Crystal Phase Engineering Research Articles

Crystal phase engineering boosted photo-electrochemical kinetics of CoSe2 for oxygen evolution catalysis

Crystal phase is an important parameter that can determine the electronic structure and catalytic properties of catalysts. In this work, we report the crystal phase dependent photo- and electrocatalytic oxygen evolution reaction (OER) performance of CoSe2. In electrocatalytic reaction, we firstly found that CoSe2 with orthorhombic phase (o-CoSe2) showed a higher OER performance than that of CoSe2 with cubic phase (c-CoSe2). In the further exploration of photocatalytic application using Fe2O3 as light harvester and CoSe2 as cocatalysts, o-CoSe2/Fe2O3 can realize the qualitative changes of photocatalytic oxygen evolution performance from “0″ to “1”. As contrast, c-CoSe2/Fe2O3 cannot work in photocatalytic oxygen evolution process under the same condition. Experimental and theoretical analysis uncover that, the key factor leading to the crystal phase-dependent performance is the decreased activation barrier of H2O on o-CoSe2 surface. This work opens up an opportunity of correlating the CoSe2 crystal phase with performance in OER.

Hcp-phased Ni nanoparticles with generic catalytic hydrogenation activities toward different functional groups

Catalytic hydrogenation is a vital industrial means to produce value-added fuels and fine chemicals, however, requiring highly efficient catalysts, especially the nonprecious ones. To date, the majority of high-performance industrial hydrogenation catalysts are made of precious metals-based materials, and any given catalyst could only be used to catalyze one or few specific reactions. Herein, we exemplify a crystal phase engineering approach to empower Ni nanoparticles (NPs) with superb intrinsic catalytic activities toward a wide spectrum of hydrogenation reactions. A facile pyrolysis approach is used to directly convert a Ni-imidazole MOF precursor into hexagonal close-packed (hcp)-phased Ni NPs on carbon support. The as-synthesized hcp-phased Ni NPs exhibit unprecedented hydrogenation catalytic activities in pure water towards nitro-, aldehyde-, ketone-, alkene- and N heterocyclic-compounds, outperforming the face-centered cubic (fcc)-Ni counterpart and the reported transition metals-based catalysts. The density functional theory calculations unveil that the presence of hcp-Ni boosts the intrinsic catalytic hydrogenation activity by coherently enhancing the substrate adsorption strength and lowering the reaction barrier energy of the rate-determining step. We anticipate that the crystal phase engineering design approach unveiled in this work would be adoptable to other types of reactions.

Promoting the Oxygen Evolution Activity of Perovskite Nickelates through Phase Engineering.

Perovskite oxides have emerged as promising candidates for the oxygen evolution reaction (OER) electrocatalyst due to their flexible lattice structure, tunable electronic structure, superior stability, and cost-effectiveness. Recent research studies have mostly focused on the traditional methods to tune the OER performance, such as cation/anion doping, A-/B-site ordering, epitaxial strain, oxygen vacancy, and so forth, leading to reasonable yet still limited activity enhancement. Here, we report a novel strategy for promoting the OER activity for perovskite LaNiO3 by crystal phase engineering, which is realized by breaking long-range chemical bonding through amorphization. We provide the first and direct evidence that perovskite oxides with an amorphous structure can induce the self-adaptive process, which helps enhance the OER performance. This is evidenced by the fact that an amorphous LaNiO3 film on glassy carbon shows a 9-fold increase in the current density compared to that of an epitaxial LaNiO3 single crystalline film. The obtained current density of 1038 μΑ cm-2 (@ 1.6 vs RHE) is the largest value among the literature reported values. Our work thus offers a new protocol to boost the OER performance for perovskite oxides for future clean energy applications.

