Showing papers by "Hong Jin Fan published in 2020"

Exceptional performance of hierarchical Ni–Fe oxyhydroxide@NiFe alloy nanowire array electrocatalysts for large current density water splitting

Abstract: Water electrolysis represents a promising sustainable hydrogen production technology. However, in practical application which requires extremely large current densities (>500 mA cm−2), the oxygen evolution reaction (OER) becomes unstable and kinetically sluggish, which is a major hurdle to large-scale hydrogen production. Herein, we report an exceptionally active and binder-free NiFe nanowire array based OER electrode that allows durable water splitting at current densities up to 1000 mA cm−2 up to 120 hours. Specifically, NiFe oxyhydroxide (shell)–anchored NiFe alloy nanowire (core) arrays are prepared via a magnetic-field-assisted chemical deposition method. The ultrathin (1–5 nm) and amorphous NiFe oxyhydroxide is in situ formed on the NiFe alloy nanowire surface, which is identified as an intrinsically highly active phase for the OER. Additionally, the fine geometry of the hierarchical electrode can substantially improve charge and mass (reactants and oxygen bubbles) transfer. In an alkaline electrolyte, this OER electrode can yield current densities of 500 and 1000 mA cm−2 stably over 120 hours at overpotentials of only 248 mV and 258 mV respectively, which are dramatically lower than any recently reported overpotentials. Notably, the integrated alkaline electrolyzer (with pure Ni nanowires as HER electrode) is demonstrated to reach the current density of 1000 mA cm−2 with super low voltage of 1.76 V, outperforming the state-of-the-art industrial catalysts. Our result may represent a critical step towards an industrial electrolyzer for large-scale hydrogen production by water splitting.

Enhanced performance of in-plane transition metal dichalcogenides monolayers by configuring local atomic structures.

Abstract: The intrinsic activity of in-plane chalcogen atoms plays a significant role in the catalytic performance of transition metal dichalcogenides (TMDs). A rational modulation of the local configurations is essential to activating the in-plane chalcogen atoms but restricted by the high energy barrier to break the in-plane TM-X (X = chalcogen) bonds. Here, we theoretically design and experimentally realize the tuning of local configurations. The electron transfer capacity of local configurations is used to screen suitable TMDs materials for hydrogen evolution reaction (HER). Among various configurations, the triangular-shape cobalt atom cluster with a central sulfur vacancy (3CoMo-VS) renders the distinct electrocatalytic performance of MoS2 with much reduced overpotential and Tafel slope. The present study sheds light on deeper understanding of atomic-scale local configuration in TMDs and a methodology to boost the intrinsic activity of chalcogen atoms. Designing and realizing local configurations can activate the in-plane chalcogen atoms of transition metal dichalcogenide to enhance the HER activity. We combine the theoretical screening (charge transfer capability) and experimental realization to achieve highly active local configurations

Fluorine-induced dual defects in cobalt phosphide nanosheets enhance hydrogen evolution reaction activity

Abstract: Introduction of defects in a controllable way is important to modulate the electronic structure of catalysts towards enhancement of electrocatalytic activity. Herein, we report that fluorine incorp...

Ferroelastic-switching-driven colossal shear strain and piezoelectricity in a hybrid ferroelectric

Abstract: Materials that can produce large controllable strains are widely used in shape memory devices, actuators and sensors Great efforts have been made to improve the strain outputs of various material systems Among them, ferroelastic transitions underpin giant reversible strains in electrically-driven ferro/piezoelectrics and thermally- or magneticallydriven shape memory alloys However, large-strain ferroelastic switching in conventional ferroelectrics is very challenging while magnetic and thermal controls are not desirable for applications Here, we demonstrate an unprecedentedly large shear strain up to 215 % in a hybrid ferroelectric, C6H5N(CH3)3CdCl3 The strain response is about two orders of magnitude higher than those of top-performing conventional ferroelectric polymers and oxides It is achieved via inorganic bond switching and facilitated by the structural confinement of the large organic moieties, which prevents the undesired 180-degree polarization switching Furthermore, Br substitution can effectively soften the bonds and result in giant shear piezoelectric coefficient (d35 ~ 4800 pm/V) in Br-rich end of the solid solution, C6H5N(CH3)3CdBr3xCl3(1-x) The superior electromechanical properties of the compounds promise their potential in lightweight and high energy density devices, and the strategy described here should inspire the development of next-generation piezoelectrics and electroactive materials based on hybrid ferroelectrics

Atomic-Layer-Deposited Amorphous MoS2 for Durable and Flexible Li–O2 Batteries

Abstract: Ming Song, Hua Tan, Xianglin Li, Alfred Iing Yoong Tok, Pei Liang, Dongliang Chao, and Hong Jin Fan

