Chunhua Yao

Highly Efficient Capillary Photoelectrochemical Water Splitting Using Cellulose Nanofiber‐Templated TiO2 Photoanodes

Light absorption, charge separation, and appropriate interfacial redox reactions are three key aspects that lead to highly effi cient solar energy conversion. [ 5–10 ] Therefore, development of highperformance PEC electrodes has been concentrated largely on engineering the band structure of photoanodes, enlarging semiconductor-electrolyte interfacial area, and enabling rapid charge separation, collection, and transportation. [ 11,12 ] High porosity three dimensional (3D) nanostructures, such as branched nanowire architectures and nanofi ber networks, offer extremely large surface area, excellent charge transport properties, as well as long optical paths for effi cient light absorption. As a result, 3D nanostructures are the current focus of a tremendous surge of interest in PEC photoanode development. [ 10,13 ]

Cellulose nanofiber-templated three-dimension TiO2 hierarchical nanowire network for photoelectrochemical photoanode

Three dimensional (3D) nanostructures with extremely large porosity possess a great promise for the development of high-performance energy harvesting and storage devices. In this paper, we developed a high-density 3D TiO2 fiber-nanorod (NR) heterostructure for efficient photoelectrochemical (PEC) water splitting. The hierarchical structure was synthesized on a ZnO-coated cellulose nanofiber (CNF) template using atomic layer deposition (ALD)-based thin film and NR growth procedures. The tubular structure evolution was in good agreement with the recently discovered vapor-phase Kirkendall effect in high-temperature ALD processes. The NR morphology was formed via the surface-reaction-limited pulsed chemical vapor deposition (SPCVD) mechanism. Under Xenon lamp illumination without and with an AM 1.5 G filter or a UV cut off filter, the PEC efficiencies of a 3D TiO2 fiber-NR heterostructure were found to be 22-249% higher than those of the TiO2-ZnO bilayer tubular nanofibers and TiO2 nanotube networks that were synthesized as reference samples. Such a 3D TiO2 fiber-NR heterostructure offers a new route for a cellulose-based nanomanufacturing technique, which can be used for large-area, low-cost, and green fabrication of nanomaterials as well as their utilizations for efficient solar energy harvesting and conversion.

Mesoporous Piezoelectric Polymer Composite Films with Tunable Mechanical Modulus for Harvesting Energy from Liquid Pressure Fluctuation

Harvesting mechanical energy from biological systems possesses great potential for in vivo powering implantable electronic devices. In this paper, a development of flexible piezoelectric nanogenerator (NG) is reported based on mesoporous poly(vinylidene fluoride) (PVDF) films. Monolithic mesoporous PVDF is fabricated by a template-free sol-gel-based approach at room temperature. By filling the pores of PVDF network with poly(dimethylsiloxane) (PDMS) elastomer, the composites modulus is effectively tuned over a wide range down to the same level of biological systems. A close match of the modulus between NG and the surrounding biological component is critical to achieve practical integration. Upon deformation, the composite NG exhibits appreciable piezoelectric output that is comparable to or higher than other PVDF-based NGs. An artificial artery system is fabricated using PDMS with the composite NG integrated inside. Effective energy harvesting from liquid pressure fluctuation (simulating blood pressure fluctuation) is successfully demonstrated. The simple and effective approach for fabricating mesoporous PVDF with tunable mechanical properties provides a promising route toward the development of self-powered implantable devices.

Cellulose‐Based Nanomaterials for Energy Applications

Cellulose is the most abundant natural polymer on earth, providing a sustainable green resource that is renewable, degradable, biocompatible, and cost effective. Recently, nanocellulose-based mesoporous structures, flexible thin films, fibers, and networks are increasingly developed and used in photovoltaic devices, energy storage systems, mechanical energy harvesters, and catalysts components, showing tremendous materials science value and application potential in many energy-related fields. In this Review, the most recent advancements of processing, integration, and application of cellulose nanomaterials in the areas of solar energy harvesting, energy storage, and mechanical energy harvesting are reviewed. For solar energy harvesting, promising applications of cellulose-based nanostructures for both solar cells and photoelectrochemical electrodes development are reviewed, and their morphology-related merits are discussed. For energy storage, the discussion is primarily focused on the applications of cellulose-based nanomaterials in lithium-ion batteries, including electrodes (e.g., active materials, binders, and structural support), electrolytes, and separators. Applications of cellulose nanomaterials in supercapacitors are also reviewed briefly. For mechanical energy harvesting, the most recent technology evolution in cellulose-based triboelectric nanogenerators is reviewed, from fundamental property tuning to practical implementations. At last, the future research potential and opportunities of cellulose nanomaterials as a new energy material are discussed.

