An Overview of Metal-Organic Framework Based Electrocatalysts: Design and Synthesis for Electrochemical Hydrogen Evolution, Oxygen Evolution, and Carbon Dioxide Reduction Reactions.

Due to the increasing global energy demands, scarce fossil fuel supplies, and environmental issues, the pursued goals of energy technologies are being sustainable, more efficient, accessible, and produce near zero greenhouse gas emissions. Electrochemical water splitting is considered as a highly viable and eco-friendly energy technology. Further, electrochemical carbon dioxide (CO2 ) reduction reaction (CO2 RR) is a cleaner strategy for CO2 utilization and conversion to stable energy (fuels). One of the critical issues in these cleaner technologies is the development of efficient and economical electrocatalyst. Among various materials, metal-organic frameworks (MOFs) are becoming increasingly popular because of their structural tunability, such as pre- and post- synthetic modifications, flexibility in ligand design and its functional groups, and incorporation of different metal nodes, that allows for the design of suitable MOFs with desired quality required for each process. In this review, the design of MOF was discussed for specific process together with different synthetic methods and their effects on the MOF properties. The MOFs as electrocatalysts were highlighted with their performances from the aspects of hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and electrochemical CO2 RR. Finally, the challenges and opportunities in this field are discussed.

Preparation of Bi/BiOBr sensitized titania nanorod arrays via a one-pot solvothermal method and construction of kanamycin photoelectrochemical aptasensors.

In this work, a photoelectrochemical (PEC) aptasensor for detecting kanamycin (KAN) was designed based on an aptamer modified Bi/BiOBr/titania nanorod array (TiO2 NRA). Bi/BiOBr was loaded onto the TiO2 NRA via a one-pot solvothermal method using glucose as a reductant. The p-n heterojunction structure constructed from chrysanthemums like BiOBr and the TiO2 NRA improves the electron transfer rate. Combined with metal Bi with the surface plasmon resonance (SPR) effect, it further increases the absorption range of visible light and enhances the light response performance of the PEC aptasensor. The KAN aptamer is fixed to the Bi/BiOBr/TiO2 NRA photoelectric material through the CN structure. Once the aptamer precisely captures KAN molecules, photocurrent changes are generated to realize the detection of KAN. The designed PEC aptasensor shows good detection performance in the linear response range of 1 pM-200 nM, and the detection limit is 0.7 pM (S/N = 3). The aptasensor was applied to the determination of KAN in milk with satisfactory results.

Vertically Aligned Silicon Carbide Nanowires/Boron Nitride Cellulose Aerogel Networks Enhanced Thermal Conductivity and Electromagnetic Absorbing of Epoxy Composites.

With the innovation of microelectronics technology, the heat dissipation problem inside the device will face a severe test. In this work, cellulose aerogel (CA) with highly enhanced thermal conductivity (TC) in vertical planes was successfully obtained by constructing a vertically aligned silicon carbide nanowires (SiC NWs)/boron nitride (BN) network via the ice template-assisted strategy. The unique network structure of SiC NWs connected to BN ensures that the TC of the composite in the vertical direction reaches 2.21 W m-1 K-1 at a low hybrid filler loading of 16.69 wt%, which was increased by 890% compared to pure epoxy (EP). In addition, relying on unique porous network structure of CA, EP-based composite also showed higher TC than other comparative samples in the horizontal direction. Meanwhile, the composite exhibits good electrically insulating with a volume electrical resistivity about 2.35 × 1011 Ω cm and displays excellent electromagnetic wave absorption performance with a minimum reflection loss of - 21.5 dB and a wide effective absorption bandwidth (< - 10 dB) from 8.8 to 11.6 GHz. Therefore, this work provides a new strategy for manufacturing polymer-based composites with excellent multifunctional performances in microelectronic packaging applications.

Improved methanogenesis in anaerobic wastewater treatment by magnetite@polyaniline (Fe3O4@PANI) composites.