Dual‐Carbon Batteries: Materials and Mechanism

Abstract: Various carbon nanomaterials are being widely studied for applications in supercapacitors and Li-ion batteries as well as hybrid energy storage devices. Dual-carbon batteries (DCBs), in which both electrodes are composed of functionalized carbon materials, are capable of delivering high energy/power and stable cycles when they are rationally designed. This Review focuses on the electrochemical reaction mechanisms and energy storage properties of various carbon electrode materials in DCBs, including graphite, graphene, hard and soft carbon, activated carbon, and their derivatives. The interfacial chemistry between carbon electrodes and electrolyte is also discussed. The perspective for further development of DCBs is presented at the end.

Enhancing bifunctionality of CoN nanowires by Mn doping for long-lasting Zn-air batteries

Abstract: Tailoring the nanostructure and composition of transition metal nitrides is highly important for their use as potent low-cost electrocatalysts. Cobalt nitride (CoN) exhibits strong catalytic activity for oxygen evolution reaction (OER). However, its poor catalytic efficiency for oxygen reduction reaction (ORR) hinders its application in rechargeable zinc-air batteries (ZABs) as the air cathode. In this work, we deploy the effective strategy of Mn doping to improve both OER and ORR activity of CoN nanowires as the cathode material for ZAB. Theoretical calculation predicts that moderate Mn doping in cobalt nitride results in a downshift of the d-band center and reduces the adsorption energy of reaction intermediates. With ~10 at% Mn dopants, stronger catalysis activities for both OER and ORR are achieved compared to pure CoN nanowires. Subsequently, both aqueous and flexible quasi-solid-state ZABs are constructed using the Mn-doped CoN nanowires array as additive-free air cathode. Both types of devices present large open circuit potential, high power density and long-cycle stability. This work pushes forward the progress in developing cost-effective ZABs.

Continuous Tuning of Au–Cu 2 O Janus Nanostructures for Efficient Charge Separation

Abstract: In photocatalysis, the Schottky barrier in metal-semiconductor hybrids is known to promote charge separation, but a core-shell structure always leads to a charge build-up and eventually shuts off the photocurrent. Here, we show that Au-Cu2 O hybrid nanostructures can be continuously tuned, particularly when the Cu2 O domains are single-crystalline. This is in contrast to the conventional systems, where the hybrid configuration is mainly determined by the choice of materials. The distal separation of the Au-Cu2 O domains in Janus nanostructures leads to enhanced charge separation and a large improvement of the photocurrent. The activity of the Au-Cu2 O Janus structures is 5 times higher than that of the core-shell structure, and 10 times higher than that of the neat Cu2 O nanocubes. The continuous structural tuning allows to study the structure-property relationship and an optimization of the photocatalytic performance.

Air Stable Organic-Inorganic Perovskite Nanocrystals@Polymer Nanofibers and Waveguide Lasing.

Abstract: Organic-inorganic hybrid perovskites have been considered as promising gain materials for lasing. Despite previous reports of lasing from nanocrystals, thin films and single crystals, the stability of perovskite lasers has been a challenge for its practical applications. Herein, a scalable strategy to prepare ultrastable perovskite@polymer hybrid fibers by employing a facile emulsion electrospinning approach is demonstrated. During the electrospinning process, polymethyl methacrylate (PMMA) first solidifies into an outer shell layer. Meanwhile, emulsion drops containing poly(vinylidene fluoride) (PVDF) and perovskite precursor are pushed inward and evolve into perovskite nanocrystals covered by PVDF. The PMMA with smooth surface benefits the light transport and the water-resistant PVDF blocks the moisture. The methylammonium lead bromide perovskite-embedded fibers can emit intensive light after storage in humid ambient environment (relative humidity >60%) or even in water. Amplified spontaneous emissions from the fibers network and waveguide lasing from chopped single fiber is demonstrated.

A micromechanical model based on hypersingular integro-differential equations for analyzing micro-crazed interfaces between dissimilar elastic materials

Abstract: The current work models a weak (soft) interface between two elastic materials as containing a periodic array of micro-crazes. The boundary conditions on the interfacial micro-crazes are formulated in terms of a system of hypersingular integro-differential equations with unknown functions given by the displacement jumps across opposite faces of the micro-crazes. Once the displacement jumps are obtained by approximately solving the integro-differential equations, the effective stiffness of the micro-crazed interface can be readily computed. The effective stiffness is an important quantity needed for expressing the interfacial conditions in the spring-like macro-model of soft interfaces. Specific case studies are conducted to gain physical insights into how the effective stiffness of the interface may be influenced by the details of the interfacial micro-crazes.