Single-crystal Cu(111) foil promotes the lateral growth of lithium rhombic dodecahedra, preventing dendritic lithium growth during plating. This is achieved through surface migration and the interaction of lithium adatoms with individual grains.

Electrolyzers and fuel cells are promising candidates for sustainable conversion of electricity to hydrogen and hydrogen to electricity, offering an energy storage solution with high efficiency and low environmental impact. However, the problem of hydrogen crossover in the polymer electrolyte membrane (PEM) presents a particular challenge, limiting the efficiency and ultimately hindering their widespread adoption. Meanwhile, graphene is a well-known nanomaterial that is reportedly practically impermeable to gases. Here, we present innovative approaches to tackle the issue of hydrogen crossover by using graphene in different forms and different cell architectures. First, we will explore pure graphene oxide (GO) as a new electrolyte material in both acid and alkaline configurations. Then we will look at thin films of GO sandwiched in Aquivion membranes as a gas barrier layer. Finally, we will demonstrate that monolayer graphene is an effective gas barrier layer when sandwiched in Nafion membranes. Similar to the case of graphene, GO also exhibits remarkable materials properties including high strength, excellent hydrogen gas barrier properties, hydrophilicity, and proton conduction assisted by acidic functional groups. These factors potentially make GO an attractive material for electrolyte membranes. We demonstrate the preparation of pure GO membranes via vacuum-filtration, and measure hydrogen permeability (2x10-2 barrer) three orders of magnitude lower than conventional Nafion membranes (30 barrer). Furthermore, we observe a significant anisotropy in ionic conductivity, attributed to the lamellar structure of GO. The resulting fuel cell power density was relatively low, due to limited conductivity (0.3 mS cm-1). To compensate for this, extremely thin (3 µm) electrode-supported GO membranes were deposited via spray deposition, resulting in improved fuel cell power density up to 79 mW cm-2. This showcases the potential of GO-based membranes in enhancing fuel cell performance. Furthermore, we present a novel class of anion exchange membrane (AEM) fabricated from KOH-modified multilayer graphene oxide paper. As with the case of acidic electrolyte membranes, these also display high tensile strength and low gas permeability. A hydroxide ion conductivity of 6 mS cm-1 was recorded and confirmed using ion blocking layers, and attributed to a water-mediated reverse Grotthuss-like mechanism. An alkaline fuel cell was assembled but a relatively low proton conductivity of 1 mW cm-2 was obtained, attributed to reaction with CO2 in the oxidant gas supply. The above studies are promising, but the low ionic conductivity of pure graphene limits the ultimate achievable fuel cell power densities. Therefore, we explored the use of ultrathin GO layers (100 nm) sandwiched in Aquivion PEMs to combine the high ionic conductivity of Aquivion with the gas barrier properties of graphene oxide (as well as CeO2 as a radical scavenger). These novel multilayer sandwich PEMs were deposited via spray deposition, resulting in just 10 µm total thickness. This method resulted in extremely high-power densities (1.6 W/cm2) and very low hydrogen crossover current density (1 mA/cm2). As such the concept of adding hydrogen blocking interlayers is shown to be highly effective. Finally, we investigate the potential of monolayer graphene as a barrier to hydrogen crossover in PEMs, since graphene reportedly presents minimal resistance to hydrogen ion transport through the basal plane. Graphene grown via chemical vapor deposition on a copper substrate was coated with Nafion via spray deposition. The copper was removed via etching in acid and then a second layer of Nafion was sprayed onto the freshly exposed graphene surface, forming a sandwich PEM. Again, this resulted in significantly reduced hydrogen crossover current, whilst having minimal impact on the power density. In conclusion, graphene is an ideal material for incorporation into PEMs to minimise hydrogen crossover. This has the potential to enhancing the performance and durability of fuel cells and electrolysers. T. Bayer, S. R. Bishop, M. Nishihara, K. Sasaki, S. M. Lyth, Journal of Power Sources 272 (2014) 239-247 T. Bayer, R. Selyanchyn, S. Fujikawa, K. Sasaki, S. M. Lyth, Journal of Membrane Science 541 (2017) 347–357 T. Daio, T. Bayer, T. Ikuta, T. Nishiyama, K. Takahashi, Y. Takata, K. Sasaki, S. M. Lyth, Scientific Reports, 5 (2015) 11807 T. Bayer, S. R. Bishop, N. H. Perry, K. Sasaki, S. M. Lyth, ACS Applied Materials and Interfaces 8, 18 (2016) 11466–11475 T. Bayer, B. V. Cunning, R. Selyanchyn, T. Daio, M. Nishihara, S. Fujikawa, K. Sasaki, S. M. Lyth, Journal of Membrane Science, 508 (2016) 51–61 M. Breitwieser, T. Bayer, A. Büchler, R. Zengerle, S. M. Lyth, S. Thiele, Journal of Power Sources, 351 (2017) 145-150

