Showing papers by "Hong Jin Fan published in 2014"
TL;DR: It is shown that a pair of perovskite cells connected in series can power the electrochemical breakdown of water into hydrogen and oxygen efficiently, and the combination of the two yields a water-splitting photocurrent density and a solar-to-hydrogen efficiency of 12.3%.
Abstract: Although sunlight-driven water splitting is a promising route to sustainable hydrogen fuel production, widespread implementation is hampered by the expense of the necessary photovoltaic and photoelectrochemical apparatus. Here, we describe a highly efficient and low-cost water-splitting cell combining a state-of-the-art solution-processed perovskite tandem solar cell and a bifunctional Earth-abundant catalyst. The catalyst electrode, a NiFe layered double hydroxide, exhibits high activity toward both the oxygen and hydrogen evolution reactions in alkaline electrolyte. The combination of the two yields a water-splitting photocurrent density of around 10 milliamperes per square centimeter, corresponding to a solar-to-hydrogen efficiency of 12.3%. Currently, the perovskite instability limits the cell lifetime.
2,140 citations
TL;DR: A thin polymer shell helps V2O5 a lot and an excellent high-rate capability and ultrastable cycling up to 1000 cycles are demonstrated.
Abstract: A thin polymer shell helps V2O5 a lot. Short V2O5 nanobelts are grown directly on 3D graphite foam as a lithium-ion battery (LIB) cathode material. A further coating of a poly(3,4-ethylenedioxythiophene) (PEDOT) thin shell is the key to the high performance. An excellent high-rate capability and ultrastable cycling up to 1000 cycles are demonstrated.
429 citations
TL;DR: Full supercapacitor devices based on the GF + Co3O4/PEDOT-MnO2 as positive electrodes exhibit the best performance compared to other three counterparts due to an optimal design of structure and a synergistic effect.
Abstract: We attempt to meet the general design requirements for high-performance supercapacitor electrodes by combining the strategies of lightweight substrate, porous nanostructure design, and conductivity modification. We fabricate a new type of 3D porous and thin graphite foams (GF) and use as the light and conductive substrates for the growth of metal oxide core/shell nanowire arrays to form integrated electrodes. The nanowire core is Co3O4, and the shell is a composite of conducting polymer (poly(3,4-ethylenedioxythiophene), PEDOT) and metal oxide (MnO2). To show the advantage of this integrated electrode design (viz., GF + Co3O4/PEDOT–MnO2 core/shell nanowire arrays), three other different less-integrated electrodes are also prepared for comparison. Full supercapacitor devices based on the GF + Co3O4/PEDOT–MnO2 as positive electrodes exhibit the best performance compared to other three counterparts due to an optimal design of structure and a synergistic effect.
411 citations
TL;DR: The outstanding electrochemical properties of the sulfide nanoarrays are a consequence of the preservation of the nanoarray architecture and rigid connection with the current collector after the anion exchange reactions.
Abstract: Metal sulfides are an emerging class of high-performance electrode materials for solar cells and electrochemical energy storage devices. Here, a facile and powerful method based on anion exchange reactions is reported to achieve metal sulfide nanoarrays through a topotactical transformation from their metal oxide and hydroxide preforms. Demonstrations are made to CoS and NiS nanowires, nanowalls, and core-branch nanotrees on carbon cloth and nickel foam substrates. The sulfide nanoarrays exhibit superior redox reactivity for electrochemical energy storage. The self-supported CoS nanowire arrays are tested as the pseudo-capacitor cathode, which demonstrate enhanced high-rate specific capacities and better cycle life as compared to the powder counterparts. The outstanding electrochemical properties of the sulfide nanoarrays are a consequence of the preservation of the nanoarray architecture and rigid connection with the current collector after the anion exchange reactions.
406 citations
TL;DR: The basic guideline for designing advanced nanostructure electrode materials is proposed, and the future research trend in the development of high power and energy density electrochemical energy storage devices is proposed.
Abstract: This article provides an overview of solution-based methods for the controllable synthesis of metal oxides and their applications for electrochemical energy storage. Typical solution synthesis strategies are summarized and the detailed chemical reactions are elaborated for several common nanostructured transition metal oxides and their composites. The merits and demerits of these synthesis methods and some important considerations are discussed in association with their electrochemical performance. We also propose the basic guideline for designing advanced nanostructure electrode materials, and the future research trend in the development of high power and energy density electrochemical energy storage devices.
