Long-term Electrochemical Stability Research Articles

KTiOPO4-structured electrode materials for metal-ion batteries: A review

The success story of the triphylite-type LiFePO4 immediately boosted the development of numerous classes of polyanion-based electrode materials for metal-ion batteries. A number of advantages including thermal and structural stability, polyanionic inductive effect, and variety of crystal types and chemical compositions render these materials attractive for grid and large-scale applications ensuring high safety standards, environmental friendliness and cost benefits. In this review, we focus on a specific family of polyanion-based electrode materials adopting the KTiOPO4-type structure that captured particular attention recently due to the unique 3D-framework. This framework features thermal, structural and long-term electrochemical cycling stability, fast ionic transport, possibility to accommodate two alkali ions per transition metal cation enabling multi-electron transitions, and unprecedented high electrode potentials for a specific redox couple among all known polyanion materials. The recent advances and overview of KTiOPO4-type and related positive and negative electrode materials for metal-ion batteries are presented with a special emphasis on the interrelations between crystal structure peculiarities and electrochemical properties.

Tuning of Trifunctional NiCu Bimetallic Nanoparticles Confined in a Porous Carbon Network with Surface Composition and Local Structural Distortions for the Electrocatalytic Oxygen Reduction, Oxygen and Hydrogen Evolution Reactions

The rational design of multi-functional catalysts that use non-noble metals to facilitate the interconversion between H2, O2 and H2O is an intense area of investigation. Bimetallic nanosystems with highly tunable electronic, structural and catalytic properties that depend on their composition, structure, and size have attracted considerable attention. Herein, we report the synthesis of bimetallic nickel-copper (NiCu) alloy nanoparticles confined in a sp2 carbon framework that exhibits tri-functional catalytic properties towards hydrogen evolution (HER), oxygen reduction (ORR) and oxygen evolution (OER) reactions. The electrocatalytic functions of the NiCu nanoalloys were experimentally and theoretically correlated with the composition-dependent local structural distortion of the bimetallic lattice at the nanoparticle surfaces. Our study demonstrated a downshift of the d-band of the catalysts that adjusts the binding energies of the intermediate catalytic species. XPS analysis revealed that the binding energy for Ni 2p3/2 band of the Ni0.25Cu0.75/C nanoparticles were shifted ~three times compared to other bimetallic systems and this was correlated to the high electrocatalytic activity observed. Interestingly, the bimetallic Ni0.25Cu0.75/C catalyst surpassed the OER performance of RuO2 benchmark catalyst exhibiting a small onset potential of 1.44 V vs RHE and an overpotential of 400 mV at 10 mA·cm-2 as well as the electrochemical long-term stability of commercial RuO2 and Pt catalysts and kept at least 90% of the initial current applied after 20000s for the OER/ORR/HER reactions. This study reveals significant insight about the structure-function relationship for non-noble bimetallic nanostructures with multifunctional electrocatalytic properties.

Fabrication and Characterization of Controlled-Morphology Self-Supported Fe/Co Layered Double Hydroxides as Catalysts for the Oxygen Evolution Reaction

Electrochemical water splitting is a promising method of hydrogen production that involves two half reactions, namely the fast hydrogen evolution reaction and the slow oxygen evolution reaction (OER). The latter reaction can be accelerated by electrocatalysts, which reduce its overpotential to improve energy conversion efficiency. Herein, Fe-doped Co layered double hydroxides on 3D Ni foam (CoxFey-LDH/NF) with different Co/Fe molar ratios were hydrothermally synthesized in a single step and evaluated as OER catalysts. Structural and electrochemical characterizations provided insights into the origin of the synergistic effect of Fe and Co on OER performance enhancement and indicated that catalyst composition, crystal/electronic structure, and surface morphology are strongly related to Fe content. The best-performing catalyst, Co3Fe1-LDH/NF, exhibited a nanoneedle morphology, an overpotential of 201 mV at a current density of 10 mA cm−2, a small Tafel slope of 47.9 mV dec−1, and satisfactory long-term electrochemical stability in 1.0 M KOH. Thus, this work emphasizes the significance of effective structure design via precise control of catalyst morphology for the development of non-precious metal electrocatalysts.

