Ultra-low Voltage Research Articles

High‐Performance Memristor Based on 2D Layered BiOI Nanosheet for Low‐Power Artificial Optoelectronic Synapses

AbstractArtificial optoelectronic synapses with both electrical and light‐induced synaptic behaviors have recently been studied for applications in neuromorphic computing and artificial vision systems. However, the combination of visual perception and high‐performance information processing capabilities still faces challenges. In this work, the authors demonstrate a memristor based on 2D bismuth oxyiodide (BiOI) nanosheets that can exhibit bipolar resistive switching (RS) performance as well as electrical and light‐induced synaptic plasticity eminently suitable for low‐power optoelectronic synapses. The fabricated memristor exhibits high‐performance RS behaviors with a high ON/OFF ratio up to 105, an ultralow SET voltage of ≈0.05 V which is one order of magnitude lower than that of most reported memristors based on 2D materials, and low power consumption. Furthermore, the memristor demonstrates not only electrical voltage‐driven long‐term potentiation, depression plasticity, and paired‐pulse facilitation, but also light‐induced short‐ and long‐term plasticity. Moreover, the photonic synapse can be used to simulate the “learning experience” behaviors of human brain. Consequently, not only the memristor based on BiOI nanosheets shows ultra‐low SET voltage and low‐power consumption, but also the optoelectronic synapse provides new material and strategy to construct low‐power retina‐like vision sensors with functions of perceiving and processing information.

Ultrasound-seeded vapor-phase-transport growth of boundary-rich layered double hydroxide nanosheet arrays for highly efficient water splitting

Noble-metal-free electrodes are of significant importance for electrochemical energy storage and conversion. Transition-metal-based layered double hydroxides (TM LDHs) show great potential as advanced electrocatalysts, but low electrochemical active areas and poor electronic conductivity limit their catalytic activity. Herein, we report a novel secondary growth strategy to synthesize ultrathin NiCoFe LDH nanosheets anchored on nickel foam (NF). By coupling ultrasound-assisted oxidation (UAO) to deposit dense seeds of low-crystalline NiCoFe LDH array on semisacrificial NF, and vapor-phase-transport (VPT) of urea for kinetic control over nanosheet thickness, hierarchical self-supported electrodes with high density of exposed active sites and abundant boundaries have been facilely obtained. The NiCoFe LDH/NF electrodes show an impressive electrocatalytic performance during oxygen evolution reaction (OER) with required overpotentials of 217 and 227 mV to achieve current densities of 50 and 100 mA cm−2 respectively, with over 150 h long-term stability, outperforming those synthesized by hydrothermal synthesis (HTT) as well as most state-of-the-art electrocatalysts. The overall water splitting device assembled using the NiCoFe LDH/NF electrode as both anode and cathode shows an ultralow cell voltage of 1.56 V to obtain 10 mA cm−2. This strategy provides a simple and scalable methodology for synthesizing high-activity catalysts for efficient electrochemical processes.

Fe2P nanoparticles embedded on Ni2P nanosheets as highly efficient and stable bifunctional electrocatalysts for water splitting

• Fe 2 P nanoparticles embedded on Ni 2 P nanosheets has been synthesized. • Fe 2 P/Ni 2 P HS delivers superior catalytic performance for water splitting. • The electron redistribution near heterointerface optimizes the ΔG H* of P sites. • The Fe 2 P/Ni 2 P heterointerface results in abundant active sites. It is urgent to develop highly efficient, stable and low-cost bifunctional electrocatalysts for overall water splitting. Herein, an iron-nickel phosphide (Fe 2 P/Ni 2 P) heterostructure, constructed by Fe 2 P nanoparticles embedded on Ni 2 P nanosheets, is strategically fabricated on nickel foam via a facile process. As a bifunctional electrocatalyst, the Fe 2 P/Ni 2 P heterostructure delivers a very low overpotential of 64 mV (or 185 mV) to reach current density of 10 mA cm −2 for hydrogen (or oxygen) evolution reaction. When simultaneously employed as both the anode and cathode electrodes, it demonstrates an ultralow cell voltage of 1.49 V@10 mA cm −2 for full water splitting with nearly 100% Faradaic efficiency, and superior long-term stability even over 100 h. Density functional theory calculations manifest that a strong heterointerface interaction could cause electron redistribution near the Fe 2 P/Ni 2 P heterointerface and optimize the Δ G H* of P sites, thus enhancing catalytic activity. Additionally, the 3D porous heterostructure is benefit to expose rich active sites and facilitate ion diffusion and gas bubble release, thus promoting the catalytic performance. This work opens up a new strategical approach for rational design of metal phosphide-based heterostructures as highly efficient and stable bifunctional electrocatalysts for water splitting.

