Applications In Energy Conversion Devices Research Articles

Polymorphic Structure of 1T´-Mo6Te6 Nanoplates and Few-atomic-layered 2H-MoTe2 for Efficient Pseudocapacitor

Te-based transitional metal dichalcogenides (TMDs) as supercapacitors are gaining substantial attention with a few reports. The integration of 1T´-Mo6Te6 nanoplates (NPs) into few-atomic-layered two dimensional (2D) 2H-MoTe2 thin film has not been realized in supercapacitive studies. Herein, we demonstrate the growth of 1T´-Mo6Te6 NP/2H-MoTe2 thin film polymorphic structure through metal organic chemical vapor deposition (MOCVD) on Si/SiO2 and thereby, the successful transfer of these polymorphic structure on a flexible nickel (Ni) foam current collector by simple chemical etching protocol for high performance supercapacitors. A layer by layer study of the Mo6Te6/MoTe2 polymorphic structure is carried out by varying the number of transfer layers on the Ni foam. The resultant supercapacitors demonstrate a three-fold enhancement in areal capacitance (1542 mFcm-2 at 10 mVs-1) compared to a single layer transferred electrode, together with remarkable electrochemical stability (96%) and high energy density (140.36 mWcm-2 at 4 mA). These supercapacitors outperform the TMD-based (Te-based) supercapacitors presented in the past, demonstrating the high potential for their application in energy conversion devices. Keywords: 2D TMD, 1T´ phase, molybdenum ditelluride, 1D/2D polymorphic structure, supercapacitor

Insight into the excellent catalytic activity of (CoMo)S2/graphene for hydrogen evolution reaction

Electrochemical water splitting has become a potential pathway for sustainable hydrogen production, where high-efficiency low-cost catalysts are highly desirable. MoS2 is a promising candidate to substitute effective but expensive Pt-based catalysts for hydrogen evolution reaction. In this work, the computer simulation results reveal that alloying with Co and compositing with graphene could significantly improve the electrocatalytic performance of MoS2 thanks to the activation of MoS2 inert surfaces and enhanced electron transport. Based on this finding, we designed and synthesized a catalyst of (CoMo)S2/graphene, which exhibits excellent performance with low onset potential (28 mV), overpotential (100 mV) for driving a current density of 10 mA cm−2, and Tafel slope (60.8 mV dec-1), superior to most of MoS2-based electrocatalysts reported in open literatures. This study supplies important information for fundamental understanding of high-efficiency non-noble electrocatalysts toward applications in energy-conversion devices.

Efficient supercapacitor based on polymorphic structure of 1T′-Mo6Te6 nanoplates and few-atomic-layered 2H-MoTe2: A layer by layer study on nickel foam

Te-based transitional metal dichalcogenides (TMDs) as supercapacitors are gaining substantial attention with a few reports. The integration of 1T′-Mo6Te6 nanoplates (NPs) into few-atomic-layered two dimensional (2D) 2H-MoTe2 thin film has not been realized in supercapacitive studies. Herein, we demonstrate the growth of 1T′-Mo6Te6 NP/2H-MoTe2 thin film polymorphic structure through metal organic chemical vapor deposition (MOCVD) on Si/SiO2 and thereby, the successful transfer of these polymorphic structure on a flexible nickel (Ni) foam current collector by simple chemical etching protocol for high performance supercapacitors. A layer by layer study of the Mo6Te6/MoTe2 polymorphic structure is carried out by varying the number of transfer layers on the Ni foam. The resultant supercapacitors demonstrate a three-fold enhancement in areal capacitance (1542 mFcm−2 at 10 mVs−1) compared to a single layer transferred electrode, together with remarkable electrochemical stability (96%) and high energy density (140.36 mWcm−2 at 4 mA). These supercapacitors outperform the TMD-based (Te-based) supercapacitors presented in the past, demonstrating the high potential for their application in energy conversion devices.

