Noble-Metal-Free High-Entropy Alloy Nanoparticles for Efficient Solar-Driven Photocatalytic CO2 Reduction.

Metal nanoparticle (NP) cocatalysts are widely investigated for their ability to enhance the performance of photocatalytic materials; however, their practical application is often limited by the inherent instability under light irradiation. This challenge has catalyzed interest in exploring high-entropy alloys (HEAs), which, with their increased entropy and lower Gibbs free energy, provide superior stability. In this study, 3.5 nm-sized noble-metal-free NPs composed of a FeCoNiCuMn HEA are successfully synthesized. With theoretic calculation and experiments, the electronic structure of HEA in augmenting the catalytic CO2 reduction has been uncovered, including the individual roles of each element and the collective synergistic effects. Then, their photocatalytic CO2 reduction capabilities are investigated when immobilized on TiO2. HEA NPs significantly enhance the CO2 photoreduction, achieving a 23-fold increase over pristine TiO2, with CO and CH4 production rates of 235.2 and 19.9 µmol g-1 h-1, respectively. Meanwhile, HEA NPs show excellent stability under simulated solar irradiation, as well high-energy X-ray irradiation. This research emphasizes the promising role of HEA NPs, composed of earth-abundant elements, in revolutionizing the field of photocatalysis.

Langmuir-Blodgett Film Formed by Amphiphilic Molecules for Facile and Rapid Construction of Zinc-Iodine Cell.

Zinc-iodine batteries (ZIBs) are promising candidates for ecofriendly, safe, and low-cost energy storage systems, but polyiodide shuttling and the complex cathode fabrication procedures have severely hindered their broader commercial usage. Herein, a protocol is developed using phospholipid-like oleylamine molecules for scalable production of Langmuir-Blodgett films, which allows the facile preparation of ZIB cathodes in less than 1 min. The resulting inhomogeneous cathode allows for the continuous conversion of iodine. Moreover, the amine group of the oleylamine molecule at the cathode is capable of producing [OA*I+]I3- charge-transfer complexes with iodine, which facilitates the rapid migration of iodine and results in a highly reversible iodine conversion process. Consequently, the as-prepared ZIBs can deliver over 2000 cycles at 0.5 mA cm-2 with a capacity retention of 75.3%. This work presents a novel, straightforward, and efficient method for the rapid construction of ZIBs.

Anti-Freezing Electrolytes in Aqueous Multivalent Metal-Ion Batteries: Progress, Challenges, and Optimization Strategies.

Aqueous rechargeable multivalent metal-ion batteries (ARMMBs) have attracted considerable attention due to their high capacity, high energy density, and low cost. However, their performance is often limited by low temperature operation, which requires the development of anti-freezing electrolytes. In this review, we summarize the anti-freezing mechanisms and optimization strategies of anti-freezing electrolytes for aqueous batteries (especially for Zn-ion batteries). Besides, we investigate the possible interactions and side reactions between electrolytes and electrodes. We also analyze the problems between electrolytes and electrodes at low temperature, and propose possible solutions. The research progress in the field of low temperature energy storage for aqueous Mg-ion, Ca-ion, and Al-ion batteries, and the challenges faced in their anti-freezing electrolytes are investigated in detail. Last but not least, the outlook on the energy storage applications of ARMMBs is provided to guide the future research.

Cation Substitution Strategy for Developing Perovskite Oxide with Rich Oxygen Vacancy-Mediated Charge Redistribution Enables Highly Efficient Nitrate Electroreduction to Ammonia.

The electrocatalytic nitrate (NO3-) reduction reaction (eNITRR) is a promising method for ammonia synthesis. However, its efficacy is currently limited due to poor selectivity, largely caused by the inherent complexity of the multiple-electron processes involved. To address these issues, oxygen-vacancy-rich LaFe0.9M0.1O3-δ (M = Co, Ni, and Cu) perovskite submicrofibers have been designed from the starting material LaFeO3-δ (LF) by a B-site substitution strategy and used as the eNITRR electrocatalyst. Consequently, the LaFe0.9Cu0.1O3-δ (LF0.9Cu0.1) submicrofibers with a stronger Fe-O hybridization, more oxygen vacancies, and more positive surface potential exhibit a higher ammonia yield rate of 349 ± 15 µg h-1 mg-1cat. and a Faradaic efficiency of 48 ± 2% than LF submicrofibers. The COMSOL Multiphysics simulations demonstrate that the more positive surface of LF0.9Cu0.1 submicrofibers can induce NO3- enrichment and suppress the competing hydrogen evolution reaction. By combining a variety of in situ characterizations and density functional theory calculations, the eNITRR mechanism is revealed, where the first proton-electron coupling step (*NO3 + H+ + e- → *HNO3) is the rate-determining step with a reduced energy barrier of 1.83 eV. This work highlights the positive effect of cation substitution in promoting eNITRR properties of perovskites and provides new insights into the studies of perovskite-type electrocatalytic ammonia synthesis catalysts.