A 10-nm-thick silicon oxide based high switching speed conductive bridging random access memory with ultra-low operation voltage and ultra-low LRS resistance

In this paper, a silicon oxide based conductive bridging random access memory (CBRAM) with an ultra-low operation voltage, a high switching speed, and an ultra-low resistance at low resistance state (LRS) is reported. The CBRAM has a sandwich structure with platinum and copper as electrode layers and an ultra-thin 10-nm-thick silicon oxide film as an insulating switching layer. The CBRAMs are fabricated with CMOS compatible materials and processes. DC I–V sweep characterizations show an ultra-low SET/RESET voltage of 0.35 V/−0.05 V, and the RESET voltage is the lowest among all ultra-low voltage CBRAMs. The CBRAM is capable of withstanding endurance tests with over 106 pulses of +0.4 V/−0.1 V with 1 μs pulse width, with the resistance at LRS maintaining at an ultra-low value of only 20 Ω, which is the lowest among all CBRAMs to date, and it is reduced by at least 2.95 times compared with prior studies. Meanwhile, the switching ratio between high resistance state and LRS is more than 1.49 × 104. Moreover, the switching time characterization of the CBRAM demonstrates an ultra-short SET/RESET time of 7/9 ns. The CBRAM has potential applications in high-speed, ultra-low voltage, and ultra-low power electronics.

Engineering crystalline CoMP-decorated (M = Mn, Fe, Ni, Cu, Zn) amorphous CoM LDH for high-rate alkaline water splitting

Rational design of non-noble metal catalysts for alkaline electrochemical water splitting under large current densities is of great significance for realizing hydrogen economy and remains a daunting challenge. Herein, a series of crystalline CoMP-decorated (M = Mn, Fe, Ni, Cu, Zn) amorphous CoM LDH nanomaterials in-situ grown on nickel foam (denoted as c-CoMP/a-CoM LDH/NF) is developed as highly efficient and stable alkaline water splitting electrocatalysts. Crystalline CoMP encountered amorphous CoM LDH structure brings the increased catalytic active sites without sacrificing charge transfer rates, more optimal intermediate adsorption/dissociation capability, and the synergistic effects between binary transition metals, leading to more favorable reaction kinetics, thus enhancing catalytic performance for oxygen evolution reaction and hydrogen evolution reaction. As a result, the optimized cell assembled by the as-proposed electrocatalysts only requires ultralow cell voltages of 1.655 and 1.722 V to drive current densities of 100 and 500 mA cm−2 in 1.0 M KOH and exhibits excellent durability over 85 h (under 100 mA cm−2), which is originated from the well-retentive hybrid crystalline/amorphous nanostructure even after undergoing surface reconstruction. The presented work deepens the insights of crystalline/amorphous heterostructure catalysts and provides a new inspiration in the design of bifunctional electrocatalysts for high-rate alkaline water splitting.

