contacts could be regulated with the electrical pulse time, and a hybrid coating (Au-TiO2/Ti) was eventually achieved after the long-term stability test under anode environment. At the compaction force of 140 N cm-2, the ICR was reduced from 19.7 mΩ cm2 of the P-Ti to 4.2 mΩ cm2 of the Au-TiO2/Ti. The corrosion current density at 1.8 V (RHE) is 0.689 µA cm-2. Both the ICR and corrosion resistance results showed that the prepared protective coating could provide comparable ICR and corrosion resistance to a dense Au coating.

Stainless Steel-Supported Amorphous Nickel Phosphide/Nickel as an Electrocatalyst for Hydrogen Evolution Reaction.

Recently, nickel phosphides (Ni-P) in an amorphous state have emerged as potential catalysts with high intrinsic activity and excellent electrochemical stability for hydrogen evolution reactions (HER). However, it still lacks a good strategy to prepare amorphous Ni-P with rich surface defects or structural boundaries, and it is also hard to construct a porous Ni-P layer with favorable electron transport and gas-liquid transport. Herein, an integrated porous electrode consisting of amorphous Ni-P and a Ni interlayer was successfully constructed on a 316L stainless steel felt (denoted as Ni-P/Ni-316L). The results demonstrated that the pH of the plating solution significantly affected the grain size, pore size and distribution, and roughness of the cell-like particle surface of the amorphous Ni-P layer. The Ni-P/Ni-316L prepared at pH = 3 presented the richest surface defects or structural boundaries as well as porous structure. As expected, the as-developed Ni-P/Ni-316L demonstrated the best kinetics, with η10 of 73 mV and a Tafel slope of ca. 52 mV dec-1 for the HER among all the electrocatalysts prepared at various pH values. Furthermore, the Ni-P/Ni-316L exhibited comparable electrocatalytic HER performance and better durability than the commercial Pt (20 wt%)/C in a real water electrolysis cell, indicating that the non-precious metal-based Ni-P/Ni-316L is promising for large-scale processing and practical use.

Synthesis, Physical Properties and Electrocatalytic Performance of Nickel Phosphides for Hydrogen Evolution Reaction of Water Electrolysis.

Nickel phosphides have been investigated as an alternative to noble metals and have emerged as potential catalysts that can efficiently catalyze the hydrogen evolution reaction (HER). However, the impacts of facet morphology and crystal structure of the nickel phosphides on their catalytic reactivity have not been systematically investigated. Herein, nickel phosphides with different crystalline states were prepared through a facile calcination treatment. It was found that the calcination treatment had important effects on the phase compositions, morphologies, and crystallinity of nickel phosphides, which are closely related to their HER activity. Generally, the crystallized Ni-P catalysts exhibited faster kinetics than the amorphous Ni-P. In particular, the Ni-P 300 showed remarkable HER performance with η10 of ca. 65 mV, along with a very low Tafel slope of ca. 44 mV dec-1 due to the increased catalytically active sites. Furthermore, the Ni-P 300 exhibited negligible decay during the 140 h galvanostatic electrolysis, showing better catalytic stability than the commercial Pt/C catalyst. Compared with the amorphous Ni-P, the boosted HER activity of the Ni-P 300 could benefit from the mixed nanocrystalline Ni2P and Ni3P, which could contribute to the Hads adsorption/desorption abilities and helped provide more activity sites, promoting the HER performance.

No Evidence of Benefits of Host Nano-Carbon Materials for Practical Lithium Anode-Free Cells.

Nano-carbon-based materials are widely reported as lithium host materials in lithium metal batteries (LMBs); however, researchers report contradictory claims as to where the lithium plating occurs. Herein, the use of pure hollow core-carbon spheres coated on Cu (PHCCSs@Cu) to study the lithium deposition behavior with respect to this type of structure in lithium anode-free cells is described. It is demonstrated that the lithium showed some initial and limited intercalation into the PHCCSs and then plated on the external carbon walls and the top surface of the carbon coating during the charging process. The unfavorable deposition of lithium inside the PHCCSs is discussed from the viewpoint of lithium-ion transport and lithium nucleation. The application potential of PHCCSs and the data from these LMB studies are also discussed.

Characteristics, kinetics, infrared analysis and process optimization of co-pyrolysis of waste tires and oily sludge.