Single-pot hydrothermal synthesis of manganese phosphate microrods as a cathode material for highly stable flexible solid-state symmetric supercapacitors

Here, we report a binder-free synthesis of microrods-like manganese phosphate thin film over stainless steel substrate by a facile, single-pot hydrothermal method. The XRD analysis reveals that, the formation of manganese phosphate [Mn3(PO4)2] material of a monoclinic crystal structure. From SEM images observed microrods like morphology of manganese phosphate with an average width of ∼25 μm. The manganese phosphate electrode shows a better electrochemical performance with a specific capacitance of 145 F g−1 at 0.2 mA cm-2 current density in 1.0 M Na2SO4 electrolyte. Moreover, the flexible solid-state symmetric electrochemical energy storage device was assembled with PVA-Na2SO4 solid gel-electrolyte consists of manganese phosphate as anode and cathode electrode. The corresponding symmetric supercapacitor achieves a high energy density of 11.7 Wh kg−1 at a high power density of 1.41 kW kg−1 with an excellent specific capacitance of 37 F g−1 at 0.1 mA cm-2 current density. Manganese phosphate shows long-term electrochemical cyclic stability at a current density of 0.8 mA cm-2 for 9000 galvanostatic charge-discharge cycles with excellent capacitance retention (99 %). This excellent capacitive performance confirms that the manganese phosphate is promising material and fabricated flexible solid-state symmetric supercapacitor has high potential in the field of portable and bendable energy storage devices.

Pyridine-modulated Ni/Co bimetallic metal-organic framework nanoplates for electrocatalytic oxygen evolution

Two-dimensional (2D) metal-organic frameworks (MOFs) are promising for electrocatalysis with high performance, as they possess large surface areas and high densities of exposed active sites. It attracts tremendous attention to obtain 2D nanostructures via simple preparation methods. Herein, a facile pyridine-modulated solvothermal synthesis of Ni/Co bimetallic MOF nanoplates (Ni x Co y -bpy(PyM)) is reported with well-defined 2D morphology with a thickness as thin as 20 nm and an aspect ratio larger than 50. These nanoplates possess oxygen evolution reaction activity as electrocatalysts in alkaline conditions. Specifically, Ni0.5Co1.5-bpy(PyM) exhibits excellent OER electrocatalytic activity with a low overpotential of 256 mV at 10 mA cm−2 and a small Tafel slope of 81.8 mV dec−1 in 1.0 mol L−1 KOH with long-term electrochemical stability for 3000 cyclic voltammetry cycles. The high catalytic activity of Ni0.5Co1.5-bpy(PyM) can be attributed to the in situ formed active hydroxide and oxyhydroxide species within the inherited 2D morphology and the optimized bimetallic ratio.

Mesoporous Carbon Microfibers for Electroactive Materials Derived from Lignocellulose Nanofibrils.

The growing adoption of biobased materials for electronic, energy conversion, and storage devices has relied on high-grade or refined cellulosic compositions. Herein, lignocellulose nanofibrils (LCNF), obtained from simple mechanical fibrillation of wood, are proposed as a source of continuous carbon microfibers obtained by wet spinning followed by single-step carbonization at 900 °C. The high lignin content of LCNF (∼28% based on dry mass), similar to that of the original wood, allowed the synthesis of carbon microfibers with a high carbon yield (29%) and electrical conductivity (66 S cm–1). The incorporation of anionic cellulose nanofibrils (TOCNF) enhanced the spinnability and the porous morphology of the carbon microfibers, making them suitable platforms for electrochemical double layer capacitance (EDLC). The increased loading of LCNF in the spinning dope resulted in carbon microfibers of enhanced carbon yield and conductivity. Meanwhile, TOCNF influenced the pore evolution and specific surface area after carbonization, which significantly improved the electrochemical double layer capacitance. When the carbon microfibers were directly applied as fiber-shaped supercapacitors (25 F cm–3), they displayed a remarkably long-term electrochemical stability (>93% of the initial capacitance after 10 000 cycles). Solid-state symmetric fiber supercapacitors were assembled using a PVA/H2SO4 gel electrolyte and resulted in an energy and power density of 0.25 mW h cm–3 and 65.1 mW cm–3, respectively. Overall, the results indicate a green and facile route to convert wood into carbon microfibers suitable for integration in wearables and energy storage devices and for potential applications in the field of bioelectronics.

