A freestanding MoO2‐decorated carbon nanofibers interlayer for rechargeable lithium sulfur battery

Lithium‐sulfur (Li‐S) battery based on sulfur cathodes is of great interest because of high capacity and abundant sulfur source. But the shuttling effect of polysulfides caused by charge‐discharge process results in low sulfur utilization and poor reversibility. Here, we demonstrate a good approach to improve the utility of sulfur and cycle life by synthesizing carbon nanofibers decorated with MoO₂ nanoparticles (MoO₂‐CNFs membrane), which plays a role of multiinterlayer inserting between the separator and the cathode for Li‐S battery. The S/MoO₂‐CNFs/Li battery showed a discharge capacity of 6.93 mAh cm^?2 (1366 mAh g^?1) in the first cycle at a current density of 0.42 mA cm^?2 and 1006 mAh g^?1 over 150 cycles. Moreover, even at the highest current density (8.4 mA cm^?2), the battery achieved 865 mAh g^?1. The stable electrochemical behaviors of the battery has achieved because of the mesoporous and interconnecting structure of MoO₂‐CNFs, proving high effect for ion transfer and electron conductive. Furthermore, this MoO₂‐CNFs interlayer could trap the polysulfides through strong polar surface interaction and increases the utilization of sulfur by confining the redox reaction to the cathode.     

Boron doping induced electronic reconfiguration of Fe-Nx sites in N-doped carbon matrix for efficient oxygen reduction reaction in both alkaline and acidic media

Developing non-precious metal-based catalysts as the substitution of precious catalysts (Pt/C) in oxygen reduction reaction (ORR) is crucial for energy devices. Herein, a template and organic solvent-free method was adopted to synthesize Fe, B, and N doped nanoflake-like carbon materials (Fe/B/N–C) by pyrolysis of monoclinic ZIF-8 coated with iron precursors and boric acid. Benefiting from introducing B into Fe–N–C, the regulated electron cloud density of Fe-N_x sites enhance the charge transfer and promotes the ORR process. The as-synthesized Fe/B/N–C electrocatalyst shows excellent ORR activity of a half-wave potential (0.90 V vs 0.87 V of Pt/C), together with superior long-term stability (95.5% current density retention after 27 h) in alkaline media and is even comparable to the commercial Pt/C catalyst (with a half-wave potential of 0.74 V vs 0.82 V of Pt/C) in an acidic electrolyte. A Zn-air battery assembled with Fe/B/N–C as ORR catalyst delivers a higher open-circuit potential (1.47 V), specific capacity (759.9 mA h g^?1_Zn at 10 mA cm^?2), peak power density (62 mW cm^?2), as well as excellent durability (5 mA cm^?2 for more than 160 h) compared to those with commercial Pt/C. This work provides an effective strategy to construct B doped Fe–N–C materials as nonprecious ORR catalyst. Theoretical calculations indicate that introduction of B could induce Fe-N_x species electronic configuration and is favorable for activation of OH1 intermediates to promote ORR process.     

Electrocatalytic performance of TiO2 with different phase state towards V2+/V3+ reaction for vanadium redox flow battery

In this paper, titanium dioxide (TiO₂) nanoparticles were employed as catalysts towards V²⁺/V³⁺ redox couple of vanadium redox flow battery (VRFB). The effect of TiO₂ phase on the electrocatalytic performance for negative couple was systematically investigated. The electrochemical properties of TiO₂ with different phase were assessed via cyclic voltammetry and electrochemical impedance spectroscopy by using AB as conductive agent. Obtained from the results, anatase TiO₂ (α‐TiO₂) exhibits superior electrocatalytic activity to rutile TiO₂ (γ‐TiO₂). The VRFB cell performs well at discharge capacity, voltage efficiency, and energy efficiency by employing α‐TiO₂‐modified negative electrode with current density varying between 50 and 100 mA cm^?2. The discharge capacity of α‐TiO₂‐modified cell with vanadium ion concentration of 1.6 M comes up to 113.5 mA h at 100 mA cm^?2 current density, which is increased by 39.1 mA h after modification for negative electrode. Moreover, the corresponding energy efficiency increases by 7.5% after modification of α‐TiO₂. Experimental results show that TiO₂ is an ideal catalyst for VRFB. Moreover, α‐TiO₂ demonstrates superior electrocatalytic performance to γ‐TiO₂ towards V²⁺/V³⁺ reaction.     

