Bifunctional CoSn(OH)6/MnO2 composite for solid-state asymmetric high power density supercapacitor and for an enhanced OER

Hierarchical S-Doped Vanadium MOFs with Multiwalled Carbon Nanotubes: A Robust Bifunctional Catalyst for Efficient Water Electrolysis

Developing nonprecious metal-based electrocatalysts with exceptional activity and durability for water electrolysis remains a significant challenge. Herein, we report a highly efficient bifunctional electrocatalyst composed of sulfur-doped vanadium metal-organic frameworks (S@V-MOF) integrated with multiwalled carbon nanotubes (MWCNTs) to promote the synergistic effect between S@V-MOF and MWCNTs and modulate the electronic structure of the catalyst, which eventually enhanced its electrocatalytic performance. The S@V-MOF/MWCNT catalyst loaded at the Ni foam electrode exhibits remarkable activity for both the hydrogen evolution reaction (HER) in acidic media and oxygen evolution reaction (OER) in alkaline media, requiring overpotentials of 48 and 227 mV, respectively, to reach a current density of 10 mA cm-2. Notably, when employed as a bifunctional catalyst in a two-electrode overall water splitting electrochemical cell, the S@V-MOF/MWCNT catalyst-loaded electrode delivers an outstanding cell voltage of 1.53 V at 10 mA cm-2 with exceptional durability. This work provides a promising strategy for designing cost-effective and efficient electrocatalysts for water electrolysis.

Metal-organic framework-derived Se-blended ZrO2 with a nitrogen-doped carbon heterostructure for electrocatalytic overall water splitting

Designing low cost, highly active and efficient non-noble metal bifunctional electrocatalysts with remarkable operational reliability for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is indispensable for large-scale water electrolysis and the development of clean energy conversion technologies. Herein, we decorated a two-dimensional (2D) selenium-blended zirconium dioxide (Se-ZrO2) on the surface of a nitrogen-doped carbon heterostructure (Se-ZrO2@NC), which was derived from Zr-metal-organic frameworks (Zr-MOFs), and loaded it on a stainless-steel mesh electrode. Accordingly, phenomenal electrocatalytic performance was observed for the Se-ZrO2@NC-loaded electrode with a minimum overpotential of 48 mV for the HER and 251 mV for the OER at 10 mA cm-2 current density in acidic and alkaline mediums, respectively. Moreover, a complete cell set up was constructed, where the OER and HER were studied at the anode and cathode, respectively, with a cell potential of 1.58 V to reach a current density of 10 mA cm-2 together with an exciting long-term stability of over 48 h. The developed Se-blended 2D transition metal dioxides on the 2D nitrogen-doped carbon heterostructure extended to a variety of catalytically active materials that would provide highly active and stable electrocatalysts for alkaline water splitting studies.

Hollow Nanooxidase Enhanced Phototherapy Against Solid Tumors

Although phototherapy has attracted extensive attention in antitumor field in recent years, its therapeutic effect is usually unsatisfactory because of the complexity and variability of the tumor microenvironment (TME). Herein, we report novel CoSn(OH)₆@CoOOH hollow carriers with oxidase properties that can enhance phototherapy. Hollow CoSn(OH)₆@CoOOH nanocubes (NCs) with a particle size of ∼160 nm were synthesized via a two-step process of coprecipitation and etching. These NCs can react with O₂ to generate singlet oxygen without hydrogen peroxide and consume glutathione, and their hollow structure can be utilized to carry drug molecules. After loading indocyanine green (ICG) and 1,2-bis(2-(4,5-dihydro-1H-imidazol-2-yl)propan-2-yl) diazene dihydrochloride (AIPH), the resulting nanosystem (HCIA) exhibited enhanced phototherapy effects through the catalytic activity of oxidase, production of alkyl radicals, and consumption of glutathione. Cell and mouse experiments showed that HCIA combined with near-infrared laser irradiation significantly inhibited the growth of 4T1 tumors. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that PI3K-Akt and MAPK signaling pathways were highly relevant to this therapeutic system. Such hollow NCs with oxidase activity have considerable potential for the design of multifunctional drug delivery vehicles for tumor therapy.