Exploring High-Activity Copper Doping Zirconia Bi-Metal Oxides Catalysts for Methane Conversion at Room Temperature

Recently, a large quantity of research has been done on the conversion of CH4.(1) Compared to photo-catalysis and thermo-catalysis with precious metal catalysts and high reaction temperatures, the electro-catalysis path, which are always performed at room temperature, demonstrates more potential. In this regard, the electrochemical oxidation and conversion of CH4 to commodity chemicals, such as wide-application liquid alcohols, shows obvious economic benefit and high energy/ conversion-efficient. Zirconia (ZrO2) has rich Lewis acid active sites and huge electron acceptability, showing a remarkable adsorption capacity of CO32-.(2) Based on the above characters, zirconia-based hybrid has attracted a lot of attention and made some breakthroughs. In particular, transition metal oxide (TMO, such as NiO and Co3O4) doping ZrO2 forming TMO/ZrO2 compound demonstrates the potential of methane oxidation with CO32- at room temperature. Compared to NiO and Co3O4, copper-based (Cu) catalysts have a high activity and a long-term durability on forming liquid and gas organics of C1 catalysis reaction system (CO2 reduction reaction) at room temperature.(3-5) Hence, we present a facile strategy of using Cu ions doping ZrO2 to activate the hybrid activity by manipulating its crystal and electronic structure. As expected, the unique cylindrical ZrO2:CuOx catalyst shows remarkable CH4 oxidation performance with large current density differences (13.35 mA cm-2) and long-term electrochemical stability (negligible attenuation (10 %) after 48 hours). According to theoretical and experimental observations of the CH4 oxidation on ZrO2: CuOx hybrid, the high activity and durability of the hybrid should be attributed to 1) strong synergistic-coupling effect; 2) the unique doping structure forming favorable electronic and crystal structure; 3) fast oxidation reaction mechanism by shortening the reaction path. The mechanism could be described as that ZrO2 facilitating CO32- adsorption, then CO32- as the oxidizing agent source rapidly oxidizes CH4 adsorbed on the surface of Cu in zirconia.Keywords: ZrO2:CuOx, Methane conversion, high activity, Unique doping structure Uncategorized

Porous LaFeO3 nanofiber with oxygen vacancies as an efficient electrocatalyst for N2 conversion to NH3 under ambient conditions

Electrocatalytic N 2 reduction to NH 3 under ambient conditions is an eco-friendly and sustainable alternative to the traditional Haber-Bosch process. However, inhibited by the high activation barrier of N 2 , this process needs efficient electrocatalysts to adsorb and activate the N 2 , enabling the N 2 reduction reaction (NRR). Herein, we report that porous LaFeO 3 nanofiber with oxygen vacancies acts as an efficient NRR electrocatalyst with abundant active sites to enhance the adsorption and activation of N 2 . When tested in 0.1 M HCl, such electrocatalyst achieves a high Faradaic efficiency of 8.77% and a large NH 3 yield rate of 18.59 µg h –1 mg cat. –1 at −0.55 V versus reversible hydrogen electrode. This catalyst also shows high long-term electrochemical stability and excellent selectivity for NH 3 formation. Density functional theory calculations reveal that, by introducing oxygen vacancy on LaFeO 3 , the subsurface metallic ions are exposed with newly localized electronic states near the Fermi level, which facilitates the adsorption and activation of N 2 molecules as well as the subsequent hydrogenation reactions. As a N 2 reduction reaction electrocatalyst, porous LaFeO 3 nanofiber with oxygen vacancies (Vo-LaFeO 3 NF) achieves a large NH 3 yield of 18.59 μg h −1 mg cat. −1 and a high Faradic efficiency of 8.77% at –0.55 V vs. RHE in 0.1 M HCl.