High performance aluminum-air battery for sustainable power generation

Metal-air battery is receiving vast attention due to its promising capabilities as an energy storage system for the post lithium-ion era. The electricity is generated through oxidation and reduction reaction within the anode and cathode. Among various types of metal-air battery, aluminum-air battery is the most attractive candidate due to its high energy density and environmentally friendly. In this study, a novel polypropylene-based dual electrolyte aluminum-air battery is developed. Polypropylene pads are used as a medium to absorb the electrolyte, isolate the anode and cathode, control the hydrogen generation in the parasitic reaction. Potassium hydroxide is used as anolyte and sulfuric acid is used as catholyte. Parametric study is conducted to investigate the effect of electrolyte concentration and polypropylene separator thickness on the performance of the battery. The results show that the dual-electrolyte system can boost the open circuit voltage to 2.2 V as compared to the single electrolyte system for 5 M of anolyte while maintaining specific discharge capacity of about 1390.92 mAh.g⁻¹. The maximum peak power density has improved dramatically from 100 mW.cm⁻² to 350 mW cm⁻² for the dual electrolyte system.     

A hybrid aluminum/hydrogen/air cell system

A hybrid aluminum/hydrogen/air cell system is developed to solve the parasitic hydrogen-generating problem in an alkaline aluminum/air battery. A H₂/air fuel cell is integrated into an Al/air battery so that the hydrogen generated by the parasitic reaction is utilized rather than wasted. A systematic study is conducted to investigate how the parasitic reaction and the added H₂/air cell affect the performance of the aluminum/air battery. The aluminum/air sub-cell has an open circuit voltage of 1.45 V and the hydrogen/air sub-cell of 1.05 V. The maximum power density of the entire hybrid system increases significantly by ∼20% after incorporating a H₂/air sub-cell. The system maximum power density ranges from 23 to 45 mW cm⁻² in 1–5 M NaOH electrolyte. The hybrid system is adaptable in concentrated alkaline electrolyte with significantly improved power output at no sacrifice of its overall efficiency.     

Experimental research on temperature rise and electric characteristics of aluminum air battery under open‐circuit condition for new energy vehicle

Due to lack of systematic research on open‐circuit voltage (OCV) and electrolyte temperature rise characteristics of aluminum air battery, in order to explore the influential factors on the OCV and electrolyte temperature rise of aluminum air battery, in this paper, for the first time, we studied the effects of different ambient temperature conditions, different concentrations of NaOH and KOH electrolyte, and pure aluminum and aluminum alloy on the OCV and electrolyte temperature rise of aluminum air battery. Results show that the OCV of aluminum air battery is obviously affected by ambient temperature conditions, electrolyte concentration, and different anode materials. The OCV range is 1.5 to 1.8 V at 0°C under different KOH‐electrolyte concentrations when aluminum alloy is used as anode material; with the increase of ambient temperature, the OCV will rise, and the range is 1.8 to 1.95 V. The working process of aluminum air battery is accompanied by the phenomenon of heat release, and the temperature rise range of electrolyte will not exceed 7°C when aluminum alloy is used as the anode material; however, the highest temperature of the electrolyte can reach 100°C when pure aluminum is used as the negative electrode material. The results of this study will provide theoretical guidance for designing aluminum air batteries and identifying their optimal operating conditions.     

High‐performance solid PEO/PPC/LLTO‐nanowires polymer composite electrolyte for solid‐state lithium battery

Solid polymer composite electrolyte (SPCE) with good safety, easy processability, and high ionic conductivity was a promising solution to achieve the development of advanced solid‐state lithium battery. Herein, through electrospinning and subsequent calcination, the Li_0.33La_0.557TiO₃ nanowires (LLTO‐NWs) with high ionic conductivity were synthesized. They were utilized to prepare polymer composite electrolytes which were composed of poly (ethylene oxide) (PEO), poly (propylene carbonate) (PPC), lithium bis (fluorosulfonyl)imide (LiTFSI), and LLTO‐NWs. Their structures, thermal properties, ionic conductivities, ion transference number, electrochemical stability window, as well as their compatibility with lithium metal, were studied. The results displayed that the maximum ionic conductivities of SPCE containing 8 wt.% LLTO‐NWs were 5.66 × 10^?5 S cm^?1 and 4.72 × 10^?4 S cm^?1 at room temperature and 60°C, respectively. The solid‐state LiFePO₄/Li cells assembled with this novel SPCE exhibited an initial reversible discharge capacity of 135 mAh g^?1 and good cycling stability at a charge/discharge current density of 0.5 C at 60°C.     

