Synthesis of Co/CeO2 hetero-particles with abundant oxygen-vacancies supported by carbon aerogels for ORR and OER

A facile method for preparing the CeMnO3 catalyst with high activity and stability of toluene oxidation: The critical role of small crystal size and Mn3+-Ov-Ce4+ sites

Volatile organic compounds (VOCs) cause severe environmental pollution and are potentially toxic to humans who have no defense against exposure. Catalytic oxidation of these compounds has thus become an interesting research topic. In this study, microcrystalline CeMnO3 catalysts were prepared by a precipitant-concentration-induced strategy and evaluated for the catalytic oxidation of toluene/benzene. The effect of crystal size on catalytic performance was confirmed by XRD, TEM, N2 adsorption-desorption, XPS, Raman, H2-TPR, and TPSR. The CeMnO3 catalyst with more Mn3+-Ov-Ce4+ active sites exhibited enhanced VOCs catalytic oxidation performance, lowest active energy, and highest turnover frequency, which was attributed to its larger surface area, lower crystal size, higher low-temperature reducibility, and presence of more oxygen defects. In-situ FTIR results suggested more oxygen vacancies can profoundly promote the conversion of benzoate to maleate species, the rate-determining step of toluene oxidation. The work provides a convenient and efficient strategy to prepare single-metal or multi-metal oxide catalysts with smaller crystal sizes for VOC oxidation or other oxidation reactions.

Modulating metal-support interaction and inducing electron-rich environment of Ni2P NPs by B atoms incorporation for enhanced hydrogen evolution reaction performance

Modulation of the electronic interaction between the metal and support has been verified as a feasible strategy to improve the electrocatalytic performance of supported-type catalysts. Here, we have successfully synthesized an electrocatalyst of Ni2P nanoparticles (NPs) anchored on B, N co-doped graphite-like carbon nanosheets (Ni2P@B, N-GC), and elucidated the main mechanism by which B atoms doping enhances electrocatalytic hydrogen evolution reaction (HER) performance. The B atoms with electron-rich characteristic not only modulate the electronic structure on carbon skeleton, but also regulate the interfacial electronic interaction between Ni2P NPs and the carbon skeleton, which can lead to the increased available electron density of Ni sites. Such optimization is conducive to accelerating proton transfer and promoting reactive activity. As revealed, the Ni2P@B, N-GC catalyst with B atoms doping exhibits superior performance to the Ni2P@N-GC catalyst in acidic, neutral and alkaline medias. In addition, the assembled Ni(OH)2@B, N-GC||Ni2P@B, N-GC electrolyzer displays prominent overall water splitting performance in alkaline solution, which only demands 1.57 V to reach 10 mA/cm2, and in complicated natural seawater electrolyte, as low as 1.59 V. Hence, the B atoms doping strategy shows the significant enhancement for HER electrocatalysis.

A 3D Covalent Organic Framework with In-situ Formed Pd Nanoparticles for Efficient Electrochemical Oxygen Reduction

Non-platinum noble metals are highly desirable for the development of highly active, stable oxygen reduction reaction (ORR) electrocatalysts for fuel cells and metal-air batteries. However, how to improve the utilization of non-platinum noble metals is an urgent issue. Herein, a highly efficient catalyst for ORR was prepared through homogeneous loading of Pd precursors by a domain-limited method in a three-dimensional covalent organic framework (COF) followed by pyrolysis. The morphology of the Pd nanoparticles (Pd NPs) was well maintained after carbonization, which was attributed to the rigid structure of the 3D COF. Thanks to the uniform distribution of Pd NPs in the carbon, the catalyst exhibited a remarkable half-wave potential of 0.906 V and a Tafel slope of 70 mV dec-1 in 0.1 M KOH, surpassing the commercial Pt/C catalyst (0.863 V and 75 mV dec-1 ). Furthermore, a maximum power density of 144.0 mW cm-2 was achieved at 252 mA cm-2 , which was significantly higher than the control battery (105.1 mW cm-2 ). This work not only provides a simple strategy for in-situ preparation of highly dispersible metal catalysts in COFs, but also offers new insights into the ORR electrocatalysis.