Crystal-phase engineering of PdCu nanoalloys facilitates selective hydrodeoxygenation at room temperature

Selective hydrodeoxygenation of biomass-derived aromatic alcohols to value-added chemical or fuel is of great importance for sustainable biomass upgrading, and hydrodeoxygenation of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) is one of the most attractive reactions. Achieving the conversion of HMF to DMF using H2 at ambient temperature is challenging. In this work, we used PdCu nanoalloys to catalyze the selective hydrodeoxygenation reaction of HMF to DMF using H2 as the reducing agent. The reaction path and the product selectivity are governed by the crystallographic phase of the PdCu nanoalloys. It was discovered that body-centered cubic (BCC) PdCu nanoalloys supported on activated carbon (AC) exhibited outstanding performance with 93.6% yield of DMF at room temperature (PdCu/AC-BCC). A combination of experimental and density functional theory (DFT) studies showed that the tilted adsorption modes of furanic intermediates on PdCu-BCC nanoalloy surfaces accounted for the high selectivity of DMF; however, furan ring was activated on PdCu face-centered cubic (FCC) nanoalloy surfaces. Furthermore, PdCu/AC-BCC could also catalyze the hydrodeoxygenation of other aromatic alcohols at room temperature while maintaining the aromatic structures. This work opens the way for selective hydrodeoxygenation of the aromatic alcohols at room temperature with the aromatic ring intact.

Seeded Synthesis of Unconventional 2H-Phase Pd Alloy Nanomaterials for Highly Efficient Oxygen Reduction.

Crystal phase engineering of noble-metal-based alloy nanomaterials paves a new way to the rational synthesis of high-performance catalysts for various applications. However, the controlled preparation of noble-metal-based alloy nanomaterials with unconventional crystal phases still remains a great challenge due to their thermodynamically unstable nature. Herein, we develop a robust and general seeded method to synthesize PdCu alloy nanomaterials with unconventional hexagonal close-packed (hcp, 2H type) phase and also tunable Cu contents. Moreover, galvanic replacement of Cu by Pt can be further conducted to prepare unconventional trimetallic 2H-PdCuPt nanomaterials. Impressively, 2H-Pd67Cu33 nanoparticles possess a high mass activity of 0.87 A mg-1Pd at 0.9 V (vs reversible hydrogen electrode (RHE)) in electrochemical oxygen reduction reaction (ORR) under alkaline condition, which is 2.5 times that of the conventional face-centered cubic (fcc) Pd69Cu31 counterpart, revealing the important role of crystal phase on determining the ORR performance. After the incorporation of Pt, the obtained 2H-Pd71Cu22Pt7 catalyst shows a significantly enhanced mass activity of 1.92 A mg-1Pd+Pt at 0.9 V (vs RHE), which is 19.2 and 8.7 times those of commercial Pt/C and Pd/C, placing it among the best reported Pd-based ORR electrocatalysts under alkaline conditions.

Activating transition metal via synergistic anomalous phase and doping engineering towards enhanced dehydrogenation of ammonia borane

Seeking high-performing non-noble transition metal catalysts for hydrogen evolution from chemical hydrogen storage media is significant. Herein we demonstrate for the first time that anomalous crystal phase engineering coupled with heteroatom doping can remarkably activate transition metal (Ni as a proof-of-concept study) for boosting ammonia borane (AB) dehydrogenation. Ni nanoparticles with designated phase (fcc or hcp phase) encapsulated in carbon (fcc-Ni/C and hcp-Ni/C) can be readily derived from Ni-based MOF. Intriguingly, hcp-Ni/C featuring unconventional hcp phase can remarkably outperform fcc-Ni/C with common fcc phase in AB dehydrogenation. Moreover, by doping Cu, dramatically promoted catalysis can be further achieved for hcp-CuNi/C. From experimental and theoretical results, delicate crystal phase together with heteroatom doping engineering can optimize electronic structure of hcp-CuNi/C, facilitating rate-determining step (H2O dissociation), thereby boosting AB hydrolysis. This study details the first insight into the phase and doping engineering over non-noble transition metals for promoting AB dehydrogenation.

Ordered PdCu-Based Core-Shell Concave Nanocubes Enclosed by High-Index Facets for Ethanol Electrooxidation.

Crystal phase engineering is a powerful strategy for regulating the performance of electrocatalysts toward many electrocatalytic reactions. Herein we demonstrate that Au@Pd1Cu concave nanocubes (CNCs) with an ordered body-centered cubic (bcc) PdCu alloy shell enclosed by many high active high-index facets can be adopted as highly active yet stable electrocatalysts for the ethanol oxidation reaction (EOR). These CNCs are more efficient than other nanocrystals with a disordered face-centered cubic (fcc) PdCu alloy surface and display high mass and specific activities of 10.59 A mgpd-1 and 33.24 mA cm-2, which are 11.7 times and 4.1 times higher than those of commercial Pd black, respectively. Our core-shell CNCs also exhibit robust durability with the weakest decay in activity after 250 potential-scanning cycles, as well as outstanding antipoisoning ability. Alloying with Cu and the ordered bcc phase surface can provide abundant OHads species to oxidize carbonaceous poison to avoid catalyst poisoning, and the exposed high-index facets on the surface can act as highly catalytic sites.

