Interface engineering triggered by carbon nanotube-supported multiple sulfides for boosting oxygen evolution

Bimetallic sulfide/N-doped carbon composite derived from Prussian blue analogues/cellulose nanofibers film toward enhanced oxygen evolution reaction

Exploiting effective, stable, and cost-efficient electrocatalysts for the water oxidation reaction is highly desirable for renewable energy conversion techniques. Constructional design and compositional manipulation are widely used approaches to efficaciously boost the electrocatalytic performance. Herein, we designed a NiFe-bimetallic sulfide/N-doped carbon composite via a two-step thermal treatment of Prussian blue analogues/cellulose nanofibers (PBA/CNFs) film. The NiFe-bimetallic sulfide/N-doped carbon composite displayed enhanced OER performance in an alkaline environment, with an overpotential of 282 mV at 10 mA cm-2, a Tafel slope of 59.71 mV dec-1, and good stability, making the composite a candidate electrocatalyst for OER-related energy equipment. The introduction of CNFs in the precursor prevented the aggregation of PBA nanoparticles (NPs), exposed more active sites, and the resulting carbon substrate enhanced the electroconductivity of the composite. Moreover, the synergistic effect of Ni and Fe in the bimetallic sulfide could modulate the configuration of electrons, enrich the catalytically active sites, and augment the electric conductivity, thus ameliorating the OER performance. This study broadens the application of MOF-CNF composites to construct hierarchical structures of metal compounds and provides some thoughts for the development of cost-effective precious-metal-free catalysts for electrocatalysis.

Nitrogen-Doped Carbon Dots Modified Fe-Co Sulfide Nanosheets as High-Efficiency Electrocatalysts toward Oxygen Evolution Reaction

Developing high-efficiency and stable oxygen evolution reaction (OER) electrocatalysts is an imperative requirement to produce green and clean hydrogen energy. In this work, the FeCoSy /NCDs composite with nitrogen-doped carbon dots (NCDs) modified Fe-Co sulfide (FeCoSy ) nanosheets is prepared by using a facile and mild one-pot solvothermal method. Benefiting from the low crystallinity and the synergistic effect between FeCoSy and NCDs, the optimal FeCoSy /NCDs-3 composite exhibits an overpotential of only 284 mV at 10 mA cm-2 , a small Tafel value of 52.1 mV dec-1 , and excellent electrochemical durability in alkaline solution. Remarkably, unlike ordinary metal sulfide electrocatalysts, the morphology, components, and structure of the FeCoSy /NCDs composite can be well retained after OER test. The NCDs modified FeCoSy composite with excellent electrocatalytic performance provides an effective approach to boost metal sulfide electrocatalysts for practical application.

Mechanochemical Pretreated Mn+1AXn (MAX) Phase to Synthesize 2D-Ti3C2Tx MXene Sheets for High-Performance Supercapacitors

Two-dimensional (2D) MXenes sheet-like micro-structures have attracted attention as an effective electrochemical energy storage material due to their efficient electrolyte/cation interfacial charge transports inside the 2D sheets which results in ultrahigh rate capability and high volumetric capacitance. In this article, Ti₃C₂T_x MXene is prepared by a combination of ball milling and chemical etching from Ti₃AlC₂ powder. The effects of ball milling and etching duration on the physiochemical properties are also explored, as well as the electrochemical performance of as-prepared Ti₃C₂ MXene. The electrochemical performances of 6 h mechanochemically treated and 12 h chemically etched MXene (BM-12H) exhibit an electric double layer capacitance behavior with an enhanced specific capacitance of 146.3 F g^-1 compared to 24 and 48 h treated samples. Moreover, 5000-cycle stability tested sample's (BM-12H) charge/discharge show increased specific capacitance due to the termination of the -OH group, intercalation of K⁺ ion and transformation to TiO₂/Ti₃C₂ hybrid structure in a 3 M KOH electrolyte. Interestingly, a symmetric supercapacitor (SSC) device fabricated in a 1 M LiPF₆ electrolyte in order to extend the voltage window up to 3 V shows a pseudocapacitance behavior due to Li on interaction/de-intercalation. In addition, the SSC shows an excellent energy and power density of 138.33 W h kg^-1 and 1500 W kg^-1, respectively. The ball milling pre-treated MXene exhibited an excellent performance and stability due to the increased interlayer distance between the MXene sheets and intercalation and deintercalation of Li⁺ ions.

Multifunctional microwave absorption materials of multiscale cobalt sulfide/diatoms co-doped carbon aerogel

Microwave absorption materials (MAMs) have attracted much attention for their potential applications in stealth technology and prevention of electromagnetic pollution problems. Multifunctional MAMs are highly demanded because they can be applied in harsh environments. Hence, based on multiscale manipulation of atomic engineering, nanostructure and microstructure, a multiscale hollow cobalt sulfide/diatoms co-doped carbon aerogel was preparedthrough the physical crosslinking of divalent ions, unidirectional freezing, kirkendall effect, and heteroatomic doping. The aerogel with a low density of 13.1 mg/mm³ has a unique "lamellar-pillar" network structure due to the growth of ice crystals during the preparation process. With the assistance of thiourea, the doping of N, S atoms and the construction of hollow cobalt sulfide are accomplished simultaneously. The ingenious integration facilitates the synergistic effect of conductive loss, defect polarization, interfacial polarization, and multiple scattering. The multiscale hollow cobalt sulfide/diatoms co-doped carbon aerogel had a maximum reflection loss of -51.96 dB and an effective absorption bandwidth of 6.4 GHz, which is higher than that of other reported MAMs. It is further verified through finite element simulation and experiments that the aerogel has an excellent microwave absorption properties. In addition, the aerogel has excellent thermal insulation and flame retardant properties. Therefore, the development of this aerogel can help to use MAMs in complex applications.