Aldehyde-functionalized porous nanocellulose for effective removal of heavy metal ions from aqueous solutions

Nanoscale sorption is a promising strategy for catalyst and purification system design. In this paper, cellulose nanofibrils (CNFs) were densely attached with aldehyde functional groups on the surface via a mild periodate oxidation process, and then applied as mesoporous sorbents to remove Cu(II) and Pb(II) from aqueous solutions. In the studied concentration range (0.6–1.0 mmol L−1), a removal capacity of 0.75 mmol g−1 for Pb(II) and 0.58 mmol g−1 for Cu(II) was obtained. It is higher than most reported results over a much broader concentration range. Furthermore, the physical chemistry of the sorption process was studied in terms of sorption kinetics, sorption isotherm study and thermodynamic study. The results showed that the sorption process is under the combined influences of reaction kinetics, film diffusion and intraparticle diffusion, and follows the Langmuir model of monolayer adsorption. The sorption is spontaneous and endothermic. This development demonstrates an ecofriendly and cost-effective method with high level effectiveness of metal ion removal.

High-density platinum nanoparticle-decorated titanium dioxide nanofiber networks for efficient capillary photocatalytic hydrogen generation

Aldehyde-functionalized cellulose nanofibers (CNFs) were applied to synthesize Pt nanoparticles (NPs) on CNF surfaces via on-site Pt ion reduction and achieve high concentration and uniform Pt NP loading. ALD could then selectively deposit TiO2 on CNFs and keep the Pt NPs uncovered due to their drastically different hydro-affinity properties. The high-temperature ALD process also simultaneously improved the crystallinity of Pt NPs and decomposed the CNF template leaving a pure anatase phase TiO2 nanofiber network decorated with high-density Pt NPs (up to 11.05 wt%). The as-prepared fibrous Pt–TiO2 network photocatalyst was integrated with CNF strips to develop a capillary setup for photocatalyzed hydrogen generation. Better reaction kinetics and higher efficiency were achieved from the capillary design compared to conventional in-electrolyte reactions. The initial H2 generation rates were 100.56–138.69 mmol g−1 h−1 from the capillary setup based on different Pt NP loadings, which were 123.3–288.6% larger than those of the in-electrolyte setup (25.88–62.11 mmol g−1 h−1). This 3D nanofibrous Pt–TiO2 capillary photocatalyst offers a brand new solution for improving the throughput of photocatalytic hydrogen production.

Nature Degradable, Flexible, and Transparent Conductive Substrates from Green and Earth-Abundant Materials

The rapid development of wearable and disposable electronic devices and the rising awareness of environmental sustainability impose growing new demands on the nature degradability of current electronic and energy systems. Here we report a new type of flexible transparent conductive paper completely made from green and earth abundant materials which are also fully degradable and recyclable. Aluminum-doped zinc oxide (AZO) was deposited by low-temperature atomic layer deposition (ALD) as the transparent conductive oxide (TCO) layer on transparent cellulose nanofibril (CNF) papers. The mesoporous structure of the CNF paper rendered strong adhesion of the AZO layer and exhibited excellent mechanical integrity and electrical conductivity within a wide range of tensile and compressive strains. The AZO-CNF paper could be completely dissolved in warm city water after one-hour stirring, demonstrating an excellent nature degradability. A flexible and transparent triboelectric nanogenerator (TENG) was further fabricated using such AZO-CNF papers with a performance that was comparable to other synthetic polymer-based systems. This work illustrated a new and promising strategy of utilizing 100% green and degradable materials in novel electronic and energy harvesting devices.