Crystal Phase-Controlled Modulation of Binary Transition Metal Oxides for Highly Reversible Li-O2 Batteries.

Reducing charge-discharge overpotential of transition metal oxide catalysts can eventually enhance the cell efficiency and cycle life of Li-O2 batteries. Here, we propose that crystal phase engineering of transition metal oxides could be an effective way to achieve the above purpose. We establish controllable crystal phase modulation of the binary MnxCo1-xO by adopting a cation regulation strategy. Systematic studies reveal an unprecedented relevancy between charge overpotential and crystal phase of MnxCo1-xO catalysts, whereas a dramatically reduced charge overpotential (0.48 V) via a rational optimization of Mn/Co molar ratio = 8/2 is achieved. Further computational studies indicate that the different morphologies of Li2O2 should be related to different electronic conductivity and binding of Li2O2 on crystal facets of MnxCo1-xO catalysts, finally leading to different charge overpotential. We anticipate that this specific crystal phase engineering would offer good technical support for developing high-performance transition metal oxide catalysts for advanced Li-O2 batteries.

Mixed-Phase Indium Oxide as a Highly Active and Stable Catalyst for the Hydrogenation of CO2 to CH3OH

Indium oxide has been demonstrated to be a suitable catalytic material for CO2 adsorption and activation, and in this study a phase-mixing strategy is used to improve its catalytic hydrogenation of CO2 to CH3OH. Mixed-phase indium oxide with controllable cubic and hexagonal phases is synthesized by a solvothermal method, and its CO2 conversion and CH3OH space-time yield are about 2 times higher than those of single-phase indium oxide. Experimental investigation shows a significant mixed-crystal effect resulting from the phase mixing, which substantially promotes oxygen vacancy formation and medium-strength CO2 adsorption and thereby enhances the catalytic performance. Furthermore, the mixed-phase catalyst is very stable and too difficult to reduce during reaction. These results give a good technique for the development of highly active and long-lived CO2 hydrogenation catalysts through crystal phase engineering.

Binary and Ternary Colloidal Cu-Sn-Te Nanocrystals for Thermoelectric Thin Films.

Recent advances in copper chalcogenide-based nanocrystals (NCs), copper sulfide, and copper selenide derived nanostructures, have drawn considerable attention. However, reports of crystal phase and shape engineering of binary or ternary copper telluride NCs remain rare. Here, a colloidal hot-injection approach for producing binary copper/tin telluride, and ternary copper tin telluride NCs with controllable compositions, crystal structures, and morphologies is reported. The crystal phase and growth behavior of these tellurides are systematically studied from both experimental and theoretical perspectives. The morphology of Cu1.29 Te NCs is modified from 1D nanorods with different aspect ratios to 2Dnanosheets and 3D nanocubes, by controlling the preferential growth of specific crystalline facets. A controllable phase transition from Cu1.29 Te to Cu1.43 Te NCs is also demonstrated. The latter can be further converted into Cu2 SnTe3 and SnTe through Sn incorporation. Temperature dependent thermoelectric properties of metal (Cu and Sn) telluride nanostructure thin films are also studied, including Cu1.29 Te, Cu1.43 Te, Cu2 SnTe3 , and SnTe. Cu2 SnTe3 is a low carrier density semimetal with compensating electron and hole Fermi surface pockets. The engineering of crystal phase and morphology control of colloidal copper tin telluride NCs opens a path to explore and design new classes of copper telluride-based nanomaterials for thermoelectrics and other applications.

Phase-Controlled 1T Transition-Metal Dichalcogenide-Based Multidimensional Hybrid Nanostructures

Phase-Controlled 1T Transition-Metal Dichalcogenide-Based Multidimensional Hybrid Nanostructures

Soft chemistry of metastable metal chalcogenide nanomaterials.