2D/3D Heterojunction perovskite light-emitting diodes with tunable ultrapure blue emissions

High performance blue light-emitting diodes are indispensable for solid-state lighting and full-color displays. Recently, tremendous efforts have been dedicated to boost the performance for blue perovskite light-emitting diodes (PeLEDs). In this work, we construct an ingenious 2D/3D heterostructure perovskite by long-chain organic halide salt post-treatment in blue perovskites for the first time. Organic halide salt post-treatment can form a 2D capping layer on the original 3D perovskite surface, thus to passivate defects and improve exciton radiative recombination rate. As a result, 2D/3D PeLEDs with tunable blue emissions (465, 475, and 486 nm), ultra-low turn-on voltages (3.0, 2.7, and 2.7 V), high brightness (928, 6727, and 9242 cd m−2), and excellent EQEs (2.11%, 6.29%, and 8.57%) are demonstrated. Moreover, due to the high phase homogeneity, the optimized PeLEDs exhibit ultrapure blue emissions (FWHM < 15 nm), in which the PeLED (465 nm) achieve ≈ 98% coverage of the Rec. 2020 standard.

Single-Crystalline Thin-Film Memory Arrays of Molecular Ferroelectrics with Ultralow Operation Voltages

Though most of the recently developed molecular ferroelectrics (MFs) exhibit excellent ferroelectric properties, the practical applications are still impeded by the limited polarization axes, poor processing capability for a high-quality thin film, and the incompatibility with matured lithography techniques for microelectronics. Here, we successfully demonstrated MF-based single-crystalline microdevice arrays using a lithography-compatible, solution-processed strategy that can avoid the above-mentioned obstacles at one time, i.e., dewetting-assisted patterning crystallization strategy. As a protype, uniform and well-aligned single-crystalline thin-film arrays of multiaxial MF [3-oxoquinuclidinium]ClO4 ([3-O-Q]ClO4) are prepared. Owing to the well-aligned crystallographic orientation and polarization direction, the obtained single-crystalline nonvolatile memory (NVM) arrays can exhibit an ultralow operating voltage of ∼1.6 V and long endurance cycles of 106, which are superior to other organic NVM devices. This work implies a promising route to high-density single-crystalline memory arrays for data storage, especially for low-cost flexible electronics.

Defect-rich low-crystalline Rh metallene for efficient chlorine-free H2 production by hydrazine-assisted seawater splitting

Seawater splitting is considered as a promising way to replace water splitting for H2 production due to the enrichment of seawater resources. However, the development of this technology has been greatly hampered by the lack of efficient electrocatalysts and the detrimental effects of chlorine electrochemistry. Herein, we report a defect-rich low-crystalline Rh metallene (l-Rh metallene) with an amorphous/crystalline hetero-phase structure for seawater electrolysis, where chlorine generation is avoided by replacing the oxygen evolution reaction (OER) with the hydrazine oxidation reaction (HzOR). Benefiting from the large surface-to-volume ratio, abundant active sites and unique electronic structure, the l-Rh metallene exhibits out-standing catalytic activity for both hydrogen evolution reaction (HER, −38 mV at 10 mA cm−2) and HzOR (−2 mV at 10 mA cm−2). Notably, an ultra-low voltage of only 28 mV is required to achieve 10 mA cm−2 in two-electrode hydrazine-assisted seawater splitting system.

Heterogeneous interface engineering for boosting electron transfer induced by MOF-derived Yolk-shell trimetallic phosphide nanospindles for robust water oxidation electrocatalysis

The heterogeneous interface engineering of nanocatalysts has been proved as an efficient strategy to promote the oxygen evolution reaction (OER) catalytic performance. Different from the conventional hollow structures, the yolk-shell construction could defend the distortion and dissolution during OER for stability improvement. However, it is still a great challenging to simultaneously construct heterogeneous interface and yolk-shell structure based on electrocatalysts with well-tuned composition and structure. Herein, we developed a facile synthetic method to prepare the yolk-shell trimetallic phosphide catalysts by starting with MIL-88A nanospindles templates. Benefitting from heterogeneous interface with fast electron transfer, yolk-shell architecture with rich channels for mass transportation, and active metal doping with electron structure modulation, the obtained CoNiFeP yolk-shell nanospindles (YSNSs) catalysts displayed superior OER catalytic properties with the overpotential of only 261 mV to deliver a current density of 10 mA cm−2 in alkaline media. Furthermore, the yolk-shell architecture endowed CoNiFeP with remarkable OER stability for 60 h. By coupling CoNiFeP with Pt/C electrodes to drive overall water splitting, an ultralow cell voltage of 1.56 V is required. The experimental and mechanistic studies indicated the optimized binding energy of *OOHad and *OHad intermediates by constructing robust phosphide interface.

