Fluorine-doped nickel cobalt oxide spinel as efficiently bifunctional catalyst for overall water splitting

Facile route of fluorine incorporation into nickel (oxy)hydroxide for improving the oxygen evolution reaction

Despite extensive development, oxygen evolution reaction (OER) catalysts still require significant overpotentials to function. In this study, we show that the overpotential of a nickel (Ni) electrode for the OER can decrease by about 100 mV with fluorine (F) incorporation, particularly by a facile electrochemical approach at room temperature.

Electrode Materials of Cobaltous Fluoride for Supercapacitor and Electrocatalysis Applications

Herein, CoF₂ was synthesized by a solvothermal method. The characterization results of the phase and morphology of the sample show that it was successfully synthesized and its morphology is composed of micron particles with uneven size and shape. The electrochemical test results of SCs in different electrolytes show that CoF₂ has electrochemical activity only in alkaline electrolytes. Notably, the electrochemical behavior of CoF₂ in LiOH solution is different from that in other alkaline solutions in that charge-discharge curve has a quasi-isosceles triangle shape and the CV curve has no obvious redox peak. That is, it has pseudocapacitance behavior in LiOH. Furthermore, CoF₂ as catalyst for HER requires an overpotential of only 168 mV to obtain current density of 10 mA cm^-2 and a Tafel slope of 116 mV dec^-1 in 1 M KOH solution. This research provides a novel way to explore excellent performance electrode materials for SC and HER.

Recent Progress on Bimetallic-Based Spinels as Electrocatalysts for the Oxygen Evolution Reaction

Electrocatalytic water splitting is a promising and viable technology to produce clean, sustainable, and storable hydrogen as an energy carrier. However, to meet the ever-increasing global energy demand, it is imperative to develop high-performance non-precious metal-based electrocatalysts for the oxygen evolution reaction (OER), as the OER is considered the bottleneck for electrocatalytic water splitting. Spinels, in particular, are considered promising OER electrocatalysts due to their unique properties, precise structures, and compositions. Herein, the recent progress on the application of bimetallic-based spinels (AFe₂ O₄ , ACo₂ O₄ , and AMn₂ O₄ ; where A = Ni, Co, Cu, Mn, and Zn) as electrocatalysts for the OER is presented. The fundamental concepts of the OER are highlighted after which the family of spinels, their general formula, and classifications are introduced. This is followed by an overview of the various classifications of bimetallic-based spinels and their recent developments and applications as OER electrocatalysts, with special emphasis on enhancing strategies that have been formulated to improve the OER performance of these spinels. In conclusion, this review summarizes all studies mentioned therein and provides the challenges and future perspectives for bimetallic-based spinel OER electrocatalysts.

Ligand Incorporating Sequence-dependent ZIF67 Derivatives as Active Material of Supercapacitor: Competition between Ammonia Fluoride and 2-Methylimidazole

The zeolitic imidazolate framework 67 (ZIF67) derivative is a potential active material of supercapacitors (SC), owing to high specific surface area and porosity and possible formation of cobalt compounds. A novel ZIF67 derivative is synthesized using a one-step solution process with cobalt precursor 2-methylimidazole (2-Melm) and ammonia fluoride in our previous work. Due to its facile synthesis and excellent electrocapacitive behavior, it is crucial to understand the competition between ammonia fluoride and 2-Melm on forming derivatives with cobalt ions and to create more efficient ZIF67 derivatives for charge storage. In this work, several ZIF67 derivatives are designed using a one-step solution process with 2-Melm and ammonia fluoride incorporated in different sequences. The reaction durations for a single ligand and two ligands are controlled. The largest capacity of 176.33 mAh/g corresponding to the specific capacitance of 1057.99 F/g is achieved for the ZIF67 derivative electrode prepared by reacting ammonia fluoride and a cobalt precursor for 0.5 h and then incorporating 2-Melm for another 23.5 h of reaction (NM0.5). This derivative composed of highly conductive CoF₂, NiF₂, Co(OH)F, and Ni(OH)F presents high specific surface area and porosity. The relevant SC presents a maximum energy density of 19.5 Wh/kg at 430 W/kg, a capacity retention of 92%, and Coulombic efficiency of 96% in 10000 cycles.