The magnetite@polyaniline (Fe3O4@PANI) composites with different Fe3O4 loadings were prepared, and their effect on methane production in anaerobic systems was investigated. The Fe3O4@PANI composite with a 40% loading of Fe3O4 showed a better performance on accelerating methane production rate than other composites. The methane production rate was increased by 26.98% at the Fe3O4@PANI dosage of 0.6 g L-1. The results of the contact angle and CLSM revealed that Fe3O4@PANI had a good bio-affinity and contact directly with bacteria and archaea. Then the mechanisms related to the enhancement of methane production by the composites were explored by the species annotation and enzyme activity. It showed that Fe3O4@PANI promoted the enrichment of DIET-related functional bacteria and archaea and improved the enzyme activity related to the acetoclastic methanogenic pathway.

Cavity-Suppressing Electrode Integrated with Multi-Quantum Well Emitter: A Universal Approach Toward High-Performance Blue TADF Top Emission OLED.

A novel device structure for thermally activated delayed fluorescence (TADF) top emission organic light-emitting diodes (TEOLEDs) that improves the viewing angle characteristics and reduces the efficiency roll-off is presented. Furthermore, we describe the design and fabrication of a cavity-suppressing electrode (CSE), Ag (12 nm)/WO3 (65 nm)/Ag (12 nm) that can be used as a transparent cathode. While the TADF-TEOLED fabricated using the CSE exhibits higher external quantum efficiency (EQE) and improved angular dependency than the device fabricated using the microcavity-based Ag electrode, it suffers from low color purity and severe efficiency roll-off. These drawbacks can be reduced by using an optimized multi-quantum well emissive layer (MQW EML). The CSE-based TADF-TEOLED with an MQW EML fabricated herein exhibits a high EQE (18.05%), high color purity (full width at half maximum ~ 59 nm), reduced efficiency roll-off (~ 46% at 1000 cd m-2), and low angular dependence. These improvements can be attributed to the synergistic effect of the CSE and MQW EML. An optimized transparent CSE improves charge injection and light outcoupling with low angular dependence, and the MQW EML effectively confines charges and excitons, thereby improving the color purity and EQE significantly. The proposed approach facilitates the optimization of multiple output characteristics of TEOLEDs for future display applications.

Interface Engineered Microcellular Magnetic Conductive Polyurethane Nanocomposite Foams for Electromagnetic Interference Shielding.

Lightweight microcellular polyurethane (TPU)/carbon nanotubes (CNTs)/ nickel-coated CNTs (Ni@CNTs)/polymerizable ionic liquid copolymer (PIL) composite foams are prepared by non-solvent induced phase separation (NIPS). CNTs and Ni@CNTs modified by PIL provide more heterogeneous nucleation sites and inhibit the aggregation and combination of microcellular structure. Compared with TPU/CNTs, the TPU/CNTs/PIL and TPU/CNTs/Ni@CNTs/PIL composite foams with smaller microcellular structures have a high electromagnetic interference shielding effectiveness (EMI SE). The evaporate time regulates the microcellular structure, improves the conductive network of composite foams and reduces the microcellular size, which strengthens the multiple reflections of electromagnetic wave. The TPU/10CNTs/10Ni@CNTs/PIL foam exhibits slightly higher SE values (69.9 dB) compared with TPU/20CNTs/PIL foam (53.3 dB). The highest specific EMI SE of TPU/20CNTs/PIL and TPU/10CNTs/10Ni@CNTs/PIL reaches up to 187.2 and 211.5 dB/(g cm-3), respectively. The polarization losses caused by interfacial polarization between TPU substrates and conductive fillers, conduction loss caused by conductive network of fillers and magnetic loss caused by Ni@CNT synergistically attenuate the microwave energy.

Efficient microwave absorber and supercapacitors derived from puffed-rice-based biomass carbon: Effects of activating temperature.

