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Li-CO2 batteries with unique reaction pathways and high theoretical capacity are powerful tools for addressing greenhouse issues. Thus, it is critical and urgent to develop highly active catalysts for the cathodes of Li-CO2 batteries to promote both CO2 reduction (CRR) and evolution reactions (CER). Herein, La0.8Sr0.2NixCu1–xO3 perovskite is in situ synthesized on multiwalled carbon nanotubes (LSNC/MWCNTs) paper as cathodes of Li-CO2 batteries. The morphology, structure, and electrochemical performance of the as-prepared cathodes are investigated systematically, as well as the reaction products and reversible reaction mechanism. As a result, the Li-CO2 batteries constructed with La0.8Sr0.2Ni0.7Cu0.3O3 (N7C3)/MWCNTs cathode exhibit remarkable electrochemical properties, showcasing a large specific capacity of 16.90 mAh cm–2 at a high specific current of 0.07 mA cm–2, a low overpotential of 0.76 V after 15 cycles rate test, and good cycling stability, maintaining a low overpotential throughout the 500 h of discharge–charging at 0.02 mA cm–2 with a cutoff capacity of 0.1 mAh cm–2 (50 cycles). The superior electrochemical performance of the N7C3/MWCNTs cathodes is attributed to the high Ni3+ content and a large amount of oxygen vacancies caused by the tuning of the atomic ratio on B-sites of perovskite crystals. The results of this work would provide an easy design option for the free-standing cathodes of Li-CO2 batteries and will inspire more original high-performance metal–air batteries. [ABSTRACT FROM AUTHOR]

Bifunctional catalysts (OER/ORR) require lower overpotentials and fast mass transfer, but developing transition metal-based bifunctional catalysts that can satisfy these requirements remains a major challenge. Herein, a composite consisting of FeCo alloy nanoparticles uniformly loaded on three-dimensional (3D) hierarchical porous nitrogen-doped carbon (FeCo/HP-NC) is rationally designed. The electronic modulation of the FeCo alloy can provide a favorable electronic structure for the OER/OER reaction, while the hierarchical porous carbon structure can facilitate not only the accessible channels but also the mass transfer for electrocatalytic reactions. Thus, FeCo/HP-NC provides modest overpotentials (E1/2 = 0.83 V, η = 0.335 V). In particular, when compared with commercially available noble catalysts, FeCo/HP-NC offers a higher power density, more stable voltage (1.43 V), and stability that exceeds 300 h as the cathode. As for this investigation, strategies for increasing the catalytic performance of oxygen electrocatalysis and the power density of energy storage applications could be proposed. [ABSTRACT FROM AUTHOR]

The development of efficient nonplatinum electrocatalysts with enhanced oxygen reduction reaction (ORR) activity and stability is of crucial importance for the commercial application of fuel cells and metal–air batteries. Metallenes exhibit excellent performance in energy and catalysis due to their unique physicochemical and electronic properties. In particular, the ultrahigh proportion of under-coordinated metal atomic sites in metallenes enhances the atom utilization and intrinsic activity, which endows them with considerable potential for catalytic applications. Herein, the synthesized two-dimensional (2D) ultrathin porous Pd metallene with amorphous/crystalline phase coexistence exhibits enhanced alkaline oxygen reduction properties, as evidenced by four-electron selectivity, lower overpotential (E1/2 = 0.944 V), high mass activity (MA = 1.44 mA/μgPd), and solid stability (only loss of 7 mV in half-wave potential after 10,000 potential cycles). Such high performance of Pd metallene is attributed to amorphous/crystalline heterophases, 2D morphology, and porous structure. DFT calculations demonstrate that the ORR catalytic performance can be effectively promoted by the amorphous structure with a modulated electronic structure. The amorphous/crystalline coexisting porous Pd metallene with excellent catalytic performance can provide the reference for metallene materials design in various fields. This study presents a scientific basis to understand the mechanism of 2D amorphous phase nanostructures for boosting the electrocatalytic performance. [ABSTRACT FROM AUTHOR]