358 citations
TL;DR: A new type of flexible Ni/Fe cell is designed and fabricated by employing Ni(OH)2 nanosheets and porous Fe2O3 nanorods grown on lightweight graphene foam (GF)/carbon nanotubes (CNTs) hybrid films as electrodes to deliver high energy/power densities and outstanding cycling stabilities.
Abstract: The development of portable and wearable electronics has promoted increasing demand for high-performance power sources with high energy/power density, low cost, lightweight, as well as ultrathin and flexible features. Here, a new type of flexible Ni/Fe cell is designed and fabricated by employing Ni(OH)2 nanosheets and porous Fe2O3 nanorods grown on lightweight graphene foam (GF)/carbon nanotubes (CNTs) hybrid films as electrodes. The assembled f-Ni/Fe cells are able to deliver high energy/power densities (100.7 Wh/kg at 287 W/kg and 70.9 Wh/kg at 1.4 kW/kg, based on the total mass of active materials) and outstanding cycling stabilities (retention 89.1% after 1000 charge/discharge cycles). Benefiting from the use of ultralight and thin GF/CNTs hybrid films as current collectors, our f-Ni/Fe cell can exhibit a volumetric energy density of 16.6 Wh/l (based on the total volume of full cell), which is comparable to that of thin film battery and better than that of typical commercial supercapacitors. Moreover...
338 citations
TL;DR: A new and highly reproducible and controllable technique for improving battery performance by utilizing atomic layer deposition to surface engineer SnO2 nanowires, resulting in a new type of hollowed SnO 2- in-TiO2 wire-in-tube nanostructure.
Abstract: SnO2 nanowires directly grown on flexible substrates can be a good electrode for a lithium ion battery. However, Sn-based (metal Sn or SnO2) anode materials always suffer from poor stability due to a large volume expansion during cycling. In this work, we utilize atomic layer deposition (ALD) to surface engineer SnO2 nanowires, resulting in a new type of hollowed SnO2-in-TiO2 wire-in-tube nanostructure. This structure has radically improved rate capability and cycling stability compared to both bare SnO2 nanowires and solid SnO2@TiO2 core-shell nanowire electrodes. Typically a relatively stable capacity of 393.3 mAh/g has been achieved after 1000 charge-discharge cycles at a current density of 400 mA/g, and 241.2 mAh/g at 3200 mA/g. It is believed that the uniform hollow TiO2 shell provides stable surface protection and the appropriate-sized gap effectively accommodates the expansion of the interior SnO2 nanowire. This ALD-enabled method should be general to many other battery anode and cathode materials, providing a new and highly reproducible and controllable technique for improving battery performance.
264 citations
TL;DR: In this article, the fabrication techniques for self-supported 3D porous graphene structures and their integrated electrodes with metal oxides/hydroxides for battery, supercapacitor, and oxygen reduction reaction applications are discussed.
244 citations
TL;DR: In this article, a flexible and lightweight Fe 2 O 3 -based lithium-ion battery anode has been developed by growing porous α-Fe 2O 3 nanorods onto carbon nanotubes-graphene foam (CNT-GF).
222 citations
TL;DR: In this paper, the authors reported the construction of SnO2 nanoflake branches onto robust TiO2 Nanotube stems, which demonstrated improved Li ion storage properties compared to powders, with more stable cycling processes and higher rate capability.
164 citations
TL;DR: In this article, quasi 1D Fe2O3-C composite nanofibers obtained by the electrospinning method, and evaluated them as anodes for Li ion batteries, were shown to have reversible capacity of 820 mA h g−1 at a current rate of 0.2 C up to 100 cycles.
Abstract: Combination of metal oxides and carbon has been a favourable practice for their applications in high-rate energy storage mesoscopic electrodes. We report quasi 1D Fe2O3–carbon composite nanofibers obtained by the electrospinning method, and evaluate them as anodes for Li ion batteries. In the half-cell configuration, the anode exhibits a reversible capacity of 820 mA h g−1 at a current rate of 0.2 C up to 100 cycles. At a higher current density of 5 C, the cells still exhibit a specific capacity of 262 mA h g−1. Compared to pure electrospun Fe2O3 nanofibers, the capacity retention of Fe2O3–C composite nanofiber electrodes is drastically improved. The good electrochemical performance is associated with the homogenous dispersed Fe2O3 nanocrystals on the carbon nanofiber support. Such a structure prevents the aggregation of active materials, maintains the structure integrity and thus enhances the electronic conductivity during lithium insertion and extraction.
TL;DR: A simple solution-based method to prepare a 3D interconnected porous network of ternary metal oxide nanostructures on macroporous nickel foam and the Li ion storage properties of both anodes are investigated.