Energy-Saving Hydrogen Production by Seawater Electrolysis Coupling Sulfion Degradation.

Electrolysis of costless and infinite seawater is a promising way toward grid-scale hydrogen production without causing freshwater stress. Practical potential of this technology, however, is hindered by low energy efficiency and anode corrosion by the detrimental chlorine chemistry in seawater in addition to unaffordable electricity expense. Herein, energy-saving hydrogen production is reported by chlorine-free seawater splitting coupling sulfion oxidation. It yields hydrogen at a low cell voltage of 0.97V, cutting the electricity consumption to 2.32kWh per m3 H2 at 300mA cm-2 . Compared to alkaline water electrolysis, the energy expense is primarily saved by 60% with 50% lower energy equivalent input. Benefiting from the ultralow cell voltage, the hazardous chlorine chemistry is fully avoided without anode corrosion regardless of Cl- crossover. Meanwhile, it also allows fast degradation of S2- pollutant from the water body to value-added sulfur with 80% efficiency, for further reducing hydrogen cost and protection of the ecosystem. Connecting such a hybrid seawater electrolyzer to a commercial solar cell can harvest the hydrogen from seawater with better sustainability. This work may offer new opportunities for low-cost hydrogen production from the unlimited ocean resources with environmental protection.

Organic-Inorganic Hybrid Gate Dielectrics Using Self-Assembled Multilayers For Low-Voltage Operating Thin-Film Transistors

Advanced electronic materials have attracted great interest for their potential use in flexible, large-area, and printable electronic applications. However, fabricating high-performance low-voltage thin-film transistors (TFTs) for those applications with these advanced semiconductors is still challenging because of a lack of dielectric materials which satisfy both the required electrical and physical performance. In this work, we report self-assembled hybrid multilayer gate dielectrics prepared using a facile solution procedure to achieve organic semiconductor and amorphous oxide semiconductor-based thin-film transistors with ultralow operating voltage. These self-assembled hybrid multilayer gate dielectrics were constructed by iterative self-assembly of synthesized bifunctional phosphonic acid-based organic molecules and ultrathin high-k hafnium oxide layers. The novel self-assembled hybrid multilayer gate dielectrics exhibit excellent dielectric properties with exceptionally large capacitances (up to 815 nF/ cm2) and low-level leakage current densities of &lt; 1.56 × 10-6 A/cm2, featureless morphology (RMS roughness &lt; 0.24 nm), and thermal stability (up to 300 °C). Consequently, these hybrid gate dielectrics can be incorporated into thin-film transistors with pentacene as p-type organic semiconductors, and with indium oxide as n-type inorganic semiconductors. The resulting TFTs functioned at ultralow voltages (&lt; ± 2 V) and achieved high transistor performances (hole mobility: 0.88 cm2 / V·s, electron mobility: 7.8 cm2 / V·s and on/off current ratio &gt;104, and threshold voltage: ± 0.5 V).

Enhancing the Resistive Switching Performance in a Physically Transient Memristor by Doping MoS2 Quantum Dots