Since the sluggish kinetics of the oxygen evolution process (OER) at the anode of water splitting remains to be a crucial bottleneck for hydrogen production, it is imperative to develop low-cost OER electrocatalysts with high efficiency. Here, (FeSe2 + CoSe2) nanoparticles loaded on nitrogen-doped three-dimensional porous carbon nanosheets (referred to as (FeSe2 + CoSe2)/N-3DCN) were prepared by freeze-drying, heat treatment and selenization. The favorable affinity and large surface area of N-3DCN enabled the synthesis of the ultrafine (FeSe2 + CoSe2) nanoparticles with a diameter of 10 nm, which were highly dispersed on carbon nanosheets and provided a significant number of active sites. The density functional theory (DFT) calculation demonstrated that the free energy of oxygen-containing intermediates during OER was optimized by coupling FeSe2 with CoSe2. The overpotential of (FeSe2 + CoSe2)/N-3DCN is 312 mV at 10 mA cm–2, which is superior to those of (FeSe2 + CoSe2) (390 mV), CoSe2/N-3DCN (377 mV), RuO2 (320 mV), and FeSe2/N-3DCN (479 mV). Additionally, after the 80 h stability test, the overpotential of (FeSe2 + CoSe2)/N-3DCN can still be maintained at 316 mV. [ABSTRACT FROM AUTHOR]

The design of transition metal dichalcogenides that satisfies the essential requirements of the hydrogen evolution reaction (HER) in alkaline solutions remains a challenge. The study gives a description of sulfur atoms into both anionic and cationic sites of WTe2, which is deliberately designed and has been rarely reported. Herein, we report 3D self-supported anionic and cationic S-substituted WTe2 nanosheet arrays constructed on a carbon cloth by a three-step synthesis method at elevated temperatures. Experimental and theoretical analysis are both executed to investigate S-WTe2/CC nanocomposites for efficient alkaline HER, and the results attest to its excellent electrocatalytic performance. The optimized S-WTe2/CC exhibits an enhanced HER activity with an overpotential of 195 mV at the current density of 10 mA cm–2, which is 2.3 and 1.7 times lower than that of WO3/CC (451 mV) and WTe2/CC (327 mV), respectively. According to density functional theory calculations, such improvement of alkaline HER is attributed to the optimized p-band electron configuration of Te atoms, higher H* intermediate adsorption, and lower H2O dissociation energy barrier by anionic and cationic co-substitution of S, which accelerate the Volmer–Heyrovsky process. The present study paves a way to the modification strategy of WTe2 electrocatalysts. [ABSTRACT FROM AUTHOR]

Oriented carbon nanotubes (CNTs) with high stiffness, excellent thermal/electrical properties, and nanoscopic rough surface make CNT carpets excellent materials for anti-icing coatings. However, the slipping and sliding of adjacent CNTs and poor adhesion at the CNT/substrate interface restrict their practical application. In this work, high-quality CNT carpets with an in situ strengthening interlayered structure (SI-CNT carpets) are developed by a one-step chemical vapor deposition (CVD) method with the assistance of seed-mediated binary catalysts (Fe3O4/AlOx). With component separation and sandwich-like structural redistribution of catalysts during the CVD process, a dense strengthening interlayer is formed in the middle of CNT carpets without damaging the nanoscopic rough surface on top. Therefore, an order of magnitude increase in Young's modulus (up to ∼500 MPa) and 2.5× improvement in the freezing delay time (TD) of water droplets (∼50 s) can be achieved, indicating high anti-icing performance and suitable mechanical stability of SI-CNT carpets for practical anti-icing application. [ABSTRACT FROM AUTHOR]