4f-2p-3d orbital overlap in a metal-organic framework-derived CeO2/CeCo-LDH heterostructure promotes water oxidation

Herein, we have demonstrated a facile method for the synthesis of CeO2/Ce-Co-LDH heterostructures using zeolitic imidazolate framework-67 as the precursor. The Ce-incorporation in Co-LDH results in 4f-2p-3d orbital overlap to tune the electronic structure whereas the oxygen-deficient CeO2 controls the interface charge transfer. This results in excellent water oxidation activity to attain 500 mA cm-2 current density at 320 overpotential.

Cu-based catalysts with the co-existence of single atoms and nanoparticles for basic electrocatalytic oxygen reduction reaction

Developing efficient and stable oxygen reduction reaction (ORR) catalysts to replace the precious Pt/C is very important for the industrial application of proton-exchange membrane fuel cells. Herein, using bismuth-based metal-organic frameworks as the substrate to disperse copper ions, we prepared a catalyst containing both Cu single atoms and Cu nanoparticles (CuSACuNP/BiCN) by a pyrolysis method. In 0.1 M KOH electrolyte, the electrocatalytic ORR performance of CuSACuNP/BiCN was superior to that of commercial Pt/C. With a hierarchical porous architecture, CuSACuNP/BiCN displayed a half-wave potential of 0.86 V vs. RHE and a diffusion-limiting current density of 5.82 mA cm-2 with a four-electron transfer process. In addition, it was stable during a 12-hour durability test. This study provides guidance for the synthesis of advanced Cu-based nano-single-atom catalytic materials for ORR applications.

CoNi Alloys Encapsulated in N-Doped Carbon Nanotubes for Stabilizing Oxygen Electrocatalysis in Zinc-Air Battery

Alloy-based catalysts with high corrosion resistance and less self-aggregation are essential for oxygen reduction/evolution reactions (ORR/OER). Here, via an in situ growth strategy, NiCo alloy-inserted nitrogen-doped carbon nanotubes were assembled on a three-dimensional hollow nanosphere (NiCo@NCNTs/HN) using dicyandiamide. NiCo@NCNTs/HN exhibited better ORR activity (half-wave potential (E_1/2) of 0.87 V) and stability (E_1/2 shift of only -13 mV after 5000 cycles) than commercial Pt/C. NiCo@NCNTs/HN displayed a lower OER overpotential (330 mV) than RuO₂ (390 mV). The NiCo@NCNTs/HN-assembled zinc-air battery exhibited high specific-capacity (847.01 mA h g^-1) and cycling-stability (291 h). Synergies between NiCo alloys and NCNTs facilitated the charge transfer to promote 4e^- ORR/OER kinetics. The carbon skeleton inhibited the corrosion of NiCo alloys from surface to subsurface, while inner cavities of CNTs confined particle growth and the aggregation of NiCo alloys to stabilize bifunctional activity. This provides a viable strategy for the design of alloy-based catalysts with confined grain-size and good structural/catalytic stabilities in oxygen electrocatalysis.

Boosting oxygen evolution electrocatalysis via CeO2 engineering on Fe2N nanoparticles for rechargeable Zn-air batteries

In the process of developing low-cost and high-performance bifunctional electrocatalysts, rational selection of catalytic components and tuning of their electronic structures to achieve synergistic effects is a feasible approach. In this work, CeO₂ was composited into Fe/N-doped carbon foam by a molten salt method to improve the electrocatalytic performance of the composite catalyst for the oxygen evolution reaction (OER). The results showed that the excitation of oxygen vacancies in CeO₂ accelerated the migration of oxygen species and enhanced the oxygen storage/release capacity of the as-prepared catalyst. Meanwhile, the size effect of CeO₂ particles enabled the timely discharge of gas bubbles from the reaction system and thus improved the OER kinetics. In addition, a large number of pyridine-N species were induced by CeO₂-doping and sequentially anchored in the carbon matrix. As a result, the Fe₂N active state was formed through the strengthened binding of Fe-N elements. Benefiting from the strong electronic interaction between Fe₂N and CeO₂ components, the optimal CeO₂-Fe₂N/NFC_-2 catalyst sample showed a good OER performance (E_j=10 = 266 mV) and ORR electrocatalytic activity (E_1/2 = 0.87 V). The practical feasibility tests indicated that the Zn-air battery assembled by the CeO₂-Fe₂N/NFC_-2 catalyst exhibited a large energy density and an excellent long-term cycling stability.