Emerging Electrochemical Energy Applications of Graphdiyne

Download : Download high-res image (101KB) Download : Download full-size image Yuliang Li is a Professor at the Institute of Chemistry, Chinese Academy of Sciences. His research interests lie in the fields of design and synthesis of functional molecules, self-assembly methodologies of low-dimension and large-size molecular aggregations structures, and chemistry of carbon and rich carbon, with particular focus on the design and synthesis of photo-/electro-active molecular heterojunction materials and nanoscale and nano-structural materials. Download : Download high-res image (146KB) Download : Download full-size image Zicheng Zuo received his doctorate degree in Professor Yuliang Li’s group in 2011 in ICCAS. He is now an associate professor in Professor Yuliang Li’s group. His research interests focus on the synthesis of graphdiyne-based materials and investigating their applications in energy conversion devices.

Fe3C/Fe2O3 heterostructure embedded in N-doped graphene as a bifunctional catalyst for quasi-solid-state zinc–air batteries

The development of nonprecious metal catalysts with highly efficient and durable activities is of great importance for high performances of zinc–air batteries. Herein, the N-doped graphene wrapped Fe3C/Fe2O3 heterostructure has been designed as a bifunctional oxygen catalyst for zinc–air batteries. In the synthesis process of the catalyst, graphene oxide (GO) can assemble with graphitic carbon nitride (g-C3N4) and FeOOH nanorods by the π−π stacking and hydrogen bonds, respectively. The assembly of GO, g-C3N4 and FeOOH nanorods results in nanostructure of carbon layers coated iron species and leads to outstanding durability in both alkaline and acidic media. The synergistic effect of nitrogen doping and Fe3C/Fe2O3 heterostructure allows the catalyst (Fe3C/Fe2O3@NGNs) to display high oxygen reduction and evolution reaction activities. The liquid zinc–air battery assembled with the catalyst presented a remarkable peak power density (139.8 mW cm−2), large specific capacity (722 mAh g−1) and excellent charging–discharging cycling performance. The quasi-solid-state zinc–air battery with the catalyst exhibited an impressive open-circuit voltage and a peak power density. Therefore, the Fe3C/Fe2O3@NGNs catalyst is expected to have a bright future for practical applications in energy conversion devices.

Flexoelectricity in Monolayer Transition Metal Dichalcogenides.

Flexoelectricity, the coupling effect of the strain gradient and charge polarization, is an important route to tune electronic properties of low-dimensional materials. Here our extensive first-principles calculations reveal that structural wrinkling and corrugation will cause significant flexoelectricity in transition metal dichalcogenide (TMD) monolayers. The flexoelectricity is induced by the strain gradients created along the finite thickness of the wrinkled TMD monolayers and becomes more dominant in determining out-of-plane polarizations with decreasing wavelengths of the TMD wrinkles. According to the first-principles calculations and whole structural symmetry, a theoretical model is developed to describe the total out-of-plane polarizations and flexoelectric effect of the wrinkled TMD monolayers. The unveiled flexoelectricity in monolayer TMDs highlights a potential for their application in energy conversion devices.

π-Conjugated Molecule Boosts Metal-Organic Frameworks as Efficient Oxygen Evolution Reaction Catalysts.

To improve the efficiency of water electrolysis, developing efficient oxygen evolution reaction (OER) electrocatalysis is extremely important due to its four-electron transfer dynamics. In this work, a π-conjugated molecule (2,3,6,7,10,11-hexahydroxytriphenylene, HHTP), which can accelerate the electron transfer, is coated directly on pristine ZIF-67, resulting in a composite named HHTP@ZIF-67, via a simple one-step solvothermal method. The obtained HHTP@ZIF-67 possesses a Brunauer-Emmett-Teller surface area of 2013.9 m2 g-1 and displays microporous behavior, which can provide enough active sites for OER. The double-layer capacitance of HHTP@ZIF-67 is also enhanced, corresponding to an enlarged electrochemical active surface area. HHTP@ZIF-67 presents a quite low overpotential of 238 mV at 10 mA cm-2 in 1.0 m KOH. This material synthesized via the simple coating strategy is promising in the application of energy conversion devices.