Environment-friendly synthesis of carbon-encapsulated SnO2 core-shell nanocubes as high-performance anode materials for lithium ion batteries

Rational design and fabrication of SnO2@C composites with tailored structures enables the advanced electrochemical behaviors for the next-generation lithium-ion batteries. Benefiting from the enhanced electronic conductivity and porous structure, the integrated composites deliver the high reversible capacity as well as the outstanding rate capability. A high discharge capacity of 745.7 mAh g−1 is achieved at 0.1 A g−1 after 150 cycles. The discharging capacity of 292.0 mAh g−1 is observed at the high rate of 2 A g−1. Remarkably, the negligible capacity degradation is discerned under low and high current density (100, 500 mA g−1) in long-term electrochemical stability test. Therefore, the novel structure design for carbon-encapsulated SnO2 makes it a promising strategy to fabricate more efficient anode materials for lithium-ion batteries.

An Overview of Stretchable Supercapacitors Based on Carbon Nanotube and Graphene

The wearable demand of modern electronic devices makes flexible and stretchable energy storage device urgently needed. Stretchable and flexible supercapacitors (SCs) are energy storage devices that provide ultrahigh power density while having long-term durability, high security, and electrochemical stability. Among different SCs electrode materials, CNTs and graphene-based materials exhibit great potential in terms of stretchable SCs due to its ultrahigh electrical conductivity, large specific surface area and good mechanical properties. In this review, the state-of-the-art process and achievements in the field of stretchable SCs enabled by CNTs and graphene are presented, which include the novel design strategy, mechanical and electrochemical properties. The final section highlights current challenges and future perspectives on research in this thriving field.

A novel sol-gel strategy for N, P dual-doped mesoporous carbon with high specific capacitance and energy density for advanced supercapacitors

Abstract In this work, a facile sol-gel strategy was developed to synthesize N/P co-doped ordered mesoporous carbons (NPMCs). By accelerating the volatilization of ethanol, a strong driving force promoted the self-assembly process among carbon precursor, surfactant and dopant at the interface of water and ethanol. The obtained NPMC showed stacked flake-like surface morphology and ordered 2D-hexagonal mesostructures with uniform pore size (4.3 nm) and high specific surface areas (938 m2 g−1). Synergistic effects of improved surface wettability by N-doping and rich active sites by P-doping rendered the NPMC with excellent electrochemical performance. Computational analyses confirmed that N, P co-doping could enhance active sites and widen potential difference of carbon materials to improve their capacitance. An ultrahigh capacitance of 392 F g−1 and an excellent rate capability were obtained. Furthermore, the assembled symmetric supercapacitor based on NPMC delivers a high energy density of 20.2 Wh kg−1 at a power density of 225 W kg−1 and exhibited an excellent long-term electrochemical stability (95% capacitance retention after 5000 cycles), which evidently reached the practical requirement for supercapacitors.

Trimetallic Mo–Ni–Co selenides nanorod electrocatalysts for highly-efficient and ultra-stable hydrogen evolution

In-situ engineering multiple-phase transition-metal based electrocatalyst with excellent performances for hydrogen evolution reaction (HER) is still a major challenge in the electrocatalysis field. Herein, the Mo–Ni–Co trimetallic selenide nanorod arrays are synthesized on a plasma-treated Ni–Co foam (MoSe2–NiSe2–CoSe2/PNCF). The synergistic effects of heterostructured crystal interfaces, the formed 1T-2H mixture phases of MoSe2, and the customized morphological design enable high electrocatalytic activity and stability for the hydrogen evolution reaction (HER) in alkaline media. The catalysts require a low overpotential of 38 mV, just above commercial Pt/C electrodes (35 mV), to deliver a benchmark current density of 10 mA cm−2 (j10). The H2 generation amount (2.6 mmol h−1) is much higher than most of the reported transition-metal based electrocatalysts. Numerical simulations attribute the high electrocatalytic activity to the increased Fermi level with multiple heterointerfaces. The catalyst presents a superior long-term electrochemical stability during continuous reactions with a high current density (j100) for over 100 h. The success of enhancing the electrocatalytic performance paves new avenues for in situ engineering transition-metal based electrocatalysts for energy-related applications.

