Now showing items 1-20 of 2725

    • Elusive Dzyaloshinskii-Moriya interaction in monolayer Fe3GeTe2

      Laref, Slimane; Kim, Kyoung-Whan; Manchon, Aurelien (Physical Review B, American Physical Society (APS), 2020-08-07) [Article]
      Using symmetry analysis and density functional theory calculations, we uncover the nature of the Dzyaloshinskii-Moriya interaction in monolayer Fe3GeTe2. We show that while such an interaction might result in small distortions of the magnetic texture in the short range, in the long range it favors in-plane Néel spin spirals along equivalent directions of the crystal structure. Whereas our results show that the observed Néel skyrmions cannot be explained by the Dzyaloshinskii-Moriya interaction at the monolayer level, they suggest that a canted magnetic texture shall arise at the boundary of Fe3GeTe2 nanoflakes or nanoribbons and, most interestingly, that homochiral planar magnetic textures could be stabilized.
    • Magneto-transport Mechanism of Individual Nanostructures via Direct Magnetoresistance Measurement in situ SEM

      Zhang, Junwei; Peng, Yong; Ma, Hongbin; Zhang, Senfu; Hu, Yang; Zeng, Xue; Deng, Xia; Guan, Chaoshuai; Chen, Rongrong; Hu, Yue; Karim, Abdul; Tao, Kun; Zhang, Mingjie; Zhang, Xixiang (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2020-08-05) [Article]
      The accurate magnetoresistance (MR) measurement of individual nanostructures is essential and important for either the enrichment of fundamental knowledge of magneto-transport mechanism or the facilitation of desired design of magnetic nanostructures for various technological applications. Herein, we report a deep investigation on the magneto-transport mechanism of single CoCu/Cu multilayered nanowire via direct magnetoresistance measurement by using our invented magnetotransport instrument in-situ scanning electron microscope (SEM). Off-axis electron holography experiments united with micromagnetic simulation prove that the CoCu layers in CoCu/Cu multilayered nanowires are formed a single-domain structure, in which the alignment of magnetic moments is mainly determined by shape anisotropy. The MR of the single CoCu/Cu multilayered nanowire is measured to be only 1.14% when the varied external field is applied along nanowire length axis, which matches with the theoretical prediction of Granular Films model. Density functional theory (DFT) calculations further disclose that spin-dependent scattering at the interface between magnetic and nonmagnetic layers is responsible for the intrinsic magnetotransport mechanism
    • Synergetic Contributions in Phase Boundary Engineering to the Piezoelectricity of Potassium Sodium Niobate Lead-Free Piezoceramics

      Lv, Xiang; Zhang, Junwei; Liu, Yao; Li, Fei; Zhang, Xixiang; Wu, Jiagang (ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2020-08-04) [Article]
      Although the pronounced piezoelectricity was obtained in (K, Na)NbO3 piezoceramics with the phase boundary engineering (PBE), the physical mechanisms remain pending. Here we revealed for the first time how PBE influences the piezoelectric properties through synergetic contributions. Cryogenic experiments confirm that PBE constructs a phase coexistence, consisting of rhombohedral (R), orthorhombic (O), and tetragonal (T) phases, with a structural softening, by which a high piezoelectric coefficient d33 of 555 pC/N and the enhanced temperature stability of strain are achieved. The phenomenological theory and transmission electron microscope demonstrate that the superior d33 hinges on the flattened Gibbs free energy and the abundant nano-domains (10-80 nm), which respectively induce the enhanced permittivity and the coexisting single-domain and multi-domain zones. In particular, we disclosed a trade-off relationship between ferroelectric domains and polarnanoregions (PNRs) and found the “double-edged sword” role of PNRs in the piezoelectricity enhancement. Therefore, this work helps understand the physical mechanisms of the piezoelectricity enhancement, benefiting the future research of lead-free piezoceramics.
    • In Situ Plasma-Grown Silicon-Oxide for Polysilicon Passivating Contacts

