Efficient Electrocatalytic Oxygen Evolution on Amorphous Nickel–Cobalt Binary Oxide Nanoporous Layers

Nanoporous Ni–Co binary oxide layers were electrochemically fabricated by deposition followed by anodization, which produced an amorphous layered structure that could act as an efficient electrocatalyst for water oxidation. The highly porous morphologies produced higher electrochemically active surface areas, while the amorphous structure supplied abundant defect sites for oxygen evolution. These Ni-rich (10–40 atom % Co) binary oxides have an increased active surface area (roughness factor up to 17), reduced charge transfer resistance, lowered overpotential (∼325 mV) that produced a 10 mA cm^–2 current density, and a decreased Tafel slope (∼39 mV decade^–1). The present technique has a wide range of applications for the preparation of other binary or multiple-metals or metal oxides nanoporous films. Fabrication of nanoporous materials using this method could provide products useful for renewable energy production and storage applications

Boron/Nitrogen Co-Doped Helically Unzipped Multiwalled Carbon Nanotubes as Efficient Electrocatalyst for Oxygen Reduction

Bamboo structured nitrogen doped multiwalled carbon nanotubes have been helically unzipped, and nitrogen doped graphene oxide nanoribbons (CN_<i>x</i>-GONRs) with a multifaceted microstructure have been obtained. CN_<i>x</i>-GONRs have then been codoped with nitrogen and boron by simultaneous thermal annealing in ammonia and boron oxide atmospheres, respectively. The effects of the codoping time and temperature on the concentration of the dopants and their functional groups have been extensively investigated. X-ray photoelectron spectroscopy results indicate that pyridinic and BC₃ are the main nitrogen and boron functional groups, respectively, in the codoped samples. The oxygen reduction reaction (ORR) properties of the samples have been measured in an alkaline electrolyte and compared with the state-of-the-art Pt/C (20%) electrocatalyst. The results show that the nitrogen/boron codoped graphene nanoribbons with helically unzipped structures (CN_<i>x</i>/CB_<i>x</i>-GNRs) can compete with the Pt/C (20%) electrocatalyst in all of the key ORR properties: onset potential, exchange current density, four electron pathway selectivity, kinetic current density, and stability. The development of such graphene nanoribbon-based electrocatalyst could be a harbinger of precious metal-free carbon-based nanomaterials for ORR applications

Graphene Nanoribbon/V₂O₅ Cathodes in Lithium-Ion Batteries

Nanocrystalline V₂O₅ particles were successfully entrapped by graphene nanoribbons (GNRs) derived from unzipped carbon nanotubes. The electrical conductivity of V₂O₅ nanoparticles was enhanced after introducing the GNRs. The 3-dimensional conductive framework in the composites plays a significant role in improving the rate performance and cyclability of the material when used as a cathode in lithium-ion batteries. By tailoring the mass ratio between the GNRs and the V₂O₅ nanoparticles, the fabricated composites can deliver a high capacity of 278 mAh g^–1 at 0.1 <i>C</i>, which is close to its theoretical value, whereas a capacity of 165 mAh g^–1 can be maintained at 2 <i>C</i>. The delivered capacity at 0.1 <i>C</i> can maintain 78% of its initial capacity after 100 cycles

Efficient Water-Splitting Electrodes Based on Laser-Induced Graphene

Electrically splitting water to H₂ and O₂ is a preferred method for energy storage as long as no CO₂ 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 H₂ and O₂. 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/cm² 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, H₂ and O₂ are simultaneously generated on either side of the plastic sheet at a current density of 10 mA/cm² at 1.66 V and can thereby be selectively captured. The demonstration provides a promising route to simple, efficient, and complete water splitting

Hydrothermally Formed Three-Dimensional Nanoporous Ni(OH)₂ Thin-Film Supercapacitors

A three-dimensional nanoporous Ni(OH)₂ thin-film was hydrothermally converted from an anodically formed porous layer of nickel fluoride/oxide. The nanoporous Ni(OH)₂ thin-films can be used as additive-free electrodes for energy storage. The nanoporous layer delivers a high capacitance of 1765 F g^–1 under three electrode testing. After assembly with porous activated carbon in asymmetric supercapacitor configurations, the devices deliver superior supercapacitive performances with capacitance of 192 F g^–1, energy density of 68 Wh kg^–1, and power density of 44 kW kg^–1. The wide working potential window (up to 1.6 V in 6 M aq KOH) and stable cyclability (∼90% capacitance retention over 10 000 cycles) make the thin-film ideal for practical supercapacitor devices

Nanocomposite of Polyaniline Nanorods Grown on Graphene Nanoribbons for Highly Capacitive Pseudocapacitors