Binary Nitrogen Precursor-Derived Porous Fe-N-S/C Catalyst for Efficient Oxygen Reduction Reaction in a Zn-Air Battery

It is still a challenge to synthesize non-precious-metal catalysts with high activity and stability for the oxygen reduction reaction (ORR) to replace the state-of-the art Pt/C catalyst. Herein, a Fe, N, S co-doped porous carbon (Fe-NS/PC) is developed by using g-C3N4 and 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ) as binary nitrogen precursors. The interaction of binary nitrogen precursors not only leads to the formation of more micropores, but also increases the doping amount of both iron and nitrogen dispersed in the carbon matrix. After a second heat-treatment, the best Fe/NS/C-g-C3N4/TPTZ-1000 catalyst exhibits excellent ORR performance with an onset potential of 1.0 V vs. reversible hydrogen electrode (RHE) and a half-wave potential of 0.868 V (RHE) in alkaline medium. The long-term durability is even superior to the commercial Pt/C catalyst. In the meantime, an assembled Zn-air battery with Fe/NS/C-g-C3N4/TPTZ-1000 as the cathode shows a maximal power density of 225 mW·cm−2 and excellent durability, demonstrating the great potential of practical applications in energy conversion devices.

Hierarchical tubular structures composed of CoPx and carbon nanotubes: Highly effective electrocatalyst for oxygen reduction

Development of high-efficiency and low-cost nonprecious-metal-based electrocatalysts with high activity and stability for oxygen reduction reaction (ORR) is critical for large-scale application in energy conversion devices. A novel approach to fabricate hierarchically porous carbon encapsulated with CoPx nanoparticles and wired with carbon nanotubes (NC@CoPx/PyCNTs) was developed. An optimal sample of the NC@CoPx/PyCNTs-900 material displayed excellent electrocatalytic performance for ORR with onset and half-wave potentials of ∼0.92 V vs. RHE and 0.80 V vs. RHE in 0.1 M KOH, respectively, as well as a small Tafel slope of 85 mV/dec. It is noteworthy that the mass activity of NC@CoPx/PyCNTs was 9.8 times higher than commercial 20% Pt/C. In addition, NC@CoPx/PyCNTs exhibited remarkable long-term cycling stability and methanol tolerance, which were superior to commercially Pt/C catalyst. The interaction of the hierarchically porous carbon, CoPx nanoparticles, and carbon nanotubes in NC@CoPx/PyCNTs were observed. Moreover, good electron conductivity and high specific surface area also contributed to the enhanced ORR performance. This work is expected to open up new avenues for the rational design and development of low-cost and highly active ORR catalysts for energy technologies.

Enhancement of nitrogen self-doped nanocarbons electrocatalyst via tune-up solution plasma synthesis.

The development of a metal-free carbon based electrocatalyst for the oxygen reduction reaction (ORR) is an essential issue for energy conversion systems. Herein, we suggest a tune-up solution plasma (SP) synthesis based on a simple one-step and cost-effective method to fabricate nitrogen self-doped graphitic carbon nanosheets (NGS) as an electrocatalyst. This novel strategy using a low-pass filter circuit provides plasma stability and energy control during discharge in pyridine, determining the graphitic structure of nanocarbons doped with nitrogen. Notably, NGS have a relatively high surface area (621 m2 g−1), and high contents of nitrogen bonded as pyridinic-N and pyrrolic-N of 55.5 and 21.3%, respectively. As an efficient metal-free electrocatalyst, NGS exhibit a high onset potential (−0.18 V vs. Ag/AgCl) and a 3.8 transferred electron pathway for ORR in alkaline solution, as well as better long-term durability (4% current decrease after 10 000 s of operation) than commercial Pt/C (22% current drop). From this point of view, the nitrogen self-doped graphitic carbon nanosheet material synthesized using the tune-up SP system is a promising catalyst for the ORR, as an alternative to a Pt catalyst for application in energy conversion devices.

