Scalable Cathodic H2O2 Electrosynthesis using Cobalt-Coordinated Nanocellulose Electrocatalyst.

Converting hierarchical biomass structure into cutting-edge architecture of electrocatalysts can effectively relieve the extreme dependency of nonrenewable fossil-fuel-resources typically suffering from low cost-effectiveness, scarce supplies, and adverse environmental impacts. A cost-effective cobalt-coordinated nanocellulose (CNF) strategy is reported for realizing a high-performance 2e-ORR electrocatalysts through molecular engineering of hybrid ZIFs-CNF architecture. By a coordination and pyrolysis process, it generates substantial oxygen-capturing active sites within the typically oxygen-insulating cellulose, promoting O2 mass and electron transfer efficiency along the nanostructured Co3O4 anchored with CNF-based biochar. The Co-CNF electrocatalyst exhibits an exceptional H2O2 electrosynthesis efficiency of ≈510.58 mg L-1 cm-2 h-1 with an exceptional superiority over the existing biochar-, or fossil-fuel-derived electrocatalysts. The combination of the electrocatalysts with stainless steel mesh serving as a dual cathode can strongly decompose regular organic pollutants (up to 99.43% removal efficiency by 30 min), showing to be a desirable approach for clean environmental remediation with sustainability, ecological safety, and high-performance.

Hierarchical Bilayer Polyelectrolyte Ion Paper Conductor for Moisture-Induced Power Generation.

Harvesting energy from air water (atmospheric moisture) promises a sustainable self-powered system without any restrictions from specific environmental requirements (e.g., solar cells, hydroelectric, or thermoelectric devices). However, the present moisture-induced power devices traditionally generate intermittent or bursts of energy, especially for much lower current outputs (generally keeping at nA or µA levels) from the ambient environment, typically suffering from inferior ionic conductivity and poor hierarchical structure design for manipulating sustained air water and ion-charge transport. Here, we demonstrate a universal strategy to design a high-performance bilayer polyelectrolyte ion paper conductor for generating continuous electric power from ambient humidity. The generator can produce a continuous voltage of up to 0.74 V and also an exceptional current of 5.63 mA across a single 1.0 mm-thick ion paper conductor. We discover that the sandwiched LiCl-nanocellulose-engineered paper promises an ion-transport junction between the negatively and positively charged bilayer polyelectrolytes for application in MEGs with both high voltage and high current outputs. Moreover, we demonstrated the universality of this bilayer sandwich nanocellulose-salt engineering strategy with other anions and cations, exhibiting similar power generation ability, indicating that it could be the next generation of sustainable MEGs with low cost, easier operation, and high performance.

Fabrication of Low-Temperature Fast Gelation ß-Cyclodextrin-Based Hydrogel-Loaded Medicine for Wound Dressings.

ß-Cyclodextrin (ß-CD) is often used as a drug carrier for biomedical materials due to its unique cavity structure. Herein, ß-CD was modified by acryloyl chloride and further copolymerized with N-isopropylacrylamide (NIPAM) and acrylic acid (AA) to obtain PNIPAM-co-ß-CD-AC. The results showed that the critical phase transition temperature of PNIPAM/ß-CD-AC could be controlled at 19 °C, and the fast sol-gel phase transition was realized in 2-10 s. The hydrophobic drug carried in this hydrogel can constantly be released for more than 6 days at pH values (pH 5.5-8), and the duration may match the recovery of the wound. As a dressing hydrogel, its rapid gel formation and inversion as well as shear-thinning behavior prevent secondary wound damage. The ß-CD-based hydrogel also has good biocompatibility and antioxidant properties, which provide a good potential choice for wound dressings, especially for exposed wounds in winter.

All-Printed Flexible Hygro-Thermoelectric Paper Generator.

