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Pt-supported carbon material-based electrocatalysts are formidably suffering from carbon corrosion when H2O and O2 molecules are present at high voltages in polymer electrolyte membrane fuel cells (PEMFCs). In this study, we discovered that the edge site of a fluorine-doped graphene nanoribbon (F-GNR) was slightly adsorbed with H2O and was thermodynamically unfavorable with O atoms after defining the thermodynamically stable structure of the F-GNR from DFT calculations. Based on computational predictions, the physicochemical and electrochemical properties of F-GNRs with/without Pt nanoparticles derived from a modified Hummer's method and the polyol process were investigated as support materials for electrocatalysts and additives in the cathode of a PEMFC, respectively. The Pt/F-GNR showed the lowest degradation rate in carbon corrosion and was effective in the cathode as additives, resulting from the enhanced carbon corrosion durability owing to the improved structural stability and water management. Notably, the F-GNR with highly stable carbon corrosion contributed to achieving a more durable PEMFC for long-term operation.

Seawater electrolysis is a promising technology for the production of hydrogen energy and seawater desalination. To produce hydrogen energy through seawater electrolysis, highly active electrocatalysts for the oxygen evolution reaction (OER) are required. Here, we report the development of a Ni-doped FeOOH anode for high-efficiency anion exchange membrane alkaline seawater electrolysis. The Ni-doped FeOOH anode showed an overpotential of only 301 mV in half-cell tests, reaching a current density of 100 mA cm−2 in 1.0 M KOH + seawater. An anion exchange membrane electrolyzer catalyzed by Ni-doped FeOOH exhibited a current density of 729 mA cm−2 in 1.0 M KOH + seawater with an energy conversion efficiency of 76.35%. Compared to the reported AEM electrolyzer operated in 1.0 M KOH, our AEM electrolyzer catalyzed with Ni-doped FeOOH operated in 1.0 M KOH + seawater exhibited higher performance.

Active and stable electrocatalysts are the key to water electrolysis for hydrogen production. This paper reports a facile direct growth method to synthesize NiFe-layered double hydroxides (LDHs) on nickel foil as an electrocatalyst for the oxygen evolution reaction. The NiFe-LDH is synthesized by a galvanic process at room temperature without any additional energy for synthesis. The synthesized NiFe-LDH is a karst landform with abundant active sites and efficient mass diffusion. The NiFe-LDH with an oxygen defect show excellent electrocatalytic performance for the OER, with a low overpotential (272 mV at 10 mA/cm2), a small Tafel slope (43 mV/dec), and superior durability. Direct growth synthesis provide excellent electrical conductivity as well as strong bonding between the catalyst layer and the substrate. In addition, this synthesis process is simple to apply in the fabrication of a large size electrode and is believed to be applicable to commercialized alkaline water electrolysis.

The low-temperature physical vapor deposition process of atomically thin two-dimensional transition metal dichalcogenide (2D TMD) has been gaining attention owing to the cost-effective production of diverse electrochemical catalysts for hydrogen evolution reaction (HER) applications. We, herein, propose a simple route toward the cost-effective physical vapor deposition process of 2D WSe2 layered nanofilms as HER electrochemical catalysts using RF magnetron sputtering at room temperature (

Uniquely nanostructured CuCo2O4 is presented as an electrocatalyst for oxygen evolution reactions (OER). CuCo2O4 particles in a chestnut-burr-like shape (CCO*, where ∗ = chestnut burr) were hydroth...