The effects of current density and amount of discharge on dendrite formation in the lithium powder anode electrode

A compacted lithium powder anode was used to improve the demerits of dendrite formation of lithium metal. Dendrite formation of lithium metal was restrained to use compacted lithium powder anode under a specific amount of discharge and the current density. In this study, the amount of discharge and the current density which suppress dendrite formation at the surface of a lithium powder electrode were investigated on an experimental basis. Discharge/charge reactions were accomplished on various values of the amount of discharge and current density by using beaker cells. It was analyzed by SEM images whether dendrite was formed or not on the surface of lithium powder electrode. From the various experiments, the relationship between current density and total amount of discharge was deduced as a simple mathematical model. From the model, the critical condition of total amount of discharge for dendrite formation in Li-powder electrode was increased from 0.1 mA cm⁻² to 1 mA cm⁻² current density. However, the critical condition of total amount of discharge was decreased over 1 mA cm⁻². Using the model, the condition whether dendrite formed or not on the Li-powder anode could be estimated.     

Flexible supercapacitor based on three‐dimensional cellulose/graphite/polyaniline composite

Fast charge‐discharge rate and high areal capacitance, along with high mechanically stability, are the pre‐requisites for flexible supercapacitors to power flexible electronic devices. In this paper, we have used three‐dimensional polyacrylonitrile graphite foam as flexible current collector for electro‐deposition of polyaniline (PANI) nanowires. The graphite foam with PANI was then used to fabricate symmetric supercapacitor. The fabricated supercapacitor in the three‐electrode system shows a high specific capacitance (C_sp) of 357 F.g^?1 and areal capacitance (C_areal) of 7142 mF.cm^?2 in 1 M H₂SO₄ at current density of 80 mA.cm^?2, while using two‐electrode system, it shows C_sp of 256 F.g^?1 and C_areal of 5120 mF.cm^?2 in 1 M H₂SO₄ at current density of 100 mA.cm^?2. The current density of 100 mA.cm^?2 is up to 10 folds higher than reported current densities of many PANI‐based supercapacitors. The high capacitance can be attributed to the spongy network of PANI‐NWs on three‐dimensional graphite surface which provides an easy path for electrolyte ions in active electrode materials. The developed supercapacitor shows specific energy of 64.8 Whkg^?1 and a specific power of 6.1 kWkg^?1 with a marginally decrease of 1.6% in C_sp after 1000^th cycles, along with coulombic efficiency retention of 87% in polyvinyl alcohol/H₂SO₄ gel electrolyte. This flexible supercapacitor exhibits great potential for energy storage application.     

A highly active composite electrocatalyst Ni–Fe–P–Nb2O5/NF for overall water splitting

This work demonstrates a facile Nb₂O₅-decorated electrocatalyst to prepare cost-effective Ni–Fe–P–Nb₂O₅/NF and compared HER & OER performance in alkaline media. The prepared electrocatalyst presented an outstanding electrocatalytic performance towards hydrogen evolution reaction, which required a quite low overpotential of 39.05 mV at the current density of ?10 mA cm^?2 in 1 M KOH electrolyte. Moreover, the Ni–Fe–P–Nb₂O₅/NF catalyst also has excellent oxygen evolution efficiency, which needs only 322 mV to reach the current density of 50 mA cm^?2. Furthermore, its electrocatalytic performance towards overall water splitting worked as both cathode and anode achieved a quite low potential of 1.56 V (10 mA cm^?2).     

Ni-doped Mn2O3 microspheres as highly efficient electrocatalyst for oxygen reduction reaction and Zn-air battery

Herein, Ni-doped Mn₂O₃ microspheres are successfully synthesized via the facile coprecipitation of metal ions and ammonium bicarbonates, followed by a heat treatment process. Ni-doped Mn₂O₃ exhibits outstanding catalytic performance toward the oxygen reduction reaction (ORR) in alkaline media with a half-wave potential of 0.801 V, limiting current density of 6.02 mA cm^?2 at 0.6 V vs. RHE, outstanding long-term durability, and strong tolerance to methanol. Furthermore, a Zn–air primary battery using Ni-doped Mn₂O₃ as an air cathode shows high open-circuit voltage of 1.52 V and high power density of 88.2 mW cm^?2, outperforming the commercial Pt/C cathode. The exceptional performance of the Ni-doped Mn₂O₃ microspheres is ascribed to the hierarchical structure, optimized particle size, and Ni incorporation into Mn₂O₃. The proposed synthesis strategy provides a new methodology for the design and fabrication of electrochemically active transition metal-doped materials as efficient electrocatalysts for a variety of energy storage and conversion reactions.     