      Alzahrani, Areej A.; Allen, Thomas; de Bastiani, Michele; Van Kerschaver, Emmanuel; Harrison, George T.; Liu, Wenzhu; De Wolf, Stefaan (Advanced Materials Interfaces, Wiley, 2020-07-29) [Article]
      Large-scale manufacturing of polysilicon-based passivating contacts for high-efficiency crystalline silicon (c-Si) solar cells demands simple fabrication of thermally stable SiOx films with well controlled microstructure and nanoscale thickness to enable quantum-mechanical tunneling. Here, plasma-dissociated CO2 is investigated to grow in situ thin (<2 nm) SiOx films on c-Si wafers as tunnel-oxides for plasma-deposited, hole-collecting (i.e., p-type) polysilicon contacts. It is found that such plasma processing offers excellent thickness control and superior structural integrity upon thermal annealing at 1000 °C, compared to state-of-the-art wet-chemical oxides. As a result, p-type polysilicon contacts are achieved on n-type c-Si wafers that combine excellent surface passivation, resulting in an implied open-circuit voltage exceeding 700 mV, with a contact resistance as low as 0.02 Ω cm2.
    • Enhanced Thermoelectric Performance and Lifetime in Acid-Doped PEDOT:PSS Films via Work Function Modification

      Villalva, Diego Rosas; Haque, Mohammed; Nugraha, Mohamad; Baran, Derya (ACS Applied Energy Materials, American Chemical Society (ACS), 2020-07-28) [Article]
      In recent years, most of the work on p-type organic thermoelectrics focus on improving the thermoelectric properties of PEDOT:PSS through a sequential doping-dedoping process. However, the air-stability of thermoelectric parameters of these systems, which is essential for the realization of reliable devices remains largely unexplored. In this study, Poly (ethyleneimine)-ethoxylate (PEIE) acts as a work function modification agent and encapsulation layer to improve the thermoelectric performance and air-stability of nitric acid (HNO3) doped PEDOT:PSS films. The evaporation of HNO3 is responsible for a simultaneous decrease in electrical conductivity and an increase in the Seebeck coefficient leading to the degradation of the power factor. PEIE reduces the evaporation of HNO3 from PEDOT:PSS, and increases the power factor from 72 to 168 μW m-1K-2. After a week of exposure to air, the films show a power factor of 124 μW m-1K-2, retaining 74% of its initial thermoelectric merits. These results underscore the importance of PEIE as a material for enhancing thermoelectric performance and air-stability in the development of polymer-based thermoelectrics.
    • Fluorophosphates: Next Generation Cathode Materials for Rechargeable Batteries

      Sharma, Lalit; Adiga, Shashishekar P.; Alshareef, Husam N.; Barpanda, Prabeer (Advanced Energy Materials, Wiley, 2020-07-27) [Article]
      Cost, safety, and cycle life have emerged as prime concerns to build robust batteries to cater to the global energy demand. These concerns are impacted by all battery components, but the realizable energy density of lithium-ion batteries (LIBs) is limited by the performance of cathodes. Thus, cathode materials have a significant role to play in advancing the performance and economics of secondary batteries. To realize next generation Li-ion and post Li-ion batteries, a variety of cathode insertion materials have been explored, but finding a cost effective and stable cathode material that can deliver high energy density has been a daunting task. Oxide cathode materials are ubiquitous in commercial applications, as they can deliver high capacity. In comparison, polyanionic insertion materials can offer tuneable (high) redox potential, operational safety, and structural as well as thermal stability. Indeed, a wide range of polyanionic materials like phosphates, borates, sulfates, and their complexes have been reported. In this article, the alkali metal fluorophosphates class of polyanionic cathodes for secondary batteries is discussed. The various reported fluorophosphate insertion materials are discussed in terms of their electrochemical and electrocatalytic properties. The historical overview, recent progress, and remaining challenges for polyanionic fluorophosphates are presented along with suggested future research directions and potential application.
    • The Role of Adding Bi0.5A0.5ZrO3 in Affecting Orthorhombic-Tetragonal Phase Transition Temperature and Electrical Properties in Potassium Sodium Niobate Ceramics