Co3S4 nanosheets on Ni foam (NS/NF) were prepared by sulfurization for various time after calcination of electrodeposited Co(OH)2. In our FE-SEM images, we observed that Co3S4 NS was vertically, or obliquely, deposited on the Ni foam. As a result, the structure contained more active sites, and active sites were highly accessible to the electrolyte for the hydrogen evolution reaction (HER). Furthermore, results of XPS and XRD analysis confirmed S-conversion from Co3O4 to Co3S4 during sulfurization. 3-Co3S4 NS/NF with sulfurization for 3 h exhibited the highest sulfur content, while Co3S4 began to desulfurize to Co9S8 after sulfurization for 4 h. The 3-Co3S4 NS/NF electrocatalyst showed a lowest overpotential of 93 mV at −10 mA/cm2, with a Tafel slope of −55.1 mV/dec in N2-purged 1 M KOH. Also, the single cell anion exchange membrane water electrolyzer (AEMWE) showed a high current density of 431 mA/cm2 with cell voltage 2.0 Vcell at 40–45 °C.

The application of electrocatalysts with high activity to a practical water electrolysis cell is a crucial challenge for the production of pure hydrogen and commercialization of the water electrolyzer. Herein, a nanosized Cu0.5Co2.5O4 catalyst synthesized by co-precipitation by adjusting pH is applied to the anion exchange membrane water electrolysis (AEMWE) cell as an anode, which is demonstrated to have higher efficiency and stability than noble metal-based anodes. The composition (Cu/Co) and morphology of Cu0.5Co2.5O4 change as the pH increases and then nanoparticles are formed at pH 11, where oxygen vacancies are formed by the etching of Cu. In the density functional theory study, the electronic structure of Co modified by Cu in the Co3O4 lattice leads to an optimal adsorption strength, resulting in a free energy diagram in which the potential of Cu0.5Co2.5O4 (1.756 V vs. reversible hydrogen electrode, RHE) is more thermodynamically favorable than that of Co3O4 (1.951 V vs. RHE). The Cu0.5Co2.5O4 catalyst has a recorded overpotential of 285 mV at 10 mA cm−2 in 1 M KOH. Furthermore, the AEMWE cell using Cu0.5Co2.5O4 as an anode exhibited a current density of 1.3 A cm−2 at 1.8 V, which is the highest performance among the reported papers and maintains around 80% energy conversion efficiency for 100 hours.

The selective and efficient electrocatalytic transformation of carbon dioxide (CO2) to multicarbon alcohols (e.g., C2H5OH and C3H7OH) is a challenge in renewable and sustainable energy research. Herein, a series of hybrid catalysts consisting of Cu nanoparticles supported on N-doped porous carbon (Cu/NPC) were prepared. It was demonstrated that the selectivity for C2H5OH or C3H7OH could be tuned by introducing N-doped porous carbon materials as cocatalysts with different pyridinic N contents, which could in situ produce a reactive CO intermediate from CO2. By varying the pyridinic N content, highly selective production of multicarbon alcohols was achieved using the Cu/NPC hybrid catalysts with a high faradaic efficiency for one pot production of multicarbon alcohols up to 73.3% at −1.05 V (vs. RHE). The faradaic efficiency for C2H5OH and C3H7OH was 64.6% and 8.7%, respectively. The pyridinic N species were likely the CO-producing sites and together with Cu catalytic sites acted cooperatively to produce C2H5OH and C3H7OH via a two-site mechanism for efficient CO2 reduction to multicarbon alcohols. These findings provide novel guidance for the rational design of electrocatalysts and for tuning the catalytic activity and selectivity for multicarbon alcohol production from CO2.

A Cu–Co–P electrocatalyst for hydrogen evolution reaction (HER) was designed with a dendritic and porous foam structure. Fabricated by one-step electrodeposition with binary alloy on a hydrogen bub...

Cobalt (Co)-incorporated MoS2 nanofibers were fabricated via a facile electrospinning method followed by sulfurization process. Co atoms in the molybdenum oxide nanofibers altered the morphology and crystal structure according to sulfurization time. The well-anchored Co-incorporated MoS2 sheets on the nanofiber surface acted as active edge sites for the hydrogen evolution reaction (HER), which exhibited high activity with an onset potential of approximately −170 mV vs NHE with a Tafel slope of 60 mV/dec. The overpotential was −330 mV vs NHE at 10 mA/cm2.