Abstract: Ternary metal oxides have been receiving wide attention in electrochemical energy storage due to their rich redox reactions and tuneable conductivity. We present a simple solution-based method to prepare a 3D interconnected porous network of ternary metal oxide (CoMoO4 and ZnCo2O4) nanostructures on macroporous nickel foam. The open-structured networks with different degrees of porosity endow them with high surface areas of electro-active sites. The Li ion storage properties of both anodes are investigated. High rate capability and long term cycling stability are achieved for both systems.
TL;DR: A new method is developed for the generation of carbon nanoflakes on various metal oxide nanostructures by combining atomic layer deposition (ALD) and glucose carbonization, which may provide a new insight into the preparation of 'oxides + carbon' hybrid electrode materials for energy storage applications.
Abstract: N anostructured carbon is widely used in energy storage devices (e.g., Li-ion and Li-air batteries and supercapacitors). A new method is developed for the generation of carbon nanofl akes on various metal oxide nanostructures by combining atomic layer deposition (ALD) and glucose carbonization. Various metal oxide@nanofl ake carbon (MO@ f -C) core-branch nanostructures are obtained. For the mechanism, it is proposed that the ALD Al 2 O 3 and glucose form a composite layer. Upon thermal annealing, the composite layer becomes fragmented and moves outward, accompanied by carbon deposition on the alumina skeleton. When tested as electrochemical supercapacitor electrode, the hierarchical MO@ f -C nanostructures exhibit better properties compared with the pristine metal oxides or the carbon coating without ALD. The enhancement can be ascribed to increased specifi c surface areas and electric conductivity due to the carbon fl ake coating. This peculiar carbon coating method with the unique hierarchical nanostructure may provide a new insight into the preparation of ‘oxides + carbon’ hybrid electrode materials for energy storage applications.
TL;DR: It is shown that the stability of the triple-layered WO3 photoanodes can be considerably enhanced by adding an ultrathin (10 nm) TiO2 protective overlayer.
Abstract: Unique nanorods/nanoparticles/nanoflakes (NRs/NPs/NFs) WO3 triple-layers are grown on a metallic W foil by a simple one-step anodization method. The triple-layered structure is formed through a self-organization process, the film thickness (up to 3 μm) being controlled by the anodization time. A first layer made of an array of WO3 densely-packed vertically-aligned NRs (1.2–1.4 μm in height) grow atop the tungsten foil, followed by a second layer of small NPs (50–80 nm) and finally a third layer made of rectangular NFs (200–300 nm). When irradiated by white light in a photoelectrochemical cell these WO3 triple-layers generate a photocurrent as high as 0.9 mA cm−2 at 1.2 V/RHE. Moreover, we show that the stability of the triple-layered WO3 photoanodes can be considerably enhanced by adding an ultrathin (10 nm) TiO2 protective overlayer.
TL;DR: In battery electrode application, the thin hollow metal branches can provide a mechanical protection of the oxide core and a highly conductive path for charges and evidently improve the electrochemical performance with higher specific capacity, rate capability, and capacity retention than the unmodified Co3O4 counterparts.
Abstract: High-performance electrochemical energy storage (EES) devices require the ability to modify and assemble electrode materials with superior reactivity and structural stability. The fabrication of different oxide/metal core-branch nanoarrays with adjustable components and morphologies (e.g., nanowire and nanoflake) is reported on different conductive substrates. Hollow metal branches (or shells) wrapped around oxide cores are realized by electrodeposition using ZnO nanorods as a sacrificial template. In battery electrode application, the thin hollow metal branches can provide a mechanical protection of the oxide core and a highly conductive path for charges. As a demonstration, arrays of Co3O4/Ni core-branch nanowires are evaluated as the anode for lithium ion batteries. The thin metal branches evidently improve the electrochemical performance with higher specific capacity, rate capability, and capacity retention than the unmodified Co3O4 counterparts.
TL;DR: Enhanced pseudocapacitive performance compared to bare Co3O4 nanosheets is demonstrated with high rate capability and excellent cycling stability.
Abstract: A novel three-dimensional (3D) metal/metal oxide core/branch array electrode has been fabricated as a supercapacitor electrode. Hollow Ni nanocorn arrays are constructed on Ni foams and act as a highly conductive and stable support to Co3O4 nanoflakes. Enhanced pseudocapacitive performance compared to bare Co3O4 nanosheets is demonstrated with high rate capability and excellent cycling stability.