      Lv, Xiang; Zhang, Nan; Wu, Jiagang; Zhang, Xixiang (Acta Materialia, Elsevier BV, 2020-07-25) [Article]
      By studying the alone and synergetic effects of Zr4+ and Bi3+ on potassium sodium niobate ((K, Na)NbO3, KNN) ceramics, we revealed how Bi0.5A0.5ZrO3 (A = K, Na, Ag, and (Na0.82K0.18)) reduces the orthorhombic-tetragonal phase transition temperature (TO–T) of KNN ceramics. Investigations into the alone effects reveal that aliovalent substitutions on K+/Na+ (Nb5+) with Bi3+ (Zr4+) inevitably destroy long-range ordering (LRO) and thus worsen piezo/ferroelectric properties. Despite this, Zr4+ can replace Nb5+ within a high content, remain an orthorhombic (O) phase, and slightly increase TO–T. Although substituting on K+/Na+ with Bi3+ decreases TO–T, it already significantly destroyed LRO before shifting TO–T to room temperature. Then, investigations into the synergetic effects show that Zr4+ acts as a buffer, Bi3+ is an accelerator, and A+ is a stabilizer. The buffer can exist in KNN ceramics within a high content and neutralizes the charges caused by the accelerator that concentrates on decreasing TO–T, and the stabilizer compensates for the stability of the perovskite phase. Their synergetic effects explain why Bi0.5A0.5ZrO3 can gradually reduce the TO–T of KNN ceramics without significantly destroying LRO. Therefore, this work helps understand how Bi0.5A0.5ZrO3 decreases TO–T and further design the phase boundary for KNN ceramics.
    • Model-Based Design of Graphite-Compatible Electrolytes in Potassium-Ion Batteries

      Zhang, Jiao; Cao, Zhen; Zhou, Lin; Liu, Gang; Park, Geon-Tae; Cavallo, Luigi; Wang, Limin; Alshareef, Husam N.; Sun, Yang-Kook; Ming, Jun (ACS Energy Letters, American Chemical Society (ACS), 2020-07-24) [Article]
      Potassium-ion batteries (KIBs) are attractive alternatives to lithium-ion batteries (LIBs) because of their lower cost and global potassium sustainability. However, designing compatible electrolytes with graphite anode remains challenging. This is because the electrolyte decomposition and/or graphite exfoliation (due to K+–solvent co-insertion) always exist, which is much harder to overcome compared to the case of LIBs because of the higher activities of K+. Herein, we report a general principle to design compatible electrolytes with the graphite anode, where the K+ can be reversibly (de)intercalated. We find that the electrolyte composition is critical to determining the graphite performance, which can be tuned by the kind of solvent, anion, additives, and concentration. We present a new interfacial model to understand the variation in performance (i.e., K+ (de)intercalation or K+–solvent co-insertion or decomposition). Our model is distinctly different from the solid electrolyte interphase interpretation. This work offers new opportunities to design high-performance KIBs and potassium-ion sulfur batteries. Particularly, we present new guideline to design electrolytes for KIBs and other advanced mobile (ion) batteries.
    • A Structurally Simple but High-Performing Donor–Acceptor Polymer for Field-Effect Transistor Applications

      Aniés, Filip; Wang, Simeng; Hodsden, Thomas; Panidi, Julianna; Fei, Zhuping; Jiao, Xuechen; Wong, Yi Hang Cherie; McNeill, Christopher R.; Anthopoulos, Thomas D.; Heeney, Martin (Advanced Electronic Materials, Wiley, 2020-07-20) [Article]
      A straightforward synthesis is reported for four structurally simple donor–acceptor conjugated polymers based on an alkylated difluorobenzotriazole and either unsubstituted bithiophene (T2) or thienylvinylthiophene (TVT) co-monomers. Two solubilizing sidechains are investigated in which the position of the branching point is moved away from the conjugated backbone. Optoelectronic measurements and density functional theory calculations show very similar energetic properties between the polymers, with a slightly narrower bandgap for the vinylene incorporating TVT polymers as a result of extended conjugation. Transistor measurements demonstrate that the simplest polymer, containing a readily available 2-decyltetradecyl sidechain with a T2 co-monomer, exhibits the best device performance, with an average saturated mobility of 0.2 cm2 V−1 s−1.
    • Fast, wafer-scale growth of a nanometer-thick graphite film on Ni foil and its structural analysis.

