Co-reporter:Qiao Wang, Fuyi Chen, Yaxing Liu, Nan Zhang, Liang An, and Roy L. Johnston
ACS Applied Materials & Interfaces October 18, 2017 Volume 9(Issue 41) pp:35701-35701
Publication Date(Web):September 27, 2017
DOI:10.1021/acsami.7b05186
Incorporating an oxophilic metal into a noble metal to produce a cost-effective Ag3Sn nanointermetallic catalyst is an emerging approach to enhance the catalytic activity of monometallic Ag in fuel cells, which is different from previous notions that consider a transition metal to increase the catalytic activity of Pt. The Ag3Sn electrocatalyst is prepared by a facile electrodeposition method and exhibits high catalytic performance for the oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR). The Ag3Sn electrocatalyst has an ORR specific activity of 0.246 mA cm–2, 1.3 times greater than the value of commercial Pt/C (0.187 mA cm–2) and a long-term stability with an 11 mV decrement in the half-wave potential and 7.01% loss of the diffusion-limiting current density after 2000 cycles, superior to that of Pt/C. Moreover, the Ag3Sn electrocatalyst delivers a surprisingly higher BOR current density of 11.332 mA cm–2 than most bimetallic Ag alloys. The better ORR catalytic activities of Ag-based alloys may arise from the ensemble effect, in which Sn atoms may promote the oxygen adsorption and Ag atoms may contribute to the removal of reaction products.Keywords: borohydride oxidation reaction; ensemble effect; intermetallic Ag3Sn; oxophilic metal; oxygen reduction reaction;
Co-reporter:Nan Zhang;Xiaoqiang Wu;Qiao Wang;Adnan Qaseem;Zhenhai Xia
Journal of Materials Chemistry A 2017 vol. 5(Issue 15) pp:7043-7054
Publication Date(Web):2017/04/11
DOI:10.1039/C6TA10948A
Highly active electrocatalysts with a novel bimetallic arrangement of atoms for the oxygen reduction reaction (ORR) are vital for the commercialization of fuel cells. An accurate understanding of the origin of activity enhancement is essential for exploiting any novel bimetallic catalyst. In this work, the reaction activation energy, reaction free energy and half-wave potential of AgCu alloys for the oxygen reduction have been investigated through both theoretical and experimental methods. The reaction activation energies on the pure Ag, core–shell Ag/Ag3Cu and alloy Ag3Cu are 1.097, 0.341 and 1.317 eV, respectively. The ORR activity is improved on core–shell Ag/Ag3Cu but deteriorated on alloy Ag3Cu nanoparticles in terms of the energy barrier for the rate-determining step during the ORR. The working potentials of pure Ag, core–shell Ag/Ag3Cu and alloy Ag3Cu are predicted to be 0.737, 0.761 and 0.675 V, respectively, indicating that the core–shell Ag/Ag3Cu nanoparticles provide the highest working potential and the lowest overpotential, which is comparable to that of the Pt(111) facets. AgCu bimetallic catalysts were prepared through the pulsed laser deposition, where the core–shell AgCu catalysts showed greater ORR activity than the alloy AgCu catalysts, which is consistent with the density functional theory calculations. Results not only indicate that a core–shell atom order should be designed for AgCu bimetallic nanoparticles to enhance their ORR activity but also provide a fundamental insight into the reason behind the synergetic effects in bimetallic catalysts.
Co-reporter:Jiali Wang;Yachao Jin;Yimin Lei;Roy L. Johnston
Advanced Functional Materials 2017 Volume 27(Issue 23) pp:
Publication Date(Web):2017/06/01
DOI:10.1002/adfm.201700260
A novel one-pot approach for synthesizing the dealloyed nanomaterials at room temperature is introduced for the first time. In such a synthetic strategy, applying modulated potentials effectively simplifies the traditional dealloying route, which usually requires additional corrosion process to dissolve nonprecious metals. The dealloyed AuNi nanodendrites (AuNi NDs) with tunable composition and uniformly elemental distribution are well developed by the one-pot strategy. Impressively, the as-synthesized AuNi NDs exhibit a higher electrochemically active area and definite improvements in electrocatalytic activity for oxygen reduction reaction (ORR) and borohydride oxidation reaction (BOR) compared to the commercial Pt/C. In particular, the AuNi NDs are 81 mV more positive in half-wave potential and about 3.1 times higher in specific activity (at 0.85 V) for the ORR than Pt/C, together with excellent stability and methanol tolerance. The superior BOR activity is highly promising compared to the previously reported catalysts. The unique nanodendritic structure with Au-rich surface and bimetallic electronic effect is the main factor to greatly enhance the bifunctional catalytic performance for the AuNi NDs. Furthermore, such a newly developed facile method is of great significance because it is one of the first examples to effectively engineer dealloyed bimetallic nanostructures via the practical and low-cost route for electrocatalytic applications.