Biomass-based carbon is gaining increasing attention because it presents a promising prospect for economic growth and social sustainable development. Moreover, it is an excellent medium for application in electromagnetic and electronic devices. Here, puffed-rice-based carbon is obtained at various activating temperatures, and when the hollow bulges on the carbon disappear, the morphology of the carbon changes into sheet-like structures. The R-800 sample displays the highest ID/IG value and demonstrates the best performance when used as both a microwave absorber and an electrode material. The minimum reflection loss (RL) and bandwidth for RL < -10 dB of the R-800 sample reach -72.1 dB and 13.2 GHz, respectively, and the bandwidth for RL < -20 dB is as large as 7.0 GHz, illustrating the widest bandwidth among the five carbon specimens. The multiple reflection effects and scattering, good impedance matching, and interfacial polarization synergistically enhance the microwave absorption performances of the sample. At 1 A g-1, the specific capacitance of the R-800 sample reaches 117.2 F g-1 and the capacitance retention remains at 85.3%. Moreover, a hybrid supercapacitor R-800//R-800 demonstrates an outstanding energy density of 15.23 Wh kg-1, power density of 5739.43 W kg-1, and high cycle stability (94.5% after 5000 cycles). This functionalized biomass carbon provides a promising media for constructing a bridge between sustainable development and biomass materials.

Work Function-Tunable Amorphous Carbon-Silver Nanocomposite Hybrid Electrode for Optoelectronic Applications.

Parameters such as electrode work function (WF), optical reflectance, electrode morphology, and interface roughness play a crucial role in optoelectronic device design; therefore, fine-tuning these parameters is essential for efficient end-user applications. In this study, amorphous carbon-silver (C-Ag) nanocomposite hybrid electrodes are proposed and fully characterized for solar photovoltaic applications. Basically, the WF, sheet resistance, and optical reflectance of the C-Ag nanocomposite electrode are fine-tuned by varying the composition in a wide range. Experimental results suggest that irrespective of the variation in the graphite-silver composition, smaller and consistent grain size distributions offer uniform WF across the electrode surface. In addition, the strong C-Ag interaction in the nanocomposite enhances the nanomechanical properties of the hybrid electrode, such as hardness, reduced modulus, and elastic recovery parameters. Furthermore, the C-Ag nanocomposite hybrid electrode exhibits relatively lower surface roughness than the commercially available carbon paste electrode. These results suggest that the C-Ag nanocomposite electrode can be used for highly efficient photovoltaics in place of the conventional carbon-based electrodes.

Boosting Multiple Interfaces by Co-Doped Graphene Quantum Dots for High Efficiency and Durability Perovskite Solar Cells.

Organic-inorganic hybrid perovskite solar cells (PSCs), as the most rapidly developing next-generation thin-film photovoltaic technology, have attracted extensive research interest, yet their efficiency, scalability, and durability remain challenging. α-Fe2O3 could be used as an electron transporting layer (ETL) of planar PSCs, which exhibits a much higher humidity and UV light-stability compared to TiO2-based planar PSCs. However, the photovoltaic conversion efficiency (PCE) of the Fe2O3-based device was still below 15% because of poor interface contact between α-Fe2O3 and perovskite and poor crystal quality of perovskites. In this work, we have engineered the interfaces throughout the entire solar cell via incorporating N, S co-doped graphene quantum dots (NSGQDs). The NSGQDs played remarkable multifunctional roles: (i) facilitated the perovskite crystal growth; (ii) eased charge extraction at both anode and cathode interfaces; and (iii) induced the defect passivation and suppressed the charge recombination. When assembled with a α-Fe2O3 ETL, the planar PSCs exhibited a significantly increased efficiency from 14 to 19.2%, with concomitant reductions in hysteresis, which created a new record of the PCE for Fe2O3-based PSCs to date. In addition, PSCs with the entire device interfacial engineering showed an obviously improved durability, including prominent humidity, UV light, and thermal stabilities. Our interfacial engineering methodology via graphene quantum dots represents a versatile and effective way for building high efficiency as well as durable PSCs.

Low optical dosage heating-reduced viscosity for fast and large-scale cleanup of spilled crude oil by reduced graphene oxide melamine nanocomposite adsorbents.

