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The availability of accurate and reliable dry sensors for electroencephalography (EEG) is vital to enable large-scale deployment of brain–machine interfaces (BMIs). However, dry sensors invariably show poorer performance compared to the gold standard Ag/AgCl wet sensors. The loss of performance with dry sensors is even more evident when monitoring the signal from hairy and curved areas of the scalp, requiring the use of bulky and uncomfortable acicular sensors. This work demonstrates three-dimensional micropatterned sensors based on a subnanometer-thick epitaxial graphene for detecting the EEG signal from the challenging occipital region of the scalp. The occipital region, corresponding to the visual cortex of the brain, is key to the implementation of BMIs based on the common steady-state visually evoked potential paradigm. The patterned epitaxial graphene sensors show efficient on-skin contact with low impedance and can achieve comparable signal-to-noise ratios against wet sensors. Using these sensors, we have also demonstrated hands-free communication with a quadruped robot through brain activity. [ABSTRACT FROM AUTHOR]

Detection and monitoring of neural signals is a fast-advancing area of research expected to impact a broad range of advanced applications, from healthcare to brain–machine and even brain-to-brain communications. Two-dimensional (2D) layered materials, such as graphene, MXenes, and transition metal dichalcogenides, could lead to the development of superior and ultrathin thin-film electrodes for neural interfaces thanks to their atomic thickness, high-conductivity properties, and potential to combine additional functionalities. This review focuses on the recent advancement of 2D materials-based thin-film sensors for monitoring of bio-physiological signals using invasive and noninvasive approaches. [ABSTRACT FROM AUTHOR]

A free-standing, 3D, macro/microstructured atomic-cobalt/cobalt-oxide-reduced-graphene-oxide (Co/Co3O4-Gr) composite has been developed for complete water splitting. The self-assembled porous morphology associated with the metal/metal oxide active sites makes the whole surface of the electrode conducive toward catalyzing hydrogen and oxygen evolution in alkaline media at a low onset potential. The liquid-crystal-mediated free-standing electrocatalyst shows oxygen evolution at the onset potential of 1.38 V and at the potential of 1.66 V for a current density of 10 mA cm−2. These potentials are comparable to the corresponding values for Ru/C (1.46 and 1.62 V, respectively). In addition, the promising hydrogen evolution performance of our composite compared to Pt/C in alkaline media makes it an efficient bifunctional electrocatalyst for comprehensive water splitting, as well as provides guidance for future electrochemical energy material technologies. [ABSTRACT FROM AUTHOR]

Tailoring the planar morphology of graphene and the generation of electron-dense active sites on its surface by heteroatom doping is one potential approach to enhance the charge storage performance of graphene based electrode materials. Herein, we have reported the preparation of a three-dimensional self-standing cellular architecture as sulfur-doped graphene foam (SGF) by using the simple self-assembly of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) polymer chains on graphene oxide followed by thermal treatment. Successful homogeneous sulfur doping in a three-dimensional (3D) framework of graphene allowed the material to have a large surface area with bulk electroactive regions on the surface for better interfacial contact with electrolyte ions and hence resulted in unprecedented energy storage capability in a flexible aqueous symmetric supercapacitor (367 F g−1 at 1 A g−1), a lithium ion battery (1697 mA h g−1 at 100 mA g−1), and a sodium ion battery (472 mA h g−1 at 50 mA g−1) as a binder-free electrode material. The outstanding electrochemical performance of the material demonstrates the potential of this synthesis approach for various heteroatom-doped self-standing nano-carbon monoliths on a small as well as a large scale for high-performance energy device fabrication for the advancement of modern electronic devices. [ABSTRACT FROM AUTHOR]