In this work, we show an effective strategy combining experimental and computational methods to explore and clarify rational design approaches utilizing transition metals for enhanced electrocatalysis of oxygen reactions. We report a bifunctional electrocatalyst synthesized by a chemical deposition of palladium (Pd) nanoparticles on three-dimensionally ordered mesoporous cobalt oxide (Pd@3DOM-Co3O4) demonstrating extreme stability and activity towards electrocatalytic oxygen reduction and evolution reactions (ORR and OER). Pd@3DOM-Co3O4 exhibits a significantly positive-shifted ORR half-wave potential of 0.88 V (vs. RHE) and a higher OER current density of 41.3 mA cm−2 measured at 2.0 V (vs. RHE) relative to non-deposited 3DOM-Co3O4. Moreover, in terms of durability, Pd@3DOM-Co3O4 demonstrates a negligible half-wave potential loss with 99.5% retention during ORR and a high current density retention of 96.4% during OER after 1000 cycles of accelerated degradation testing (ADT). Ab-initio computational simulation of the oxygen reactions reveals that the modification of the electronic structure by combining Pd and Co3O4 lowers the Pd d-band center and enhances the electron abundance at the Fermi level, resulting in improved kinetics and conductivity. Furthermore, it is elucidated that the enhanced electrochemical stability is attributed to an elevated carbon corrosion potential (Ucorr,C) for the Pd@3DOM-Co3O4 surface and an increased dissolution potential (Udiss) of Pd nanoparticles. Meanwhile, synergistic improvements in the bifunctional activity resulting from the combination of Pd and 3DOM-Co3O4 were confirmed by both electrochemical and physical characterization methods, which highlights the practical viability of Pd@3DOM-Co3O4 as an efficient bifunctional catalyst for rechargeable metal-air batteries.

Developing high-efficiency and low-cost oxygen-evolving electrodes in anion exchange membrane (AEM) water electrolysis technology is one of the major challenges. Herein, it is demonstrated that the surface corrosion of a conventional Ni foam electrode in the presence of Fe3+ and V3+ cations can transform it into an electrode with a high catalytic performance for oxygen evolution reaction (OER). The corroded electrode consists of a ternary NiFeV layered double hydroxide (LDH) nanosheet array supported on the Ni foam surface. This NiFeV LDH electrode achieves an OER current density of 100 mA cm-2 at an overpotential of 272 mV in 1 m KOH, outperforming the IrO2 catalyst by 180 mV. Density functional theory calculations reveal that the unique structure and the presence of vanadium in NiFeV LDH play a key role in achieving improved OER activity. When coupled with a commercial Pt/C cathode catalyst, the resulting AEM water electrolyzer achieves a cell current density as high as 2.1 A cm-2 at a voltage of only 1.8 Vcell in 1 m KOH, which is similar to the performance of the proton exchange membrane water electrolyzer obtained from the IrO2 and Pt/C catalysts pair.

Under acidic conditions, IrO2 exhibits high catalytic activity with respect to the oxygen evolution reaction (OER). However, the practical application of Ir-based catalysts is significantly limited owing to their high cost in addition to the scarcity of the metal. Therefore, it is necessary to improve the efficiency of the utilization of such catalysts. In this study, IrO2-coated Ti felt (IrO2/Ti) electrodes were prepared as high-efficiency catalysts for the OER under acidic conditions. By controlling the surface roughness of the Ti substrate via wet etching, the optimum Ti substrate surface area for application in the IrO2/Ti electrode was determined. Additionally, the IrO2 film that was electrodeposited on the 30 min etched Ti felt had a large surface area and a uniform morphology. Furthermore, there were no micro-cracks and the electrode obtained (IrO2/Ti-30) exhibited superior catalytic performance with respect to the OER, with a mass activity of 362.3 A gIr-1 at a potential of 2.0 V (vs. RHE) despite the low Ir loading (0.2 mg cm-2). Therefore, this proposed strategy for the development of IrO2/Ti electrodes with substrate surface control via wet etching has potential for application in the improvement of the efficiency of catalyst utilization with respect to the OER.