The metastable nature of metal chalcogenide nanomaterials (MCNs) provides us with fresh perspectives and plentiful grounds in the search of new strategies for physicochemical tuning. In the past decade, numerous efforts have been devoted to synthesizing and modifying diverse emerging MCNs based on their "soft chemistry", that is, gently regulating the composition, structure, phase, and interface while not entirely disrupting the original features. This tutorial review focuses on design principles based on the metastability of MCNs, such as ion mobility and vacancy, thermal and structural instability, chemical reactivity, and phase transition, together with corresponding soft chemical approaches, including ion-exchange, catalytic growth, segregation or coupling, template grafting or transformation, and crystal-phase engineering, and summarizes recent advances in their preparation and modification. Finally, prospects for the future development of soft chemistry-directed synthetic guidelines and metastable metal chalcogenide-derived nanomaterials are proposed and highlighted.

Rutile-Coated B-Phase TiO2 Heterojunction Nanobelts for Photocatalytic H2 Evolution

In the field of photocatalysis, the crystal phase engineering of titanium dioxide is a research hotspot. Titanium dioxide heterojunctions often exhibit better photocatalytic performance than single...

Crystal phase engineering Zn0.8Cd0.2S nanocrystals with twin-induced homojunctions for photocatalytic nitrogen fixation under visible light

Newly developed photocatalysts usually focus on structuring active sites, for enhancing chemical adsorption and reducing activation energy barrier in photocatalysis nitrogen fixation. However, lots of photocatalysts suffer from electron-hole pairs’ recombination in the bulk or on the surface during transportation. Herein, twinned Zn0.8Cd0.2S nanocrystals were successfully applied to photocatalytic nitrogen fixation, affording an ammonia production rate of 66.91 μmol g−1 h−1 under visible light with an AQE of 3.77 % at 420 nm, which were 17-fold and 3-fold higher than the activities of CdS and ZnS, respectively. The inner homojunction enhanced carriers’ transportation, and improved electrons density on zinc blend segment, which could facilitate adsorption of nitrogen and ·H gaining, finally, the nitrogen activation and reduction proceeded through the six electrons reduction process on (111) facets. These results confirm that twinned Zn0.8Cd0.2S nanocrystal is a kind of promising new photocatalyst for solar-driven nitrogen reduction to ammonia.

Ethylene Selectivity in Electrocatalytic CO2 Reduction on Cu Nanomaterials: A Crystal Phase-Dependent Study.

The crystal phase of metal nanocatalysts significantly affects their catalytic performance. Cu-based nanomaterials are unique electrocatalysts for CO2 reduction reaction (CO2RR) to produce high-value hydrocarbons. However, studies to date are limited to the conventional face-centered cubic (fcc) Cu. Here, we report a crystal phase-dependent catalytic behavior of Cu, after the successful synthesis of high-purity 4H Cu and heterophase 4H/fcc Cu using the 4H and 4H/fcc Au as templates, respectively. Remarkably, the obtained unconventional crystal structures of Cu exhibit enhanced overall activity and higher ethylene (C2H4) selectivity in CO2RR compared to the fcc Cu. Density functional theory calculations suggest that the 4H phase and 4H/fcc interface of Cu favor the C2H4 formation pathway compared to the fcc Cu, leading to the crystal phase-dependent C2H4 selectivity. This study demonstrates the importance of crystal phase engineering of metal nanocatalysts for electrocatalytic reactions, offering a new strategy to prepare novel catalysts with unconventional phases for various applications.

Cd-Rich Alloyed CsPb1- x Cd x Br3 Perovskite Nanorods with Tunable Blue Emission and Fermi Levels Fabricated through Crystal Phase Engineering.

One‐dimensional semiconductor nanostructures have already been used for a variety of optoelectronic applications. Metal halide perovskites have emerged in recent years as promising high‐performance optoelectronic materials, but reports on 1D nanorods (NRs) of all‐inorganic halide perovskites are still scarce. This work demonstrates a synthetic strategy toward cesium‐based inorganic perovskite NRs by exploiting composition‐controlled crystal phase engineering. It is accomplished for Cd‐rich mixed‐cation CsPb1‐ xCdxBr3 nanocrystals, where the initial 1D hexagonal perovskite phase drives the growth of the 1D NRs, as supported by first‐principles calculations. The band gaps of the resulting NRs are tunable by varying the Cd‐content, and the highly uniform CsPb0.08Cd0.92Br3 NRs (with an average length of 84 nm and width of 16 nm) exhibit a true blue‐color emission centered at 460 nm, with a high quantum yield of 48%. Moreover, this work also demonstrates the tunability of the Fermi levels in the films made of CsPb1‐ xCdxBr3 alloyed nanocrystals, where samples with highest Cd content show an increase of the electron concentration and a related increase in the conductivity.