A series of NiCo 2 P-based electrocatalysts, which were wrapped by CeO 2 whose oxygen vacancies (V O ) are partially filled with phosphorus atoms (named as NiCo 2 P x /P x FVo-CeO 2 , where x refers to the consumption of NaH 2 PO 2 ·H 2 O), have been fabricated to improve the electrocatalytic reactivity of NiCo 2 P toward hydrogen evolution in alkaline solution. In the novel catalysts, the P atoms fill the oxygen vacancies, elevate the chemical valence state of Ni 2+ and Co 3+ , and increase the hydride acceptors, which reinforcing the promoting effect of CeO 2 in the hydrogen evolution reaction (HER). Moreover, the negatively charged P atoms capture the positively charged protons more easily, benefiting the Volmer step during HER. Furthermore, the synergistic effect between oxygen vacancies and the filled P atoms accelerates the migration rate of electrons/ions and increases the electrochemical active area. All of the above are advantageous to the hydrogen evolution of NiCo 2 P x /P x FVo-CeO 2 in alkaline electrolyte. As a result, the overpotential as low as 33.6 mV is achieved for NiCo 2 P 0.3 /P 0.3 FVo-CeO 2 in alkaline media to drive a current density of 10 mA cm -2 . The reactivity is superior to that of Pt/C at a large current density along with a Tafel slope of 61.24 mV dec -1 and long-term durability, which giving a new technology for efficient transition-metal catalyst candidates toward HER in alkaline solution.

Conductive epoxy composites are of great interest due to their applications in electronics. They are usually made by mixing powdered conductive fillers with epoxy. However, the conductivity of the composite is limited by the low filler content because increasing filler content causes processing difficulties and reduces the mechanical properties of the epoxy host. We describe here the use of ultra-stiff graphene foams (uGFs) as three-dimensional (3D) continuous conductive fillers for epoxy resins. The powder metallurgy method was used to produce the dense uGFs monoliths that resulted in a very high filler content of 32 wt % in the uGF-epoxy composite, while the density of epoxy was only increased by 0.09 g/cm 3 . The composite had an electrical conductivity of 41.0 ± 6.3 S/cm, which is among the highest of all of the polymer-based composites with non-conductive polymer matrices and comparable with the conductive polymer matrices reported to date. The compressive modulus of the composite showed a remarkable improvement of >1700% compared to pure epoxy. We have demonstrated that the 3D uGF filler substantially improves the conductivity and reinforces the polymer matrix with a high filler content while retaining a density similar to that of the epoxy alone.

As a promising bifunctional electrocatalyst for water splitting, NiFe-layered double hydroxide (NiFe LDH) demonstrates an excellent activity toward oxygen evolution reaction (OER) in alkaline solution. However, its hydrogen evolution reaction (HER) activity is challenged owing to the poor electronic conductivity and insufficient electrochemical active sites. Therefore, a three-dimensional self-supporting metal hydroxide/oxide electrode with abundant oxygen vacancies is prepared by electrodepositing CeO x nanoparticles on NiFe LDH nanosheets. According to the density functional theory calculations and experimental studies, the oxygen vacancies at the NiFe LDH/CeO x interface can be introduced successfully because of the positive charges accumulation resulting from the local electron potential difference between NiFe LDH and CeO x . The oxygen vacancies accelerate the electron/ion migration rates, facilitate the charge transfer, and increase the electrochemical active sites, which give rise to an efficient activity toward HER in alkaline solution. Furthermore, NF@NiFe LDH/CeO x needs a lower potential of 1.51 V to drive a current density of 10 mA cm -2 in overall water splitting and demonstrates a superior performance compared with the benchmark Pt/C and RuO 2 , which is indicated to be a promising bifunctional electrode catalyst.

Electrically splitting water to H 2 and O 2 is a preferred method for energy storage as long as no CO 2 is emitted during the supplied electrical input. Here we report a laser-induced graphene (LIG) process to fabricate efficient catalytic electrodes on opposing faces of a plastic sheet, for the generation of both H 2 and O 2 . The high porosity and electrical conductivity of LIG facilitates the efficient contact and charge transfer with the requisite electrolyte. The LIG-based electrodes exhibit high performance for hydrogen evolution reaction and oxygen evolution reaction with excellent long-term stability. The overpotential reaches 100 mA/cm 2 for HER, and OER is as low as 214 and 380 mV with relatively low Tafel slopes of 54 and 49 mV/dec, respectively. By serial connecting of the electrodes with a power source in an O-ring setup, H 2 and O 2 are simultaneously generated on either side of the plastic sheet at a current density of 10 mA/cm 2 at 1.66 V and can thereby be selectively captured. The demonstration provides a promising route to simple, efficient, and complete water splitting.