Heating under low solar radiation intensity is demonstrated to facilitate the cleaning of crude oil by the hydrophobic nanocomposite adsorbents of reduced graphene oxide (RGO) melamine sponge (MS@RGO) foams. The heat generated by the irradiation reduces the viscosity of the crude oil, and consequently increases the oil-diffusion coefficient of the pores of the MS@RGO foams and speeds up the oil-sorption rate. Even under a solar radiation intensity as low as 2 kW m-2, the temperature of crude oil rapidly rises to 68 °C or higher within 10 min. It only takes 29 s to completely absorb 6 g of crude oil at 60 °C by three tiny pieces of MS@RGO foam. This work makes better use of the excellent photothermal conversion characteristics of crude oil, and its photothermal conversion mechanism under simulated solar radiation is also discussed. This methodology can be adopted to clean up viscous crude oil or extract other chemicals effectively at a large scale, and provides a complete solution for the cleanup of crude oil in the sea or on the beach for actual engineering applications.

A highly Li+-conductive HfNb24O62 anode material for superior Li+ storage.

Highly Li+-conductive HfNb24O62 is explored as a new intercalation-type niobium-based oxide anode material for superior Li+ storage. HfNb24O62 owns a Wadsley-Roth shear structure with a large unit-cell volume, leading to a large Li+ diffusion coefficient. HfNb24O62 shows a large capacity, safe operating potential, high rate performance and good cyclability.

Carbon nitride nanoplatelet photocatalysts heterostructured with B-doped carbon nanodots for enhanced photodegradation of organic pollutants.

Decorating electron-accepting materials on carbon nitride (C3N4) is a promising strategy to construct heterostructure catalysts for improved photocatalytic abilities. In this study, B-doped carbon-dots (B-C-dots) decorated C3N4 (C3N4/B-C-dots) catalysts were fabricated through the surface deposition. The benefits from integration of B-C-dots and C3N4 are four folds: (i) increasing surface area; (ii) improving visible light absorption; (iii) promoting the transfer of photoinduced carriers; and (iv) reducing the recombination of photoinduced carriers. The optimum photocatalytic activity of B-C-dots/C3N4 for Rhodamine B (Rh B) (or tetracycline hydrochloride (TC)) degradation was about 7.21 (6.56) and 4.80 (4.35) times higher than that of C3N4 and C-dots/C3N4, respectively, exhibiting both remarkable stability and repeatability. Moreover, enhanced photocatalytic activity of C3N4/B-C-dots could also be attributed to the type-II heterojunction formed between C3N4 and B-C-dots caused by B doping.

Optimizing graphene content in a NiSe/graphene nanohybrid counter electrode to enhance the photovoltaic performance of dye-sensitized solar cells.

Nickel selenide (NiSe) nanoparticles were grown on graphene nanosheets (GN) with different mass ratios to obtain their corresponding NiSe/GNx (x = 0.25 to 1.00) nanohybrids by a facile in situ hydrothermal process to integrate the advantages of the high specific surface area of graphene and the homogeneously immobilized catalytic sites of NiSe. The nanohybrid with a mass ratio of 1 : 0.50 (i.e., NiSe/GN0.50) exhibited higher electrocatalytic activity and electrolyte diffusion. Thus, NiSe/GN0.50 exhibited an improved photo-conversion efficiency (PCE) of 12% (η = 8.62%) compared to a standard Pt (η = 7.68%)-based dye-sensitized solar cell (DSSC). This improved PCE mainly originated from the catalytic ability of NiSe and the multiple interfacial electron transfer pathways of graphene, resulting in enhanced charge transfer and fast tri-iodide reduction kinetics at the counter electrode/electrolyte interface. The results obtained from the cyclic voltammetry (CV), electrochemical AC-impedance (EIS) and Tafel polarization studies validated the synergistic effects of NiSe and GN and the high potential of this nanohybrid as an efficient counter electrode (CE) for DSSCs.

Tungsten oxide nanostructures and nanocomposites for photoelectrochemical water splitting.