We prepare three-dimensional honeycomb-like Cu0.81Co2.19O4 nanosheet arrays supported by Ni foam via electrochemical codeposition of cobalt and copper hydroxides on Ni foam followed by thermal oxidation. The codeposition with Cu changes the morphology of the cobalt hydroxide deposit to form honeycomb-like nanostructures, significantly decreasing the onset potential for oxygen evolution. The Cu0.81Co2.19O4 anode displays an exceptionally low overpotential of 290 mV at a current density of 10 mA cm–2 in 1 M KOH, and an anion-exchange membrane water electrolysis cell employing the above anode achieves a current density of 100 mA cm–2 at 1.68 V in 0.1 M KOH.

Indium removal and recovery on a carbon electrode under a microbial fuel cell (MFC)-based oxidation/reduction reaction were examined using synthetic wastewater. More than 90% of In3+ ions were removed after continuous operation of the MFC for 14 days with an average current generation of ∼50 μA. During operation, indium particulates formed on the cathode carbon electrode. Scanning electron microscopy equipped with X-ray energy dispersive spectroscopy showed that they were composed of amorphous and crystalline indium hydroxides (In(OH)3 and In(OH)·H2O). When the current flow was reversed to drive the oxidation of the particles to recover the indium from indium hydroxides, a few indium oxide (In2O3) nanocrystals with a rectangular platelet shape formed on the electrode, while the majority of the amorphous and crystalline indium hydroxides re-dissolved into the aqueous environment. Overall, these results demonstrate a feasible route towards the MFC-based recovery of indium with the simultaneous generation of bioelectricity.

Ni-based electrocatalysts for replacement of precious metal electrocatalyst, the cathode materials of anion exchange membrane water electrolyzer (AEMWE), are seriously unstable and low activity at hydrogen production conditions. This study develops a high-performance, durable non-precious metal electrocatalyst for AEMWE, which show improved activity and durability. First, Ni/C was alloyed with Co and supported on carbon cloth coated with microporous carbon layer to improve the electrocatalytic activity of the hydrogen evolution reaction (HER) electrocatalyst; then, oxide (Ni/Co-O) was locally formed on the synthesized NiCo/C to increase its activity and durability. Specifically, this oxide increased the coverage of OH− ions, formed hydrogen spillover channels, and promoted the HER. Further, its improved electrochemical durability was attributed to the high bond dissociation energy of the metal oxide. The electrocatalyst was also evaluated as the cathode in single-cell (1-cell) and stack cell (5-cell) AEMWE systems to demonstrate that this superior performance would translate to the commercial scale.

Developing high-performance and low-cost oxygen-evolving electrodes is one of major challenges in electrochemical water splitting technology. We demonstrated that the aqueous-phase corrosion of a conventional Ni foam in the presence of exotic Fe3+ cations can directly transform it into an electrode with high catalytic activity and stability for oxygen evolution reaction (OER). The surface of the corroded electrode consisted of densely packed, small Ni0.75Fe2.25O4 nanoparticles with sizes less than 5 nm. This electrode required an overpotential of only 192 mV to reach an OER current density of 10 mA/cm2 in 1 M KOH, outperforming the state-of-the-art IrO2 catalyst by 73 mV. Density functional theory calculations revealed that the unique surface structure and iron composition of Ni0.75Fe2.25O4 nanoparticles play a key role in achieving an improved OER activity. When coupled with a Pt/C hydrogen-evolving catalyst, the resulting anion-exchange membrane (AEM) water electrolyzer achieved an overall water-splitting current density as high as 2.0 A/cm2 at a cell voltage of 1.9 V in 1 M KOH, which was 1.7 times that obtained from the IrO2 and Pt/C catalyst pair and also much greater than reported values from other AEM water electrolyzers. By revisiting and exploiting a traditional corrosion process, our work opens a simple, cost-effective, and scalable route to a high-performance OER electrode for efficient AEM water electrolysis.