Co-reporter:Adnan Qaseem, Fuyi Chen, Xiaoqiang Wu, Nan Zhang, Zhenhai Xia
Journal of Power Sources 2017 Volume 370(Volume 370) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.jpowsour.2017.10.004
•Ag nanoparticles on Co, N embedded graphene are prepared by hydrothermal route.•Ag develops into crystalline morphology while cobalt forms amorphous oxide.•As-synthesized material show superior catalytic activity and stability during ORR.•Particle size refinement and d-band center shift of Ag improves its ORR activity.•Ag/Co-NGr is methanol tolerant and functions with stable profile in Zn-air battery.Silver nanoparticles supported on cobalt and nitrogen embedded reduced graphene oxide, Ag/Co-NGr, are synthesized by one-step hydrothermal route with remarkable catalytic activity for oxygen reduction reaction (ORR). As-synthesized electrocatalyst exhibits half-wave potential (0.82 V) comparable to commercial Pt/C (0.85 V), specific activity (0.45 mA cm−2) better than commercial Pt/C (0.35 mA cm−2) along with superior stability in alkaline environment (≈95% activity retention after 5000s compared to 80% for Pt/C). Moreover, Ag/Co-NGr is highly tolerant to methanol poisoning during ORR and delivers an excellent specific capacity of 789 mAh.g−1Zn with energy density of 947 Wh. kg−1 at a current density of 20 mA cm−2 in a Zn-air battery. For the first time, it is proven that particle size refinement and electronic perturbation of Ag nanoparticles take place due to metal-support interactions between Ag and Co/NGr. d-band center of Ag in Ag/Co-NGr upshifts toward the Fermi level with respect to the Ag/NGr as a result of charge transfer between Ag and Co/NGr. The superior catalytic activity and excellent stability of Ag/Co-NGr is attributed to the structural and electronic modification of Ag nanoparticles by Co and N elements on graphene.Download high-res image (344KB)Download full-size image
Co-reporter:Yimin Lei;Jian Li;Zhan Wang;Jun Sun;Hongwei Liu;Xiaohua Ma;Zongwen Liu
Nanoscale (2009-Present) 2017 vol. 9(Issue 13) pp:4601-4609
Publication Date(Web):2017/03/30
DOI:10.1039/C6NR08046D
Crystallography of phase transformation combining transmission electron microscopy (TEM) with in situ heating techniques and X-ray diffraction (XRD) can provide critical information regarding solid-state phase transitions and the transition-induced interfaces in TiO2 nanomaterials theoretically and experimentally. Two types of reduced titanium oxides (Ti3O5, Ti6O11) are found during ex situ and in situ heating of TiO2 (B) nanofibers with a specific morphology of the {100} single form (SF) in air and vacuum. The results indicate that the phase transformation process from TiO2 (B) follows the TiO2 (B) → Ti3O5 → Ti6O11 → anatase sequence for the nanofibers with the {100} SF. The occurrence of such a phase transition is selective to the morphology of TiO2 (B) nanofibers. The corresponding orientation relationships (COR) between the four phases are revealed according to the TEM characterization. Four types of coherent interfaces, following the CORs are also found. They are TiO2 (B)/Ti3O5, TiO2 (B)/Ti6O11, Ti6O11/anatase and TiO2 (B)/anatase respectively. The habit plane for the TiO2 (B) to Ti3O5 transition is calculated as the {100}TB by using the invariant line model. The detailed atomic transformation mechanism is elucidated based on the crystallographic features of the four phases.
Co-reporter:Xiaoqiang Wu, Fuyi Chen, Nan Zhang, Adnan Qaseem and Roy L. Johnston
Journal of Materials Chemistry A 2016 vol. 4(Issue 9) pp:3527-3537
Publication Date(Web):29 Jan 2016
DOI:10.1039/C5TA09266C
Highly active electrocatalysts with good long term stability are vital for the commercialization of metal air batteries and alkaline fuel cells which involve the oxygen reduction reaction (ORR) at the cathode end. Herein, we developed a pulsed laser deposition (PLD) technique for the precise fabrication of silver–copper metallic glass (AgCu-MG) electrocatalysts. This PLD technique provides excellent control over the surface microtopography along with high flexibility for the deposition of different compositions of silver–copper metallic glass electrocatalysts onto nickel foam. Among all investigated Ag-based catalysts, AgCu-MG catalysts exhibit high electrocatalytic activity with a half-wave potential of 0.67 V (vs. RHE) which can be in situ enhanced by dealloying treatment in N2 saturated 0.1 M KOH solution. In situ dealloying of the AgCu-MG provides exceptional ORR catalytic activity with a half-wave potential of 0.78 V (vs. RHE) at 1600 rpm, which is comparable to 0.81 V (vs. RHE) of commercial Pt/C-20%. The AgCu-MG electrocatalyst showed excellent long-term stability in rechargeable zinc–air batteries. After 1000 charge–discharge cycles at 20 mA cm−2, the discharge voltage of batteries was stable at 1.0 V demonstrating the potential application of AgCu-MG as an alternative to Pt/C-20% in zinc–air batteries and alkaline fuel cells.
Co-reporter:Adnan Qaseem, Fuyi Chen, Xiaoqiang Wu and Roy L. Johnston
Catalysis Science & Technology 2016 vol. 6(Issue 10) pp:3317-3340
Publication Date(Web):04 Mar 2016
DOI:10.1039/C5CY02270C
The oxygen reduction reaction (ORR) plays a crucial role in electrochemical energy conversion and storage devices such as alkaline fuel cells and metal–air batteries. These systems, which could employ non-platinum catalysts for oxygen reduction, are cheaper and stable alternatives to their expensive counterparts like proton exchange membrane fuel cells (PEMFCs) working on platinum based catalysts. Various binary and ternary silver nanoalloys have been reported to act as efficient electrocatalysts for the ORR in alkaline fuel cells and batteries. Herein, we present a critical review on the recent advances made in silver nanoalloy electrocatalysts for the ORR in alkaline media. The mechanism of ORR on nanoalloys is described; the effect of structure and composition of various silver nanoalloys (including Ag–Cu, Ag–Pd, Ag–Au, Ag–Co etc.) on their ORR activity and stability is discussed. The rational design of electrocatalysts in order to maximize the number of catalytically active sites on the surface of the electrocatalysts for the ORR is also reviewed. Finally, we provide insights into the remaining challenges and directions for future perspectives and research.