A facile and cost-effective approach to the fabrication of a nanocomposite material of polyaniline (PANI) and graphene nanoribbons (GNRs) has been developed. The morphology of the composite was characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron microscopy, and X-ray diffraction analysis. The resulting composite has a high specific capacitance of 340 F/g and stable cycling performance with 90% capacitance retention over 4200 cycles. The high performance of the composite results from the synergistic combination of electrically conductive GNRs and highly capacitive PANI. The method developed here is practical for large-scale development of pseudocapacitor electrodes for energy storage

Carbon-Free Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions

A nanoporous Ag-embedded SnO₂ thin film was fabricated by anodic treatment of electrodeposited Ag–Sn alloy layers. The ordered nanoporous structure formed by anodization played a key role in enhancing the electrocatalytic performance of the Ag-embedded SnO₂ layer in several ways: (1) the roughness factor of the thin film is greatly increased from 23 in the compact layer to 145 in the nanoporous layer, creating additional active sites that are involved in oxygen electrochemical reactions; (2) a trace amount of Ag (∼1.7 at %, corresponding to a Ag loading of ∼3.8 μg cm^–2) embedded in the self-organized SnO₂ nanoporous matrix avoids the agglomeration of nanoparticles, which is a common problem leading to the electrocatalyst deactivation; (3) the fabricated nanoporous thin film is active without additional additives or porous carbon that is usually necessary to support and stabilize the electrocatalyst. More importantly, the Ag-embedded SnO₂ nanoporous thin film shows outstanding bifunctional oxygen electrochemical performance (oxygen reduction and evolution reactions) that is considered a promising candidate for use in metal-air batteries. The present technique has a wide range of applications for the preparation of other carbon-free electrocatalytic nanoporous films that could be useful for renewable energy production and storage applications

Three-Dimensional Thin Film for Lithium-Ion Batteries and Supercapacitors

Three-dimensional heterogeneously nanostructured thin-film electrodes were fabricated by using Ta₂O₅ nanotubes as a framework to support carbon-onion-coated Fe₂O₃ nanoparticles along the surface of the nanotubes. Carbon onion layers function as microelectrodes to separate the two different metal oxides and form a nanoscale 3-D sandwich structure. In this way, space-charge layers were formed at the phase boundaries, and it provides additional energy storage by charge separation. These 3-D nanostructured thin films deliver both excellent Li-ion battery properties (stabilized at 800 mAh cm^–3) and supercapacitor (up to 18.2 mF cm^–2) performance owing to the synergistic effects of the heterogeneous structure. Thus, Li-ion batteries and supercapacitors are successfully assembled into the same electrode, which is promising for next generation hybrid energy storage and delivery devices

Nanoporous Silicon Oxide Memory

Oxide-based two-terminal resistive random access memory (RRAM) is considered one of the most promising candidates for next-generation nonvolatile memory. We introduce here a new RRAM memory structure employing a nanoporous (NP) silicon oxide (SiO_<i>x</i>) material which enables unipolar switching through its internal vertical nanogap. Through the control of the stochastic filament formation at low voltage, the NP SiO_<i>x</i> memory exhibited an extremely low electroforming voltage (∼1.6 V) and outstanding performance metrics. These include multibit storage ability (up to 9-bits), a high ON–OFF ratio (up to 10⁷ A), a long high-temperature lifetime (≥10⁴ s at 100 °C), excellent cycling endurance (≥10⁵), sub-50 ns switching speeds, and low power consumption (∼6 × 10^–5 W/bit). Also provided is the room temperature processability for versatile fabrication without any compliance current being needed during electroforming or switching operations. Taken together, these metrics in NP SiO_<i>x</i> RRAM provide a route toward easily accessed nonvolatile memory applications

Cobalt Nanoparticles Embedded in Nitrogen-Doped Carbon for the Hydrogen Evolution Reaction

There is great interest in renewable and sustainable energy research to develop low-cost, highly efficient, and stable electrocatalysts as alternatives to replace Pt-based catalysts for the hydrogen evolution reaction (HER). Though nanoparticles encapsulated in carbon shells have been widely used to improve the electrode performances in energy storage devices (e.g., lithium ion batteries), they have attracted less attention in energy-related electrocatalysis. Here we report the synthesis of nitrogen-enriched core–shell structured cobalt–carbon nanoparticles dispersed on graphene sheets and we investigate their HER performances in both acidic and basic media. These catalysts exhibit excellent durability and HER activities with onset overpotentials as low as ∼70 mV in both acidic (0.5 M H₂SO₄) and alkaline (0.1 M NaOH) electrolytes, and the overpotentials needed to deliver 10 mA cm^–2 are determined to be 265 mV in acid and 337 mV in base, further demonstrating their potential to replace Pt-based catalysts. Control experiments reveal that the active sites for HER might come from the synergistic effects between the cobalt nanoparticles and nitrogen-doped carbon