The ecology was severely harmed by waste tires (WT) and oily sludge (OS). The OS and WT combinations' co-pyrolysis features, synergistic effects, and gas products were studied using thermogravimetric-infrared spectroscopy (TG-FTIR). To study kinetics and optimize pyrolysis, the Coats-Redfern and response surface methods were used. The results revealed that the OS and WT co-pyrolysis has synergistic effects. The major pyrolysis temperature range and the pyrolysis residual rate increased as the heating rate increased, and the E of the reaction increased. The strength of small-molecular-gases precipitation was modified by increasing the ratio of WT to OS, which increased OS pyrolysis. CH4, CO2, CO, and H2O are the most common gas products. The minimum estimated E and residual amount were 40.599 kJ/mol and 39.33%, respectively, when the WT mixture ratio was 58.7% and the heating rate was 10 °C/min. All the study contributes basic data to the development of the treatment of OS and WT in collaboration.

Advanced titanium dioxide fluidizable nanowire photocatalysts.

In photocatalytic water splitting, fluidization is known to minimize the adverse effects of mass-transfer, poor radiation distribution, parasitic back-reactions and photocatalyst handling difficulties, which limit the scalability of immobilized-film and suspended slurry photocatalysts. Fluidization of one-dimensional TiO2 photocatalyst particles, such as nanorods, -wires and -ribbons, is highly desired as it further enhances the efficiency of photocatalytic reaction, due to their peculiar photo-electrochemical characteristics that result in more effective separation of photo-generated charges and absorption of photons. However, the harsh physical environment of a fluidized bed reactor does not readily allow for nanostructured TiO2 photocatalysts, as the fine features would be quickly removed from the particle surface. Here, we propose a scalable method for fabrication of rutile TiO2 nanorods on porous glass beads as a 3D protective substrate to reduce the attrition rate caused by fluidization. The quality of the synthesized nanorod films was optimized through controlling a growth quality factor, R q, allowing for good quality films to be grown in different batch amounts and different hydrothermal reactor sizes. The utilization of porous glass beads substrate has reduced the attrition rate, and the protective features of the particles reduced the rate of attrition by an order of magnitude, compared to a particulate photocatalyst, to near negligible levels. Such considerably reduced attrition makes the as-developed porous glass beads supported rutile TiO2 nanorods a viable fluidizable photocatalyst candidate for various applications, including water splitting and degradation of organic compounds.

Cost-Effective Fabrication of Modified Palygorskite-Reinforced Rigid Polyurethane Foam Nanocomposites.

Integration of nanoclay minerals into rigid polyurethane foams (RPUFs) is a cost-effective solution to enhance foam's performance via environmental protection technology. In this work, palygorskite/RPUFs nanocomposites (Pal/RPUFNs) with excellent mechanical properties and thermal stability were prepared via a one-step method, using 4,4'-diphenylmethane diisocyanate and polyether polyol as the starting materials, coupled with Pal modified by silane coupling agent KH570. The effects of the modified Pal on the mechanics, morphology, and thermal properties of the nanocomposites were studied systematically. When the content of the modified Pal was 8 wt% of polyether polyol, the elastic modulus and compressive strength of the Pal/RPUFNs were increased by ca. 131% and 97%, respectively. The scanning electron microscopy images indicated that the addition of the modified Pal significantly decreased the cell diameter of the Pal/RPUFNs. The results of thermogravimetric and derivative thermogravimetry analyses revealed that the addition of the modified Pal increased the thermal weight loss central temperature of the Pal/RPUFNs, showing better thermal stability in comparison with the pure RPUFs. A self-made evaluation device was used to estimate the thermal insulation ability of the Pal/RPUFNs. It was found that the small cell size and uniform cellular structure were keys to improving the thermal insulation performance of the RPUFs. The prepared Pal/RPUFNs are expected to have great potential in the field of building insulation.

Rational Design of Multimodal Porous Carbon for the Interfacial Microporous Layer of Fuel Cell Oxygen Electrodes.