      Deokar, Geetanjali; Genovese, Alessandro; Da Costa, Pedro M. F. J. (Nanotechnology, IOP Publishing, 2020-07-18) [Article]
      The growth of graphite on polycrystalline Ni by chemical vapor deposition (CVD) and the microstructural relation of the graphitic films and the metallic substrate continues to puzzle the scientific community. Here, we report the wafer-scale growth of a nanometer-thick graphite film (~100 nm, NGF) on Ni foil via a fast-thermal CVD approach (5 min growth). Moreover, we shed light on how localized thickness variations of the NGF relate to the Ni surface topography and grain characteristics. While on a macro-scale (mm2), the NGF film looks uniform - with a few hundreds of highly ordered graphene layers (d0002 = 0.335 nm), when studied at the micro- and nano-scales, few-layer graphene sections can be identified. These are present at a density of 0.1-3% areas in 100 µm2, can be as thin as two layers, and follow an epitaxial relation with the [111] fcc-Ni planes. Throughout the 50 cm2 NGF, the sharp graphite/substrate interfaces are either composed of a couple of NiCx layers or a graphene layer. Moreover, the NGF was successfully transferred on SiO2/Si substrate by a wet chemical etching method. The as-produced NGFs could complement or offer an alternative to the mm-thick films produced from natural graphite flakes or polymer sheets.
    • Atomic Layer Deposition of Vanadium Oxide as Hole-Selective Contact for Crystalline Silicon Solar Cells

      Yang, Xinbo; Xu, Hang; Liu, Wenzhu; Bi, Qunyu; Xu, Lujia; Kang, Jingxuan; Hedhili, Mohamed N.; Sun, Baoquan; Zhang, Xiaohong; De Wolf, Stefaan (Advanced Electronic Materials, Wiley, 2020-07-16) [Article]
      High carrier recombination loss at the contact regions has become the dominant factor limiting the power conversion efficiency (PCE) of crystalline silicon (c-Si) solar cells. Dopant-free carrier-selective contacts are being intensively developed to overcome this challenge. In this work, vanadium oxide (VOx ) deposited by atomic layer deposition (ALD) is investigated and optimized as a potential hole-selective contact for c-Si solar cells. ALD VOx films are demonstrated to simultaneously offer a good surface passivation and an acceptable contact resistivity (ρc) on c-Si, achieving a best contact recombination current density (J 0) of ≈40 fA cm−2 and a minimum ρc of ≈95 mΩ.cm2. Combined with a high work function of 6.0 eV, ALD VOx films are proven to be an effective hole-selective contact on c-Si. By the implementation of hole-selective VOx contact, the state-of-the-art PCE of 21.6% on n-type c-Si solar cells with a high stability is demonstarted. These results demonstrate the high potential of ALD VOx as a stable hole-transport layer for photovoltaic devices, with applications beyond c-Si, such as perovskite and organic solar cells.
    • Additive manufacturing assisted van der Waals integration of 3D/3D hierarchically functional nanostructures