Hydrogen production from photoelectrochemical (PEC) water splitting using semiconductor photocatalysts has attracted great attention to realize clean and renewable energy from solar energy. The visible light response of WO3 with a long hole diffusion length (∼150 nm) and good electron mobility (∼12 cm2 V-1 s-1) makes it suitable as the photoanode. However, WO3 suffers from issues including rapid recombination of photoexcited electron-hole pairs, photo-corrosion during the photocatalytic process due to the formation of peroxo-species, sluggish kinetics of photogenerated holes, and slow charge transfer at the semiconductor/electrolyte interface. This work highlights the approaches to overcome these drawbacks of WO3 photoanodes, including: (i) the manipulation of nanostructured WO3 photoanodes to decrease the nanoparticle size to promote hole migration to the WO3/electrolyte interface which benefits the charge separation; (ii) doping or introducing oxygen vacancies to improve electrical conductivity; exposing high energy crystal surfaces to promote the consumption of photogenerated holes on the high-active crystal face, thereby suppressing the recombination of photogenerated electrons and holes; (iii) decorating with co-catalysts to reduce the overpotential which inhibits the formation of peroxo-species; (iv) other methods such as coupling with narrow band semiconductors to accelerate the charge separation and controlling the crystal phase via annealing to reduce defects. These approaches are reviewed with detailed examples.

Hydrothermally Synthesized Li4Ti5O12 Nanotubes Anode Material with Enhanced Li-Ion Battery Performances.

Hollow Li4Ti5O12 nanotubes were synthesized by stirring in a heated oil bath using P25 as titanium source and lithium hydroxide as lithium source. The as-prepared samples displayed a nanotube structure, with diameter of about 20~50 nm and length of 0.4 µm. The specific surface area of as-prepared samples reached 153.2 m²g-1. It is demonstrated that the Li4Ti5O12 nanotubes with improved performance can be obtained by hollow structure and high specific surface area. In consequence, it delivered a high reversible initial discharge capacity of 174.2 mAh g-1 at 0.5 C rate. A stable capacity of 170.9 mAh g-1 was delivered when the rate was reduced back to 0.5 C, suggesting good structural stability of the nanocable, high reversibility even after high rate charge- discharge, and good cycle stability. In addition, a capacity of 134.9 mAh g-1 and 98 mAhg-1 could be retained at a high rate of 5 C and 10 C, indicating excellent rate performances.

Sandwich-like NiCo layered double hydroxide/reduced graphene oxide nanocomposite cathodes for high energy density asymmetric supercapacitors.

Nanocomposites with a well-defined sandwich-like nanostructure were prepared via in situ growing NiCo-layered double hydroxide nanosheets with tunable Ni/Co ratios on reduced graphene oxide (rGO). Electrochemical impedance spectra and N2 adsorption/desorption isotherms confirmed that these sandwich nanostructures effectively promoted charge transport and enlarged the specific surface area. The nanocomposites with Ni : Co = 2 : 1 exhibited a maximum specific capacitance of 2130 F g-1 at 2 A g-1, excellent rate capability (72.7% retention at 15 A g-1), and cycling stability. Asymmetric supercapacitors were assembled with these nanocomposite cathodes and rGO as a negative electrode (anode), and demonstrated an energy density of 34.5 W h kg-1 at a power density of 772 W kg-1, while maintaining a capacity retention of 86.7% after 10 000 cycles at 5 A g-1. The robust electrochemical properties indicate the composites as promising electrodes for electrochemical energy storage devices.

Iridium-Based Catalysts for Solid Polymer Electrolyte Electrocatalytic Water Splitting.

Chemical energy conversion/storage through water splitting for hydrogen production has been recognized as the ideal solution to the transient nature of renewable energy sources. Solid polymer electrolyte (SPE) water electrolysis is one of the most practical ways to produce pure H2 . Electrocatalysts are key materials in the SPE water electrolysis. At the anode side, electrode materials catalyzing the oxygen evolution reaction (OER) require specific properties. Among the reported materials, only iridium presents high activity and is more stable. In this Minireview, an application overview of single iridium metal and its oxide catalysts-binary, ternary, and multicomponent catalysts of iridium oxides and supported composite catalysts-for the OER in SPE water electrolysis is presented. Two main strategies to improve the activity of an electrocatalyst system, namely, increasing the number of active sites and the intrinsic activity of each active site, are reviewed with detailed examples. The challenges and perspectives in this field are also discussed.

