Fabrication of Al-Ni Alloys for Fast Hydrogen Production from Hydrolysis in Alkaline Water.

Hydrogen generation through the hydrolysis of aluminum alloys has attracted significant attention because it generates hydrogen directly from alkaline water without the need for hydrogen storage technology. The hydrogen generation rate from the hydrolysis of aluminum in alkaline water is linearly proportional to its corrosion rate. To accelerate the corrosion rate of the aluminum alloy, we designed Al-Ni alloys by continuously precipitating an electrochemically noble Al3Ni phase along the grain boundaries. The Al-0.5~1 wt.% Ni alloys showed an excellent hydrogen generation rate of 16.6 mL/cm2·min, which is about 6.4 times faster than that of pure Al (2.58 mL/cm2·min). This excellent performance was achieved through the synergistic effects of galvanic and intergranular corrosion on the hydrolysis of Al. By raising the solution temperature to 50 °C, the optimal rate of hydrogen generation of Al-1 wt.% Ni in 10 wt.% NaOH solutions at 30 °C can be further increased to 54.5 mL/cm2·min.

An Inorganic-Rich SEI Layer by the Catalyzed Reduction of LiNO3 Enabled by Surface-Abundant Hydrogen Bonding for Stable Lithium Metal Batteries.

Lithium (Li) metal anodes (LMAs) are promising anode candidates for realizing high-energy-density batteries. However, the formation of unstable solid electrolyte interphase (SEI) layers on Li metal is harmful for stable Li cycling; hence, enhancing the physical/chemical properties of SEI layers is important for stabilizing LMAs. Herein, thiourea (TU, CH4 N2 S) is introduced as a new catalyzing agent for LiNO3 reduction to form robust inorganic-rich SEI layers containing abundant Li3 N. Due to the unique molecular structure of TU, the TU molecules adsorb on the Cu electrode by forming CuS bond and simultaneously form hydrogen bonding with other hydrogen bonds accepting species such as NO3 - and TFSI- through its NH bonds, leading to their catalyzed reduction and hence the formation of inorganic-rich SEI layer with abundant Li3 N, LiF, and Li2 S/Li2 S2 . Particularly, this TU-modified SEI layer shows a lower film resistance and better uniformity compared to the electrochemically and naturally formed SEI layers, enabling planar Li growth without any other material treatments and hence improving the cyclic stability in Li/Cu half-cells and Li@Cu/LiFePO4  full-cells.

Realization of a 594 Wh kg-1 Lithium-Metal Battery Using a Lithium-Free V2 O5 Cathode with Enhanced Performances by Nanoarchitecturing.

To realize a high-energy lithium metal battery (LMB) using a high-capacity Li-free cathode, in this work, nanoplate-stacked V2 O5 with dominantly exposed (010) facets and a relatively short [010] length is proposed to be used as a cathode. The V2 O5 nanostructure can be fabricated via a modified hydrothermal method, including a Li+ crystallization inhibitor, followed by heat treatment. In particular, the enlargement of the favorable Li+ diffusion pathway in the [010] direction and the formation of a robust hierarchical nanoplate-stacked structure in the modified V2 O5 improves the electrochemical kinetics and stability; as a result, the nanoplate-stacked V2 O5 electrode exhibits a higher capacity and rate performance (258 mAh g-1 at 50 mA g-1 [0.17 C], 140 mAh g-1 at 1 A g-1 [3.4 C]) and cycling capability (79% capacity retention after 100 cycles at 0.5 C) compared to the previously reported V2 O5 nanobelt electrode. Notably, the LMB composed of Li//nanoplate-stacked V2 O5 full-cells shows high specific energy densities of 594.1 and 296.2 Wh kg-1 at 0.1 and 1.0 C, respectively, and a high Coulombic efficiency of 99.6% during 50 cycles.

Lignin-Based Materials for Sustainable Rechargeable Batteries.

This review discusses important scientific progress, problems, and prospects of lignin-based materials in the field of rechargeable batteries. Lignin, a component of the secondary cell wall, is considered a promising source of biomass. Compared to cellulose, which is the most extensively studied biomass material, lignin has a competitive price and a variety of functional groups leading to broad utilization such as adhesive, emulsifier, pesticides, polymer composite, carbon precursor, etc. The lignin-based materials can also be applied to various components in rechargeable batteries such as the binder, separator, electrolyte, anode, and cathode. This review describes how lignin-based materials are adopted in these five components with specific examples and explains why lignin is attractive in each case. The electrochemical behaviors including charge-discharge profiles, cyclability, and rate performance are discussed between lignin-based materials and materials without lignin. Finally, current limitations and future prospects are categorized to provide design guidelines for advanced lignin-based materials.