Co-reporter:Naveed Shahzad, Fuyi Chen, Muhammad Khan
Materials Letters 2016 Volume 163() pp:266-269
Publication Date(Web):15 January 2016
DOI:10.1016/j.matlet.2015.10.096
•Pulsed laser deposition of Ag nanoparticles on TiO2 photoanodes.•Assembly of Ag nanoparticles sensitized solar cells.•Comparison between pulsed laser deposition and immersion techniques.•Compact morphology and narrow size distribution of Ag NPs observed after PLD.•Jsc of 2.85 mA cm−2 with open circuit voltage of 276 mV were achieved.Plasmonic metals such as gold, silver and copper are optically attractive photosensitizers owing to its unique optical properties at nano-scaled level, where the unique surface plasmon resonance (SPR) phenomenon becomes operative. These photosensitizers are usually deposited by immersion techniques which impart poor control on density of these photosensitizers dispersed on semiconductors. Herein, we report the deposition of silver NPs on TiO2 semiconductor by employing pulsed laser deposition (PLD). PLD efficiently deposits Ag NPs on TiO2 with effective control on NPs distribution on photoanodes which, ultimately, tune the photovoltaic (PV) characteristics of the resultant NPs sensitized solar cells, since the formed NPs sizes and morphology, and their spatial distribution on semiconductor have a significant influence on the PEC performance.
Co-reporter:Xiaoqiang Wu, Fuyi Chen, Yachao Jin, Nan Zhang, and Roy L. Johnston
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 32) pp:17782
Publication Date(Web):July 22, 2015
DOI:10.1021/acsami.5b04061
A carbon-free and binder-free catalyst layer composed of a Ag–Cu nanoalloy on Ni foam was used as the air cathode in a zinc–air battery for the first time. The Ag–Cu catalyst was prepared using pulsed laser deposition. The structures of the catalysts were found to consist of crystalline Ag–Cu nanoalloy particles with an average size of 2.58 nm embedded in amorphous Cu films. As observed in the X-ray photoelectron spectra, the Ag 3d core levels shifted to higher binding energies, whereas the Cu 2p core levels shifted to lower binding energies, indicating alloying of the silver and copper. Rotating disk electrode measurements indicated that the oxygen reduction reaction (ORR) proceeded through a four-electron pathway on the Ag50Cu50 and Ag90Cu10 nanoalloy catalysts in alkaline solution. Moreover, the catalytic activity of Ag50Cu50 in the ORR is more efficient than that of Ag90Cu10. By performing charge and discharge cycling measurements, the Ag50Cu50 catalyst layer was confirmed to have a maximum power density of approximately 86.3 mW cm–2 and an acceptable cell voltage at 0.863 V for current densities up to 100 mA cm–2 in primary zinc–air batteries. In addition, a round-trip efficiency of approximately 50% at a current density of 20 mA cm–2 was also obtained in the test.Keywords: nanoalloy; oxygen reduction reaction; primary zinc−air battery; pulsed laser deposition; rechargeable zinc−air battery
Co-reporter:Hongkai Wang, Fuyi Chen, Weiyin Li, Tian Tian
Journal of Power Sources 2015 Volume 287() pp:150-157
Publication Date(Web):1 August 2015
DOI:10.1016/j.jpowsour.2015.04.054
•A novel class of Au-GSH cluster was observed to enhance H2 generation in the visible.•Two kinds of TiO2 nanotube were designed to explore the potential of Au-GSH cluster.•The cooperation adding EDTA produced a photocurrent 6 times higher than Au-GSH alone.•The enhancement mechanism was synergistically confirmed by a simplified PEC system.The wide band-gap of TiO2 semiconductors hinders the photocatalytic hydrogen generation under visible light. In this research, we introduce glutathione-protected gold (Au-GSH) nanoclusters as a sensitizer to extend the active region of TiO2 up to a wavelength of 510 nm under visible light spectrum. We demonstrate that Au-GSH nanoclusters are capable of enhancing photocatalytic effects for hydrogen generation in photo-electrochemical cells (PECs). The combined effects of metal nanoclusters and sacrificial agent (EDTA) enhance the photocurrent up to six times more than what can be achieved using Au-GSH nanoclusters without EDTA. Moreover, the mechanisms of interaction between Au-GSH nanoclusters and EDTA have been investigated through instantaneous photoresponse measurements. A single electrode system has been designed to simplify PECs for hydrogen generation, which exhibits the same enhanced photocatalytic effect.