A new cost-effective amperometric proton selective sensor utilizing a single microhole interface between two immiscible electrolyte solutions (ITIES) is developed. The sensing methodology is based on measuring currents associated with proton transfer across the interface assisted by a proton selective ionophore. The ellipse shaped micro-interface was first fabricated by simple mechanical punching with a sharp needle on a thin PVC film (12 μm thick) commercially available as a food wrapping material. The microhole was then filled up with a gellified polyvinylchloride (PVC)-2-nitrophenyloctylether (NPOE) to create a single microhole liquid/liquid interface. Direct ion transfer reactions across the polarized interface serving as ion sensing platforms were studied using cyclic voltammetry. In order to enhance the selectivity of proton sensing, a proton selective ionophore, octadecyl isonicotinate (ETH1778), was incorporated into the organic gel layer and their electrochemical sensing characteristics were investigated using cyclic voltammetry and differential pulse stripping voltammetry. As an example, we employed the proton selective sensor for the determination of glucose concentrations. The detection scheme involves two steps: (i) protons are first generated by the oxidation of glucose with glucose oxidase in the aqueous phase; and (ii) the current associated with the proton transfer across the interface is then measured for correlating the concentration of glucose. [ABSTRACT FROM AUTHOR]

A facile synthesis of three-dimensional (3D) network of copper confined nitrogen-doped graphene (NG)/carbon nanotube (CNT) with high atomic percentage of nitrogen (10.1 at.%) has been reported. The homogenous intercalation of the CNT network in-between the graphene layers decorated with copper nanoparticles take place which inhibits the self-agglomeration within the lattice and enhance the volumetric storage capability. The composite electrode demonstrates exceptionally high specific capacitance of 1250 mA h/g obtained at a current density of 0.1 A/g which is 3.4 times greater than the theoretical capacity of graphite (372 mA h/g). The discharge-charge profiles (from 0.002 to 3 V) with reversible battery capacity exhibit a stable state of the lithium-ion batteries which were observed at high rate capability of 420 mA h/g at a current density of 1 A/g even after 500 cycles. The enhancement of the electrochemical performance could be attributed to the 3D electrically conductive networks of copper confined nitrogen-doped graphene/carbon nanotubes (Cu@ N -Gr/CNT]). • 3-dimensional nanostructured copper confined nitrogen-doped graphene/carbon nanotube. • Contains high nitrogen content of 10.1 atomic wt.%. • Investigated as anode for lithium ion battery. • Specific capacitance of 1250 mA h/g at a current density of 0.1 A/g. • High rate capacitance of 420 mA h/g at a current density of 1 A/g after 500 cycles. [ABSTRACT FROM AUTHOR]

Objective . Brain-machine interfaces are key components for the development of hands-free, brain-controlled devices. Electroencephalogram (EEG) electrodes are particularly attractive for harvesting the neural signals in a non-invasive fashion. Approach. Here, we explore the use of epitaxial graphene (EG) grown on silicon carbide on silicon for detecting the EEG signals with high sensitivity. Main results and significance. This dry and non-invasive approach exhibits a markedly improved skin contact impedance when benchmarked to commercial dry electrodes, as well as superior robustness, allowing prolonged and repeated use also in a highly saline environment. In addition, we report the newly observed phenomenon of surface conditioning of the EG electrodes. The prolonged contact of the EG with the skin electrolytes functionalize the grain boundaries of the graphene, leading to the formation of a thin surface film of water through physisorption and consequently reducing its contact impedance more than three-fold. This effect is primed in highly saline environments, and could be also further tailored as pre-conditioning to enhance the performance and reliability of the EG sensors., (Creative Commons Attribution license.)

A novel flexible three-dimensional (3D) architecture of nitrogen and sulfur codoped graphene has been successfully synthesized via thermal treatment of a liquid crystalline graphene oxide-doping agent composition, followed by a soft self-assembly approach. The high temperature process turns the layer-by-layer assembly into a high surface area macro- and nanoporous free-standing material with different atomic configurations of graphene. The interconnected 3D network exhibits excellent charge capacitive performance of 305 F g(-1) (at 100 mV s(-1)), an unprecedented volumetric capacitance of 188 F cm(-3) (at 1 A g(-1)), and outstanding energy density of 28.44 Wh kg(-1) as well as cycle life of 10 000 cycles as a free-standing electrode for an aqueous electrolyte, symmetric supercapacitor device. Moreover, the resulting nitrogen/sulfur doped graphene architecture shows good electrocatalytic performance, long durability, and high selectivity when they are used as metal-free catalyst for the oxygen reduction reaction. This study demonstrates an efficient approach for the development of multifunctional as well as flexible 3D architectures for a series of heteroatom-doped graphene frameworks for modern energy storage as well as energy source applications.