Accumulation of water at the interface of the cathode catalyst layer (CCL) and the diffusion media is a major cause of performance loss in H2/air fuel cells. Proper engineering of the interface by the use of advanced materials and preparation methods can effectively reduce the extent of this loss by improving the transport of water and gas across this interface. Herein, we present detailed modeling results of water and gas transport across this interface for in-house synthesized carbon material with multiple levels of porosity and by considering the interfacial properties of the carbon material and the microporous layer (MPL). The oxygen reduction reaction and the counter-flow transport of oxygen and water within the CCL and MPL pores were modeled considering a partially flooded interface. Well-characterized multimodal porous carbon was chosen as a candidate material for this study, and the effects of all the various levels of porosity in the MPL, wettability, permeability, and the quality of contact between the MPL and CCL on the transport phenomena of fluids were investigated. This study provides new insights into the balance of opposing transport phenomena on the local and overall performance of the catalyst layer and rationalizes the design parameters for an MPL material based on both the material and interfacial properties.

Properties, optimized morphologies, and advanced strategies for photocatalytic applications of WO3 based photocatalysts.

The development of WO3 based photocatalysts has gained considerable attention across the world, especially in the realm of environmental remediation and energy production. WO3 has a band gap of 2.5- 2.7 eV that falls under the visible region and is thus a potential candidate to utilize in various photocatalytic processes. As an earth-abundant metal oxide, WO3 discovered in 1976 displayed excellent electronic and morphological properties, good stability, and enhanced photoactivity with diverse crystal phases. Also, it unveils non-toxicity, high stability in drastic conditions, biocompatibility, low cost, excellent hole mobility (10 cm2 V-1s-1), and tunable band gap. This review provides a comprehensive overview of the different properties of WO3 inclusive of crystallographic, electrical, optical, thermoelectrical, and ferroelectric properties. The different morphologies of WO3 based on dimensions were obtained by adopting different fabrication methods including inspecting their effects on the efficiency of WO3. Numerous strategies to construct an ideal photocatalyst such as engineering crystal facets, surface defects, doping, heterojunction formation explaining specifically type-II, Z-scheme, and S-scheme mechanisms with addition to carbonaceous based WO3 nanocomposites are summed up to explore the photocatalytic performance. The typical application of WO3 is deliberated in detail involving the role and efficiency of WO3 in pollutant degradation, CO2 photoreduction, and water splitting. Besides, other applications of WO3 as gas-sensor, bio-sensor, decomposition of VOCs, heavy metals ions adsorption, and antimicrobial property are also included. Moreover, the numerous aspects responsible for the high efficiency of WO3-based nanocomposites with their challenges, opportunities, and future aspects are summarized. Hopefully, this review may inspire researchers to explore new ideas to boost the production of clean energy for the next generation.

Preparation and Performance Study of the Anodic Catalyst Layer via Doctor Blade Coating for PEM Water Electrolysis.

The membrane electrode assembly (MEA) is the core component of proton exchange membrane (PEM) water electrolysis cell, which provides a place for water decomposition to generate hydrogen and oxygen. The microstructure, thickness, IrO2 loading as well as the uniformity and quality of the anodic catalyst layer (ACL) have great influence on the performance of PEM water electrolysis cell. Aiming at providing an effective and low-cost fabrication method for MEA, the purpose of this work is to optimize the catalyst ink formulation and achieve the ink properties required to form an adherent and continuous layer with doctor blade coating method. The ink formulation (e.g., isopropanol/H2O of solvents and solids content) were adjusted, and the doctor blade thickness was optimized. The porous structure and the thickness of the doctor blade coating ACL were further confirmed with the in-plane and the cross-sectional SEM analyses. Finally, the effect of the ink formulation and the doctor blade thickness of the ACL on the cell performance were characterized in a PEM electrolyzer under ambient pressure at 80 °C. Overall, the optimized doctor blade coating ACL showed comparable performance to that prepared with the spraying method. It is proved that the doctor blade coating is capable of high-uniformity coating.

Ordered Porous TiO2@C Layer as an Electrocatalyst Support for Improved Stability in PEMFCs.