Enhanced light-harvesting by plasmonic hollow gold nanospheres for photovoltaic performance.

A ‘sandwich'-structured TiO2NR/HGN/CdS photoanode was successfully fabricated by the electrophoretic deposition of hollow gold nanospheres (HGNs) on the surface of TiO2 nanorods (NRs). The HGNs presented a wide surface plasmon resonance character in the visible region from 540 to 630 nm, and further acted as the scatter elements and light energy ‘antennas' to trap the local-field light near the TiO2NR/CdS layer, resulting in the increase of the light harvesting. An outstanding enhancement in the photochemical behaviour of TiO2NR/HGN/CdS photoanodes was attained by the contribution of HGNs in increasing the light absorption and the number of electron-hole pairs of photosensitive semiconductors. The optimized photochemical performance of TiO2NR/HGN/CdS photoanodes by using plasmonic HGNs demonstrated their potential application in energy conversion devices.

Chemical crosslinking engineered nitrogen-doped carbon aerogels from polyaniline-boric acid-polyvinyl alcohol gels for high-performance electrochemical capacitors

The hierarchically porous nitrogen-doped polyaniline-boric acid-polyvinyl alcohol (PBP) carbon aerogels (PBP/CAs) are synthesized through chemical crosslinking engineered and KOH activation processes. The optimal sample with a high BET surface area of 2675 m2 g−1, a wide micropore and mesopores size distribution (0.5–4 nm), in-situ nitrogen-doping (0.50%) and surface hydrophilicity (contact angle is 12.9°), exhibits a high specific capacitance of 497 F g−1 in 1 mol L−1 H2SO4 and 400 F g−1 in 6 mol L−1 KOH at a current density of 1 A g−1, and delivers excellent cycling stability with the capacitance retention of 92.80% and 90.71% after 10000 cycles at 30 A g−1, respectively. And it also reveals a high energy density of 12.60 Wh Kg−1 and 11.05 Wh Kg−1 in acid and alkaline electrolytes, respectively. More significantly, the assembled capacitors can be directly applied to degrade azo dye of 4-aminoazobenzene. Our work not only highlights the advantages of one-pot chemical crosslinking route to prepare nitrogen-doped PBP/CAs under ambient condition (e.g. room temperature, cost-effective raw materials, time-saving and routine equipment et al.), but also offers competitive electrodes for high-performance pH-universal electrochemical double-layer capacitor with a potential broad application in energy conversion devices.

Layer-by-layer assemblies of highly connected polyelectrolyte capped-Pt nanoparticles for electrocatalysis of hydrogen evolution reaction

Herein we present a simple one-step method to produce polyelectrolyte-capped Pt nanoparticles able to be assembled into layer-by-layer arrays with a linear dependence of the amount of deposited material on the number of dipping cycles. The resulting supramolecular films where fully characterized by AFM, XPS and ATR-FTIR. The electrochemical evaluation by cyclic voltammetry showed good electrochemical connection between the nanoparticles in both acidic and neutral solutions. The films assembled on graphite electrodes showed catalysis of the H2 production and the interconnection between nanoparticles proved to be effective up to 20 bilayers. Results presented here reveal an easy procedure to obtain stable arrays of well-dispersed electroactive 2nm-diameter Pt nanoparticles on a variety of substrates with direct potential applications in energy conversion devices.