Hexavalent chromium wastewater is produced in electroplating processes and the heavy metal industry, highlighting the need for an environmentally friendly treatment and the recovery of chromium. This study compared the performance of microbial fuel cells implemented with a proton exchange membrane (PEM-MFC) and a bipolar membrane (BPM-MFC) using hexavalent chromium from electroplating wastewater as the catholyte. The removal of hexavalent chromium and simultaneous bioelectricity generation were enhanced significantly using a BPM. On the other hand, in the PEM-MFC, the lower pH of the electroplating wastewater (pH 1.8) in the cathodic chamber decreased the anodic pH due to proton diffusion through the PEM, and inhibited the bioelectrochemical reaction. Scanning electron microscopy showed that the reduced chromium particles precipitated on the cathode carbon electrode during the MFC operation. The precipitate was identified as amorphous chromium oxide particles by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy.

A novel electrochemical nanofilm sensor for 1-hydroxypyrene (1-OHP) was developed based on a molecular imprinted TiO2 gel matrix, which was prepared with Ti(O-n-Bu)4 and 1-OHP using sol–gel technology. Cyclic voltammetry (CV) showed that guest binding on the non-imprinted sensor resulted in nearly the same current changes for all guest molecules, indicating non-specific binding onto the TiO2 gel matrix. In contrast, binding at the molecular imprinted sensor revealed that the selectivity for 1-OHP relative to structurally related guest molecules was estimated to be 1.8–6.7 times greater at 1 × 10−9 M, reflecting its specific adsorption and binding capacity for the template molecule.

A series of binary PtRu catalysts with different Pt:Ru atomic ratios in a range from 7:3 to 3:7 are synthesized on carbon support using the colloidal method; they are then used for electrooxidation of glycerol in acidic media. X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy analyses are used to investigate the particle size, size distribution, and structural and electronic properties of the prepared catalysts. The addition of Ru content to the Pt-based catalysts caused structural and electronic modifications over the PtRu alloy catalyst formation. The electrocatalytic activities of PtRu/C series catalysts are investigated by using the cyclic voltammetry technique. Among the prepared catalysts, the Pt5Ru5/C catalyst shows enhanced catalytic activity at least 40% higher than that of the Pt/C catalyst, with improved stability for glycerol electrooxidation; these improvements can be attributed to the structural and electronic modifications of the Pt catalysts. Using an electrocatalytic batch reactor, product analysis after the oxidation reaction is performed by high-performance liquid chromatography to determine and compare the reaction pathways on the Pt/C and PtRu/C catalysts. To understand different catalytic activities of glycerol oxidation on the PtRu alloy surfaces, density functional theory (DFT) calculations have been performed and discussed with the experimental results.

The production of hydrogen from water via solar energy conversion has attracted immense attention as a potential solution for addressing energy supply issues. We demonstrated a stable and efficient organic-inorganic hybrid photoelectrochemical (H-PEC) cell. Modifying the surface energy and structure of the organic photoactive layer using multi-functional nanomaterials including –OH-modified NiO nanoparticles and reduced graphene oxide (RGO) led to a 2.8-fold enhancement of the water splitting performance in a single junction H-PEC cell. The enhanced performance was attributed to the i) improved water-wettability, ii) enhanced charge extraction property by band-edge alignment, and iii) the catalytic effect of the introduced NiO-OH nanoparticles. In addition, because of the effects of the RGO layer preventing water penetration and photo-corrosion during the oxidation of water, a distinguishable long-term stability was achieved from the H-PEC cell with an RGO capping layer. The best performance was obtained from the organic-inorganic hybrid multi-junction PEC cells consisting of the WO 3 photo-anode (activated under UV irradiation) and the H-PEC cell (activated under visible light irradiation). The H-PEC cell with a WO 3 photo-anode exhibited significantly enhanced stability and performance by a factor of 11.6 higher than photocurrent of the single H-PEC cell.