Resistive random-access memory has attracted tremendous attention and numerous investigations as a promising next-generation nonvolatile memory device to address the physical limits of flash memory. Particularly, physically transient resistive switching memory is intensively researched for its degradable and environmentally friendly characteristics. Zinc oxide ($\mathrm{Zn}\mathrm{O}$), as a low-cost biocompatible and biodegradable material, has been widely used in the dielectric layer, yet many previous studies on $\mathrm{Zn}\mathrm{O}$-based memory devices show unsatisfactory switching properties. In this work, ${\mathrm{Mo}\mathrm{S}}_{2}$ quantum dots (QDs) are added between the $\mathrm{W}$ bottom electrode and $\mathrm{Zn}\mathrm{O}$ insulator by spin coating ($\mathrm{W}/{\mathrm{Mo}\mathrm{S}}_{2}$ QD$/\mathrm{Zn}\mathrm{O}/\mathrm{Ag}$) to improve its resistive switching behavior. The modified device exhibits distinctly better properties, including more-uniform switching parameters (low- and high-resistance states, ${V}_{\mathrm{set}}$, ${V}_{\mathrm{reset}}$), ultralow threshold voltages, and steady retention. Moreover, we transfer the device onto polyvinyl alcohol substrate, making it fully degradable, and it is completely dissolved in phosphate-buffered solution after 40 min. These results indicate that the ${\mathrm{Mo}\mathrm{S}}_{2}$ QD--optimized transient resistive switching memory shows great potential in green electronics, implantable biomedical devices, and secure information-storage applications.

Interfacial electronic modulation on heterostructured NiSe@CoFe LDH nanoarrays for enhancing oxygen evolution reaction and water splitting by facilitating the deprotonation of OH to O

NiSe@CoFe LDH/NF heteroarrays show superior OER and overall water splitting performance owing to in-situ growth for strengthening the stability, and the heterointerfacial electronic modulation for facilitating the deprotonation of OH to O during OER process. • NiSe@CoFe LDH heteroarrays were constructed by selenization and electrodeposition. • Three-dimensional heterostructure enable more accessible active sites for OER. • Interfacial electronic modulation enable the facilitating deprotonation of OH to O. • NiSe@CoFe LDH heteroarrays exhibits superior OER and water splitting performance. Achieving low-cost and high-efficiency oxygen evolution reaction (OER) catalysts by interfacial engineering has attracted numerous attentions. Herein, the combination of selenization of Ni foam (NF) and successive electrodeposition growth of CoFe LDH was proposed to synthesize the three-dimensional heterostructure of NiSe nanowires and CoFe LDH nanosheets on NF (NiSe@CoFe LDH/NF) which can enable more accessible active sites, enhanced structural stability, and eliminate contact resistance for OER process. The optimal NiSe@CoFe LDH/NF possesses superior OER performance with ultralow overpotential of 203 and 236 mV to achieve 10 and 100 mA cm −2 , low Tafel slope of 90.3 mV dec −1 and robust stability in 1.0 M KOH electrolyte. Density functional theory (DFT) calculations unveil that the interfacial synergism on NiSe@CoFe LDH can induce electrons redistribution by charge transfer from CoFe LDH to NiSe, and reduce the energy barrier of deprotonation of OH to O as the rate-limiting step by the stronger chemical bond of Fe-O in OER, and thus significantly increase the intrinsic OER activity. Moreover, the two-electrode configuration based on NiSe@CoFe LDH/NF||Pt/C/NF couple for driving water splitting can achieve a current density of 300 mA cm −2 at an ultralow voltage of 1.69 V with super stability (100 h). This work provides deep insights into the roles of interfacial electronic modulation by fabrication the three-dimensional heterostructure to design high-efficiency electrocatalysts for OER.

Covalent Coupling of Porphyrins with Monolayer Graphene for Low-Voltage Synaptic Transistors.

Synaptic devices emulating biological synapses are a key building component of artificial neural networks. Porphyrins and graphene, as two kinds of emerging electronic materials, have attracted extensive attention in the research of photoelectric devices due to their excellent structural and functional properties. Herein, we present a photonic synaptic transistor based on porphyrin-graphene covalent hybrids utilizing 5,10,15,20-tetrakis (4-aminophenyl)-21H,23H-porphine and monolayer graphene linked through the diazo addition reaction. The photonic synaptic device successfully simulates several essential biological functions, and the synaptic plasticity can be regulated by adjusting the parameters of light spikes and gate voltages of the device. Moreover, learning and memory behaviors under different wavelengths are studied to imitate the learning efficiency of humans in diverse emotional states. It is worth noting that all the synaptic functions can be realized at a low operating voltage of -10 mV, which is much lower than that required by most reported photonic synaptic devices. These results indicate that covalent coupling products of porphyrins with graphene have broad prospects in the construction of synaptic transistors and may arouse new research advances in neuromorphic devices with ultralow operating voltage and low energy consumption.