Self-supported phosphorus-doped CoMoO4 rod bundles for efficient hydrogen evolution

Herein, a series of phosphorus-doped CoMoO4 rod bundles electrocatalysts on 3D nickel foams have been successfully synthesized and exploited as efficient hydrogen evolution reaction (HER) electrocatalyst in 1 M KOH. The incorporation of phosphorus into CoMoO4 can significantly promote the HER activity, and the CoMoO4 bundles phosphorized at 350 °C exhibited the optimum activity, which only required low overpotentials of 56 and 148 mV to deliver cathodic current densities of 10 mA cm−2 and 100 mA cm−2, respectively. This electrode also presented considerable long-term electrochemical stability with negligible delay after 30 h operation and 3000 accelerated cyclic voltammetry cycles. Our study provides a superior earth-abundant catalyst for efficient HER in alkaline media, which also suggests that P doping engineering is an effective way to boost the HER activity of transition metal-based oxides.

Amorphous MoOX-Stabilized single platinum atoms with ultrahigh mass activity for acidic hydrogen evolution

It is highly desirable to develop Pt single-atom (SA) catalysts with an optimized mass activity for acidic hydrogen evolution reaction (HER), but it remains a significant challenge. In this study, a new Pt SA strongly coupled with amorphous MoOX (Pt-SA/ɑ-MoOx) is rationally designed. The synergistic effect between unsaturated Pt atoms and defective MoOx can significantly lower the reaction barrier contributing to the fast HER reaction kinetics. Hence, Pt-SA/ɑ-MoOx exhibits an ultrahigh mass activity of 52.0 A mgPt−1 at an overpotential of 50 mV, corresponding to better acidic HER activity than those reported previously for Pt SA-based catalysts. Furthermore, Pt-SA/ɑ-MoOx shows Pt-like kinetics with a small Tafel slope of 123 mV dec−1 and outstanding long-term electrochemical stability for 20 h. This developed synthetic method is also extended for the fabrication of other amorphous MoOx-supported SA catalysts (e.g. Ir, Au and Pb). As far as we know, our study reports the first example of the combination of metal SA and amorphous oxide for highly efficient electrocatalysis.

Aloe vera-peel derived porous carbon integrated Co/Mn-oxide based nano-hybrids: An efficient electrocatalyst in advanced photovoltaics

We propose a facile strategy to synthesize highly electrocatalytic active nanohybrids by the integration of aloe vera-peel derived porous carbon into manganese-based and cobalt/manganese-based oxides. These nanohybrids exhibit unique three-dimensional porous network structures and possess high surface areas, providing numerous catalytic sites and multiple rapid electron transfer channels. In this work, the as-synthesized nanohybrids are used as accelerants for tri-iodide reduction in dye-sensitized solar cells, resulting in attractive cell efficiency and superior electrochemical stability. The solar cell with low-cost bio-based carbon integrated cobalt/manganese-oxide counter electrode exhibits higher photovoltaic efficiency than that of platinum electrode (7.01% vs. 6.44%). In addition, hybrid catalyst loaded counter electrodes also demonstrate long-term electrochemical stability in I3−/I− electrolyte, retaining 97% of its initial efficiency (6.83%/7.01%) in working cell, after going through multiple cyclic voltammetry scans. The utilization of synergistic effects of high performance constituents and controlled morphology is a key strategy to intensify the catalytic activity, electrochemical stability, and power conversion efficiency in advanced photovoltaics.

Water-stable O3-type layered Na transition metal oxides enabling environment friendly ‘aqueous processing’ of electrodes with long-term electrochemical stability

Tuning the TM-ion ‘slab thickness’ and alkali metal-ion ‘inter-slab spacing’ of Na-TM-oxides in opposite terms (and also suppressing TM-dissolution in electrolyte) leads to outstanding air/water-stability and long-term electrochemical stability.

Dual nitrogen sources co-doped mesoporous carbon with ultrahigh rate capability for high-performance supercapacitors