Proton exchange membrane fuel cells (PEMFCs) are the most promising clean energy source in the 21st century. In order to achieve a high power density, electrocatalytic performance, and electrochemical stability, an ordered array structure membrane electrode is highly desired. In this paper, a new porous Pt-TiO2@C ordered integrated electrode was prepared and applied to the cathode of a PEMFC. The utilization of the TiO2@C support can significantly decrease the loss of catalyst caused by the oxidation of the carbon from the conventional carbon layer due to the strong interaction of TiO2 and C. Furthermore, the thin carbon layer coated on TiO2 provides the rich active sites for the Pt growth, and the ordered support and catalyst structure reduces the mass transport resistance and improves the stability of the electrode. Due to its unique structural characteristics, the ordered porous Pt-TiO2@C array structure shows an excellent catalytic activity and improved Pt utilization. In addition, the as-developed porous ordered structure exhibits superior stability after 3000 cycles of accelerated durability test, which reveals an electrochemical surface area decay of less than 30%, considerably lower than that (i.e., 80%) observed for the commercial Pt/C.

PtSe2 /Pt Heterointerface with Reduced Coordination for Boosted Hydrogen Evolution Reaction.

PtSe2 is a typical noble metal dichalcogenide (NMD) that holds promising possibility for next-generation electronics and photonics. However, when applied in hydrogen evolution reaction (HER), it exhibits sluggish kinetics due to the insufficient capability of absorbing active species. Here, we construct PtSe2 /Pt heterointerface to boost the reaction dynamics of PtSe2 , enabled by an in situ electrochemical method. It is found that Se vacancies are induced around the heterointerface, reducing the coordination environment. Correspondingly, the exposed Pt atoms at the very vicinity of Se vacancies are activated, with enhanced overlap with H 1s orbital. The adsorption of H. intermediate is thus strengthened, achieving near thermoneutral free energy change. Consequently, the as-prepared PtSe2 /Pt exhibits extraordinary HER activity even superior to Pt/C, with an overpotential of 42 mV at 10 mA cm-2 and a Tafel slope of 53 mV dec-1 . This work raises attention on NMDs toward HER and provides insights for the rational construction of novel heterointerfaces.

Response surface optimization, combustion characteristics and kinetic analysis of mixed fuels of Fenton/CaO conditioned municipal sewage sludge and rice husk.

The co-combustion characteristics and kinetics of Fenton/CaO conditioned MSS, and biomass rice husk (RH) are studied by thermogravimetry, and the condition optimization was carried out by response surface methodology (RSM). The results show that the mixed fuel with RH is helpful to decrease Ti and Tb values and increase combustion characteristic index (CCI). The CCI of MSS after conditioning is 0.59-0.88 times lower than that of the pure MSS. In addition, the total Em of S2, MSS/RH mixed combustion after Fenton/CaO conditioning is lower, the combustion reactivity is stronger. According to RSM, the optimum conditions are considered to be: RH mixing ratio 56%, Fenton/CaO conditioner dosage 147 mg g-1 dry solids, heating rate 30 K min-1, the maximum CCI 25.3305 × 10-7%2 °C-3 min-2, and the minimum Em 10.6403 kJ min-1. This study supplies new insights into combustion technology of sludge.

Dense Pt Nanowire Electrocatalyst for Improved Fuel Cell Performance Using a Graphitic Carbon Nitride-Decorated Hierarchical Nanocarbon Support.

An innovative strategy is presented to engineer supported-Pt nanowire (NW) electrocatalysts with a high Pt content for the cathode of hydrogen fuel cells. This involves deposition of graphitic carbon nitride (g-CN) onto 3D multimodal porous carbon (MPC) (denoted as g-CN@MPC) and using the g-CN@MPC as an electrocatalyst support. The protective coating of g-CN on the MPC provides good stability for the electrocatalyst support against electrochemical oxidation, and also enhances oxygen adsorption and provides additional active sites for the oxygen reduction reaction. Compared with commercial carbon black Vulcan XC-72R (denoted as VC) support material, the larger hydrophobic surface area of the g-CN@MPC enables the supported high-content Pt NWs to disperse uniformly on the support. In addition, the unique 3D interconnected pore networks facilitate improved mass transport within the g-CN@MPC support material. As a result, the g-CN@MPC-supported high-content Pt catalysts show improved performance with respect to their counterparts, namely, MPC, VC, and g-CN@VC-supported Pt NW catalysts and the conventional Pt nanoparticle (NP) catalyst (i.e., Pt(20 wt%)NPs/VC (Johnson Matthey)) used as the benchmark. More importantly, the g-CN-tailored high-content Pt NW (≈60 wt%) electrocatalyst demonstrates high PEM fuel cell power/performance at a very low cathode catalyst loading (≈0.1 mgPt  cm-2 ).