Transition Metal Non-Oxides as Electrocatalysts: Advantages and Challenges

The identification of hydrogen as green fuel in the near future has stirred global realization toward a sustainable outlook and thus boosted extensive research in the field of water electrolysis focusing on the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). A huge class of compounds consisting of transition metal-based nitrides, carbides, chalcogenides, phosphides, and borides, which can be collectively termed transition metal non-oxides (TMNOs), has emerged recently as an efficient class of electrocatalysts in terms of performance and longevity when compared to transition metal oxides (TMOs). Moreover, the superiority of TMNOs over TMOs to effectively catalyze not only OERs but also HERs and ORRs renders bifunctionality and even trifunctionality in some cases and therefore can replace conventional noble metal electrocatalysts. In this review, the crystal structure and phases of different classes of nanostructured TMNOs are extensively discussed, focusing on recent advances in design strategies by various regulatory synthetic routes, and hence diversified properties of TMNOs are identified to serve as next-generation bi/trifunctional electrocatalysts. The challenges and future perspectives of materials in the field of energy conversion and storage aiding toward a better hydrogen economy are also discussed in this review.

Facile deposition of palladium oxide (PdO) nanoparticles on CoNi2S4microstructures towards enhanced oxygen evolution reaction

Strong demand for renewable energy resources and clean environments have inspired scientists and researchers across the globe to carry out research activities on energy provision, conversion, and storage devices. In this context, development of outperform, stable, and durable electrocatalysts has been identified as one of the major objectives for oxygen evolution reaction (OER). Herein, we offer facile approach for the deposition of few palladium oxide (PdO) nanoparticles on the cobalt-nickel bi-metallic sulphide (CoNi₂S₄) microstructures represented as PdO@ CoNi₂S₄using ultraviolet light (UV) reduction method. The morphology, crystalline structure, and chemical composition of the as-prepared PdO@ CoNi₂S₄composite were probed through scanning electron microscopy, powder x-ray diffraction, high resolution transmission electron microscopy, energy dispersive spectroscopy and x-ray photoelectron spectroscopy techniques. The combined physical characterization results revealed that ultraviolet light (UV) light promoted the facile deposition of PdO nanoparticles of 10 nm size onto the CoNi₂S₄and the fabricated PdO@ CoNi₂S₄composite has a remarkable activity towards OER in alkaline media. Significantly, it exhibited a low onset potential of 1.41 V versus reversible hydrogen electrode (RHE) and a low overpotential of 230 mV at 10 mA cm^-2. Additionally, the fabricated PdO@ CoNi₂S₄composite has a marked stability of 45 h. Electrochemical impedance spectroscopy has shown that the PdO@CoNi₂S₄composite has a low charge transfer resistance of 86.3 Ohms, which favours the OER kinetics. The PdO@ CoNi₂S₄composite provided the multiple number of active sites, which favoured the enhanced OER activity. Taken together, this new class of material could be utilized in energy conversion and storage as well as sensing applications.

NiCo2O4 nanoparticles inlaid on sulphur and nitrogen doped and co-doped rGO sheets as efficient electrocatalysts for the oxygen evolution and methanol oxidation reactions

The present work depicts the fabrication of NiCo₂O₄ decorated on rGO, and doped and co-doped rGO and its electrocatalytic activity towards the oxygen evolution reaction and methanol oxidation reaction. The NiCo₂O₄ catalyst with S-doped rGO outperformed the other catalysts, indicating that the sulphur atoms attached on rGO possess low oxophilicity and optimum free energy. This results in facile adsorption of the intermediate products formed during the OER and a rapid release of O₂ molecules. The same catalyst requires an overpotential of 1.51 V vs. RHE to attain the benchmark current density value of 10 mA cm^-2 and shows a Tafel slope of 57 mV dec^-1. It also reveals outstanding stability during its operation for 10 h with a minimum loss in potential. On the other hand, NiCo₂O₄/S,N-rGO reveals superior activity with high efficiency and stability in catalyzing methanol oxidation. The catalyst delivered a low onset potential of 0.12 V vs. Hg/HgO and high current density of 203.4 mA cm^-2 after addition of 0.5 M methanol, revealing the outstanding performance of the electrocatalyst.