MOF-derived cobalt manganese phosphide as highly efficient electrocatalysts for hydrogen evolution reaction

Hydrogen is considered as a viable alternative to traditional fossil fuels. Hydrogen evolution reaction (HER) by electrochemical water splitting is the most reliable and effective way for the sustainable production of pure hydrogen. The design and synthesis of highly active and stable non-noble-metal-based electrocatalysts is the core of the large-scale application of this technology. Herein, peony petal-like CoMnP/NF nanomaterials growing on nickel foam (NF) are prepared via facile hydrothermal and phosphorization methods. The results showed that CoMnP/NF had excellent HER activity in acidic and alkaline media. In 0.5 M H₂SO₄, CoMnP/NF only needed 66.6 mV overpotential to drive the current density of 10 mA cm^?2, with a Tafel slope of 38.8 mV dec^?1. In addition, a particularly low overpotential of 53.9 mV and Tafel slope of 63 mV dec^?1 are required to achieve the same current density in the 1 M KOH electrolyte. Meanwhile, the electrocatalyst showed good stability after 1000 cyclic voltammetry tests and 12 h I-T tests. In the 1 M KOH electrolyte, the current density of 10 mA cm^?2 achieved with only 1.70 V battery voltage, and the electrocatalyst showed excellent stability. The performance of CoMnP/NF can be attributed to the synergistic effect between Co and Mn atoms and the high electrochemical surface area (ECSA). This study provides a valuable strategy for the synthesis of non-precious metals and high-performance catalytic materials.     

Tailoring cation vacancies in Co,Ni phosphides for efficient overall water splitting

High-efficiency water splitting catalysts are competitive in energy conversion and clean energy production. Herein, a bifunctional water splitting catalyst CoNiP with cation vacancy defects (CoNiP–V) is constructed through defect engineering. The results show that abundant cation vacancy defects in CoNiP–V are bifunctional active centers in the process of water electrolysis, which enhance the activity of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). In 1.0 mol L^?1 potassium hydroxide, CoNiP–V requires a pretty low overpotential of 58 mV to reach a geometrical current density of 10 mA cm^?2 for HER. To deliver a current density of 100 mA cm^?2, only 137 mV and 340 mV of overpotential are needed for HER and OER, respectively. Moreover, the cell with CoNiP–V as both cathode and anode exhibits good stability, which only needs 1.61 V to achieve a current density of 100 mA cm^?2, and the cell voltage barely rises 10% after 100 h’ test under 100 mA cm^?2. Therefore, CoNiP–V is promising for the development of efficient water splitting catalysts.     

Structural regulation of Fe–Co prussian blue analogues by incorporation of Pt for enhanced electrocatalytic overall water splitting

The specific properties of easy manufacturing, open frameworks, and high specific surface area endow prussian blue analogues (PBAs) as promising electrode materials for water splitting. Herein, we reported the successful application of interface engineering strategy to introduce low content of Pt species to boost the electrocatalytic activity of FeCo PBAs by ammonia etching and subsequent calcination. The resulting PtCo alloy modified FeCo PBAs (PtCo–FeCo PBAs) complex reveals modest electrocatalytic activity with low overpotentials (η) of 139 mV for hydrogen evolution reaction (HER) and 310 mV for oxygen evolution reaction (OER) at 10 mA cm^?2 in alkaline electrolyte. Remarkably, the PtCo–FeCo PBAs only required small cell voltage of 1.68 V to drive 10 mA cm^?2 for overall water splitting and the ideal electrocatalytic activity can be maintained for more than 50 h at a current density of 10 mA cm^?2. The structural analysis unveils that the strong interaction between FeCo PBAs host and PtCo alloy resulting in charge redistribution and ultimately lead to high electrocatalytic activity and stability of PtCo–FeCo PBAs for both HER and OER.     

A novel structure of ceramics electrolyte for future lithium battery

In order to fabricate large scale all-solid-state Li battery, we suggested a novel structure of solid electrolyte, which is composed of porous electrolyte supported by honeycomb-type electrolyte. A possibility of fabrication of the honeycomb-supported porous electrolyte and a compatibility of this structure with all-solid-state battery were examined using LLT (Li_0.35La_0.55TiO₃) solid electrolyte which is one of the anticipated solid electrolytes due to its high Li ion conductivity. A porous layer membrane with 3 dimensionally ordered (3DOM) macroporous structure was prepared by a colloidal crystal templating method. The porous honeycomb was fabricated by pushing the membrane into holes of honycomb using a needle followed by calcination. The 3DOM membrane and honeycmb electrolyte were sintered well each other. After filling the 3DOM pores with LiMn₂O₄ cathode material, the compatibility of this novel porous honeycomb electrolyte with all-solid-state battery was examined. The LiMn₂O₄/porous honeycomb cell clearly demonstrated charge and discharge behaviors, indicating the porous honeycomb structure can be applied to the all-solid-state battery. The discharge capacity was 71 mA h g⁻¹ (1.3 mA h cm⁻²) at 30 °C.     

