Entropy-Driven Ostwald Ripening Reversal Promotes the Formation of Low-Platinum Intermetallic Fuel Cell Catalysts.

Strain engineering has been widely used to optimize platinum-based oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cells (PEMFCs). PtM3 (M is base metals), a well-known high-compressive-strain intermetallic alloy, shows promise as a low platinum ORR catalyst due to high intrinsic activity. However, during the alloying of Pt with a threefold amount of M, a notable phase separation between Pt and M may occur, with M particles rapidly sintering while Pt particles grow slowly, posing a challenge in achieving a well-defined PtM3 intermetallic alloy. Here, an entropy-driven Ostwald ripening reversal phenomenon is discovered that enables the synthesis of small-sized Pt(FeCoNiCu)3 intermetallic ORR catalysts. High entropy promotes the thermodynamic driving force for the alloying Pt with M, which triggers the Ostwald ripening reversal of sintered FeCoNiCu particles and facilitates the formation of uniform Pt(FeCoNiCu)3 intermetallic catalysts. The prepared Pt(FeCoNiCu)3 catalysts exhibit a high specific activity of 3.82 mA cm-2, along with a power density of ≈1.3 W cm-2 at 0.67 V and 94 °C with a cathode Pt loading of 0.1 mg cm-2 in H2-air fuel cell.

A Composite Structure of Cu3 Ge/Ge/C Anode Promise Better Rate Property for Lithium Battery.

Much effort has been made to search for high energy and high power density electrode materials for lithium ion batteries. Here, a composite structure among Ge, C and Cu3Ge in Cu3Ge/Ge/C materials with a high rate performance of lithium batteries has been reported. Such Cu3Ge/Ge/C composite is synthesized through the in-situ formation of Ge, C and Cu3Ge by one-pot reaction. Density function theory (DFT) calculations and electrochemical impedance spectroscopy (EIS) suggest a higher electron mobility of the hibrid Cu3Ge/Ge/C composites through the in-situ preparation. As a result, remarkable charge rate over 300 C (fast delithiated capability) and outstanding cycling stability (≈0.02% capacity decay per cycle for 500 cycles at 0.5 C) are achieved for the Cu3Ge/Ge/C composites anode. These Cu3Ge/Ge/C composites demonstrate another perspective to explore the energy storage materials and should provide a new pathway for the design of advanced electrode materials.

Phase-Transition-Induced Surface Reconstruction of Rh1 Site in Intermetallic Alloy for Propane Dehydrogenation.

The fine-tuning of the geometric and electronic structures of active sites plays a crucial role in catalysis. However, the intricate entanglement between the two aspects results in a lack of interpretable design for active sites, posing a challenge in developing high-performance catalysts. Here, we find that surface reconstruction induced by phase transition in intermetallic alloys enables synergistic geometric and electronic structure modulation, creating a desired active site microenvironment for propane dehydrogenation. The resulting electron-rich four-coordinate Rh1 site in the RhGe0.5Ga0.5 intermetallic alloy can accelerate the desorption of propylene and suppress the side reaction and thus exhibits a propylene selectivity of ∼98% with a low deactivation constant of 0.002 h-1 under propane dehydrogenation at 550 °C. Furthermore, we design a computational workflow to validate the rationality of the microenvironment modulation induced by the phase transition in an intermetallic alloy.

Hexagonal perovskite Sr6(Co0.8Fe0.2)5O15 as an efficient electrocatalyst towards the oxygen evolution reaction.

The high overpotential required for the oxygen evolution reaction (OER)-due to the transfer of four protons and four electrons-has greatly hindered the commercial viability of water electrolysis. People have been committed to the development of alternative precious metal-free OER electrocatalysts, especially electrocatalysts for alkaline media. In this study, we report the application of Sr6(Co0.8Fe0.2)5O15 (SCF-H) perovskite oxide with a hexagonal phase structure in the field of OER electrocatalysis. Synthesized by a simple and universal sol-gel method, the SCF-H perovskite oxide shows prominent OER activity with an overpotential of 318 mV at a current density of 10 mA cm-2 and a Tafel slope of only 54 mV dec-1, which is significantly better than the cubic phase structure SrCo0.8Fe0.2O3-δ (SCF-C), benchmark noble-metal oxide RuO2 and Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF). Compared with cubic SCF-C, the hexagonal SCF-H perovskite oxide has abundant surface oxygen species (O22-/O-), a faster charge transfer rate, and a higher electrochemical surface area. In addition, the DFT calculation results show that the center of the O p-band of SCF-H is closer to the Fermi level than that of SCF-C, which leads to the better OER activity of SCF-H. This work finds that the new hexagonal structure perovskite may become a promising OER electrocatalyst.

High-Voltage and Super-Stable Aqueous Sodium-Zinc Hybrid Ion Batteries Enabled by Double Solvation Structures in Concentrated Electrolyte.

Aqueous sodium-zinc hybrid ion batteries are attracting extensive attention due to high energy density, low cost, and environmental friendliness. Unfortunately, there are still some drawbacks associated with the low voltage and cycle performance degradation that limit their practical application. Here, a concentrated aqueous electrolyte with solvation-modulated Zn2+ is reported that reduces the hydrogen evolution reaction on the surface of Zn metal, avoiding the generation of ZnO and uneven deposition. Accordingly, the Zn anode exhibits 1600 h Zn plating/stripping and ≈99.96% Coulombic efficiency after 700 cycles. In addition, solvation-modulated Na+ promotes the excellent structural stability of zinc hexacyanoferrate (ZnHCF) due to the rhombohedral-rhombohedral rather than rhombohedral-cubic phase transition. A ZnHCF//Zn full cell delivers an average voltage of 1.76 V and 98% capacity retention after 2000 cycles at 5 C rates.