Recent advances on preparation and environmental applications of MOF-derived carbons in catalysis

Carbon materials derived from metal organic frameworks (MOFs) have excellent properties of high surface area, high porosity, adjustable pore size, high conductivity and stability, and their applications in catalysis have become a rapidly expanding research field. In this review, we have summarized the synthesis strategies of MOF-derived carbons with different physical and chemical properties, obtained through direct carbonization, co-pyrolysis and post-treatment. The potential applications of derived carbons, especially monometal-, bimetal-, nonmetal-doped and metal-free carbons in organo-catalysis, photocatalysis and electrocatalysis are analyzed in detail from the environmental perspective. In addition, the improvement of catalytic efficiency is also considered from the aspects of increasing active sites, enhancing the activity of reactants and promoting free electron transfer. The function and synergy of various species of the composites in the catalytic reaction are summarized. The reaction paths and mechanisms are analyzed, and research ideas or trends are proposed for further development.

Advances in Template Prepared Nano-Oxides and their Applications: Polluted Water Treatment, Energy, Sensing and Biomedical Drug Delivery

The nano-oxide materials with special structures prepared by template methods have a good dispersion, regular structures and high specific surface areas. Therefore, in some areas, improved properties are observed than conventional bulk oxide materials. For example, in the treatment of dye wastewater, the treatment efficiency of adsorbents and catalytic materials prepared by template method was about 30 % or even higher than that of conventional samples. This review mainly focuses on the progress of inorganic, organic and biological templates in the preparation of micro- and nano- oxide materials with special morphologies, and the roles of the prepared materials as adsorbents and photocatalysts in dye wastewater treatment. The characteristics and advantages of inorganic, organic and biological template are also summarized. In addition, the applications of template method prepared oxides in the field of sensors, drug carrier, energy materials and other fields are briefly discussed with detailed examples.

One-step co-precipitation synthesis of novel BiOCl/CeO2composites with enhanced photodegradation of rhodamine B

BiOCl/CeO₂composites were synthesized by a facile one-step co-precipitation method and showed good photodegradation activity of rhodamine B (RhB).

Morphological interference of two different cobalt oxides derived from a hydrothermal protocol and a single two-dimensional metal organic framework precursor to stabilize the β-phase of PVDF for flexible piezoelectric nanogenerators

Here, we have fabricated a piezoelectric nanogenerator (PENG) composed of a Co-oxide (Co₃O₄) doped electro active PVDF based nanocomposite for efficient piezoelectric energy harvesting application where the Co₃O₄ inclusion favours nucleation and polar β-phase stabilization in the nanocomposite. The morphological effect on the nucleation and β-phase stabilisation of PVDF has been explored experimentally. The flake-like morphology of Co₃O₄ nanoparticles, synthesized by using a MOF, has a more effective surface area to nucleate and stabilise the β-phase of PVDF than that of rod-like (hydrothermal) and spherical (commercial) nanoparticles. The PENG with PVDF and the 1.5 wt% MOF based Co₃O₄ (MPNG) shows an excellent open circuit voltage (∼37 V) and short circuit current (∼0.711 μA) upon human finger tapping. The maximum power density generated from the MPNG is ∼8.55 μW cm^-2, which is well sufficient for the driving of portable electronic devices like LEDs, calculator wrist watches, humidity sensors etc. Also, from various easily accessible mechanical and biomechanical energy sources like heel pressing, walking, and machine vibration, the MPNG is capable of harvesting energy.