Performance Benchmarking of TFET and FinFET Digital Circuits from a Synthesis-Based Perspective

Miniaturization and portable devices have reshaped the electronic device landscape, emphasizing the importance of high performance while maintaining energy efficiency to ensure long battery life. FinFET and Tunnel-FET technologies have emerged as attractive alternatives to overcome the limitations of supply voltage scaling for ultra-low power applications. This work compares the performance of 10 nm FinFET- and TFET-based digital circuits from basic logic gates up to an 8k gates low-power microprocessor. When compared with their FinFET-based counterparts, the TFET-based logic gates have lower leakage power when operated below 300 mV, show higher input capacitance, and exhibit a reduced propagation delay under different fan-in and fan-out conditions. Our comparative study was extended to the synthesis of an MSP-430 microprocessor through standard cell libraries built particularly for this work. It is demonstrated that the TFET-based synthesized circuits operating at ultra-low voltages achieve a higher performance in terms of speed at the cost of increased power consumption. When the speed requirements are relaxed, the TFET-based designs are the most energy-efficient alternative. It is concluded that the TFET is an optimal solution for ultra-low voltage design.

Interfacial Regulation of Electron‐enhanced Co2P−CuP2 Sheet‐like Heterostructure as a Robust Bifunctional Electrocatalyst for Overall Water Splitting and Zn−H2O Cell

AbstractConstructing the precious metal‐free bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is highly desirable for overall water splitting and energy conversion devices in an alkaline medium. Here, the interface regulation strategy aims to synthesize a sheet‐like Co2P−CuP2 heterostructure supported on nickel foam (NF) through hydrothermal reaction, electrodeposition and phosphating treatment. The Co2P−CuP2/NF exhibits extraordinary electrocatalytic performance with overpotentials of 220 mV and 93 mV for OER and HER at a current density of 10 mA cm−2, respectively. Remarkably, an electrolyzer cell originated from Co2P−CuP2/NF electrodes required an ultralow cell voltage of 1.77 V@500 mA cm−2 and 2.38 V@1000 mA cm−2 for overall water splitting with prominent stability of at least 160 h. In addition, the Zn−H2O cell is assembled with Co2P−CuP2/NF as the cathode, achieving a high power density of 19.8 mW cm−2 and long‐term stability of 120 h. The electron transfer between Co and Cu species in the Co2P−CuP2/NF heterojunction can effectively improve the interaction between the active sites and the intermediates, thereby enhancing the electrocatalytic activity. This work opens up new insights into the preparation of highly active and durable bimetallic phosphide catalysts for water splitting and Zn−H2O cells.

A Tree-Based Architecture for High-Performance Ultra-Low-Voltage Amplifiers

In this paper, we introduce a novel tree-based architecture which allows the implementation of Ultra-Low-Voltage (ULV) amplifiers. The architecture exploits a body-driven input stage to guarantee a rail-to-rail input common mode range and body-diode loading to avoid Miller compensation, thanks to the absence of high-impedance internal nodes. The tree-based structure improves the CMRR of the proposed amplifier with respect to the conventional OTA architectures and allows achievement of a reasonable CMRR even at supply voltages as low as 0.3 V and without tail current generators which cannot be used in ULV circuits. The bias currents and the static output voltages of all the stages implementing the architecture are accurately set through the gate terminals of biasing transistors in order to guarantee good robustness against PVT variations. The proposed architecture and the implementing stages are investigated from an analytical point of view and design equations for the main performance metrics are presented to provide insight into circuit behavior. A 0.3 V supply voltage, subthreshold, ultra-low-power (ULP) OTA, based on the proposed tree-based architecture, was designed in a commercial 130 nm CMOS process. Simulation results show a dc gain higher than 52 dB with a gain-bandwidth product of about 35 kHz and reasonable values of CMRR and PSRR, even at such low supply voltages and considering mismatches. The power consumption is as low as 21.89 nW and state-of-the-art small-signal and large-signal FoMs are achieved. Extensive parametric and Monte Carlo simulations show the robustness of the proposed circuit to PVT variations and mismatch. These results confirm that the proposed OTA is a good candidate to implement ULV, ULP, high performance analog building blocks for directly harvested IoT nodes.