Co-reporter:Naveed Shahzad, Fuyi Chen, Lirong He, Weiyin Li, Hongkai Wang
Journal of Power Sources 2015 Volume 294() pp:609-619
Publication Date(Web):30 October 2015
DOI:10.1016/j.jpowsour.2015.06.124
•Synthesis of monometallic and alloyed Ag–Cu clusters through salt reduction method.•Synthesis of mesoporous TiO2 through sol-hydrothermal technique.•Spray-coating technique to deposit clusters on TiO2 photoanodes.•Cu-rich alloyed clusters exhibit Jsc of 2.87 mAcm−2 and Voc of 691 mV with PCE 1.1%.•Ag sensitizers demonstrate high Jsc whereas Cu sensitizers exhibit high Voc.Metal clusters (CLs) are recognized as a new class of sensitizers in a metal-cluster-sensitized solar cell (MCSC) which is an extension to well-recognized dye-sensitized solar cells (DSSCs). The function performed by dyes in DSSCs has predominately been executed by metal CLs in MCSCs. The distinct behavior of CLs at nano-scaled level can enhance their significance in photovoltaic applications. Recently, metal CLs have been explored as sensitizers in a solar cell, and the efficiency of the cell has been reported to be more than 2%. Herein, we present glutathione-protected Ag–Cu bimetallic CLs (alloyed CLs or nanoalloys) as sensitizer in MCSCs. Spray-coating technique has been employed to deposit CLs on photoanodes. The TiO2 modified with Cu rich alloyed CLs exhibit the short circuit photocurrent (Jsc) of 2.87 mAcm−2 with Voc of 691 mV. EIS and Mott–Schottky analysis have been performed to explicate the processes occurring inside MCSCs. Comparative study has been conducted to elucidate the effect of alloying on photo-electrochemical (PEC) response. Our results lay the foundations for exploring other nanoalloys as sensitizers in solar cells because nanoalloys present a greater degree of flexibility in properties, structure, size, and the composition of the constituent elements.
Co-reporter:Yachao Jin, Fuyi Chen
Electrochimica Acta 2015 Volume 158() pp:437-445
Publication Date(Web):10 March 2015
DOI:10.1016/j.electacta.2015.01.151
•Ag-Cu dendrites are observed for the first time to exhibit high catalytic activity for oxygen reduction reaction.•Ag-Cu dendrites are directly synthesized through galvanic displacement on the current collector layer made of Ni foams.•A bifunctional air cathode is fabricated using Ag-Cu dendrites as a carbon-free, binder-free catalyst layer.•Both the primary and rechargeable zinc–air batteries fabricated by Ag-Cu catalysts exhibit excellent performance.An inexpensive, facile galvanic displacement reaction for the direct growth of silver–copper (Ag-Cu) catalysts on nickel foams is developed for the first time. The resulting Ag-Cu catalysts exhibit dendritic morphologies. Ag and Cu atoms are in their metallic state while the presence of CuO and Cu2O are limited on the surface of catalyst. The catalysts demonstrate high catalytic activity for oxygen reduction reaction (ORR) in alkaline solution, as evaluated by both linear scanning voltammetry and rotating disk electrode polarization measurements. The ORR catalysed by Ag-Cu catalyst in alkaline solution proceeds through a four-electron pathway. An air cathode is fabricated using Ag-Cu catalyst as a carbon-free, binder-free catalyst layer. Using this Ag-Cu catalyst based air cathode, both the primary and rechargeable zinc-air batteries show excellent battery performance. The specific capacity of the primary zinc-air battery is 572 mAh g−1. Especially, the rechargeable zinc-air battery shows high round-trip efficiency, appealing stability at a long charge-discharge cycle period.
Co-reporter:Naveed Shahzad and Fuyi Chen
RSC Advances 2015 vol. 5(Issue 99) pp:81093-81102
Publication Date(Web):16 Sep 2015
DOI:10.1039/C5RA15414F
Metal clusters (CLs) and nanoparticles (NPs) are promising on account of their unique properties which cannot be achieved from their bulk counterparts. Discrete electronic excitations in metal CLs and the characteristic surface plasmon resonance (SPR) phenomenon in metal NPs make them optically attractive and versatile photosensitizers in photovoltaic (PV) applications. A visible-light driven photo-electrochemical (PCE) response of a plasmonic sensitizer in a metal NP/semiconductor composite assembly can be tuned with plasmonic metal NP sizes. Therefore, it is highly desirable to explore the PEC response of a plasmonic sensitizer as a function of its NP size. In this work, a study focusing on the PEC performance of a plasmonic sensitizer as a function of its NP size has been realized through synthesizing a series of ligand-protected Au NPs at ambient conditions using various reductants, since each reductant in coordination with the ligand forms metal ion complexes which influence the reduction potentials of metals through variation in the pH of the system, and ultimately, these changes affect the reaction dynamics and tune the NP sizes and morphology. A superior PEC response of glucose-assisted synthesis of Au NPs in NP sensitized solar cells (NPSCs) with power conversion efficiency greater than 1.5% has been observed, and attributed to the relatively fine NP sizes and uniform distribution on TiO2 photoanodes. It is expected that our study will assist in exploration of different sized Au NPs in diverse applications.