Three-dimensional (3D) microprinting is considered a next-generation manufacturing process for the production of microscale components; however, the narrow range of suitable materials, which include mainly polymers, is a critical issue that limits the application of this process to functional inorganic materials. Herein, we develop a generalised microscale 3D printing method for the production of purely inorganic nanocrystal-based porous materials. Our process is designed to solidify all-inorganic nanocrystals via immediate dispersibility control and surface linking-induced interconnection in the nonsolvent linker bath and thereby creates multibranched gel networks. The process works with various inorganic materials, including metals, semiconductors, magnets, oxides, and multi-materials, not requiring organic binders or stereolithographic equipment. Filaments with a diameter of sub-10 μm are printed into designed complex 3D microarchitectures, which exhibit full nanocrystal functionality and high specific surface areas as well as hierarchical porous structures. This approach provides the platform technology for designing functional inorganics-based porous materials.

Anode-free lithium (Li) batteries that function via direct Li plating/stripping on metal current collectors have garnered significant interest in metallic Li as an ideal negative electrode. However, the dendritic Li growth creates unoccupied space in the battery, diminishing the volumetric energy density. Our research reveals that Li adatoms can be repositioned on metal substrates via surface migration by interacting with individual grains after electro-adsorption of Li ions. By examining the Li morphologies on various type of substrates, we demonstrate that near-zero migration barrier of Li adatoms, especially on single-crystal Cu(111) foils, is a key parameter that inhibits Li dendrites by initiating horizontal growth in a faceted nucleation shape, showing capacity retention of 92.5% for 50 cycles with excess Li (vs. 18.7% for polycrystal Cu). Based on our findings, we highlight the importance of developing the metal current collector with near-zero migration barrier of Li adatoms for anode-free Li batteries.

We report a study of the kinetics of dissolution of (100) and (110) single-crystal diamond plates ("D(100)" and "D(110)") in thin films of nickel (Ni) and cobalt (Co). This dissolution occurs at the metal-D(100) or metal-D(110) interface and was studied in the presence and also in the absence of water vapor at temperatures near 1000 degrees C. The single-crystal D(100) dissolves in Ni, and also in Co, in the temperature range 900-1050 degrees C. The dissolution is too slow to measure below 900 degrees C. In an argon (Ar) atmosphere (under an Ar(g) flow at 1000 sccm and 1 atm pressure, with no water vapor present in the reaction chamber) and at any temperature in the range 900-1050 degrees C, the metal film is rapidly saturated with dissolved carbon (C), thin graphite films form on the free metal surface and at the metal-D interface during heating at or above 650 degrees C, and the dissolution of the diamond then stops. For addition of water vapor, its partial pressure was controlled by using a water bubbler immersed in a constant temperature bath and Ar(g) was used as the carrier gas. We discovered two different regimes (I and II) for the kinetics of dissolution of D(100) and D(110), in which the rate-determining step was the removal of carbon atoms on the open metal surface (regime I, lower partial pressure of water vapor) or dissolution of diamond at the metal-diamond interface (regime II, higher partial pressure of water vapor) that yielded different Arrhenius parameters. Time-of-flight-secondary ion mass spectrometry depth profiles show the concentration gradient of C from a certain depth into the metal film surface down to the M-D(100) interface, and residual gas analyzer measurements show that the gas products formed in the presence of water vapor on the metal surface are CO and H2. It was found that the rate of dissolution of diamond in Co was higher than that in Ni for both D(100) and D(110) and for both regimes I and II, and possible reasons are suggested. We also found that D(111) could not be dissolved at the Ni/D(111) and Co/D(111) interface in the presence of water vapor (over the same range of sample temperatures). The reaction paths for dissolution of C at the M-D(100) or M-D(110) interface and for removal of C from the free surfaces of Ni and Co were assessed through density functional theory modeling at 1273 K.