Crystal phase dependent solar driven hydrogen evolution catalysis over cobalt diselenide

The design of robust metallic transition metal dichalcogenides (TMDs)-based materials for photocatalytic water splitting is desirable but challenging. Here we report the exploration and crystal phase engineering of metallic CoSe2 as cocatalysts for photocatalytic hydrogen evolution. The potential of orthorhombic and cubic CoSe2 (i.e. o-CoSe2, c-CoSe2) as cocatalysts are evaluated by theoretical simulation. Experimentally, o-CoSe2 and c-CoSe2 are rationally anchored to ultrathin g-C3N4 nanosheets, which provides a platform to evaluate the practical photocatalytic activity. The experimental results reveal the crystal phase dependent hydrogen evolution catalysis, i.e., the hydrogen evolution can be proceeded more efficiently on o-CoSe2 surface compared to c-CoSe2. We demonstrate that o-CoSe2 possesses more favorable hydrogen adsorption capacity and can thus tune the rate-determining step, i.e., the surface conversion from H+ to H2, leading to enhanced performance. The presented results provide insights into the role of phase engineering and a strategy for enhanced catalysis.

Exploring the band structure of Wurtzite InAs nanowires using photocurrent spectroscopy

We use polarized photocurrent spectroscopy in a nanowire device to investigate the band structure of hexagonal Wurtzite InAs. Signatures of optical transitions between four valence bands and two conduction bands are observed which are consistent with the symmetries expected from group theory. The ground state transition energy identified from photocurrent spectra is seen to be consistent with photoluminescence emitted from a cluster of nanowires from the same growth substrate. From the energies of the observed bands we determine the spin orbit and crystal field energies in Wurtzite InAs. This information is essential to the development of crystal phase engineering of this important III-V semiconductor.

Engineering crystal phase of polytypic CuInS2 nanosheets for enhanced photocatalytic and photoelectrochemical performance

Crystal phase engineering on CuInS2 (CIS) nanocrystals, especially polytypic structure, has become one of the research hotspots to design the advanced materials and devices for energy conversion and environment treatment. Here, the polytypic CIS nanosheets (NSs) including zincblende/wurtzite and chalcopyrite/wurtzite types were first time achieved in a hot-injection system using oleic acid and liquid paraffin as the reaction media. As-obtained polytypic CIS NSs exhibit significantly enhanced light-absorption ability and visible-light-driven photocatalytic performance originating from the rational hetero-crystalline interfaces and surface defect states, which efficiently inhibit the recombination of photo-generated carriers. Meanwhile, the polytypic CIS NSs were spin-coated onto the surface of fluorinated-tin oxide glass substrate and used as the photoelectrode, which shows an excellent photoelectrochemical (PEC) activity in aqueous solution. The present work not only provides a facile, rapid, low-cost, and environmental-friendly synthesis strategy to design the crystal phase and defect structure of ternary chalcogenides, but also demonstrates the relationships between the polytypic structure and photocatalytic/photoelectrochemical properties.

Gas-assisted transformation of gold from fcc to the metastable 4H phase

The metastable hexagonal 4H-phase gold has recently attracted extensive interest due to its exceptional performance in catalysis. However, gold usually crystallizes to its lowest free energy structure called face-centered cubic (fcc). The phase transformation from the stable fcc phase to the metastable 4H phase is thus of great significance in crystal phase engineering. Herein, we report this unusual phenomenon on a 4H gold nanorod template with the aid of CO gas and an electron beam. In situ transmission electron microscopy was used to directly visualize the interface propagation kinetics between the 4H-Au-nanorod and fcc-Au nanoparticle. Epitaxial growth was initiated at the contact interface, and then propagated to convert all parts of these fcc nanoparticles to 4H phase. Density functional theory calculations and ab initio molecular dynamics simulations show that the CO molecules can assist the Au diffusion process and promote the flexibility of Au particles during the epitaxial growth. The phase transformation was driven by the reduction of Gibbs free energy by eliminating the interface between fcc and 4H phases.