Structure induced tunable magnetic properties of Zn substituted Mn1−xZnxFe2O4(x= 0–1) NPs

Mn1−xZnxFe2O4 nanoparticles (MZ NPs) owing to their Zn content dependent tunable magnetic properties have potential applications in energy conversion devices and in nanomedicine. It is a well-recognised fact that magnetism of MZ NPs has critical dependence on degree of Zn substitution at tetrahedral sites. In addition, the role of cation distribution between the tetrahedral and octahedral sites for a particular degree of Zn-substitution, i.e. the degree of inversion (δ) also influences their magnetic characteristics. However, the exact correlation between distribution of bivalent metal ions between tetrahedral and octahedral sites and corresponding magnetic characteristics is not well understood. In order to explore this structural dependence of magnetic characteristics of MZ NPs, a series of Mn1−x Zn x Fe2O4 (x = 0−1) nanoparticles have been synthesized by chemical co-precipitation method. Saturation magnetisation and Curie temperature of MZ NPs are strongly correlated with the degree of inversion and exchange interactions between the magnetic ions, while the coercivity and remanence is independent of it and only depends on crystallite size. Both saturation magnetisation and Curie temperature decreases with increasing Zn substitution into spinel matrix. This could be attributed to the weakening of strong (A-B) inter lattice super exchange interaction instead partial substitution of Zn at octahedral Mn sites.

Nitrogen‐Doped Hierarchical Porous Carbons Derived from Sodium Alginate as Efficient Oxygen Reduction Reaction Electrocatalysts

AbstractThe exploration of earth‐abundant and low‐cost eco‐friendly materials with an excellent electrocatalytic performance is crucial for sustainable energy development. In this work, 3 D N‐doped hierarchical porous carbon (NC) materials with an interconnected mesoporous/macroporous structure have been synthesized by the simple single‐step pyrolysis of naturally available sodium alginate in the presence of urea. The systematic investigation of the pyrolysis temperature on the performance in the oxygen reduction reaction in 0.1 m KOH solution indicates that the catalyst obtained at 900 °C (NC‐900) exhibits the best catalytic performance because of the high degree of graphitization and the unique hierarchical porous structure. Furthermore, NC‐900 exhibits an excellent durability and a remarkable resistance to methanol poisoning compared to Pt/C in alkaline solution. This work highlights the significance and potential of biomass‐derived hierarchical porous carbon materials for applications in energy conversion devices.

Low power loss in Fe65.5Cr4Mo4Ga4P12B5.5C5 bulk metallic glasses

Power loss – one of the important application-oriented magnetic properties of ferromagnetic metallic glasses – has been well studied in glassy ribbons rather than bulk metallic glasses. This paper studies the influence of frequency, induction, annealing, and specimen thickness on the total power loss – which is divided into hysteresis loss, classical eddy current loss, and excess eddy current loss – of bulk ferromagnetic Fe65.5Cr4Mo4Ga4P12B5.5C5 glasses. The total power loss of bulk glasses increases with frequency and peak induction and follows a power relation, similar to what has been observed in glassy ribbons. Annealing decreases both the hysteresis loss and the classical eddy current loss, resulting in a lower total power loss. The ratio of excess eddy current loss to classical eddy current loss deceases with increasing specimen thickness. The excess eddy current loss is negligible for our thickest glass and comparable to the classical eddy current loss for our thinner glasses. In contrast, the excess eddy current loss is often at least one to two orders of magnitude greater than the classical eddy current loss in glassy ribbons. The low total power loss achieved in bulk ferromagnetic glasses should be beneficial to their practical applications in energy conversion devices.

Development of low viscous ionic liquids: the dependence of the viscosity on the mass of the ions

Straightforward syntheses of selected non-deuterated, partially deuterated, and fully deuterated room temperature ionic liquids (ILs) with the anions tris(pentafluoroethyl)trifluorophosphate, tetracyanoborate, and methyl sulfate were developed. The viscosity and the density of these ionic liquids were measured at various temperatures. The dissociation rate of the ionic liquid, the sizes of the cation and the anion, and the nature of the inter-ionic interaction are not influenced by deuteration, but viscosity is. All deuterated ionic liquids possess a higher viscosity and density in comparison to non-deuterated ones. The explanation of this phenomenon is given and discussed based on the modified Stokes-Einstein equation with a parameter which reflects the mass of the diffused particles. This new knowledge supports the recent development of novel low viscous inert ionic liquids which are of particular interest for the application in energy conversion devices. Deuterated ionic liquids are valuable media for the investigation of chemical reactions, natural products, and bio-materials by means of the NMR spectroscopy.