The conversion of ubiquitous hygrothermal resources into renewable energy offers significant potential for cable-free, self-powered systems that can operate worldwide without regard to climatic or geographic limitations. Here, an all-printed flexible hygro-thermoelectric paper generator is demonstrated that uses bifunctional mobile ions and electrons to make the moist-diffusion effect, the Soret effect, and the Seebeck effect work synergistically. In the ordinary hygrothermal settings, it generates an unconventional hygro-thermoelectric output pattern and shows almost a dozen-fold increase in positive hygro-thermopower of 26.70 mV K-1 and also another negative hygro-thermopower of -15.71 mV K-1 compared to pure thermopower. A single paper generator can produce a giant 680 mV displaying typical cyclic sinusoidal waveform characters with volt-sized amplitudes. The ion-electron conductive ink is easily printable and consists primarily of a Bi2 Te3 /PEDOT:PSS thermoelectric matrix modulated with a hygroscopic glycerol that releases ion charges for moist-diffusion effect and Soret effect, as well as electron charges for Seebeck effect. The emerged hygro-thermoelectric harvesting strategy from surrounding hygrothermal resources offers a revolutionary approach to the next generation of hybrid energy with cost-efficiency, flexibility, and sustainability, and also enables large-scale roll-to-roll production.

Regulating crystallization dynamics and crystal orientation of methylammonium tin iodide enables high-efficiency lead-free perovskite solar cells.

Tin (Sn)-based perovskite solar cells (PSCs) have attracted much attention because they are more environmentally friendly than lead-based PSCs. However, the fast crystallization of Sn-based perovskite films and the easy oxidation of Sn2+ to Sn4+ hinder the improvement of their efficiency and stability. In this work, ethylammonium bromide (EABr) was added to methylammonium tin iodide (MASnI3) perovskite precursor solution to regulate the crystallization dynamics and improve the film morphology. The results show that the large EA+ ions slow down the crystallization process of Sn-based perovskites and form a smooth perovskite film with high crystallinity, while the added Br- anions further improved the crystallinity and orientation of the perovskite film. Under the combined action of EA+ and Br- ions, the as-produced PSCs achieved a champion power conversion efficiency (PCE) of 9.59%. The EABr additive also retarded the oxidation of Sn2+, and the solar cell device maintained 93% of its initial efficiency after 30 days in a nitrogen-filled glove box without being encapsulated. This work provides a new strategy for the realization of high-efficiency Sn-based PSCs.

Efficient Stabilization and Passivation for Low-Temperature-Processed γ-CsPbI3 Solar Cells.

The inorganic CsPbI3 perovskite has attracted tremendous attention in the photovoltaic fields for its chemical stability and suitable band gap. Generally, CsPbI3 solar cells with decent performances adopted high annealing temperature to form high-quality black-phase perovskite films. The high-temperature process hinders its practical application and further development. Hence, fabricating stable black-phase CsPbI3 at low temperature is imperative and necessary. In this work, a new additive p-xylilenediamine bromide (PhDMADBr) is reported to facilitate the synthesis of solution-processed, high-quality, and stable γ-CsPbI3 films at a surprisingly low temperature of 60 °C. The additive with an appropriate content can effectively improve both the film morphology and crystallinity of γ-CsPbI3 perovskite films. PhDMADBr anchors to the perovskite surface or grain boundaries as a protection through hydrogen bonding between its ammonium cations and CsPbI3. In addition, the Br element introduced by the additive passivates I- vacancies in perovskite films, resulting in the improvement of both phase stability and devices' performance. Finally, the PSCs based on the modified γ-CsPbI3 perovskite film achieve a champion efficiency of 12.71%. Moreover, the device retains 85% of its original efficiency after being kept for 1000 h.

Biopolymers Derived from Trees as Sustainable Multifunctional Materials: A Review.

The world is currently transitioning from a fossil-fuel-driven energy economy to one that is supplied by more renewable and sustainable materials. Trees as the most abundant renewable bioresource have attracted significant attention for advanced materials and manufacturing in this epochal transition. Trees are composed with complex structures and components such as trunk (stem and bark), leaf, flower, seed, and root. Although many excellent reviews have been published regarding advanced applications of wood and wood-derived biopolymers in different fields, such as energy, electronics, biomedical, and water treatment, no reviews have revisited and systematically discussed functional materials and even devices derived from trees in a full scope yet. Therefore, a timely summary of the recent development of materials and structures derived from different parts of trees for sustainability is prsented here. A concise introduction to the different parts of the trees is given first, which is followed by the corresponding chemistry and preparation of functional materials using various biopolymers from trees. The most promising applications of biopolymer-based materials are discussed subsequently. A comprehensive review of the different parts of trees as sustainable functional materials and devices for critical applications is thus provided.