Long-term antibacterial stable reduced graphene oxide nanocomposites loaded with cuprous oxide nanoparticles.

Stable reduced graphene oxide-cuprous oxide (rGO-Cu2O) nanocomposites with long-term antibacterial activities were prepared by reducing copper sulfate supported on GO using ascorbic acid as reducing agent in the presence of polyethylene glycol (PEG) and sodium hydroxide at room temperature. The rGO provided a protective barrier for Cu2O, preventing Cu2O from reacting with external solution to leach copper ions too quickly. Meanwhile, the rGO also promoted the separation of photoexcited charge carriers of Cu2O nanoparticles to enhance the oxidative stress reactive and protected Cu2O from falling apart in the phosphate buffered solution (PBS) solution to prolong the generation time of reactive oxygen species (ROS). More importantly, the large specific surface area of rGO improved the dispersibility of Cu2O by electrostatic interaction. The synergistic effect of sustained release of copper ions, elevated ROS production ability and uniform dispersion of rGO-Cu2O nanocomposites resulted in the excellent antibacterial activities of rGO-Cu2O nanocomposites against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) which were maintained around 70% and 65% and were increased by 40% and 35% compared with free Cu2O after immersing 30 days in PBS solutions.

Progress on the Photocatalytic Reduction Removal of Chromium Contamination.

Rapid industrialization leads to increased wastewater discharge encompassing hexavalent chromium (Cr(VI)), which leads to serious environmental problems of toxicity and potential carcinogenicity. Removal of these species is normally carried out by ion-exchange, precipitation, membrane filtration, sorption, photocatalytic reduction, etc. This review mainly focuses on the photocatalytic and photoelectrocatalytic (PEC) reduction of Cr (VI), because of their advantages over other methods such as reduced risk of secondary pollution by non-reduced Cr (VI), no sludge formation, no need for a large amount of chemical reagents, clean and easy installation. The main factors influencing the photocatalytic reduction efficiency of Cr (VI) such as catalyst activity, solution pH, Cr adsorption on the catalyst and additives, are briefly discussed. Finally, a special emphasis is provided to the photoelectrocatalytic (PEC) reduction of Cr (VI).

Constructing efficient mixed-ion perovskite solar cells based on TiO2 nanorod array.

Oriented TiO2 nanorod array (TiO2 NA) is very attractive in the fields of halide perovskite solar cells (PSCs) due to its fewer grain boundaries and high crystallinity for effective charge collection. The optimization of TiO2 nanostructures has been proved to be an effective approach for efficient PSCs. On the other hand, tuning the crystallization of perovskite films on top of the TiO2 NA is very important for efficient TiO2-NA based PSCs. Herein, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) were used to study the crystallization of different mixed-ion Cs0.1(FA0.83MA0.17)0.9Pb(I0.83Br0.17)3 perovskite (in which MA = CH3NH3+, and FA = CH(NH2)2+) films, from different perovskite precursor concentrations, on the TiO2 nanorod arrays. A mechanism was proposed to reveal the inherent connection between the precursor concentration and the crystallite growth of the perovskite film prepared with anti-solvent quenching process. Meanwhile, both faster charge separation at perovskite/TiO2 NA interface and longer charge transport were observed on thicker perovskite film with larger grains, revealed by the time-resolved method. However, atomic force microscopy (AFM) results indicated that too thick perovskite film impaired the charge collection owing to the increased recombination. By balancing the charge collection and film thickness, highly efficient PSCs were prepared with a champion power conversion efficiency (PCE) of 19.33% with little hysteresis. The study highlights a great potential of incorporating oriented one-dimensional electron extraction materials in high-performance PSCs and other applications.