Growth of Bouquet-like Zn2GeO4 Crystal Clusters in Molten Salt and Understanding the Fast Na-Storage Properties.

The exploration of high-performance anode materials is imperative for the development of sodium-ion batteries (SIBs). Herein, a molten-salt-assisted approach is developed to prepare crystallized Zn2GeO4 clusters constructed by interconnected nanorods, and the Na-ion storage mechanism is studied systemically through in situ X-ray diffraction, ex situ X-ray photoelectron spectroscopy, and high-resolution transmission microscopy associated with galvanostatic intermittent titration technique. The Zn2GeO4 anode undergoes conversion reactions followed by the alloying reaction. The large channel in the Zn2GeO4 crystal structure ensures insertion of sodium ions. The amorphous transformation during the initial discharge process increases the active site for the fast electrochemical reaction. As the anode for SIBs, the Zn2GeO4 cluster exhibits good rate capability with a capacity retention of 111.1 mA h g-1 at 20 A g-1 in half cells and 118.9 mA h g-1 at 2 A g-1 in full cells, associated with a capacity of 184.2 mA h g-1 at 0.5 A g-1 after 500 cycles. The ex situ scanning electron microscopy images of the electrode material disclose that the hierarchical structure can accommodate the volume variation of Zn2GeO4 during discharge/charge cycling, facilitating long cycling stability. The investigation of Zn2GeO4 provides new insight for the development of high-rate anode materials for SIBs.

Preparation of Sb nanoparticles in molten salt and their potassium storage performance and mechanism.

Sb nanoparticles with a size of 55 nm are fabricated via the reduction of SbCl3 by metallic Al in the molten salt of SbCl3 at 80 °C. In situ XRD patterns and ex situ Raman spectra show that the potassium storage mechanism is an alloying-type with the formation of a cubic K3Sb phase when fully potassiated and an amorphous phase when fully depotassiated. As an anode for potassium-ion batteries, Sb nanoparticles coated with graphene could deliver a reversible capacity of 381 mA h g-1 at 100 mA g-1, and maintain a capacity of 210 mA h g-1 at 500 mA g-1 for 200 cycles.

One-step thermolysis synthesis of two-dimensional ultrafine Fe3O4 particles/carbon nanonetworks for high-performance lithium-ion batteries.

To tackle the issue of inferior cycle stability and rate capability for Fe3O4 anode materials in lithium ion batteries, ultrafine Fe3O4 nanocrystals uniformly encapsulated in two-dimensional (2D) carbon nanonetworks have been fabricated through thermolysis of a simple, low-cost iron(iii) acetylacetonate without any extra processes. Moreover, compared to the reported Fe3O4/carbon composites, the particle size of Fe3O4 is controllable and held down to ∼3 nm. Benefitting from the synergistic effects of the excellent electroconductive carbon nanonetworks and uniform distribution of ultrafine Fe3O4 particles, the prepared 2D Fe3O4/carbon nanonetwork anode exhibits high reversible capacity, excellent rate capability and superior cyclability. A high capacity of 1534 mA h g(-1) is achieved at a 1 C rate and is maintained without decay up to 500 cycles (1 C = 1 A g(-1)). Even at the high current density of 5 C and 10 C, the 2D Fe3O4/carbon nanonetworks maintain a reversible capacity of 845 and 647 mA h g(-1) after 500 discharge/charge cycles, respectively. In comparison with other reported Fe3O4-based anodes, the 2D Fe3O4/carbon nanonetwork electrode is one of the most attractive of those in energy storage applications.

A Deep Reduction and Partial Oxidation Strategy for Fabrication of Mesoporous Si Anode for Lithium Ion Batteries.

A deep reduction and partial oxidation strategy to convert low-cost SiO2 into mesoporous Si anode with the yield higher than 90% is provided. This strategy has advantage in efficient mesoporous silicon production and in situ formation of several nanometers SiO2 layer on the surface of silicon particles. Thus, the resulted silicon anode provides extremely high reversible capacity of 1772 mAh g(-1), superior cycling stability with more than 873 mAh g(-1) at 1.8 A g(-1) after 1400 cycles (corresponding to the capacity decay rate of 0.035% per cycle), and good rate capability (∼710 mAh g(-1) at 18A g(-1)). These promising results suggest that such strategy for mesoporous Si anode can be potentially commercialized for high energy Li-ion batteries.

SnS2- Compared to SnO2-Stabilized S/C Composites toward High-Performance Lithium Sulfur Batteries.

The common sulfur/carbon (S/C) composite cathodes in lithium sulfur batteries suffer gradual capacity fading over long-term cycling incurred by the poor physical confinement of sulfur in a nonpolar carbon host. In this work, these issues are significantly relieved by introducing polar SnO2 or SnS2 species into the S/C composite. SnO2- or SnS2-stabilized sulfur in porous carbon composites (SnO2/S/C and SnS2/S/C) have been obtained through a baked-in-salt or sealed-in-vessel approach at 245 °C, starting from metallic tin (mp 231.89 °C), excess sulfur, and porous carbon. Both of the in situ-formed SnO2 and SnS2 in the two composites could ensure chemical interaction with lithium polysulfide (LiPS) intermediates proven by theoretical calculation. Compared to SnO2/S/C, the SnS2/S/C sample affords a more appropriate binding effect and shows lower charge transfer resistance, which is important for the efficient redox reaction of the adsorbed LiPS intermediates during cycling. When used as cathodes for Li-S batteries, the SnS2/S/C composite with sulfur loading of 78 wt % exhibits superior electrochemical performance. It delivers reversible capacities of 780 mAh g(-1) after 300 cycles at 0.5 C. When further coupled with a Ge/C anode, the full cell also shows good cycling stability and efficiency.