We report a comprehensive analysis of the Electromagnetic (EM) properties of graphene aerogel-based shielding materials prepared by freeze casting. Controlling the freeze casting temperature allows for tailoring the pore sizes of graphene aerogels, which further affects the permittivity and EM shielding properties. To protect the aerogel structures from collapsing during high temperature heat-treatment, we used Melamine sponge (MS) as a supporting strut. Through a comparison with bare aerogels, we find that the presence of MS can significantly modify both the reflection and absorption performances and that an absorption-dominated shielding material can be obtained. After heat-treatment at 1000 degrees C for two hours, the MS-supported aerogel sample (MS-aero) showed a shielding efficiency of 55.8 dB. Our work shows that the material composition and the microstructural architecture of aerogels crucially influence their electromagnetic shielding efficiency.

We report a versatile method to make liquid metal composites by vigorously mixing gallium (Ga) with non-metallic particles of graphene oxide (G-O), graphite, diamond, and silicon carbide that display either paste or putty-like behavior depending on the volume fraction. Unlike Ga, the putty-like mixtures can be kneaded and rolled on any surface without leaving residue. By changing temperature, these materials can be stiffened, softened, and, for the G-O-containing composite, even made porous. The gallium putty (GalP) containing reduced G-O (rG-O) has excellent electromagnetic interference shielding effectiveness. GalP with diamond filler has excellent thermal conductivity and heat transfer superior to a commercial liquid metal-based thermal paste. Composites can also be formed from eutectic alloys of Ga including Ga-In (EGaIn), Ga-Sn (EGaSn), and Ga-In-Sn (EGaInSn or Galinstan). The versatility of our approach allows a variety of fillers to be incorporated in liquid metals, potentially allowing filler-specific "fit for purpose" materials.

Nanocellulose is a promising new membrane material for fuel cells, with much lower cost and environmental impact compared with Nafion or Aquivion. It is mechanically strong, is an excellent hydrogen barrier and has reasonable proton conductivity. Here, sulfonation of cellulose nanofibers is performed to enhance the conductivity (up to 2 × 10 − 3 S cm − 1 ) without compromising the membrane integrity, and fuel cells are fabricated with 30 µm-thick “paper” membranes. The hydrogen crossover current is two orders of magnitude lower than for Nafion fuel cells with equivalent thickness, but the power density is rather low. Spray-coating is used to deposit 8 µm-thick membranes directly onto the electrocatalyst layer, in a process analogous to 3D printing or additive manufacturing. The resulting paper fuel cell has high current density (> 0.8 A cm − 2 ) and power density (156 mW cm − 2 ) under standard measurement conditions (H 2 /air; 80°C; 95% RH; 0.1 MPa), attributed to decreased membrane resistance. The cost of the spray-painted cellulose membranes is calculated to be ~ 50 $ m − 2 , which is much lower than that of Nafion, even without taking into consideration economies of scale. This new concept in electrochemical energy conversion paves the way for the mass production of affordable, recyclable fuel cells. Graphic abstract

Gallium and many of its alloys remain in liquid phase across impressively wide temperature ranges. Here such liquid metals are proposed as reaction media for the carbonization of low thermal stability polymeric precursors at high temperatures. Plain and cross-linked polyvinyl alcohol are chosen as representatives of such polymers. We show that due to the immiscibility of organic carbons within the liquid metal phase, these polymers that would otherwise vaporize at elevated temperatures, can function as precursors for the formation of carbonaceous films. The thin polymeric films are placed in an intimate contact with the liquid metal surface before thermal processing and show amorphous to graphitic-like characteristics after carbonization. Graphitic-like properties were obtained when a high melting point graphitization catalyst, such as copper, was co-alloyed. The proposed work can be expanded to explore other metallic elements within the bulk of gallium-based alloys for the carbonization of polymeric precursors at large-scales.