Cellulose Nanofiber-Reinforced Ionic Conductors for Multifunctional Sensors and Devices.

Ionic conductors are normally prepared from water-based materials in the solid form and feature a combination of intrinsic transparency and stretchability. The sensitivity toward humidity inevitably leads to dehydration or deliquescence issues, which will limit the long-term use of ionic conductors. Here, a novel ionic conductor based on natural bacterial cellulose (BC) and polymerizable deep eutectic solvents (PDESs) is developed for addressing the abovementioned drawbacks. The superstrong three-dimensional nanofiber network and strong interfacial interaction endow the BC-PDES ionic conductor with significantly enhanced mechanical properties (tensile strength of 8 × 105 Pa and compressive strength of 6.68 × 106 Pa). Furthermore, compared to deliquescent PDESs, BC-PDES composites showed obvious mechanical stability, which maintain good mechanical properties even when exposed to high humidity for 120 days. These materials were demonstrated to possess multiple sensitivity to external stimulus, such as strain, pressure, bend, and temperature. Thus, they can easily serve as supersensitive sensors to recognize physical activity of humans such as limb movements, throat vibrations, and handwriting. Moreover, the BC-PDES ionic conductors can be used in flexible, patterned electroluminescent devices. This work provides an efficient strategy for making cellulose-based sustainable and functional ionic conductors which have broad application in artificial flexible electronics and other products.

Controllable Two-dimensional Perovskite Crystallization via Water Additive for High-performance Solar Cells.

Steering the crystallization of two-dimensional (2D) perovskite film is an important strategy to improve the power conversion efficiency (PCE) of 2D perovskite solar cells (PVSCs). In this paper, the deionized water (H2O) additive is introduced into the perovskite precursor solution to prepare high-quality 2D perovskite films. The 2D perovskite film treated with 3% H2O shows a good surface morphology, increased crystal size, enhanced crystallinity, preferred orientation, and low defect density. The fabricated 2D PVSC with 3% H2O exhibits a higher PCE compared with that without H2O (12.15% vs 2.29%). Furthermore, the shelf stability of unsealed devices with 3% H2O under ambient environment is significantly improved. This work provides a simple method to prepare high-quality 2D perovskite films for efficient and stable 2D PVSCs.

Enhanced Crystallinity of Triple-Cation Perovskite Film via Doping NH4SCN.

The trap-state density in perovskite films largely determines the photovoltaic performance of perovskite solar cells (PSCs). Increasing the crystal grain size in perovskite films is an effective method to reduce the trap-state density. Here, we have added NH4SCN into perovskite precursor solution to obtain perovskite films with an increased crystal grain size. The perovskite with increased crystal grain size shows a much lower trap-state density compared with reference perovskite films, resulting in an improved photovoltaic performance in PSCs. The champion photovoltaic device has achieved a power conversion efficiency of 19.36%. The proposed method may also impact other optoelectronic devices based on perovskite films.

Highly Stretchable, Transparent, and Conductive Wood Fabricated by in Situ Photopolymerization with Polymerizable Deep Eutectic Solvents.

