Memristive Devices with Highly Repeatable Analog States Boosted by Graphene Quantum Dots

Memristive devices, having a huge potential as artificial synapses for low‐power neural networks, have received tremendous attention recently. Despite great achievements in demonstration of plasticity and learning functions, little progress has been made in the repeatable analog resistance states of memristive devices, which is, however, crucial for achieving controllable synaptic behavior. The controllable behavior of synapse is highly desired in building neural networks as it helps reduce training epochs and diminish error probability. Fundamentally, the poor repeatability of analog resistance states is closely associated with the random formation of conductive filaments, which consists of oxygen vacancies. In this work, graphene quantum dots (GQDs) are introduced into memristive devices. By virtue of the abundant oxygen anions released from GQDs, the GQDs can serve as nano oxygen‐reservoirs and enhance the localization of filament formation. As a result, analog resistance states with highly tight distribution are achieved with nearly 85% reduction in variations. In addition the insertion of GQDs can alter the energy band alignment and boost the tunneling current, which leads to significant reduction in both switching voltages and their distribution variations. This work may pave the way for achieving artificial neural networks with accurate and efficient learning capability.     

Incorporating Nitrogen‐Doped Graphene Quantum Dots and Ni3S2 Nanosheets: A Synergistic Electrocatalyst with Highly Enhanced Activity for Overall Water Splitting

A noble‐metal‐free electrocatalyst is fabricated via in situ formation of nanocomposite of nitrogen‐doped graphene quantum dots (NGQDs) and Ni₃S₂ nanosheets on the Ni foam (Ni₃S₂‐NGQDs/NF). The resultant Ni₃S₂‐NGQDs/NF can serve as an active, binder‐free, and self‐supported catalytic electrode for direct water splitting, which delivers a current density of 10 mA cm^?2 at an overpotential of 216 mV for oxygen evolution reaction and 218 mV for hydrogen evolution reaction in alkaline media. This bifunctional electrocatalyst enables the construction of an alkali electrolyzer with a low cell voltage of 1.58 V versus reversible hydrogen electrode (RHE) at 10 mA cm^?2. The experimental results and theoretical calculations demonstrate that the synergistic effects of the constructed active interfaces are the key factor for excellent performance. The nanocomposite of NGQDs and Ni₃S₂ nanosheets can be promising water splitting electrocatalyst for large‐scale hydrogen generation or other energy storage and conversion applications.     

Graphene Oxide Quantum Dots Exfoliated From Carbon Fibers by Microwave Irradiation: Two Photoluminescence Centers and Self‐Assembly Behavior

Graphene oxide quantum dots (GOQDs) attract great attention for their unique properties and promising application potential. The difficulty in the formation of a confined structure, and the numerous and diverse oxygen‐containing functional groups results in a low emission yield to GOQDs. Here, GOQDs with a size of about 5 nm, exfoliated from carbon fibers by microwave irradiation, are detected and analyzed. The exfoliated GOQDs are deeply oxidized and induce large numbers of epoxy groups and ether bonds, but only a small amount of carbonyl groups and hydroxyl groups. The subdomains of sp² clusters, involving epoxy groups and ether bonds, are responsible for the two strong photoluminescence emissions of GOQDs under different excitation wavelengths. Moreover, GOQDs tend to self‐assemble at the edges of their planes to form self‐assembly films (SAFs) with the evaporation of water. SAFs can further assemble into different 3D patterns with unique microstructures such as sponge bulk, sponge ball, microsheet, sisal, and schistose coral, which are what applications such as supercapacitors, cells, catalysts, and electrochemical sensors need. This method for preparation of GOQDs is easy, quick, and environmentally friendly, and this work may open up new research interests about GOQDs.