Co-reporter:Yachao Jin; Fuyi Chen;Yimin Lei ;Xiaoqiang Wu
ChemCatChem 2015 Volume 7( Issue 15) pp:2377-2383
Publication Date(Web):
DOI:10.1002/cctc.201500228
Abstract
A highly efficient Ag-Cu electrocatalyst is synthesized by the electrodeposition method and characterized with respect to its catalytic activity in the oxygen reduction reaction (ORR) and its tolerance to carbonate ions in a zinc-air battery. Cyclic voltammetry and rotating-disk electrode analyses suggest that the Ag50Cu50 electrocatalyst is 2.5 times more catalytically active in the ORR than a pure Ag catalyst and catalyzes the ORR through a four-electron pathway. Field-emission TEM characterization shows that the surface-roughened Ag-Cu electrocatalyst comprises small nanoplatelets with diameters of 40–50 nm. Cu atoms are partially alloyed in Ag lattices in these nanoplatelets. The Ag-Cu electrocatalysts are assembled into the primary and secondary zinc-air batteries as carbon-free and binder-free catalyst layers. The open circuit voltage and the discharge voltage of the primary zinc-air battery at 20 mA cm−2 are 1.49 and 1.17 V, respectively. The round-trip efficiency and increased polarization of the rechargeable zinc-air battery are 56.4 and 0.2 %, respectively, after 100 cycles at 20 mA cm−2. The Ag-Cu electrocatalyst shows good catalytic activity in the oxygen evolution reaction in an alkaline battery and good tolerance of carbonate ions on the cathode side.
Co-reporter:Zuwei Yin, Fuyi Chen
Journal of Power Sources 2014 Volume 265() pp:273-281
Publication Date(Web):1 November 2014
DOI:10.1016/j.jpowsour.2014.04.123
•We prepare 3D NiCu precursor by galvanic replacement reaction between Ni foam and copper ion.•CuCl2 is the best dipping solution because the formation and hydrolysis of CuCln1−n.•An activation process was done to remove the oxide.•CV treatment was done to fabricate a hierarchical architectural structure.•The hierarchical architectural NiCu electrode has the best HER activity of all the electrodes.A NiCu composite electrode with hierarchical structure has been successfully fabricated by an electrochemical method, which consisted of galvanic replacement reaction (GRR), activation process and cyclic voltammetry (CV) treatment. The three-dimensional (3D) Ni–Cu precursors were prepared firstly by dipping Ni foam into three kinds of different copper ion solutions and identified that CuCl2 is a favorite electrolyte. This may be attributed to the adsorption of chloride ion on copper surface to form the CuCln1−n complex and the hydrolysis of CuCln1−n. After an activation process to reduce the hydrolytic product Cu2O into Cu, a CV treatment was performed to form a hierarchical structure to improve the surface area and to heighten the hydrogen evolution reaction (HER) activity. The optimal number of CV cycles is 3.
Co-reporter:Zuwei Yin, Fuyi Chen
Electrochimica Acta 2014 Volume 117() pp:84-91
Publication Date(Web):20 January 2014
DOI:10.1016/j.electacta.2013.11.102
•We brush-plated NiCu layer instead of conventional electrodeposition.•Deposition-dealloying cycles was done to roughen the surface of NiCu layer.•Selective dissolution of Cu was done to fabricate a hierarchical porous structure.•The roughened porous NiCu layer was dipped in NiCl2 solution.•Porous Ni(OH)2/NiCu electrode has the best HER activity of all the electrodes.A hierarchical porous Ni(OH)2/NiCu electrode was fabricated by a novel electrochemical method, which included brush plating, cyclic voltammetry (CV) treatment, electrochemical dealloying and hydrolysis. We firstly discussed the feasibility of using brushing plating to produce NiCu precursors. Then we found that the CV treatment can be used to yield a roughened NiCu surface; thereafter, the selective dissolution of Cu can be used to further improve the surface area. Through controlling the cycle number and time of dealloying, we can get a hierarchical porous NiCu which exhibit highest hydrogen evolution reaction activity. Subsequently, the obtained hierarchical porous NiCu immersed in 0.1 M NiCl2 to get a hierarchical porous Ni(OH)2/NiCu electrode. The influence of immersing time was also discussed. The fabricated hierarchical porous Ni(OH)2/NiCu electrode exhibits higher hydrogen evolution reaction (HER) activity than those of the brush-plated NiCu and porous NiCu electrodes, which can be attributed to the unique hierarchical porous structure and the synergy between the Ni(OH)2 and NiCu surfaces.
Co-reporter:Xiu-Na Xing, Guang-Hua Chen, Ying-Ying Du, Wen-Jie Li, Hai-Yang Li, Hong-Nian Li, Wei-Yin Li, Fu-Yi Chen
Chemical Physics Letters 2014 Volumes 616–617() pp:11-15
Publication Date(Web):25 November 2014
DOI:10.1016/j.cplett.2014.10.021
•The side chain of PC61BM directly participates in the solar absorption.•Detailed energy level diagram for the solar absorption is provided.•Distortion or length change of the side chain alters the photoabsorption obviously.We have studied the role of the phenyl-butyric-acid-methyl-ester side chain in the solar absorption of fullerene derivatives PC61BM. The UV–Vis–NIR spectra are calculated with the linear response theory within time-dependent density functional theory. The initial and final orbitals of the optical transitions in solar spectrum range are analyzed in detail. The electronic states of the side chain hybridize with the states of C60 cage, increasing the number of the initial orbitals of the solar absorption. So the side chain directly participates in the solar absorption. A distortion or length change of the side chain has obvious effects on the photoabsorption.
Co-reporter:Yimin Lei;Jie Sun;Hongwei Liu;Xuan Cheng; Fuyi Chen; Zongwen Liu
Chemistry - A European Journal 2014 Volume 20( Issue 36) pp:11313-11317
Publication Date(Web):
DOI:10.1002/chem.201403272
Abstract
The phase transition from H2Ti3O7 to TiO2 (B) in a 1D single nanocrystal of H2Ti3O7 was observed by in situ heating in a transmission electron microscope experimentally. The results indicate a typical monoclinic-to-monoclinic crystallographic orientation relationship between the two phases. Moreover, the fundamental building blocks and invariant deformation element model were both adopted to reveal the atomic mechanism and predict the crystallographic orientation relationship quantitatively for the phase transition. The prediction was precisely consistent with TEM results.