The fermi-level pinning phenomenon, which occurs at the metal&ndash, semiconductor interface, not only obstructs the achievement of high-performance field effect transistors (FETs) but also results in poor long-term stability. This paper reports on the improvement in gate-bias stress stability in two-dimensional (2D) transition metal dichalcogenide (TMD) FETs with a titanium dioxide (TiO2) interfacial layer inserted between the 2D TMDs (MoS2 or WS2) and metal electrodes. Compared to the control MoS2, the device without the TiO2 layer, the TiO2 interfacial layer deposited on 2D TMDs could lead to more effective carrier modulation by simply changing the contact metal, thereby improving the performance of the Schottky-barrier-modulated FET device. The TiO2 layer could also suppress the Fermi-level pinning phenomenon usually fixed to the metal&ndash, semiconductor interface, resulting in an improvement in transistor performance. Especially, the introduction of the TiO2 layer contributed to achieving stable device performance. Threshold voltage variation of MoS2 and WS2 FETs with the TiO2 interfacial layer was ~2 V and ~3.6 V, respectively. The theoretical result of the density function theory validated that mid-gap energy states created within the bandgap of 2D MoS2 can cause a doping effect. The simple approach of introducing a thin interfacial oxide layer offers a promising way toward the implementation of high-performance 2D TMD-based logic circuits.

The immobilization of Cyt. c (cytochrome c) on C60 (fullerene) nanohybrid TiO2 (titanium dioxide) gel films assembled with C60, Ti(O–nBu)4 and Cyt. c was realized by a surface sol–gel process. Interestingly, C60 was used without any surface modification of the film formation and exhibited good electrochemical performance. Additionally, the surface morphologies of the TiO2 and TiO2/C60 nanocomposite thin films showed remarkable uniformity over a wide area, however, the surface morphology depends on the deposition of Cyt. c, which densely covers the surface with adsorbed Cyt. c molecules. The cyclic voltammetry of the outer-most fullerene films revealed high stability, as well as, a pair of current peaks characteristic of a weak redox system with anodic and cathodic peak potentials at 0.262 V and 0.137 V. The electrochemical properties of thin films can be attributed to the redox system of the C60 layer deposited on the TiO2 gel layer. A pair of well-defined quasi-reversible redox peaks generated by Cyt. c are easily achieved because of the efficient assembly on the C60-modified electrode. In this work, we suggest the efficient introduction of C60 into a TiO2 gel matrix, evaluating the electrochemical characteristics of Cyt. c assembly.

The oxygen reduction reaction, ORR, performances of graphene-supported palladium (Pd) and palladium alloys (Pd3X: X = Ag, Co and Fe) catalysts with highly dispersed catalyst particles are investigated in acidic and alkaline conditions using a rotating disk electrode, RDE. Graphene nanosheet, GNS, supported Pd based catalysts are fabricated without surfactant through the impregnation of Pd and 2nd metal precursors on GNS, leading to small and uniformly dispersed nanoparticles, even when high metal loading of up to 60 wt.% are deposited on supports. The ab-initio density functional theory, DFT, calculations, which are based on the d-band center theory, have been applied to correlate with the results of the ORR performances obtained by half-cell tests. Additionally, the cohesive energy, Ecoh, and dissolution potential, Um, for the Pd nanoparticles have been calculated to understand thermodynamic stability. To elucidate the d-band center shift, the Pd 3d5/2 core-level binding energies for Pd/GNS, Pd3Ag/GNS, Pd3Fe/GNS and Pd3Co/GNS have been investigated by X-ray photoelectron spectroscopy, XPS. The GNS-supported Pd, or Pd-based alloy-nanoparticle catalyst shows good ORR activity under acidic and alkaline conditions, suggesting it may offer potential replacement for Pt for use in cathode electrodes of anion-exchange membrane fuel cell, AEMFC, and acid based polymer electrolyte fuel cell, PEMFC.