Nitrogen-doped ordered mesoporous carbon (N-OMC) was synthesized through evaporation induced self-assembly (EISA) technique by using pyrrole and carbamide as N sources. The obtained N-OMC has high-ordered 2D-hexagonal mesostructures with uniform pore size and high specific surface area. When pyrrole and carbamide were simultaneously employed as N sources, the sample shows higher subtotal percentage of pyridinic and pyrrolic N, leading to better electrochemical performance. As-prepared N-OMC with dual N sources (N12-OMC-1) possesses an ultra-high specific capacitance of 310 F g−1 at the current density of 1.0 A g−1 and remains 245 F g−1 (nearly 80% of its capacitance at 1.0 A g−1) at 20 A g−1, achieving both high rate capability and high specific capacitance. N12-OMC-1 based symmetrical supercapacitor demonstrates the highest energy density of 17.8 Wh kg−1 at a power density of 225 W kg−1 and maintains 12.2 Wh kg−1 at a very high output power density of 13500 W kg−1 in 1 M Na2SO4 electrolyte. Moreover, the N12-OMC-1 based symmetrical supercapacitor exhibits an excellent long-term electrochemical stability with 96.2% capacitance retention and 97% coulombic efficiency after 5000 cycles. Outstanding performances of N12-OMC-1 make it a potential candidate for supercapacitor applications.

Facile one-step synthesis of tunable nanochain-like Fe–Mo–B: A highly efficient and stable catalyst for oxygen evolution reaction

Exploring high-performance and cost-effective non-noble metal electrocatalysts towards oxygen evolution reaction (OER) is critical for large-scale hydrogen production via water splitting. Herein, a series of ternary Fe–Mo–B materials with nanochain-like structure have been successfully fabricated by a green and feasible electroless deposition method. When the molar ratio of Mo/(Mo + Fe) precursor is tuned to 3/100, as-fabricated nanochain-like Fe–Mo–B shows remarkable OER performance with a low overpotential of only 253 mV at current density of 10 mA cm−2 and a small Tafel slope of 63 mV dec−1. In addition, it demonstrates a preeminent long-term electrochemical stability for continuous oxygen generation under alkaline condition. The enhanced OER performance benefits from the synergistic effects between Fe and Mo, bringing about the large electrocatalytic active surface area and fast electronic transfer rate. The work may pave a new path to reasonable design and construct metal-boride-based catalyst with excellent activity for electrocatalytic OER.

Self-supported hierarchical CoFe-LDH/NiCo2O4/NF core-shell nanowire arrays as an effective electrocatalyst for oxygen evolution reaction

Design and synthesis of three-dimension (3D) nanowire arrays (NWAs) electrocatalyst with a core-shell structure have been considered as an efficient way to enhance the performances for the oxygen evolution reaction (OER). In this work, novel hierarchical CoFe-LDH/NiCo2O4/Ni foam (CoFe-LDH/NCO/NF) core-shell nanowire arrays have been fabricated via a facile two-step strategy. The as-obtained nanocomposites were characterized by multiple methods, and their electrocatalytic properties for OER have also been evaluated. The unique structural and component features for the as-prepared 3D nanocomposites facilitate the enhancement of the OER performances. CoFe-LDH/NCO/NF nanocomposites display an excellent OER electrocatalytic activity with a low overpotential of 273 mV at 20 mA cm−2, as well as an outstanding long-term electrochemical stability with a 90% current preservation during a 32 h test. The remarkable electrocatalytic performances of the CoFe-LDH/NCO/NF electrode ascribe to the strong synergistic effect between the NiCo2O4 (NCO) nanowires core and the CoFe-LDH nanosheets shell at the interface. Our work provides a novel sight on the rational design of 3D core/shell nanoarrays electrode materials for OER.

Decorated by Cu nanoparticles CoS2 nanoneedle array for effective water oxidation electrocatalysis

Developing active, stable and cost-effective transition metal electrocatalysts for increasing the rate of the oxygen evolution reaction (OER) is crucial for renewable energy conversion, but still remains challenging. In this communication, we report a novel Cu-nanoparticle decorated CoS2 nanoneedle array on Ti mesh (Cu@CoS2/TM) as an efficient electrocatalyst for alkaline water oxidation. Benefiting from a large active surface area and a strong interfacial interaction between Cu and CoS2, Cu@CoS2/TM exhibits excellent OER performance in alkaline media with only a small overpotential of 277 mV to deliver 50 mA cm−2. This value is 62 mV less than that of CoS2/TM. Cu@CoS2/TM achieves a high turnover rate of 0.25 mol O2 s−1 at 400 mV, which is approximately 1.7 times higher than that of CoS2/TM. Notably, Cu@CoS2/TM also demonstrates superior long-term electrochemical stability.