Layered Porous Graphitic Carbon Nitride Stabilized Effective Co2SnO4 Inverse Spinel as a Bifunctional Electrocatalyst for Overall Water Splitting

Developing an efficient, low-cost, and non-noble metal oxide-based nanohybrid material for overall water splitting is a highly desirable approach to promote clean energy harnessing and to minimize environmental issues. Accordingly, we proposed an interfacial engineering approach to construct layered porous graphitic carbon nitride (g-C₃N₄)-stabilized Co₂SnO₄ inverse spinel nanohybrid materials as highly active bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline medium. Here, a Co₂SnO₄/g-C₃N₄ nanohybrid with a layered porous g-C₃N₄ stabilized cubelike inverse spinel has been synthesized with an enhanced surface area via a simple one-pot hydrothermal method. Besides, detailed structural and morphological characterizations were carried out using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission-scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared (FT-IR), and Brunauer-Emmett-Teller (BET) analysis. Briefly, XPS analysis has revealed the existence of a strong coupling bond at the interface between a definite proportion of g-C₃N₄ nanosheets and the inverse spinel, which act as an electron transport channel to explore the exceptional performances for HER and OER. Compared to the Co₂SnO₄ inverse spinel lattice or g-C₃N₄ nanosheets, the prepared Co₂SnO₄/g-C₃N₄ nanohybrid-loaded 316 SSL mesh electrode showed excellent and stable electrocatalytic performances with very low overpotentials of 41 mV for HER and 260 mV for OER to reach the current density of 10 mA cm^-2. To understand the electrocatalytic phenomena, the faradic efficiency was calculated for the prepared bifunctional electrocatalyst as 96%, which effectively would favor water electrolysis. Accordingly, the Co₂SnO₄/g-C₃N₄ nanohybrid-loaded electrodes were constructed, and the minimum cell voltage was found to be 1.52 V to reach the current density of 10 mA cm^-2, which is comparable to the standard RuO₂∥Pt/C in two-electrode systems. Thus, the developed nanohybrid-based electrocatalyst could be an alternative to noble metal-centered systems for highly efficient overall water splitting.

Embedding Co2P nanoparticles in Cu doping carbon fibers for Zn-air batteries and supercapacitors

Developing highly efficient and non-precious materials for Zn-air batteries (ZABs) and supercapacitors (SCs) are still crucial and challenging. Herein, electronic reconfiguration and introducing conductive carbon-based materials are simultaneously conducted to enhance the ZABs and SCs performance of Co₂P. We develop a simple and efficient electrospinning technology followed by carbonization process to synthesize embedding Co₂P nanoparticles in Cu doping carbon nanofibers (Cu-Co₂P/CNFs). As a result, the 7% Cu-Co₂P/CNFs presents high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity (half-wave potential of 0.792 V for ORR, an overpotential of 360 mV for OER). The ZABs exhibit a power density of 230 mW cm^-2and excellent discharge-charge stability of 80 h. In addition, the 7% Cu-Co₂P/CNFs show the specific capacitance of 558 F g^-1at 1 A g^-1. Moreover, the 7% Cu-Co₂P/CNFs//CNFs asymmetric supercapacitor was assembled applying 7% Cu-Co₂P/CNFs electrode and pure CNFs, which exhibits a high energy density (25.9 Wh kg^-1), exceptional power density (217.5 kW kg^-1) and excellent cycle stability (96.6% retention after 10 000 cycles). This work may provide an effective way to prepared Co₂P based materials for ZABs and SCs applications.

Mesoporous nanostructures of NiCo-LDH/ZnCo2O4 as an efficient electrocatalyst for oxygen evolution reaction