In this report, we demonstrated a reliable switching effect of carbon nanotube (CNT) field-effect transistor (FET) devices integrated with 99% semiconducting CNT as a channel and high-k oxide as the dielectric. CNT FET devices with high-k oxides of Al-ZrHfO2 and Al2O3 were electrically characterized and compared. There was no considerable hysteresis in the Al2O3-based CNT FET device. The Al-ZrHfO2 with a tetragonal phase-based high dielectric constant (~47), designed by an atomic layer deposition process, showed a reliable switching effect as well as low operation voltage (2 was proposed as a primary mechanism to explain a current change of a counterclockwise direction and threshold voltage (Vth) shift for transfer properties. The suggested charge trapping model within bulk oxide was experimentally proven since the hysteresis from the adsorption/desorption of gas molecules to CNT surface was negligible. Endurance characteristics of the CNT switching devices remained stable without any serious current fluctuation during a repetitive cycling test. The memory device with reliable switching properties as well as low operation power would pave a road toward next-generation memory components of portable electronic gadgets.

The long-term stability and superior device reliability through the use of delicately designed metal contacts with two-dimensional (2D) atomic-scale semiconductors are considered one of the critical issues related to practical 2D-based electronic components. Here, we investigate the origin of the improved contact properties of alloyed 2D metal-semiconductor heterojunctions. 2D WSe2-based transistors with mixed transition layers containing van der Waals (M-vdW, NbSe2/WxNb1-xSe2/WSe2) junctions realize atomically sharp interfaces, exhibiting long hot-carrier lifetimes of approximately 75,296 s (78 times longer than that of metal-semiconductor, Pd/WSe2 junctions). Such dramatic lifetime enhancement in M-vdW-junctioned devices is attributed to the synergistic effects arising from the significant reduction in the number of defects and the Schottky barrier lowering at the interface. Formation of a controllable mixed-composition alloyed layer on the 2D active channel would be a breakthrough approach to maximize the electrical reliability of 2D nanomaterial-based electronic applications.

Heterostructures of compositionally and electronically variant two-dimensional (2D) atomic layers are viable building blocks for ultrathin optoelectronic devices. We show that the composition of interfacial transition region between semiconducting WSe2 atomic layer channels and metallic NbSe2 contact layers can be engineered through interfacial doping with Nb atoms. WxNb1–xSe2 interfacial regions considerably lower the potential barrier height of the junction, significantly improving the performance of the corresponding WSe2-based field-effect transistor devices. The creation of such alloyed 2D junctions between dissimilar atomic layer domains could be the most important factor in controlling the electronic properties of 2D junctions and the design and fabrication of 2D atomic layer devices.

Oxygen evolution reaction (OER) plays a vital role in many energy conversion and storage processes including electrochemical water splitting for the production of hydrogen and carbon dioxide reduction to value-added chemicals. IrO2 and RuO2 , known as the state-of-the-art OER electrocatalysts, are severely limited by the high cost and low earth abundance of these noble metals. Developing noble-metal-free OER electrocatalysts with high performance has been in great demand. In this review, recent advances in the design and synthesis of noble-metal-free OER electrocatalysts including Ni, Co, Fe, Mn-based hydroxides/oxyhydroxides, oxides, chalcogenides, nitrides, phosphides, and metal-free compounds in alkaline, neutral as well as acidic electrolytes are summarized. Perspectives are also provided on the fabrication, evaluation of OER electrocatalysts and correlations between the structures of the electrocatalysts and their OER activities.

Perpendicularly attached MoS2 nanosheets on MoO2 conductive nanofibers were synthesized by combining electrospinning, calcination, and sulfurization processes. Compared to randomly stacked MoS2 nanosheets on MoO2 nanofiber, they show greater hydrogen evolution reaction (HER) performance (i.e., onset potential of -180 mV versus normal hydrogen electrode with the Tafel slope of 59 mV dec-1). HER performance decreases with increasing MoS2 nanocrystal size.