A highly reversible, dendrite-free zinc metal anodes enabled by a dual-layered interface

Aqueous rechargeable zinc ion batteries (AZIBs) are gaining increasing interest owning to their merits of high safety, cost-effectiveness, environmental benignity, and high energy. However, the uncontrolled Zn dendrite growth, gas generation, and severe corrosion stemming from the side reactions between Zn metal anodes and aqueous electrolytes significantly restrict the practical application of AZIBs. Herein, an organic-inorganic dual protection layer (Nafion/Zn3(PO4)2, NFZP), which is featured with organic layer (Nafion) on the top and inorganic layer (Zn3(PO4)2) at the bottom, is built on the surface of Zn electrodes (NFZP@Zn). The dual-layered interface can not only suppress dendrite growth but also inhibit the side reactions. The decorated NFZP@Zn electrode can maintain an ultralong plating/stripping cycling life of 2800 h with an ultralow voltage hysteresis (45 mV) at a current density of 0.5 mA cm−2. When coupled with a MnO2 cathode, the full cells with NFZP@Zn anodes demonstrated significantly improved cycling stability. This work paves the road for the future development of AZIBs.

Partially oxidized ruthenium aerogel as highly active bifunctional electrocatalyst for overall water splitting in both alkaline and acidic media

In this study, a general strategy is demonstrated to prepare a partially oxidized three-dimensional (3D) porous ruthenium (Ru) aerogel with distinct porous architecture and unique Ru/RuO2 interface. The optimized partially oxidized Ru aerogel catalyst exhibits an exceptional HER performance, which is even superior to the benchmark Pt/C catalyst, and an outstanding OER efficiency that is better than commercial RuO2 in both alkaline and acidic solutions. Furthermore, a two-electrode configuration based on the partially oxidized Ru aerogel as both anode and cathode for the overall water splitting exhibits an ultra-low working voltage of 1.467 V in 1 M KOH and 1.468 V in 0.5 M H2SO4 at 10 mA cm−2 as well as a satisfactory long-term stability, outperforming the device composed of Pt/C||RuO2 catalysts. This research opens up a new avenue to develop highly efficient 3D porous aerogel electrocatalysts toward overall water splitting applications.

Fabrication of crystalline submicro-to-nano carbon wire for achieving high current density and ultrastable current

Crystalline carbon nanowire arrays were fabricated taking advantage of near-field electrospinning and stress decyanation. A novel fabrication method for carbon nanowires with radii ranging from ~2.15 µm down to ~25 nm was developed based on implementing nitrogen pretreatment on the silica surface and then aligning polymer nanofibers during near-field electrospinning at an ultralow voltage. Stress decyanation was implemented by subsequently pyrolyzing a polymer nanofiber array on the silica surface at 1000 °C for 1 h in an N2 atmosphere, thus obtaining a crystalline carbon nanowire array with a nanostructured surface. Various crystalline nanostructures were fabricated on the nanowire surface, and their electrochemical performance was evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Crystalline carbon wires with diameters ranging from micrometers to submicrometers displayed carbon nanoelectrode-like behavior with their CV curve having a sigmoidal shape. A highly crystalline carbon nanowire array showed distinct behavior, having a monotonically increasing straight line as its CV curve and a semicircular EIS spectrum; these results demonstrated its ultrastable current, as determined by electron transfer. Furthermore, nanocrystalline-structured carbon wires with diameters of ~305 nm displayed at least a fourfold higher peak current density during CV (4000 mA/m2) than highly crystalline carbon nanowires with diameters of ~100 nm and porous microwires with diameters of ~4.3 µm.