Co-reporter:Yi Rao, Yimin Lei, Xiangyuan Cui, Zongwen Liu, Fuyi Chen
Journal of Alloys and Compounds 2013 Volume 565() pp:50-55
Publication Date(Web):15 July 2013
DOI:10.1016/j.jallcom.2013.02.185
•Cu atom tends to occupy the core position in the Ag–Cu nanoclusters.•Global minimum of Ag12Cu1 cluster is predicted to be cuboctahedral shape.•High symmetry clusters have high magnetic moment.•Icosahedral core–shell Ag12Cu1 cluster has ferromagnetic properties.The structural, optical and magnetic properties of Ag13, Ag12Cu1 and Cu13 clusters have been investigated using density functional theory calculations. The global minimum of the Ag12Cu1 cluster is predicted to be cuboctahedral (COh) core–shell structure with Oh point group symmetry while the icosahedral (Ih) core–shell isomer has a higher HOMO–LUMO gap and higher magnetic moment. The optical absorption spectrum of the Ih Ag12Cu1 has three absorption peaks at 2.17, 2.41 and 2.65 eV, compared with that the COh Ag12Cu1 has one main absorption peak at 2.51 eV. The characteristics in electronic density of states (DOSs) show that Ih core–shell Ag12Cu1 has ferromagnetic properties like pure Au13, Ag13 nanoclusters. The sizable split between spin up and spin down DOS of d states in the inner Cu atom and sp states in the outer Ag atoms bring in large magnetic moment to Ih Ag12Cu1 cluster.
Co-reporter:Yarong Kang
Journal of Applied Electrochemistry 2013 Volume 43( Issue 7) pp:667-677
Publication Date(Web):2013 July
DOI:10.1007/s10800-013-0563-0
In this work, dendritic silver–copper (Ag–Cu) nanostructures were synthesised on a copper foil by electrodeposition and subsequently galvanic displacement reaction without any surfactant. The crystalline nature of the nanostructures was examined by X-ray diffraction, and the morphology of the material was investigated by field-emission scanning electron microscopy. The applied potential, displacement reaction time, and silver nitrate solution concentration exerted different effects on the nanoparticle shape. And a possible growth mechanism of the Ag–Cu dendrites was proposed based on the experimental results. The electrochemical properties of the Ag–Cu dendrite-modified electrode were characterised by linear sweep voltammetry. The reduction peak potential of hydrogen peroxide (H2O2) was about −0.25 V (vs. a saturated calomel electrode), which indicated that the as-synthesised Ag–Cu dendrites had favourable electroreduction activity towards hydrogen peroxide. At the same time, we found that the solution pH also affected the electrocatalytic ability of the dendrites for H2O2 reduction, which was important for the design of a NaBH4–H2O2 battery.
Co-reporter:Weiyin Li
Journal of Nanoparticle Research 2013 Volume 15( Issue 7) pp:
Publication Date(Web):2013 July
DOI:10.1007/s11051-013-1809-9
The structures and properties of 13-atom silver and copper bimetallic clusters are systematically investigated by density functional theory (DFT) in the theoretical frame of the generalised gradient approximation (GGA) exchange-collection function. Optical absorption, Raman spectra, vibrational spectra, as well as electronic and magnetic properties are calculated by DFT/GGA and semi-core pseudopotentials. The following lowest-energy structures in the 13-atom Ag–Cu clusters are obtained: cuboctahedron for pure Ag13, icosahedrons for pure Cu13, Ag1Cu12, Ag6Cu7 and Ag12Cu1; and amorphous motifs for AgmCu13−m when m = 2–5 and 7–11. Ag2Cu11, Ag7Cu6 and Ag11Cu2 are magic clusters. The Ag2Cu11 cluster exhibits high energetic stability, strong electronic stability, multipole surface plasmon resonance (SPR) mode and small dipole moment. The Ag6Cu7 cluster is a Janus-separated cluster that possesses the strongest electronic stability with a band gap of 0.424 eV and a vertical ionisation potential of 5.8417 eV. The amorphous Ag7Cu6 cluster shows an Ag–Cu alloyed motif. The blue shift of the maximum SPR peak becomes increasingly evident as silver atoms are added. All Raman and vibrational spectra exhibit many significant vibration modes within the wavenumber ranges of 0–270 and 0–306.55 cm−1, respectively. Ferroelectric and ferromagnetic behaviours are observed in the 13-atom Ag–Cu nanoalloys, indicating their new potential applications in nonlinear optical devices.