Electron Modulation and Morphology Engineering Jointly Accelerate Oxygen Reaction to Enhance Zn-Air Battery Performance

Combining morphological control engineering and diatomic coupling strategies, heteronuclear FeCo bimetals are efficiently intercalated into nitrogen-doped carbon materials with star-like to simultaneously accelerate oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The half-wave potential and kinetic current density of the ORR driven by FeCoNC/SL surpass the commercial Pt/C catalyst. The overpotential of OER is as low as 316 mV (η₁₀ ), and the mass activity is at least 3.2 and 9.4 times that of mononuclear CoNC/SL and FeNC/SL, respectively. The power density and specific capacity of the Zn-air battery with FeCoNC/SL as air cathode are as high as 224.8 mW cm^-2 and 803 mAh g^-1 , respectively. Morphologically, FeCoNC/SL endows more reactive sites and accelerates the process of oxygen reaction. Density functional theory reveals the active site of the heteronuclear diatomic, and the formation of FeCoN5C configuration can effectively tune the d-band center and electronic structure. The redistribution of electrons provides conditions for fast electron exchange, and the change of the center of the d-band avoids the strong adsorption of intermediate species to simultaneously take into account both ORR and OER and thus achieve high-performance Zn-air batteries.

Ordered intermetallic compounds combining precious metals and transition metals for electrocatalysis

Ordered intermetallic alloys with significantly improved activity and stability have attracted extensive attention as advanced electrocatalysts for reactions in polymer electrolyte membrane fuel cells (PEMFCs). Here, recent advances in tuning intermetallic Pt- and Pd-based nanocrystals with tunable morphology and structure in PEMFCs to catalyze the cathodic reduction of oxygen and the anodic oxidation of fuels are highlighted. The fabrication/tuning of ordered noble metal-transition metal-bonded intermetallic PtM and PdM (M = Fe, Co) nanocrystals by using high temperature annealing treatments to promote the activity and stability of electrocatalytic reactions are discussed. Furthermore, the further improvement of the efficiency of this unique ordered intermetallic alloys for electrocatalysis are also proposed and discussed. This report aims to demonstrate the potential of the ordered intermetallic strategy of noble and transition metals to facilitate electrocatalysis and facilitate more research efforts in this field.

Interface Synergistic Effect from Hierarchically Porous Cu(OH)2@FCN MOF/CF Nanosheet Arrays Boosting Electrocatalytic Oxygen Evolution

The electrolysis of water is an efficient and environmentally friendly technology for large-scale hydrogen production. However, the oxygen evolution reaction (OER) involves a multi-electron–proton coupling transfer step that limits the efficiency of water splitting. Therefore, there is an urgent need to develop electrocatalysts with expected activity and stability to accelerate the kinetics of the oxygen evolution reaction. In this paper, hierarchically porous Cu(OH)2@(Fe, Co, Ni)MOF/CF nanosheet (denoted as Cu(OH)2@FCN MOF/CF) arrays were successfully prepared by the hydrothermally induced in situ growth of FCN MOF nanosheets using modified Cu(OH)2 nanowires as carriers; herein, the tuned active species of metal ligands in the FCN MOF composition structure are used as the main catalytic reaction size in the OER. The synergistic effect of a unique porous structure and the active metal-ligand species in the MOF render the catalyst a large electrochemically active surface area and more active species. Then, the active material is fully contacted with the electrolyte to expose more electrochemically active sites, thus greatly improving the electrocatalytic activity and durability of the OER. Specifically, the Cu(OH)2@FCN MOF/CF delivers a minimum overpotential of 290 mV and low Tafel slope of 96.15 mV·dec−1 at 10 mA·cm−2 as well as ultra-long cycling stability. The resulted OER performance is superior to most reported MOF-based electrocatalysts. This novel structural design not only provides a new strategy for the facile preparation of low-cost and high-efficiency OER electrocatalysts but also paves an avenue for the development of other MOF-based composite electrocatalysts with excellent electrocatalytic performances.

Boosting of Oxygen Evolution Reaction Performance through Defect and Lattice Distortion Engineering

Developing efficient, stable, and inexpensive electrocatalyst for oxygen evolution reaction (OER) is significant for development and utilization of clean energy. Defects in electrocatalysts strongly impact their chemical properties and can...