The rational design of high-performance, flexible, transparent, electrically conducting sensor attracts considerable attention. However, these designed devices predominantly utilize glass and plastic substrates, which are expensive and not environmentally friendly. Here, novel transparent and conductive woods (TCWs) were fabricated by using renewable wood substrates and low-cost conductive polymers. Polymerizable deep eutectic solvents (PDES), acrylic-acid (AA)/choline chloride (ChCl), were used as backfilling agents and in situ photopolymerized in the delignified wood, which endowed the materials with high transparency (transmittance of 90%), good stretchability (strain up to 80%), and high electrical conductivity (0.16 S m-1). The retained cellulose orientation and strong interactions between the cellulose-rich template and poly(PDES) endow TCWs with excellent mechanical properties. Moreover, TCWs exhibited excellent sensing behaviors to strain/touch, even at low strain. Therefore, these materials can be used to detect weak pressure such as human being's subtle bending-release activities. This work provides a new route to fabricate functional composite materials and devices which have promising potential for electronics applications in flexible displays, tactile skin sensors, and other fields.

Perovskite Solar Cells with ZnO Electron-Transporting Materials.

Perovskite solar cells (PSCs) have developed rapidly over the past few years, and the power conversion efficiency of PSCs has exceeded 20%. Such high performance can be attributed to the unique properties of perovskite materials, such as high absorption over the visible range and long diffusion length. Due to the different diffusion lengths of holes and electrons, electron transporting materials (ETMs) used in PSCs play a critical role in PSCs performance. As an alternative to TiO2 ETM, ZnO materials have similar physical properties to TiO2 but with much higher electron mobility. In addition, there are many simple and facile methods to fabricate ZnO nanomaterials with low cost and energy consumption. This review focuses on recent developments in the use of ZnO ETM for PSCs. The fabrication methods of ZnO materials are briefly introduced. The influence of different ZnO ETMs on performance of PSCs is then reviewed. The limitations of ZnO ETM-based PSCs and some solutions to these challenges are also discussed. The review provides a systematic and comprehensive understanding of the influence of different ZnO ETMs on PSCs performance and potentially motivates further development of PSCs by extending the knowledge of ZnO-based PSCs to TiO2 -based PSCs.

Rapid fabrication of transparent film directly from wood fibers with microwave-assisted ionic liquids technology.

Presently flexibly transparent film or nanopaper from all cellulose was mostly fabricated by assembling cellulose nanofibers disintegrated from macroscopic wood fibers which mostly suffers from potential environmental toxicity or high cost. In this work, we firstly reported an all-cellulose transparent film fabricated by a novel microwave-assisted ionic liquids technology (MILT). The use of MILT for treating the original all-cellulose paper brings nearly 2.6 fold-increases in optical transmission, and 2.0 fold-increases in tensile property compared to those without microwave assistance. More importantly, by contrast with the partial dissolution of cellulose in typical DMAC/LiCl, ILs, NaOH/urea, the MILT is extremely time-saved with responding to the highest increase in mechanical property because the high efficient surface dissolution and welding bind individual sheets together under a micro environment.

Rapid ILs-polishing Processes Toward Flexible Nanostructured Paper with Dually High Transparency and Haze.

Biodegradable highly nanostructured paper has received great interest in past years due to its excellent optical properties which facilitate its wide applications in green flexible electronics and devices. However, energy and/or time-consuming procedure during the process of fabricating most nanostructured transparent paper are presently the main obstacle to their scalable production. In this work, we demonstrated a novel nanostructured paper with dually high transparency (∼91%) and high haze (∼89%) that was directly fabricated from original paper with rapid ILs-polishing processes. The whole fabricating time only requires 10 min. Compared to the previously reported nanopaper made of the isolated cellulose nanofibers by pure mechanical and/or chemical approaches, this work presented herein is devoted to use green ILs to polish directly the micrometer-sized fibrous paper into the nanostructured paper. This new method brings a rapid fabrication of transparent nanostructured paper while also retaining dual intriguing properties both in optical transmittance and haze. This work is capable of fabricating next-generation flexible and highly transparent and haze paper by a high-speed roll-to-roll manufacturing process with a much lower cost.

Realizing Full Coverage of Stable Perovskite Film by Modified Anti-Solvent Process.