Co-reporter:Zuwei Yin, Fuyi Chen
Surface and Coatings Technology 2013 Volume 228() pp:34-40
Publication Date(Web):15 August 2013
DOI:10.1016/j.surfcoat.2013.04.001
•We did two different nickel immersion pretreatments prior to EN plating.•No. 2 nickel immersion providing a better corrosion resistance is chosen.•The polarization curve and EIS was used to measure the corrosion properties.•We did double nickel immersion after first pretreatments.•Cross using the two different methods can provide the best corrosion resistance.Ni–P alloys with 7 wt% to 10 wt% phosphorus were deposited by sodium hypophosphite onto industrially pure aluminum substrates after different pretreatments. Two nickel immersion pretreatments (NIPs) were tested prior to electroless Ni–P plating, and their effects on the corrosion properties of the Ni–P alloy layers were evaluated using polarization curves and electrochemical impedance spectroscopy. The surface morphology and chemical composition of the Ni–P coatings were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis. Both proposed NIPs were found to improve the corrosion resistance. Thus, a double NIP method similar to the double zincate treatment method was developed. The alloy layer pretreated by this developed method showed the highest corrosion resistance, which can be mainly attributed to the high phosphorus content and low microporosity.
Co-reporter:Dengyao Li;Jian Liu
Journal of Materials Science: Materials in Electronics 2013 Volume 24( Issue 8) pp:2761-2766
Publication Date(Web):2013 August
DOI:10.1007/s10854-013-1167-5
Titanium dioxide (TiO2) layers were prepared by the pyrolysis of an ethanolic solution of di-iso-propoxy-titanium bis(acetylacetonate) in aerosol form, and then electrodeposited with Ag nanoparticles on their surface. The morphology and photoelectrochemical properties of the resulting Ag nanoparticles (NPs) on TiO2 films were found to be significantly tuned by varying the electrodeposition time in an aqueous electrolyte containing AgNO3 and KNO3. Photocurrent density–voltage curves and electrochemical impedance spectra revealed that the Ag NPs remarkably improved the short-circuit current density and open circuit voltage, and considerably reduced the electrochemical impedance. Therefore, Ag NPs deposition enhanced the photo-absorption of the TiO2 layer, excited photoelectrons by localised surface plasmon resonance, promoted photo-induced charge separation, and prevented electron–hole recombination.
Co-reporter:Fuyi Chen;Roy L. Johnston
Plasmonics 2009 Volume 4( Issue 2) pp:147-152
Publication Date(Web):2009 June
DOI:10.1007/s11468-009-9087-1
In this paper, we examine the plasmonic properties of silver nanoparticles, with an emphasis on the sensitivity of the extinction spectra on the supporting substrate: silica (SiO2) microsphere and indium tin oxide (ITO) coated glass slide, on which silver particles are deposited electroless and electrochemically, respectively. The microstructures and phases of these nanoparticles are characterized by transmission electron microscopy, field emission electron microscopy and X-ray diffraction analysis. The surface plasmon resonance (SPR) properties which are experimentally measured in the ultraviolet-visible-near infrared spectral region are compared to electrodynamics calculations based on the discrete dipole approximation. A wide SPR band ranging from 400 to 800 nm is observed for the silver nanoparticles on a silica microsphere, which is similar to the plasmon resonance characteristics of metal nanoshells. The SPR of a conducting substrate, however, has an effect on the plasmonic properties of silver nanoparticles at longer wavelength.
Co-reporter:Fuyi Chen, Wanqi Jie, Xiaomei Cai
Thin Solid Films 2008 Volume 516(Issue 10) pp:2823-2828
Publication Date(Web):31 March 2008
DOI:10.1016/j.tsf.2007.04.167
CdS films were prepared on a glass substrate and their growth was analyzed as a function of the supersaturation ratio in dilute solutions. Nanocrystalline CdS with a hexagonal (wurtzite) structure is present in the CdS films and aggregated into colloidal particles. The particle size increases from 117 nm to 357 nm when the relative supersaturation ratio (Sr) increases from 0.4 to 1.0, but particle size decreases to 149 nm and the absorption edge blue shifts from 488 nm to 456 nm when Sr increases further to 4.0. The evolution of the CdS film is explained on the basis of the proposed growth kinetic model.
Co-reporter:Fuyi Chen;Wanqi Jie
Crystal Research and Technology 2007 Volume 42(Issue 11) pp:1082-1086
Publication Date(Web):28 JUN 2007
DOI:10.1002/crat.200710955
Photoluminescence (PL) emitted from Cd1-xZnxS and CdS1-ySey solid solution semiconductor was significantly stronger than PL from the pure CdS and CdSe semiconductor. The samples were prepared using an improved Se-S-Na2S flux route. Photoluminescence in Cd1-xZnxS crystal was brightly yellow at the room temperature under VU radiation. The phase and composition of the solid solution was measured by the XRD and was confirmed by UV-NIS spectrum as x of 0.3 and y of 0.2. The enhanced photoluminescence was presumably due to the introduction of extra defect (vacancies) by solid solution action and consequently the increasing of luminescence center concentration. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Co-reporter:Nan Zhang, Fuyi Chen, Xiaoqiang Wu, Qiao Wang, Adnan Qaseem and Zhenhai Xia
Journal of Materials Chemistry A 2017 - vol. 5(Issue 15) pp:NaN7054-7054
Publication Date(Web):2017/03/10
DOI:10.1039/C6TA10948A
Highly active electrocatalysts with a novel bimetallic arrangement of atoms for the oxygen reduction reaction (ORR) are vital for the commercialization of fuel cells. An accurate understanding of the origin of activity enhancement is essential for exploiting any novel bimetallic catalyst. In this work, the reaction activation energy, reaction free energy and half-wave potential of AgCu alloys for the oxygen reduction have been investigated through both theoretical and experimental methods. The reaction activation energies on the pure Ag, core–shell Ag/Ag3Cu and alloy Ag3Cu are 1.097, 0.341 and 1.317 eV, respectively. The ORR activity is improved on core–shell Ag/Ag3Cu but deteriorated on alloy Ag3Cu nanoparticles in terms of the energy barrier for the rate-determining step during the ORR. The working potentials of pure Ag, core–shell Ag/Ag3Cu and alloy Ag3Cu are predicted to be 0.737, 0.761 and 0.675 V, respectively, indicating that the core–shell Ag/Ag3Cu nanoparticles provide the highest working potential and the lowest overpotential, which is comparable to that of the Pt(111) facets. AgCu bimetallic catalysts were prepared through the pulsed laser deposition, where the core–shell AgCu catalysts showed greater ORR activity than the alloy AgCu catalysts, which is consistent with the density functional theory calculations. Results not only indicate that a core–shell atom order should be designed for AgCu bimetallic nanoparticles to enhance their ORR activity but also provide a fundamental insight into the reason behind the synergetic effects in bimetallic catalysts.