Weaving Aerogels into 3D Ordered Hyperelastic Hybrid Carbon Assemblies.

The development of a 3D carbon assembly with a combination of extraordinary electrochemical and mechanical properties is desirable yet challenging. Herein, an ultralight and hyperelastic nanofiber-woven hybrid carbon assembly (NWHCA) is fabricated by nanofiber weaving of isotropic porous and mechanical brittle quasi-aerogels. Upon subsequent pyrolysis, metallogel-derived quasi-aerogel hybridization and nitrogen/phosphorus co-doping are integrated into the NWHCA. Finite element simulation indicates that the 3D lamella-bridge architecture of NWHCA with the quasi-aerogel hybridization contributes to resisting plastic deformation and structural damage under high compression, experimentally demonstrated by complete deformation recovery at 80% compression and unprecedented fatigue resistance (>94% retention after 5000 cycles). Due to the superelasticity and quasi-aerogel integration, the zinc-air battery assembled based on NWHCA shows excellent electrochemical performance and flexibility. A proof-of-concept integrated device is presented, in which the flexible battery powers a piezoresistive sensor, using the NWHCA as the air cathode and the elastic conductor respectively, which can detect full-range and sophisticated motions while attached to human skin. The nanofiber weaving strategy allows the construction of lightweight, superelastic, and multifunctional hybrid carbon assemblies with great potential in wearable and integrated electronics.

Bio-Inspired Aerobic-Hydrophobic Janus Interface on Partially Carbonized Iron Heterostructure Promotes Bifunctional Nitrogen Fixation.

Competition from hydrogen/oxygen evolution reactions and low solubility of N2 in aqueous systems limited the selectivity and activity on nitrogen fixation reaction. Herein, we design an aerobic-hydrophobic Janus structure by introducing fluorinated modification on porous carbon nanofibers embedded with partially carbonized iron heterojunctions (Fe3 C/Fe@PCNF-F). The simulations prove that the Janus structure can keep the internal Fe3 C/Fe@PCNF-F away from water infiltration and endow a N2 molecular-concentrating effect, suppressing the competing reactions and overcoming the mass-transfer limitations to build a robust "quasi-solid-gas" state micro-domain around the catalyst surface. In this proof-of-concept system, the Fe3 C/Fe@PCNF-F exhibits excellent electrocatalytic performance for nitrogen fixation (NH3 yield rate up to 29.2 µg h-1 mg-1 cat. and Faraday efficiency (FE) up to 27.8 % in nitrogen reduction reaction; NO3 - yield rate up to 15.7 µg h-1 mg-1 cat. and FE up to 3.4 % in nitrogen oxidation reaction).

Soluble porous organic cages as homogenizers and electron-acceptors for homogenization of heterogeneous alloy nanoparticle catalysts with enhanced catalytic activity.

The creation of ultrafine alloy nanoparticles (<5 nm) that can maintain surface activity and avoid aggregation for heterogeneous catalysis has received much attention and is extremely challenging. Here, ultrafine PtRh alloy nanoparticles imprisoned by the cavities of reduced chiral covalent imine cage (PtRh@RCC3) are prepared successfully by an organic molecular cage (OMC) confinement strategy, while the soluble RCC3 can act as a homogenizer to homogenize the heterogeneous PtRh alloy in solution. Moreover, the X-ray absorption near-edge structure (XANES) results show that the RCC3 can act as an electron-acceptor to withdraw electrons from Pt, leading to the formation of higher valence Pt atoms, which is beneficial to improving the catalytic activity for the reduction of 4-nitrophenol. Attributed to the synergistic effect of Pt/Rh atoms and the unique function of the RCC3, the reaction rate constants of Pt1Rh16@RCC3 are 49.6, 8.2, and 5.5 times than those of the Pt1Rh16 bulk, Pt@RCC3 and Rh@RCC3, respectively. This work provides a feasible strategy to homogenize heterogeneous alloy nanoparticle catalysts in solution, showing huge potential for advanced catalytic application.