An automated metal powder three-dimensional (3D) printing method for in situ synthesis of free-standing 3D graphene foams (GFs) was successfully modeled by manually placing a mixture of Ni and sucrose onto a platform and then using a commercial CO 2 laser to convert the Ni/sucrose mixture into 3D GFs. The sucrose acted as the solid carbon source for graphene, and the sintered Ni metal acted as the catalyst and template for graphene growth. This simple and efficient method combines powder metallurgy templating with 3D printing techniques and enables direct in situ 3D printing of GFs with no high-temperature furnace or lengthy growth process required. The 3D printed GFs show high-porosity (∼99.3%), low-density (∼0.015g cm -3 ), high-quality, and multilayered graphene features. The GFs have an electrical conductivity of ∼8.7 S cm -1 , a remarkable storage modulus of ∼11 kPa, and a high damping capacity of ∼0.06. These excellent physical properties of 3D printed GFs indicate potential applications in fields requiring rapid design and manufacturing of 3D carbon materials, for example, energy storage devices, damping materials, and sound absorption.

The cathodic oxygen reduction reaction (ORR) is essential in the electrochemical energy conversion of fuel cells. Here, through the NH 3 atmosphere annealing of a graphene oxide (GO) precursor containing trace amounts of Ru, we have synthesized atomically dispersed Ru on nitrogen-doped graphene that performs as an electrocatalyst for the ORR in acidic medium. The Ru/nitrogen-doped GO catalyst exhibits excellent four-electron ORR activity, offering onset and half-wave potentials of 0.89 and 0.75 V, respectively, vs a reversible hydrogen electrode (RHE) in 0.1 M HClO 4 , together with better durability and tolerance toward methanol and carbon monoxide poisoning than seen in commercial Pt/C catalysts. X-ray adsorption fine structure analysis and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy are performed and indicate that the chemical structure of Ru is predominantly composed of isolated Ru atoms coordinated with nitrogen atoms on the graphene substrate. Furthermore, a density function theory study of the ORR mechanism suggests that a Ru-oxo-N 4 structure appears to be responsible for the ORR catalytic activity in the acidic medium. These findings provide a route for the design of efficient ORR single-atom catalysts.

The drive for significant advancement in battery capacity and energy density inspired a revisit to the use of Li metal anodes. We report the use of a seamless graphene-carbon nanotube (GCNT) electrode to reversibly store Li metal with complete dendrite formation suppression. The GCNT-Li capacity of 3351 mAh g -1 GCNT-Li approaches that of bare Li metal (3861 mAh g -1 Li ), indicating the low contributing mass of GCNT, while yielding a practical areal capacity up to 4 mAh cm -2 and cycle stability. A full battery based on GCNT-Li/sulfurized carbon (SC) is demonstrated with high energy density (752 Wh kg -1 total electrodes, where total electrodes = GCNT-Li + SC + binder), high areal capacity (2 mAh cm -2 ), and cyclability (80% retention at >500 cycles) and is free of Li polysulfides and dendrites that would cause severe capacity fade.

Here we show that a versatile binary catalyst solution of Fe 3 O 4 /AlO x nanoparticles enables homogeneous growth of single to few-walled carbon nanotube (CNT) carpets from three-dimensional carbon-based substrates, moving past existing two-dimensional limited growth methods. The binary catalyst is composed of amorphous AlO x nanoclusters over Fe 3 O 4 crystalline nanoparticles, facilitating the creation of seamless junctions between the CNTs and the underlying carbon platform. The resulting graphene-CNT (GCNT) structure is a high-density CNT carpet ohmically connected to the carbon substrate, an important feature for advanced carbon electronics. As a demonstration of the utility of this approach, we use GCNTs as anodes and cathodes in binder-free lithium-ion capacitors, producing stable devices with high-energy densities (∼120 Wh kg -1 ), high-power density capabilities (∼20,500 W kg -1 at 29 Wh kg -1 ), and a large operating voltage window (4.3 to 0.01 V).