A "cooling-contraction" method to separate large-area (up to 4.2 cm in lateral size) graphene oxide (GO)-assembled films (of nanoscale thickness) from substrates is reported. Heat treatment at 3000 °C of such free-standing macroscale films yields highly crystalline "macroassembled graphene nanofilms" (nMAGs) with 16-48 nm thickness. These nMAGs present tensile strength of 5.5-11.3 GPa (with ≈3 µm gauge length), electrical conductivity of 1.8-2.1 MS m-1 , thermal conductivity of 2027-2820 W m-1 K-1 , and carrier relaxation time up to ≈23 ps. As a demonstration application, an nMAG-based sound-generator shows a 30 µs response and sound pressure level of 89 dB at 1 W cm-2 . A THz metasurface fabricated from nMAG has a light response of 8.2% for 0.159 W mm-2 and can detect down to 0.01 ppm of glucose. The approach provides a straightforward way to form highly crystallized graphene nanofilms from low-cost GO sheets.

Principal defects found in graphite films include grain boundaries and wrinkles. These defects are well known to have detrimental effects on properties such as thermal and electrical conductivities...

Graphene‐based hybrid carbons composed of a mix of AB‐stacked and turbostratic regions are reported. Macroscopic graphene films consisting of stacked graphenes are prepared using a liquid crystal graphene oxide dispersion. The graphene films are then infiltrated with bioinspired adhesives, catecholamines, and polymerized to obtain graphene/poly(catecholamine) composites. After heat treatment up to 3000 ºC, the composite films are transformed to have both AB‐stacked (mainly from graphene oxide) and turbostratic (mainly from poly(catecholamines)) structures, and exhibit significantly improved mechanical properties compared to the films having a predominant AB‐stacked structure made from only graphene oxide. They have almost twice the fracture strength (1012 ± 146 MPa) and ≈1.5× increase of both Young's modulus (21.87 ± 2.24 GPa) and strain‐to‐failure (8.91 ± 0.50%). In addition, the films have an in‐plane electrical conductivity as high as 1320 ± 159 S cm−1. Such hybrid‐carbon films with the indicated mechanical and electrical properties have many promising uses, such as for light‐weight structural materials, and in flexible electronics such as for wearable heaters or in sensing electrodes.

Non-platinum group metal (non-PGM) catalysts for the oxygen reduction reaction (ORR) are set to reduce the cost of polymer electrolyte membrane fuel cells (PEFCs) by replacing platinum at the cathode. We previously developed unique nitrogen-doped carbon foams by template-free pyrolysis of alkoxide powders synthesized using a high temperature and high pressure solvothermal reaction. These were shown to be effective ORR electrocatalysts in alkaline media. Here, we present a new optimised synthesis protocol which is carried out at ambient temperature and pressure, enabling us to safely increase the batch size to 2 g, increase the yield by 60%, increase the specific surface area to 1866 m(2) g(-1), and control the nitrogen content (between 1.0 and 5.2 at%). These optimized nitrogen-doped carbon foams are then utilized as effective supports for Fe-N-C catalysts for the ORR in acid media, whilst multiphysics modelling is used to gain insight into the electrochemical performance. This work highlights the importance of the properties of the carbon support in the design of Pt-free electrocatalysts.

Pt-free cathode catalysts are attracting increased interest to replace platinum in polymer electrolyte membrane fuel cells (PEFCs). Heat-treated nitrogen-doped carbons decorated with iron have been the most widely studied alternative. However, lack of understanding of the formation of active sites and degradation mechanisms in such catalysts is hindering their progress. Here, we use a nitrogen-doped carbon foam support with optimised porosity, surface area, and conductivity which is then infiltrated with three different iron precursors: iron (II) acetate (FeAc); iron (III) chloride (FeCl3); and iron phthalocyanine (FePc). These are then pyrolyzed to form Fe-N-C-based ORR electrocatalysts. This approach takes advantage of an already optimized conductive, porous, high surface area and temperature-stable support. The stability of the support helps to separate the role of the different iron precursors from other factors in the generation of catalytic active sites. High temperature X-ray absorption fine structure (HT-XAFS) and high temperature X-ray photoelectron spectroscopy (HT-XPS) were employed to study changes in the iron precursors during the synthesis of Fe-N-C electrocatalysts. Furthermore, near ambient pressure XPS (NAP-XPS) and in-situ electrochemical XAFS were performed to study the interaction between the synthesized catalysts and oxygen. These results are then related to the electrochemical activity.