Lead-free solution-processed solid-state photovoltaic devices based on formamidinium tin triiodide (FASnI3) and cesium tin triiodide (CsSnI3) perovskite semiconductor as the light harvester are reported. In this letter, we used solvent engineering and anti-solvent dripping method to fabricate perovskite films. SnCl2 was used as an inhibitor of Sn4+ in FASnI3 precursor solution. We obtained the best films under the function of toluene or chlorobenzene in anti-solvent dripping method and monitored the oxidation of FASnI3 films in air. We chose SnF2 as an additive of CsSnI3 precursor solution to prevent the oxidation of the Sn2+, improving the stability of CsSnI3. The experimental results we obtained can pave the way for lead-free tin-based perovskite solar cells (PSCs).

Enhanced Performance of Planar Perovskite Solar Cells Using Low-Temperature Solution-Processed Al-Doped SnO2 as Electron Transport Layers.

Lead halide perovskite solar cells (PSCs) appear to be the ideal future candidate for photovoltaic applications owing to the rapid development in recent years. The electron transport layers (ETLs) prepared by low-temperature process are essential for widespread implementation and large-scale commercialization of PSCs. Here, we report an effective approach for producing planar PSCs with Al3+ doped SnO2 ETLs prepared by using a low-temperature solution-processed method. The Al dopant in SnO2 enhanced the charge transport behavior of planar PSCs and increased the current density of the devices, compared with the undoped SnO2 ETLs. Moreover, the enhanced electrical property also improved the fill factors (FF) and power conversion efficiency (PCE) of the solar cells. This study has indicated that the low-temperature solution-processed Al-SnO2 is a promising ETL for commercialization of planar PSCs.

Solvent annealing of PbI2 for the high-quality crystallization of perovskite films for solar cells with efficiencies exceeding 18.

While most work carried out to date has focused on the solvent annealing of perovskite, in the present work, we focused on the solvent annealing of lead iodide. Based on the two-step spin-coating method, we designed a screening method to search for an effective solvent annealing process for PbI2. PbI2 films were annealed in diverse solvent atmospheres, including DMF, DMSO, acetone, and isopropanol (IPA). We found that the solvent annealing of PbI2 in the DMF, acetone, and IPA atmospheres resulted in dense PbI2 films, which impeded the complete conversion of PbI2 to CH3NH3PbI3. Surprisingly, employing the DMSO solvent annealing process for PbI2 led to porous PbI2, which facilitated the complete conversion of PbI2 to perovskite with larger grain sizes. Solar cells fabricated using the DMSO solvent annealing process exhibited the best efficiency of 18.5%, with a fill factor of 76.5%. This unique solvent annealing method presents a new way of controlling the perovskite film quality for highly efficient solar cells.

Transparent Electrode and Magnetic Permalloy Made from Novel Nanopaper.

We report a novel partial dissolution strategy to liberate uniform cellulose nanofibers with diameter of 5-10 nm from macroscopic cellulose fibers and promote separation of nanofibers in an aqueous environment by forming water-soluble sodium carboxymethylcellulose (CMC) through heterogeneous sodium acetoxylation of cellulose. With the obtained cellulose nanofibers, we fabricated nanopapers which exhibit high optical transparency of 90.5% (@550 nm) with promising mechanical properties and high thermal stability. By directly depositing Ag nanowires on a wet nanofiber sheet, we fabricated a flexible transparent electrode with 86.5% (@550 nm) transparency and 26.2 Ω/sq sheet resistance (Rs). Meanwhile, we studied the magnetic properties of sputter deposited thin film of permalloy on nanopaper which exhibited a similar magnetic coercivity and a close saturation magnetization to conventional silicon dioxide-based permalloy.

Rapid Dissolving-Debonding Strategy for Optically Transparent Paper Production.

Transparent paper is an alternative substrate for electronic devices due to its unique properties. However, energy-intensive and/or time-consuming procedures currently limit the scalable production of transparent paper. In this report, we demonstrate a rapid process to fabricate optically transparent paper with regenerative cellulose fibers (RCFs) by employing a dissolving-debonding strategy. The RCFs have an average width of 19.3 µm and length of several hundred microns and are prepared into transparent paper by vacuum filtration. This new dissolving-debonding approach enables high production efficiency while creating transparent paper with excellent optical and mechanical properties.