Two-dimensional molybdenum carbides: potential thermoelectric materials of the MXene family

A newly synthesized family of two-dimensional transition metal carbides and nitrides, so-called MXenes, exhibit metallic or semiconducting properties upon appropriate surface functionalization. Owing to their intrinsic ceramic nature, MXenes may be suitable for energy conversion applications at high temperature. Using the Boltzmann theory and first-principles electronic structure calculations, we explore the thermoelectric properties of monolayer and multilayer M2C (M = Sc, Ti, V, Zr, Nb, Mo, Hf, and Ta) and M2N (M = Ti, Zr, and Hf) MXenes functionalized with F, OH, and O groups. From our calculations, it turns out that monolayer and multilayer nanosheets of Mo2C acquire superior power factors to other MXenes upon any type of functionalization. We therefore propose the functionalized Mo2C nanosheets as potential thermoelectric materials of the MXene family. The exceptional thermoelectric properties of the functionalized Mo2C nanosheets are attributed to the peculiar t2g band shapes, which are a combination of flat and dispersive portions. These types of band shapes allow Mo2C to gain a large Seebeck coefficient and simultaneously a good electrical conductivity at low carrier concentrations.

Photovoltaic performance enhancement of CdS quantum dot-sensitized TiO2 photoanodes with plasmonic gold nanoparticles

The CdS quantum dot-sensitized TiO2 films with plasmonic gold nanoparticles were designed as photoanodes by the electrodeposition of gold combined with the “successive ionic layer adsorption and reaction” (SILAR) method for CdS deposition on porous TiO2 films. A prominent enhancement in light absorption of Au/TiO2/CdS hybrid was attained by efficient light scattering of gold plasmons as sub-wavelength antennas and concentrators. The photogenerated electron formed in the near-surface region of TiO2 and CdS were facilitated to transfer to the plasmonic gold, resulting in the enhancement of photocurrent and incident photon-to-current conversion efficiency of hybrid photoanode upon photoirradiation. Furthermore, the photovoltaic response of hybrid was highly tunable with respect to the number of SILAR cycles applied to deposit CdS. The thicker absorber layer with less porous structure and larger CdS crystals might limit the electrolyte diffusion into the hybrid electrode and impose a barrier for electron tunneling and transferring. The highly versatile and tunable properties of Au/TiO2/CdS photoanodes demonstrated their potential application in energy conversion devices.

Layer-by-layer assembled porous CdSe films incorporated with plasmonic gold and improved photoelectrochemical behaviors

A simple method for creating three-dimensional porous wurtzite CdSe films incorporated with plasmonic gold by the electrochemical layer-by-layer assembly was proposed. A prominent enhancement in light absorption of CdSe films was attained by the efficient light scattering of gold plasmons as sub-wavelength antennas and concentrators and the near-field coupling of gold plasmons with the neighboring porous CdSe films. The broadband photocurrent enhancement of Au–CdSe composite systems in the visible light range and the local current maximum between 600 and 700nm suggested the cooperative action of antenna effects and electromagnetic field enhancement resulting from localized surface plasmon excitation of gold. Furthermore, the photoelectrochemical response of porous Au–CdSe composite films was highly tunable with respect to the number of Au–CdSe bilayer. The optimal short-circuit current and open-circuit potential were obtained in a four-layer Au–CdSe system because the thicker absorber layer with less porous structure might limit the electrolyte diffusion into the hybrid electrode and impose a barrier for electron tunneling and transferring. The highly versatile and tunable properties of assembled porous Au–CdSe composite films demonstrated their potential application in energy conversion devices.