Photoemission, from core levels and valence band, and low-energy electron diffraction (LEED) have been employed to investigate the electronic and structural properties of novel graphene-ferromagnetic (G-FM) systems,\ud obtained by intercalation of one mono-layer (1ML) and several layers (4ML) of Co on G grown on Ir(111).\ud Upon intercalation of 1ML of Co, the Co lattice is resized to match the Ir-Ir lattice parameter, resulting in a\ud mismatched G/Co/Ir(111) system. The intercalation of further Co layers leads to a relaxation of the Co lattice\ud and a progressive formation of a commensurate G layer lying on top. We show the C 1s line shape and the band\ud structure of G in the two artificial phases, mismatched and commensurate G/Co, through a comparison with the\ud electronic structure of G grown directly on a Co thick film. Our results show that while the G valence band\ud mainly reflects the hybridization with the d states of Co, regardless of the structural phase, the C 1s line shape\ud is very sensitive to the rumpling of the G layer and the coordination of carbon atoms with the underlying Co.\ud Even in the commensurate (1x1) G/Co phase, where graphene is in register with the Co film, from the angular\ud dependence of the C 1s core level we infer the presence of a double component, due to in-equivalent adsorption\ud sites of carbon sub-lattices

Engineering of highly performing nanomaterials, capable of rapid detection of trace concentrations of gas molecules at room temperature, is key to the development of the next generation of miniaturized chemical sensors. Here, a highly performing nanoheterojunctions layout is presented for the rapid room‐temperature chemical sensing of volatile organic compounds down to ten particles per billion concentrations. The layout consists of a 3D network of nickel oxide–zinc oxide (NiO–ZnO) p–n semiconductors with grain size of ≈20 nm nanometers and a porosity of ≈98%. Notably, it is observed that the formation of the p–n heterojunctions by decoration of a ZnO nanoparticle networks with NiO increases the sensor response by more than four times while improving the lower limit of detection. Under solar light irradiation, the optimal NiO–ZnO nanoheterojunction networks demonstrate a strong and selective room‐temperature response to two important volatile organic compounds utilized for breath analysis, namely acetone and ethanol. Furthermore, these NiO–ZnO nanoheterojunctions show an inverse response to acetone from that observed for all others reducing gas molecules (i.e., ethanol, propane, and ethylbenzene). It is believed that these novel insights of the optoelectrochemical properties of ultraporous nanoheterojunction networks provide guidelines for the future design of low‐power solid‐state chemical sensors.

Here, we show 3D nanoarchitectures comprising integrated GO–ZnO heterojunctions for either room temperature sensing of ppb volatile biomarkers or response to UV light, showcasing their applicability as chemoresistors and visible-blind photodetectors.

The lithium−sulfur (Li−S) system is a promising material for the nextgeneration of high energy density batteries with application extending from electrical vehicles to portable devices and aeronautics. Despite progress, the energy density of current Li−S technologies is still below that of conventional intercalation-type cathode materials due to limited stability and utilization efficiency at high sulfur loading. Here, we present a conducting polymer hydrogel integrated highly performing free-standing three-dimensional (3D) monolithic electrode architecture for Li−S batteries with superior electrochemical stability and energy density. The electrode layout consists of a highly conductive three-dimensional network of N,P codoped carbon with welldispersed metal−organic framework nanodomains of ZIF-67 and HKUST-1. The hierarchical monolithic 3D carbon networks provide an excellent environment for charge and electrolyte transport as well as mechanical and chemical stability. The electrically integrated MOF nanodomains significantly enhance the sulfur loading and retention capabilities by inhibiting the release of lithium polysulfide specificities as well as improving the charge transfer efficiency at the electrolyte interface. Our optimal 3D carbon-HKUST-1 electrode architecture achieves a very high areal capacity of >16 mAh cm −2 and volumetric capacity (C V ) of 1230.8 mAh cm −3 with capacity retention of 82% at 0.2C for over 300 cycles, providing an attractive candidate material for future high-energy density Li−S batteries.