      Fu, Jui-Han; Lu, Ang-Yu; Madden, Nathan J.; Wu, Christine C.; Chen, Yen-Chang; Chiu, Ming-Hui; Hattar, Khalid; Krogstad, Jessica A.; Chou, Stanley S.; Li, Lain-Jong; Kong, Jing; Tung, Vincent (Communications Materials, Springer Science and Business Media LLC, 2020-07-15) [Article]
      Van der Waals (vdW) integration, in which pre-engineered two-dimensional building blocks are physically assembled together in a chosen sequence through weak vdW interactions, holds promise toward previously unattainable applications. However, when extended to create 3D/3D monoliths, the lack of physical bonding coupled with the inherent rigidity and surface roughness between 3D building blocks makes it challenging for broader implementation of composites, catalysis, and energy applications. Here we demonstrate that electrostatically exfoliated two-dimensional layered materials can be additively manufactured to create complex layouts with selectively engineered composition in both lateral and vertical directions. Subsequent room-temperature dewetting creates non-covalent hinges through folded edges to concurrently interlock and nanostructure the two-dimensional inks into 3D building blocks. The result is the 3D/3D vdW mono- and heterostructures that are mechanically robust, electrically conductive, electrochemically active over a broad pH range and even radiation tolerant in nature
    • Janus Monolayers of Magnetic Transition Metal Dichalcogenides as an All-in-One Platform for Spin-Orbit Torque

      Smaili, Idris; Laref, Slimane; Garcia, Jose H.; Schwingenschlögl, Udo; Roche, Stephan; Manchon, Aurelien (arXiv, 2020-07-15) [Preprint]
      We theoretically predict that vanadium-based Janus dichalcogenide monolayers constitute an ideal platform for spin-orbit-torque memories. Using first principles calculations, we demonstrate that magnetic exchange and magnetic anisotropy energies are higher for heavier chalcogen atoms, while the broken inversion symmetry in the Janus form leads to the emergence of Rashba-like spin-orbit coupling. The spin-orbit torque efficiency is evaluated using optimized quantum transport methodology and found to be comparable to heavy nonmagnetic metals. The coexistence of magnetism and spin-orbit coupling in such materials with tunable Fermi-level opens new possibilities for monitoring magnetization dynamics in the perspective of non-volatile magnetic random access memories.
    • Speed enhancement of magnetic logic-memory device by insulator-to-metal transition

      Pu, Yuchen; Mou, Hongming; Lu, Ziyao; Nawaz, Seeraz; Wang, Guilin; Zhang, Zhigang; Yang, Yuanjun; Zhang, Xixiang; Zhang, Xiaozhong (Applied Physics Letters, AIP Publishing, 2020-07-14) [Article]
      Complementary metal-oxide-semiconductor logic circuits used in conventional computers require frequent communication with external nonvolatile memory, causing the memory wall problem. Recently reported magnetic logic with reconfigurable logic operation and built-in nonvolatile memory can potentially bridge this gap. However, its high-frequency performance is not well studied. Here, we first perform experimental and theoretical investigation on the switching time of magnetic logic-memory devices combining magnetic units and negative differential resistance (NDR) of semiconductors. It is found that the switching time of S-type NDR (transistor circuits) in logic operations is 300 ns and determined by the transistor’s internal turn-on properties. We then propose a magnetic logic-memory device by coupling the anomalous Hall effect in magnetic materials and the insulator-to-metal transition in VO2. Our device realizes reliable output (output ratio > 1000%), a low work magnetic field (<20 mT), and excellent high-frequency performance (switching time ¼ 1–10 ns).
    • Large Barocaloric Effect with High Pressure-Driving Efficiency in a Hexagonal MnNi0.77Fe0.23Ge Alloy

      Zeng, Qingqi; Shen, Jianlei; Liu, Enke; Xi, Xuekui; Wang, Wenhong; Wu, Guangheng; Zhang, Xixiang (Chinese Physics Letters, IOP Publishing, 2020-07-14) [Article]
      The hydrostatic pressure is expected to be an effective knob to tune the magnetostructural phase transitions of hexagonal MM'X alloys (M and M' denote transition metals and X represents main group elements). We perform magnetization measurements under hydrostatic pressure on an MM'X martensitic MnNi20.77Fe0.23Ge alloy. The magnetostructural transition temperature can be efficiently tuned to lower temperatures by applying moderate pressures, with a giant shift rate of -151 K/GPa. A temperature span of 30 K is obtained under the pressure, within which a large magnetic entropy change of -23 J⋅kg-1K-1 in a field change of 5 T is induced by the mechanical energy gain due to the large volume change. Meanwhile, a decoupling of structural and magnetic transitions is observed at low temperatures when the martensitic transition temperature is lower than the Curie temperature. These results show a multi-parameter tunable caloric effect that benefits the solid-state cooling.
    • A new concept to enhance piezoelectricity and temperature stability in KNN ceramics