A Universal Polyiodide Regulation Using Quaternization Engineering toward High Value-Added and Ultra-Stable Zinc-Iodine Batteries.

The development of aqueous rechargeable zinc-iodine (Zn-I2 ) batteries is still plagued by the polyiodide shuttle issue, which frequently causes batteries to have inadequate cycle lifetimes. In this study, quaternization engineering based on the concept of "electric double layer" is developed on a commercial acrylic fiber skeleton ($1.55-1.7 kg-1 ) to precisely constrain the polyiodide and enhance the cycling durability of Zn-I2 batteries. Consequently, a high-rate (1 C-146.1 mAh g-1 , 10 C-133.8 mAh g-1 ) as well as, ultra-stable (2000 cycles at 20 C with 97.24% capacity retention) polymer-based Zn-I2 battery is reported. These traits are derived from the strong electrostatic interaction generated by quaternization engineering, which significantly eliminates the polyiodide shuttle issue and simultaneously realizes peculiar solution-based iodine chemistry (I- /I3 - ) in Zn-I2 batteries. The quaternization strategy also presents high practicability, reliability, and extensibility in various complicated environments. In particular, cutting-edge Zn-I2 batteries based on the concept of derivative material (commercially available quaternized resin) demonstrate ≈100% capacity retention over 17 000 cycles at 20 C. This work provides a general and fresh insight into the design and development of large-scale, low-cost, and high-performance zinc-iodine batteries, as well as, other novel iodine storage systems.

Nitrogen-doped hollow carbon nanoflowers from a preformed covalent triazine framework for metal-free bifunctional electrocatalysis.

Fabrication of nitrogen-doped hollow carbon nanostructures is of great importance for achieving efficient electron and ion transport as a metal-free electrocatalyst. Herein, we report a step-wise polymerization and carbonization route to prepare N-doped hollow carbon nanoflowers (N-HCNFs) with a high nitrogen content up to 5.3 at%. A preformed covalent triazine framework (CTF) network assembled on a melamine-cyanuric acid (MCA) supermolecular crystal was achieved via a step-wise polymerization. The subsequent carbonization was conducted to obtain hollow and porous carbon materials with a unique flower-shape. Excellent electrochemical oxygen reduction reaction (ORR) performance with a positive half-wave potential of 0.84 V (vs. RHE) was achieved with excellent stability and methanol resistance in alkaline media. Furthermore, for the hydrogen evolution reaction (HER), a low overpotential of 243 mV at a current density of 10 mA cm-2 and a small Tafel slope of 111 mV dec-1 in acidic media were shown.

Gradient phosphorus-doping engineering and superficial amorphous reconstruction in NiFe2O4 nanoarrays to enhance the oxygen evolution electrocatalysis.

A better solid-liquid-gas three-phase boundary is vital for low energy cost oxygen evolution reaction (OER), making the designed regulation of interfacial atmosphere necessary. Herein, we find that the OER electrocatalysis can be dramatically improved by synergistically forming disordered electronic structures and superficial amorphous layers, as superficial oxyhydroxide, phosphorus-doped NiFe2O4 nanoarrays on nitrogen-doped carbon nanofibers (OP-NiFe2O4/NCNFs). Unveiled by the depth-profiling analysis from the X-ray photoelectron spectroscopy, the contents of phosphorous doping in the OP-NiFe2O4 nanoarrays change dynamically from outside to inside due to its in situ superficial reconstruction into the oxyhydroxide layer, thereby accelerating electron transfer between heterogeneous phases. As revealed by density functional theory calculations, this amorphous oxyhydroxide layer and dynamically varied phosphorous content would positively shift the d-band center of the NiFe2O4-related compounds, leading to lower adsorption energy towards water molecule. Thus, the OP-NiFe2O4/NCNF electrocatalyst displays a low overpotential of 260 mV at a current density of 10 mA cm-2 and a small Tafel slope of 44.8 mV dec-1 in an alkaline medium.