Increasing energy demands for pollution-free and renewable energy technologies have stimulated intense research on the development of inexpensive, highly efficient, and stable non-noble metal electrocatalysts for oxygen evolution reaction (OER). In this study, a superior OER performance was achieved using a tri-metallic (Zn, Co, Ni) high-performance electrocatalyst. We successfully fabricated a peony-flower-like hierarchical ZnCo₂O₄ through an additive-free hydrothermal reaction followed by heat treatment. Then NiCo-LDH (layered double hydroxides) nano-flakes was electrodeposited on the ZnCo₂O₄/GCE surface to prepare NiCo-LDH/ZnCo₂O₄/GCE which was used as electrode for OER. The structure and morphology of the catalysts were characterized by several techniques including Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, elemental mapping and Brunauer-Emmett-Teller method. The NiCo-LDH/ZnCo₂O₄ catalyst provided high catalytic activity toward OER under alkaline condition (1.0 M KOH) with a low overpotential of 260 mV to drive the benchmark current density of 10 mA cm^-2 and Tafel slope of 62 mV dec^-1, as well as long-term stability and high turnover frequency of 0.0641 s^-1 at overpotential of 340 mV. The NiCo-LDH/ZnCo₂O₄ catalyst was found to perform significantly better than NiCo-LDH, ZnCo₂O₄, NiCo-LDH/Co₃O₄, Co₃O₄, and commercial RuO₂ catalysts. The outstanding OER performance of NiCo-LDH/ZnCo₂O₄ catalyst, which may be attributed to the large specific surface area, accelerated mass and electron transport, and synergistic effect of multiple hybrid materials, makes it a promising catalyst for OER.

A mild reduction of Co-doped MnO2 to create abundant oxygen vacancies and active sites for enhanced oxygen evolution reaction

Efficient and non-precious-metal-based catalysts (e.g., manganese-based oxides) for the oxygen evolution reaction (OER) remain a substantial challenge. Creation of oxygen vacancies of manganese-based oxides with the aim to enhance their intrinsic activities is rarely reported, and there is a critical requirement for a mild and facile synthesis strategy to create abundant oxygen vacancies on manganese-based oxides. Herein, Co-doped MnO₂ nanowires were reduced by NaBH₄ solution at room temperature; then, MnCo₂O_4.5 nanosheets with abundant oxygen vacancies and active sites were formed on the surface of Co-doped MnO₂ nanowires. Benefiting from the reduction strategy, the fabricated hierarchical Co-doped-MnO₂@MnCo₂O_4.5 nanowire/nanosheet nanocomposites exhibit higher catalytic activity (an overpotential of 250 mV at a current density of 10 mA cm^-2 in 1.0 M KOH solution) than pristine Co-doped MnO₂ nanowires. The calculated TOF of Co-doped-MnO₂@MnCo₂O_4.5 is 0.034 s^-1 at the overpotential of 300 mV, which is 136-fold higher than that of Co-doped-MnO₂. The excellent OER performance was attributed to the synergistic advantages of abundant oxygen vacancies and active sites over the hierarchical nanowire-nanosheet architectures.

Anchoring γ-MnO2 within β-NiCo(OH)2 as an Interfacial Electrode Material for Boosting Power Density in an Asymmetric Supercapacitor Device and for Oxygen Evolution Catalysis

The great challenge is to improve the high-competence electrochemical supercapacitor (ES) and oxygen evolution reaction (OER) electrocatalyst with earth-abundant transition metals rather than using limited noble metals. Herein, we developed a facile strategy to introduce two different phases such as α-MnO₂ or γ-MnO₂ on porous hexagonal bimetallic β-NiCo(OH)₂-layered double hydroxide (LDH) nanosheets for an enhanced bifunctionality and to ease out interfacial redox reaction kinetics. Due to the rational intend of LDH morphology and well-retained starlike γ-MnO₂ nanostructures, the bifunctional LDHs exhibit commendable activities toward ESs and in the OER study. Importantly, the γ-MnO₂ phase loaded at β-NiCo(OH)₂ LDHs shows superior ESs or electrocatalytic OER performance in comparison with the α-MnO₂ phase on LDHs. Besides, the assembled fabricated asymmetric supercapacitor (FASC) device possesses convincing energy (24.43 W h/kg) and power densities (5312 W/kg) and enabled us to glow a 1.4 V light-emitting diode for 45 s. Accordingly, three-/two-electrode systems or the solid-state FASC device has exhibited high efficiency in ESs. Also, the optimized γ-MnO₂ phase on β-NiCo(OH)₂ LDHs with the detailed mass ratio of Ni and Co has displayed the OER performance comparable to commercial RuO₂. The electrochemical studies and structural classifications offer in-depth analysis on the electrochemical behaviors, especially the stability in both ES and OER studies, signifying a promising aspirant in the alternative energy field.