      Lv, Xiang; Wu, Jiagang; Zhang, Xixiang (Chemical Engineering Journal, Elsevier BV, 2020-07-11) [Article]
      To relieve the sensitivity of piezoelectric coefficient (d33) to composition and strengthen temperature stability of strain in potassium sodium niobate {(K, Na)NbO3, KNN} ceramics, we proposed a new concept, tuning the trade-off between long-range ordering (LRO) and polar nanoregions (PNRs), and realized it by tailoring the content of bismuth (Bi) in an already-constructed multiphase coexistence, namely, 0.96(K0.48Na0.52)(Nb0.955Sb0.045)O3-0.04(BixNa4-3x)0.5ZrO3-0.3 mol%Fe2O3 ceramics. We obtained not only the high retention of > 83% at x = 0.80–1.10 in d33 but also higher d33 at x = 0.90–0.95, relieving the sensitivity of d33 to composition. We also obtained not only the enhanced strain but also the high retention of ≥ 79% over a wide temperature range of 20–180 °C at x = 1.10, irrespective of the electric field, strengthening the temperature stability. We demonstrated that high d33 values hinge on the trade-off between LRO and PNRs, and the enhanced temperature stability of strain originates from the diffused multiphase coexistence and the reduced contribution of domain switching. Therefore, the new concept helps further design high-performance KNN-based ceramics for practical application.
    • Defect Passivation in Perovskite Solar Cells by Cyano-Based π-Conjugated Molecules for Improved Performance and Stability

      Wang, Kai; Liu, Jiang; Yin, Jun; Aydin, Erkan; Harrison, George T.; Liu, Wenzhu; Chen, Shanyong; Mohammed, Omar F.; De Wolf, Stefaan (Advanced Functional Materials, Wiley, 2020-07-09) [Article]
      Defects at the surface and grain boundaries of metal–halide perovskite films lead to performance losses of perovskite solar cells (PSCs). Here, organic cyano-based π-conjugated molecules composed of indacenodithieno[3,2-b]thiophene (IDTT) are reported and it is found that their cyano group can effectively passivate such defects. To achieve a homogeneous distribution, these molecules are dissolved in the antisolvent, used to initiate the perovskite crystallization. It is found that these molecules are self-anchored at the grain boundaries due to their strong binding to undercoordinated Pb2+. On a device level, this passivation scheme enhances the charge separation and transport at the grain boundaries due to the well-matched energetic levels between the passivant and the perovskite. Consequently, these benefits contribute directly to the achievement of power conversion efficiencies as high as 21.2%, as well as the improved environmental and thermal stability of the PSCs. The surface treatment provides a new strategy to simultaneously passivate defects and enhance charge extraction/transport at the device interface by manipulating the anchoring groups of the molecules.
    • Interface Matters: Enhanced Photoluminescence and Long-Term Stability of Zero-Dimensional Cesium Lead Bromide Nanocrystals via Gas-Phase Aluminum Oxide Encapsulation.