Metal-organic frameworks derived self-supported Ni2P nanorod arrays for electrocatalytic hydrogen evolution

The development of efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) is of importance. Herein, we demonstrate a self-supported Ni₂P nanostructure with nanorod arrays morphology, fabricated by directly growing metal-organic frameworks (MOFs) on the commercial nickel foam prior to phosphorization treatment, as an electrocatalyst for HER. This electrocatalyst exhibits remarkable electrocatalytic HER activity in an alkaline electrolyte, affording current densities of 10 and 100 mA cm^?2 at the overpotentials of 120 and 168 mV, respectively, accompanied with a low Tafel slope of 37 mV dec^?1. Furthermore, this electrocatalyst shows a current density of 105 mA cm^?2, and this current density can be retained for more than 20 h, suggesting its superior stability. This remarkable HER performance is believed a result of superiority for its structural integrality and mechanical stability.     

All solid-state battery with sulfur electrode and thio-LISICON electrolyte

A high-capacity type of all solid-state battery was developed using sulfur electrode and the thio-LISICON electrolyte. New nano-composite of sulfur and acetylene black (AB) with an average particle size of 1–10 nm was fabricated by gas-phase mixing and showed a reversible capacity of 900 mAh g⁻¹ at a current density of 0.013 mA cm⁻².     

Mo-incorporated three-dimensional hierarchical ternary nickel-cobalt-molybdenum layer double hydroxide for high-efficiency water splitting

Flowers-like 3D hierarchical ternary NiCoMo-layered double hydroxide (NiCoMo-LDH) spheres have been fabricated in substrate-free route via a one-pot hydrothermal method and utilized as efficient electrocatalysts for the OER and HER. The well-structured 3D hierarchical flowers were composed of numerous two-dimensional nanosheets, which inherently possess considerable electrochemical active sites, thereby enhancing catalytic activity. NiMo and CoMo binary LDHs, with similar morphology, were also prepared to illustrate the efficiency of the ternary LDH. The results indicate higher electrocatalytic activity for the ternary LDH as compared to binary LDHs under alkaline conditions. The NiCoMo-LDH required an overpotential as low as 202 and 93 mV to deliver a constant anodic and cathodic current density of 10 mA cm^?2 for the OER and HER, respectively. Furthermore, the NiCoMo-LDH exhibited remarkable HER activity, affording a low overpotential of 198 mV at a current density of ?100 mA cm^?2. Moreover, it could offer a stable current density of 10 mA cm^?2 for overall water splitting at 1.62 V in 1 M KOH with long-term stability for 20 h. The double-layer capacitance (C_dl) value indicated that the NiCoMo-LDH significantly influenced interface conductivity and the electrochemical active surface area. The ternary NiCoMo-LDH electrode yielded low Tafel slope values of 54 and 51 mVdec^?1 for the OER and HER. Owing to the efficient incorporation of Ni, Co, and Mo in a layered structure, synergetic effect, and high electrochemical surface area, the NiCoMo-LDH exhibited remarkable electrocatalytic activity. Such eco-friendly ternary LDHs can be used in rechargeable metal–air batteries for industrial applications.     

PdCo bimetallic nano-electrocatalyst as effective air-cathode for aqueous metal-air batteries

For wide application of metal-air batteries, the key factor is the development of catalysts for air cathodes. In the present study, PdCo/C bimetallic nanocatalysts are prepared by a facile borohydride reduction method. To improve the activity and stability, the catalysts are heat-treated at 200 °C in H₂/Ar atmosphere from 4 h to 24 h. The optimal heat-treatment time is found to be 8 h, at which the highest activity for both oxygen reduction reaction and oxygen evolution reaction is obtained. With the 8 h heat-treated PdCo/C catalyst, the rechargeable zinc-air battery exhibits a high power density of 180 mW cm^?2 and retains stability for more than 50 h at a discharge-charge current density of 10 mA cm^?2, while the magnesium-air battery obtains a power density of more than 200 mW cm^?2 and remains stable within 8 h at a discharge current density of 65 mA cm^?2.