Co-reporter:Adnan Qaseem, Fuyi Chen, Xiaoqiang Wu and Roy L. Johnston
Catalysis Science & Technology (2011-Present) 2016 - vol. 6(Issue 10) pp:NaN3340-3340
Publication Date(Web):2016/03/04
DOI:10.1039/C5CY02270C
The oxygen reduction reaction (ORR) plays a crucial role in electrochemical energy conversion and storage devices such as alkaline fuel cells and metal–air batteries. These systems, which could employ non-platinum catalysts for oxygen reduction, are cheaper and stable alternatives to their expensive counterparts like proton exchange membrane fuel cells (PEMFCs) working on platinum based catalysts. Various binary and ternary silver nanoalloys have been reported to act as efficient electrocatalysts for the ORR in alkaline fuel cells and batteries. Herein, we present a critical review on the recent advances made in silver nanoalloy electrocatalysts for the ORR in alkaline media. The mechanism of ORR on nanoalloys is described; the effect of structure and composition of various silver nanoalloys (including Ag–Cu, Ag–Pd, Ag–Au, Ag–Co etc.) on their ORR activity and stability is discussed. The rational design of electrocatalysts in order to maximize the number of catalytically active sites on the surface of the electrocatalysts for the ORR is also reviewed. Finally, we provide insights into the remaining challenges and directions for future perspectives and research.
Co-reporter:Jiali Wang, Fuyi Chen, Yachao Jin and Roy L. Johnston
Journal of Materials Chemistry A 2016 - vol. 4(Issue 45) pp:NaN17837-17837
Publication Date(Web):2016/10/27
DOI:10.1039/C6TA07519C
Bimetallic AuNi nanodendrite catalysts have been prepared for the oxygen reduction reaction (ORR) in alkaline media by a facile electrodeposition and electrochemical dealloying method. The dealloyed AuNi catalyst consists of hierarchical dendrites with a high electrochemically active surface area. The half-wave potential (E1/2) of the dealloyed AuNi catalyst is 0.896 V vs. RHE, exhibiting about 67 and 27 mV positive shift relative to the commercial Pt/C and as-prepared (before dealloying) AuNi catalysts, respectively. Compared to the commercial Pt/C catalyst, the dealloyed AuNi achieves a 2.8-fold improvement in specific activity at 0.8 V vs. RHE and suffers less degradation of the ORR activity after 5000 potential cycles. The ORR catalyzed by the bimetallic AuNi catalyst proceeds through a four-electron pathway in basic solution. TEM and XPS characterizations indicate that the enhancement of ORR activity is attributed to the favorable morphology and electronic effect caused by the incorporation of Ni atoms into the Au substrate. Dealloyed AuNi hierarchical dendrites possess great application potential as cathode electrocatalysts in metal-air batteries and alkaline fuel cells due to the facile preparation, high ORR activity and long-term cycling durability.
Co-reporter:Xiaoqiang Wu, Fuyi Chen, Nan Zhang, Adnan Qaseem and Roy L. Johnston
Journal of Materials Chemistry A 2016 - vol. 4(Issue 9) pp:NaN3537-3537
Publication Date(Web):2016/01/29
DOI:10.1039/C5TA09266C
Highly active electrocatalysts with good long term stability are vital for the commercialization of metal air batteries and alkaline fuel cells which involve the oxygen reduction reaction (ORR) at the cathode end. Herein, we developed a pulsed laser deposition (PLD) technique for the precise fabrication of silver–copper metallic glass (AgCu-MG) electrocatalysts. This PLD technique provides excellent control over the surface microtopography along with high flexibility for the deposition of different compositions of silver–copper metallic glass electrocatalysts onto nickel foam. Among all investigated Ag-based catalysts, AgCu-MG catalysts exhibit high electrocatalytic activity with a half-wave potential of 0.67 V (vs. RHE) which can be in situ enhanced by dealloying treatment in N2 saturated 0.1 M KOH solution. In situ dealloying of the AgCu-MG provides exceptional ORR catalytic activity with a half-wave potential of 0.78 V (vs. RHE) at 1600 rpm, which is comparable to 0.81 V (vs. RHE) of commercial Pt/C-20%. The AgCu-MG electrocatalyst showed excellent long-term stability in rechargeable zinc–air batteries. After 1000 charge–discharge cycles at 20 mA cm−2, the discharge voltage of batteries was stable at 1.0 V demonstrating the potential application of AgCu-MG as an alternative to Pt/C-20% in zinc–air batteries and alkaline fuel cells.