The understanding of recombination of photogenerated electron/hole pairs at defect sites is a key enabler to develop bismuth vanadate (BiVO 4 ) photoanodes at scale and low cost for photoelectrochemical water splitting. Here, we report a systematic investigation of the impact of vanadium vacancies on the efficiency of BiVO 4 photoanodes for water photooxidation. X-ray photoelectron and photoluminescence spectroscopies reveal that the surfaces of nanostructured BiVO 4 photoanodes obtained by high-temperature synthesis, here used as the model system, suffer from vanadium deficiency and display an increased recombination rate of photoexcited electron/hole pairs. Our simulation indicates that these vanadium vacancies (V V ) create a new sub-band gap level in the proximity of the Fermi level of BiVO 4 . These levels act as recombination centers, explaining the subpar onset potentials and photocurrent densities for water photooxidation observed with these vanadium-deficient BiVO 4 photoanodes. We show that once the V V are eliminated, by a facile post-treatment of the BiVO 4 photoanodes, the photoluminescence lifetimes of the photogenerated carriers are significantly prolonged and the number of catalytically accessible sites is increased. As a result, the photocurrent during water oxidation is increased twofold, achieving 2 mA cm −2 against the standard hydrogen electrode in a 1 M potassium borate buffer electrolyte. These findings provide insights into the critical role played by the vanadium vacancies on the optoelectronic properties of BiVO 4 and a scalable approach for its effective fabrication on large-scale surfaces.

Scaling graphene from a two-dimensional (2D) ideal structure to a three-dimensional (3D) millimeter-sized architecture without compromising its remarkable electrical, optical, and thermal properties is currently a great challenge to overcome the limitations of integrating single graphene flakes into 3D devices. Herewith, highly connected and continuous nanoporous graphene (NPG) samples, with electronic and vibrational properties very similar to those of suspended graphene layers, are presented. We pinpoint the hallmarks of 2D ideal graphene scaled in these 3D porous architectures by combining the state-of-the-art spectromicroscopy and imaging techniques. The connected and bicontinuous topology, without frayed borders and edges and with low density of crystalline defects, has been unveiled via helium ion, Raman, and transmission electron microscopies down to the atomic scale. Most importantly, nanoscanning photoemission unravels a 3D NPG structure with preserved 2D electronic density of states (Dirac cone like) throughout the porous sample. Furthermore, the high spatial resolution brings to light the interrelationship between the topology and the morphology in the wrinkled and highly bent regions, where distorted sp 2 C bonds, associated with sp 3 -like hybridization state, induce small energy gaps. This highly connected graphene structure with a 3D skeleton overcomes the limitations of small-sized individual graphene sheets and opens a new route for a plethora of applications of the 2D graphene properties in 3D devices.

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The development of high-performing sensing materials, able to detect ppb-trace concentrations of volatile organic compounds (VOCs) at low temperatures, is required for the development of next-generation miniaturized wireless sensors. Here, we present the engineering of selective room-temperature (RT) chemical sensors, comprising highly porous tin dioxide (SnO 2 )–graphene oxide (GO) nanoheterojunction layouts. The optoelectronic and chemical properties of these highly porous (>90%) p–n heterojunctions were systematically investigated in terms of composition and morphologies. Optimized SnO 2 –GO layouts demonstrate significant potential as both visible–blind photodetectors and selective RT chemical sensors. Notably, a low GO content results in an excellent UV light responsivity (400 A W –1 ), with short rise and decay times, and RT high chemical sensitivity with selective detection of VOCs such as ethanol down to 100 ppb. In contrast, a high concentration of GO drastically decreases the RT response to ethanol and results in good selectivity to ethylbenzene. The feasibility of tuning the chemical selectivity of sensor response by engineering the relative amount of GO and SnO 2 is a promising feature that may guide the future development of miniaturized solid-state gas sensors. Furthermore, the excellent optoelectronic properties of these SnO 2 –GO nanoheterojunctions may find applications in various other areas such as optoelectronic devices and (photo)electrocatalysis.