Understanding an Exceptionally Fast and Stable Li-Ion Charging of Highly Fluorinated Graphene with Fine-Controlled C-F Configuration.

Fluorine (F) atoms with the highest electronegativity and low polarizability can easily modify the surface and composition of carbon-based electrode materials. However, this is accompanied by complete irreversibility and uncontrolled reactivity, thus hindering their use in rechargeable electronic devices. Therefore, understanding the electrochemical effects of the C-F configuration might lead to achieving superior electrochemical properties. Here, we demonstrate that the fluorinated and simultaneously reduced graphene oxide (FrGO) was easily synthesized through direct gas fluorination. The as-prepared 11%-FrGO electrode exhibited a high capacity (1365 mAh g-1 at 0.1 A g-1), remarkable rate capability, and good stability (64% retention after 1000 cycles at 5 A g-1). Furthermore, the annealed FrGO (11%-FrGO(A)) electrode in which the C-F bond configurations were controlled by facile thermal treatment shows long-term stability (80% retention after 1000 cycles at 5 A g-1). Above a certain content, F atoms enhance Li-ion adsorption and electron transfer, accelerate Li-ion diffusion, and facilitate the formation of a solid electrolyte interphase layer. In particular, the C-F configuration plays a significant role in retaining the capacity under harsh recharging conditions. The results in this study could provide valuable insights into the field of rechargeable devices.

Enhancing the Capacity and Stability of a Tungsten Disulfide Anode in a Lithium-Ion Battery Using Excess Sulfur.

Tungsten disulfide (WS2) is a transition metal disulfide and a promising anode material due to its layered structure, making it favorable for attaining lithium-ion batteries with rate capability and thermal/mechanical stability. Although WS2 has a rich redox chemistry and a large density, which can increase the specific capacity and volumetric energy density, it still has an inferior specific capacity and poor long-term stability for practical use due to its insufficient space for the accommodation of lithium ions and large volume change during cycling. Herein, to overcome the chronic limitations of WS2-based anodes, we propose a micron-sized tungsten disulfide/reduced graphene oxide composite by employing excess sulfur (Sx-WS2/r-GO). In particular, the excess sulfur modifies the polarity of r-GO by chemically binding on the r-GO sheet during WS2 formation, leading to an increase in the adsorption strength due to WS2. Moreover, the excess sulfur increases the lattice parameter of WS2 and decreases the crystallinity degree, securing additional sites for the accommodation of lithium ions. Therefore, the excess sulfur can increase the specific capacity and impede the separation of the pulverized WS2 nanoparticles, hence mitigating structural decay during cycling. As a result, the Sx-WS2/r-GO anode exhibits an enhanced specific capacity of 1426 mAh g-1 at 0.4 A g-1 and a high cyclic performance, with 87.9% capacity retention after 4000 cycles at a high current density (2.0 A g-1).

In Situ Self-Formed Nanosheet MoS3/Reduced Graphene Oxide Material Showing Superior Performance as a Lithium-Ion Battery Cathode.

Although lithium-sulfur (Li-S) batteries have 5-10 times higher theoretical capacity (1675 mAh g-1) than present commercial lithium-ion batteries, Li-S batteries show a rapid and continuous capacity fading due to the polysulfide dissolution in common electrolytes. Here, we propose the use of a sulfur-based cathode material, amorphous MoS3 and reduced graphene oxide (r-GO) composite, which can be substituted for the pure sulfur-based cathodes. In order to enhance kinetics and stability of the electrodes, we intentionally pulverize the microsized MoS3 sheet into nanosheets and form an ultrathin nano-SEI on the surface using in situ electrochemical methods. Then, the pulverized nanosheets are securely anchored by the oxygen functional group of r-GO. As a result, the electrochemically treated MoS3/r-GO electrode shows superior performance that surpasses pure sulfur-based electrodes; it exhibits a capacity of about 900 mAh g-1 at a rate of 5C for 2500 cycles without capacity fading. Moreover, a full-cell battery employing the MoS3/r-GO cathode with a silicon-carbon composite anode displays a 3-5 times higher energy density (1725 Wh kg-1/7100 Wh L-1) than present LIBs.

Electrospun Nb-doped TiO2 nanofiber support for Pt nanoparticles with high electrocatalytic activity and durability.