Free-standing robust three-dimensional (3D) rebar graphene foams (GFs) were developed by a powder metallurgy template method with multiwalled carbon nanotubes (MWCNTs) as a reinforcing bar, sintered Ni skeletons as a template and catalyst, and sucrose as a solid carbon source. As a reinforcement and bridge between different graphene sheets and carbon shells, MWCNTs improved the thermostability, storage modulus (290.1 kPa) and conductivity (21.82 S cm -1 ) of 3D GF resulting in a high porosity and structurally stable 3D rebar GF. The 3D rebar GF can support >3150× the foam's weight with no irreversible height change, and shows only a ∼25% irreversible height change after loading >8500× the foam's weight. The 3D rebar GF also shows stable performance as a highly porous electrode in lithium ion capacitors (LICs) with an energy density of 32 Wh kg -1 . After 500 cycles of testing at a high current density of 6.50 mA cm -2 , the LIC shows 78% energy density retention. These properties indicate promising applications with 3D rebar GFs in devices requiring stable mechanical and electrochemical properties.

Large-area graphene has emerged as a promising material for use in flexible and transparent electronics due to its flexibility and optical and electronic properties. The anchoring of transition metal nanoparticles on large-area single-layer graphene is still a challenge. Here, we report an in situ preparation of carbon nano-onion-encapsulated Fe nanoparticles on rebar graphene, which we term rivet graphene. The hybrid film, which allows for polymer-free transfer and is strong enough to float on water with no added supports, exhibits high optical transparency, excellent electric conductivity, and good hole/electron mobility under certain tensile/compressive strains. The results of contact resistance and transfer length indicate that the current in the rivet graphene transistor does not just flow at the contact edge. Carbon nano-onions encapsulating Fe nanoparticles on the surface enhance the injection of charge between rivet graphene and the metal electrode. The anchoring of Fe nanoparticles encapsulated by carbon nano-onions on rebar graphene will provide additional avenues for applications of nanocarbon-based films in transparent and flexible electronics.

High-quality microsized ultrathin single-crystalline anatase TiO2 nanosheets (MS-TiO2) with exposed {001} facets were synthesized by a facile and low-cost two-step process that combines a graphene oxide (GO)-assisted hydrothermal method with calcination. Both GO and HF play an important role in the formation of well dispersed MS-TiO2. As a novel microsized (1-4 μm) ultrathin two-dimensional (2D) material, MS-TiO2 possesses much higher lateral size and aspect ratio compared to common 2D nanosized (30-60 nm) ultrathin TiO2 nanosheets (NS-TiO2), resulting in excellent electronic conductivity and superior electron transfer and diffusion properties. Here, we fabricated MS-TiO2 and NS-TiO2, both of which were incorporated with the TiO2 nanoparticles (P25) to constitute the hybrid photoanode of dye-sensitized solar cells (DSSCs), and explored the effect of the lateral size (nano- and micro-) of ultrathin TiO2 nanosheets on their electron transfer and diffusion properties. Benefiting from the faster electron transfer rate and short diffusion path of the MS-TiO2, the MS-TiO2/P25 gains the more superior performance compared to pure P25 and NS-TiO2/P25 in the application of DSSCs. Moreover, it is expected that the novel high aspect ratio MS-TiO2 may be applied in diverse fields including photocatalysis, photodetectors, lithium-ion batteries and others concerning the environment and energy.

A simple and scalable method which combines traditional powder metallurgy and chemical vapor deposition is developed for the synthesis of mesoporous free-standing 3D graphene foams. The powder metallurgy templates for 3D graphene foams (PMT-GFs) consist of particle-like carbon shells which are connected by multilayered graphene that shows high specific surface area (1080 m(2) g(-1)), good crystallization, good electrical conductivity (13.8 S cm(-1)), and a mechanically robust structure. The PMT-GFs did not break under direct flushing with DI water, and they were able to recover after being compressed. These properties indicate promising applications of PMT-GFs for fields requiring 3D carbon frameworks such as in energy-based electrodes and mechanical dampening.