Microwave solvothermal synthesis of Component-Tunable High-Entropy oxides as High-Efficient and stable electrocatalysts for oxygen evolution reaction

Transition-metal-based high-entropy oxides (HEOs) are appealing electrocatalysts for oxygen evolution reaction (OER) due to their unique structure, variable composition and electronic structure, outstanding electrocatalytic activity and stability. Herein, we propose a scalable high-efficiency microwave solvothermal strategy to fabricate HEO nano-catalysts with five earth-abundant metal elements (Fe, Co, Ni, Cr, and Mn) and tailor the component ratio to enhance the catalytic performance. (FeCoNi₂CrMn)₃O₄ with a double Ni content exhibits the best electrocatalytic performance for OER, namely low overpotential (260 mV@10 mA cm^-2), small Tafel slope and superb long-term durability without obvious potential change after 95 h in 1 M KOH. The extraordinary performance of (FeCoNi₂CrMn)₃O₄ can be attributed to the large active surface area profiting from the nano structure, the optimized surface electronic state with high conductivity and suitable adsorption to intermediate benefitting from ingenious multiple-element synergistic effects, and the inherent structural stability of the high-entropy system. In addition, the obvious pH value dependable character and TMA⁺ inhibition phenomenon reveal that the lattice oxygen mediated mechanism (LOM) work together with adsorbate evolution mechanism (AEM) in the catalytic process of OER with the HEO catalyst. This strategy provides a new approach for the rapid synthesis of high-entropy oxide and inspires more rational designs of high-efficient electrocatalysts.

Reprogramming thermodynamic-limiting oxidation cycle in NiFe-based oxygen evolution electrocatalyst through Mo doping induced surface reconstruction

Engineering of robust nonprecious electrocatalysts toward anodic oxygen evolution reaction (OER) is of great significance for lowering the cost and energy consumption for renewable fuel production. Herein, we report NiFeMoO_x nanosheets as high-performance OER electrocatalyst through promoting the thermodynamic-limiting oxidation cycle process in NiFe oxyhydroxide via high-valence Mo doping. The NiFeMoO_x nanosheets are prepared by an elaborate in-situ solvothermal etching-depositing process with NiFe alloy framework as substrate and metal precursors. The resultant nanosheets exhibit outstanding alkaline OER activity, requires only 235/282/327 mV overpotentials to achieve current density of 10/100/300 mA cm^-2, respectively, with a good long-term stability at 20 mA cm^-2 for 72 h. Besides, the Tafel slope low to 28.1 mV dec^-1 indicates a favorable OER kinetics. The superior catalytic activity of NiFeMoO_x nanosheets should be attributed to the lower oxidation states of Ni and Fe induced by high-valence dopant, leading to easier surface reconstruction at low charge oxidation cycling during OER, thereby effectively reducing the overpotential. The synergy between the electronic effect among multimetallic sites and the unique morphology is expected to inspire the development of robust OER electrocatalyst for industrial application.

Highly efficient oxygen evolution reaction enabled by phosphorus-boron facilitating surface reconstruction of amorphous high-entropy materials

Efficient, cost-effective and durable electrocatalysts are highly required to overcome the slow kinetics and high overpotential of oxygen evolution reaction (OER). Here we report a series of novel amorphous high-entropy borophosphate catalysts FeCoNiMBPO_x (M = Mg, Al, Cr, Mn) prepared by a low-temperature reduction method. The leaching of boron and phosphorus accelerates the surface self-reconstruction of FeCoNiMnBPO_x, and the subsequently formed high-oxidation-state metal-OOH species is beneficial to improve the catalyst performance. Moreover, the unique amorphous structure with abundant defects provides more active sites for OER. As a return, all the samples exhibit excellent OER activity and stability. Among them, FeCoNiMnBPO_x with the highest conductivity and the largest electrochemical active surface area (ECSA) exhibits the best electrocatalytic performance, requiring only low overpotentials of 248 mV and 294 mV to reach current densities of 10 mA cm^-2 and 100 mA cm^-2, respectively. This sample also shows an exceptional durability for 50 h without a significant increase in potential, which is superior to that of the benchmark RuO₂ electrocatalyst. The combination of the adsorbate evolution mechanism (AEM) and the lattice oxygen-mediated mechanism (LOM) are responsible for the excellent catalyst performance. This work provides new ideas for designing high-activity multiple-element catalysts.

Fe and P dual-doped nickel carbonate hydroxide/carbon nanotube hybrid electrocatalysts for an efficient oxygen evolution reaction

Designing cost-effective and highly active oxygen evolution reaction (OER) electrocatalysts is critical for large-scale hydrogen production from electrocatalytic water splitting. Herein, Fe and P dual-doped nickel carbonate hydroxide/carbon nanotubes (Fe, P-NiCH/CNTs) were fabricated through a solvothermal method. By virtue of the optimized electronic structure, improved conductivity and enriched active sites, the as-fabricated Fe, P-NiCH/CNT hybrid electrocatalyst exhibits superior OER activity, with a low overpotential of 222 mV at 20 mA cm^-2 and robust durability, confirming its potential as a highly efficient OER electrocatalyst. Moreover, theoretical calculations demonstrate that the doped Fe and surface adsorbed PO₄^3- can regulate the electronic structure of evolved NiOOH and decrease the energy barrier of the rate-determining step, thus leading to improved OER activity. The strategy presented in this work can also be employed to fabricate other transition metal carbonate hydroxides for various electrocatalytic applications.