This study explores a facile method to prepare an efficient and durable support for Pt catalyst of polymer electrolyte membrane fuel cell (PEMFC). As a candidate, Nb-doped TiO2 (Nb-TiO2) nanofibers are simply fabricated using an electrospinning technique, followed by a heat treatment. Doping Nb into the TiO2 nanofibers leads to a drastic increase in electrical conductivity with doping level of up to 25 at. % (Nb0.25Ti0.75O2). Pt nanoparticles are synthesized on the prepared 25 at. % Nb-doped TiO2-nanofibers (Pt/Nb-TiO2) as well as on a commercial powdered carbon black (Pt/C). The Pt/Nb-TiO2 nanofiber catalyst exhibits similar oxygen reaction reduction (ORR) activity to that of the Pt/C catalyst. However, during an accelerated stress test (AST), the Pt/Nb-TiO2 nanofiber catalyst retained more than 60% of the initial ORR activity while the Pt/C catalyst lost 65% of the initial activity. The excellent durability of the Pt/Nb-TiO2 nanofiber catalyst can be attributed to high corrosion resistance of TiO2 and strong interaction between Pt and TiO2.

Bi-axial grown amorphous MoSx bridged with oxygen on r-GO as a superior stable and efficient nonprecious catalyst for hydrogen evolution.

Amorphous molybdenum sulfide (MoSx) is covalently anchored to reduced graphene oxide (r-GO) via a simple one-pot reaction, thereby inducing the reduction of GO and simultaneous doping of heteroatoms on the GO. The oxygen atoms form a bridged between MoSx and GO and play a crucial role in the fine dispersion of the MoSx particles, control of planar MoSx growth, and increase of exposed active sulfur sites. This bridging leads to highly efficient (-157 mV overpotential and 41 mV/decade Tafel slope) and stable (95% versus initial activity after 1000 cycles) electrocatalyst for hydrogen evolution.

A stable lithiated silicon-chalcogen battery via synergetic chemical coupling between silicon and selenium.

Li-ion batteries dominate portable energy storage due to their exceptional power and energy characteristics. Yet, various consumer devices and electric vehicles demand higher specific energy and power with longer cycle life. Here we report a full-cell battery that contains a lithiated Si/graphene anode paired with a selenium disulfide (SeS2) cathode with high capacity and long-term stability. Selenium, which dissolves from the SeS2 cathode, was found to become a component of the anode solid electrolyte interphase (SEI), leading to a significant increase of the SEI conductivity and stability. Moreover, the replacement of lithium metal anode impedes unwanted side reactions between the dissolved intermediate products from the SeS2 cathode and lithium metal and eliminates lithium dendrite formation. As a result, the capacity retention of the lithiated silicon/graphene-SeS2 full cell is 81% after 1,500 cycles at 268 mA gSeS2-1. The achieved cathode capacity is 403 mAh gSeS2-1 (1,209 mAh cmSeS2-3).

Hierarchical networks of redox-active reduced crumpled graphene oxide and functionalized few-walled carbon nanotubes for rapid electrochemical energy storage.

Crumpled graphene is known to have a strong aggregation-resistive property due to its unique 3D morphology, providing a promising solution to prevent the restacking issue of graphene based electrode materials. Here, we demonstrate the utilization of redox-active oxygen functional groups on the partially reduced crumpled graphene oxide (r-CGO) for electrochemical energy storage applications. To effectively utilize the surface redox reactions of the functional groups, hierarchical networks of electrodes including r-CGO and functionalized few-walled carbon nanotubes (f-FWNTs) are assembled via a vacuum-filtration process, resulting in a 3D porous structure. These composite electrodes are employed as positive electrodes in Li-cells, delivering high gravimetric capacities of up to ∼170 mA h g(-1) with significantly enhanced rate-capability compared to the electrodes consisting of conventional 2D reduced graphene oxide and f-FWNTs. These results highlight the importance of microstructure design coupled with oxygen chemistry control, to maximize the surface redox reactions on functionalized graphene based electrodes.

Design of an Advanced Membrane Electrode Assembly Employing a Double-Layered Cathode for a PEM Fuel Cell.

The membrane electrolyte assembly (MEA) designed in this study utilizes a double-layered cathode: an inner catalyst layer prepared by a conventional decal transfer method and an outer catalyst layer directly coated on a gas diffusion layer. The double-layered structure was used to improve the interfacial contact between the catalyst layer and membrane, to increase catalyst utilization and to modify the removal of product water from the cathode. Based on a series of MEAs with double-layered cathodes with an overall Pt loading fixed at 0.4 mg cm(-2) and different ratios of inner-to-outer Pt loading, the MEA with an inner layer of 0.3 mg Pt cm(-2) and an outer layer of 0.1 mg Pt cm(-2) exhibited the best performance. This performance was better than that of the conventional single-layered electrode by 13.5% at a current density of 1.4 A cm(-2).