      Bose, Riya; Zheng, Yangzi; Guo, Tianle; Yin, Jun; Hedhili, Mohamed N.; Zhou, Xiaohe; Veyan, Jean-Francois; Gereige, Issam; Al-Saggaf, Ahmed; Gartstein, Yuri N.; Bakr, Osman; Mohammed, Omar F.; Malko, Anton V. (ACS applied materials & interfaces, American Chemical Society (ACS), 2020-07-09) [Article]
      Cesium lead halide perovskite nanocrystals (PNCs), while possessing facile chemical synthesis routes and high photoluminescence (PL) properties, are still challenged by issues of instability and degradation. Although atomic layer deposition (ALD) of metal oxides has been one of the common encapsulation approaches for longer term stability, its application inevitably resulted in severe loss of emission efficiency and at times partial loss of structural integrity of perovskites, creating a bottleneck in its practical viability. We demonstrate a nondestructive modified gas-phase technique with codeposition of both precursors trimethylaluminum and water to dramatically enhance the PL emission in zero-dimensional (0D) Cs4PbBr6 PNCs via alumina encapsulation. X-ray photoelectron spectroscopy analysis of Cs4PbBr6 films reveals the alumina deposition to be accompanied by elemental composition changes, particularly by the reduction of the excessive cesium content. Ab initio density functional theory simulations further unfold that the presence of excess Cs on the surface of PNCs leads to decomposition of structural [PbBr6]4- octahedra in the 0D perovskite lattice, which can be prevented in the presence of added hydroxyl groups. Our study thus unveils the pivotal role of the PNC surface composition and treatment in the process of its interaction with metal oxide precursors to control the PL properties as well as the stability of PNCs, providing an unprecedented way to use the conventional ALD technique for their successful integration into optoelectronic and photonic devices with improved properties.
    • NiCo/NiCo–OH and NiFe/NiFe–OH core shell nanostructures for water splitting electrocatalysis at large currents

      Zhu, Weijie; Chen, Weixin; Yu, Huanhuan; Zeng, Ye; Ming, Fangwang; Liang, Hanfeng; Wang, Zhoucheng (Applied Catalysis B: Environmental, Elsevier BV, 2020-07-09) [Article]
      A big challenge in practical water splitting is the sluggish reaction kinetics at high current densities that essentially requires efficient electrocatalysts to lower the overpotentials. While exciting progress has been made in noble metal-based catalysts, earth-abundant materials that can actively catalyze the water splitting at high current densities (e.g. ≥500 mA cm−2) are rare. In this work, we show that a rational design of the catalysts could promote the charge transfer, facilitate the gas release, as well as boost the surface active sites, and therefore significantly enhance the electrocatalytic activity toward both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Using NiCo/NiCo−OH and NiFe/NiFe−OH as examples, we achieved ultralow overpotentials of 184 and 296 mV at 500 mA cm−2 in 1M KOH for HER and OER, respectively. More importantly, the alkaline electrolyzer based on these two materials is able to actively drive the overall water splitting at 1000 mA cm−2 for at least 300 h at a low cell voltage without significant performance decay, which is much superior to the state-of-the-art 20 % Pt/C||RuO2 combination. Our work points out a promising pathway to achieve inexpensive electrocatalysts for practical water splitting at high currents.
    • Low Temperature Scalable Deposition of Copper (I) Thiocyanate Films via Aerosol-Assisted Chemical Vapour Deposition

      Mohan, Lokeshwari; Ratnasingham, Sinclair R.; Panidi, Julianna; Anthopoulos, Thomas D.; Binions, Russell; McLachlan, Martyn A.; Briscoe, Joe (Crystal Growth & Design, American Chemical Society (ACS), 2020-07-09) [Article]
      Copper (I) thiocyanate (CuSCN) is a stable, wide bandgap (>3.5 eV), low-cost p-type semiconductor widely used in a variety of optoelectronic applications, including thin film transistors, organic light-emitting diodes and photovoltaic cells. For CuSCN to have impact in the commercial fabrication of such devices, large area, low-cost deposition techniques are required. Here, we report a novel technique for deposition of CuSCN that addresses these challenges. Aerosol-assisted chemical vapour deposition (AACVD) is used to deposit highly crystalline CuSCN films at low temperature. AACVD is a commercially viable technique due to its low cost and inherent scalability. In this study the deposition temperature, CuSCN concentration and carrier gas flow rate were studied and optimised, resulting in homogeneous films grown over areas approaching 30 cm2. At the optimised values i.e. 60 C using a 35 mg/ml solution and a carrier gas flow rate of 0.5 dm3/min, the film growth rate is around 100 nm/min. We present a thorough analysis of the film growth parameters and the subsequent morphology, composition, structural and optical properties of the deposited thin films.