We report a new approach to making highly dense, oriented, and crystalline graphite films from heat-treated and pressed graphene oxide (G-O). By introducing small-diameter reduced graphene oxide (rG-O) flakes into the graphene oxide starting material, we found that after heat treatment at 3,000 degrees C, the sample density and atomic order substantially improved over a film composed, at the outset, only of pure G-O flakes. A subsequent mechanical press increased the density but reduced the atomic order. A second 3,000 degrees C heat treatment restored the graphitic structure with graphitization metrics exceeding even those of the first heat treatment. The optimized graphitic film with an original concentration of 15 wt% reduced G-O in G-O gave well-oriented graphitic films with a density of 2.1 g cm(-3), cross-plane thermal conductivity of 5.65 W m(-1) K-1, and in-plane thermal conductivity of 2,025 +/- 25 W m(-1) K-1.

A macroscopic film (2.5 cm × 2.5 cm) made by layer-by-layer assembly of 100 single-layer polycrystalline graphene films is reported. The graphene layers are transferred and stacked one by one using a wet process that leads to layer defects and interstitial contamination. Heat-treatment of the sample up to 2800 °C results in the removal of interstitial contaminants and the healing of graphene layer defects. The resulting stacked graphene sample is a freestanding film with near-perfect in-plane crystallinity but a mixed stacking order through the thickness, which separates it from all existing carbon materials. Macroscale tensile tests yields maximum values of 62 GPa for the Young's modulus and 0.70 GPa for the fracture strength, significantly higher than has been reported for any other macroscale carbon films; microscale tensile tests yield maximum values of 290 GPa for the Young's modulus and 5.8 GPa for the fracture strength. The measured in-plane thermal conductivity is exceptionally high, 2292 ± 159 W m-1 K-1 while in-plane electrical conductivity is 2.2 × 105 S m-1 . The high performance of these films is attributed to the combination of the high in-plane crystalline order and unique stacking configuration through the thickness.

Ab initio calculations have been performed on the liquid gallium–hydrogen system at 100 °C. Gallium was found to interact with both free hydrogen atoms and H2, transferring charge in the process. F...

We report the effect of single crystal graphene on carbonization and graphitization of thin film polymers.

A folding technique is reported to incorporate large‐area monolayer graphene films in polymer composites for mechanical reinforcement. Compared with the classic stacking method, the folding strategy results in further stiffening, strengthening, and toughening of the composite. By using a water–air‐interface‐facilitated procedure, an A5‐size 400 nm thin polycarbonate (PC) film is folded in half 10 times to a ≈0.4 mm thick material (1024 layers). A large PC/graphene film is also folded by the same process, resulting in a composite with graphene distributed uniformly. A three‐point bending test is performed to study the mechanical performance of the composites. With a low volume fraction of graphene (0.085%), the Young's modulus, strength, and toughness modulus are enhanced in the folded composite by an average of 73.5%, 73.2%, and 59.1%, respectively, versus the pristine stacked polymer films, or 40.2%, 38.5%, and 37.3% versus the folded polymer film, proving a remarkable mechanical reinforcement from the combined folding and reinforcement of graphene. These results are rationalized with combined theoretical and computational analyses, which also allow the synergistic behavior between the reinforcement and folding to be quantified. The folding approach could be extended/applied to other 2D nanomaterials to design and make macroscale laminated composites with enhanced mechanical properties.

Even though the rheological behavior of aqueous graphene oxide (G-O) dispersions has been shown to be strongly time-dependent, only few transient measurements have been reported in the literature. In this work, we attempt to fill the gap between transient and steady shear rheological characterizations of aqueous G-O dispersions in the concentration range of 0.004 < ϕ < 3.5 wt%, by conducting comprehensive rheological measurements, including oscillatory shear flow, transient shear flow, and steady shear flow. Steady shear measurements have been performed after the evaluation of transient properties of the G-O dispersions, to assure steady-state conditions. We identify the critical concentration ϕ c = 0.08 wt% (where G-O sheets start to interact) from oscillatory shear experiments. We find that the rheology of G-O dispersions strongly depends on the G-O concentration ϕ . Transient measurements of shear viscosity and first normal stress difference suggest that G-O dispersions behave like nematic polymeric liquid crystals at ϕ / ϕ c = 25, in agreement with other work reported in the literature. G-O dispersions also display a transition from negative to positive values of the first normal stress difference with increasing shear rates. Experimental findings of aqueous graphene oxide dispersions are compared and discussed with models and experiments reported for nematic polymeric liquid crystals, laponite, and organoclay dispersions.