Electrochemical Preparation of N-Doped Cobalt Oxide Nanoparticles with High Electrocatalytic Activity for the Oxygen-Reduction Reaction

A non-traditional biomass-derived N, P, and S ternary self-doped 3D multichannel carbon ORR electrocatalyst

A synthetic non-traditional biomass-derived ORR catalyst is developed to overcome traditional shortcomings, that is, the existence of solid micron blocks and fewer heteroatoms.

Integrated N-Co/Carbon Nanofiber Cathode for Highly Efficient Zinc-Air Batteries

In order to reduce the charge-transfer resistance, ohmic resistance, and ionic and electronic resistances arising from the polymer binder, designing and constructing self-standing and binder-free porous electrodes are very significant for energy storage and conversion devices. Herein, self-standing and binder-free porous N-Co carbon nanofiber (N-Co/CNF) cathodes are prepared for zinc-air batteries (ZABs) by an in situ electrospinning/plasma-etching method. The morphology and activity of the prepared electrodes are investigated by several characterization techniques. The prepared specimens exhibit a multilayered CNF structure, and a new CoN compound is produced after plasma-etching treatment. The N-Co/CNF-300-10 cathode demonstrates excellent electrocatalytic performance toward oxygen reduction reaction, with an onset potential and a half-wave potential of 0.995 and 0.853 V (vs reversible hydrogen electrode), respectively, which is comparable to that of 20% Pt/C. The N-Co/CNF-300-10 cathode acting as a self-standing electrode for ZABs exhibits a maximum discharge power density as high as 229 mW cm^-2 and a specific capacity of 659.6 mA h g_Zn^-1, which are much higher than those of the commercial catalysts, benefiting from the self-standing porous structure, N-doping, and more defects and active sites induced by plasma-etching. It provides an effective way to construct a self-standing porous electrode with controllable compositions for rechargeable metal-air batteries.

Prompt Electrodeposition of Ni Nanodots on Ni Foam to Construct a High-Performance Water-Splitting Electrode: Efficient, Scalable, and Recyclable

In past decades, Ni-based catalytic materials and electrodes have been intensively explored as low-cost hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts for water splitting. With increasing demands for Ni worldwide, simplifying the fabrication process, increasing Ni recycling, and reducing waste are tangible sustainability goals. Here, binder-free, heteroatom-free, and recyclable Ni-based bifunctional catalytic electrodes were fabricated via a one-step quick electrodeposition method. Typically, active Ni nanodot (NiND) clusters are electrodeposited on Ni foam (NF) in Ni(NO3)2 acetonitrile solution. After drying in air, NiO/NiND composites are obtained, leading to a binder-free and heteroatom-free NiO/NiNDs@NF catalytic electrode. The electrode shows high efficiency and long-term stability for catalyzing hydrogen and oxygen evolution reactions at low overpotentials (10ηHER = 119 mV and 50ηOER = 360 mV) and can promote water catalysis at 1.70 V@10 mA cm-2. More importantly, the recovery of raw materials (NF and Ni(NO3)2) is quite easy because of the solubility of NiO/NiNDs composites in acid solution for recycling the electrodes. Additionally, a large-sized (S ~ 70 cm2) NiO/NiNDs@NF catalytic electrode with high durability has also been constructed. This method provides a simple and fast technology to construct high-performance, low-cost, and environmentally friendly Ni-based bifunctional electrocatalytic electrodes for water splitting.

Multifunctional nanostructured electrocatalysts for energy conversion and storage: current status and perspectives

Electrocatalytic oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) have attracted widespread attention because of their important role in the application of various energy storage and conversion devices, such as fuel cells, metal-air batteries and water splitting devices. However, the sluggish kinetics of the HER/OER/ORR and their dependency on expensive noble metal catalysts (e.g., Pt) obstruct their large-scale application. Hence, the development of efficient and robust bifunctional or trifunctional electrocatalysts in nanodimension for both oxygen reduction/evolution and hydrogen evolution reactions is highly desired and challenging for their commercialization in renewable energy technologies. This review describes some recent developments in the discovery of bifunctional or trifunctional nanostructured catalysts with improved performances for application in rechargeable metal-air batteries and fuel cells. The role of the electronic structure and surface redox chemistry of nanocatalysts in the improvement of their performance for the ORR/OER/HER under an alkaline medium is highlighted and the associated reaction mechanisms developed in the recent literature are also summarized.

Core@shell structured Co–CoO@NC nanoparticles supported on nitrogen doped carbon with high catalytic activity for oxygen reduction reaction

A composite with a hierarchical structure consisting of nitrogen doped carbon nanosheets with the deposition of nitrogen doped carbon coated Co–CoO nanoparticles (Co–CoO@NC/NC) has been synthesized by a simple procedure involving the drying of the reaction mixture containing Co(NO₃)₂, glucose, and urea and its subsequent calcination. The drying step is found to be necessary to obtain a sample with small and uniformly sized Co–CoO nanoparticles. The calcination temperature has a great effect on the catalytic activity of the final product. Specifically, the sample prepared at the calcination temperature of 800 °C shows better catalytic activity of the oxygen reduction reaction (ORR). Urea in the reaction mixture is crucial to obtain the sample with the uniformly sized Co–CoO nanoparticles and also plays an important role in improving the catalytic activity of the Co–CoO@NC/NC. Additionally, there exists a strong electronic interaction between the Co–CoO nanoparticles and the NC. Most interestingly, the Co–CoO@NC/NC is highly efficient for the ORR and can deliver an ORR onset potential of 0.961 V vs. RHE and a half-wave potential of 0.868 V vs. RHE. Both the onset and half-wave potentials are higher than those of most catalysts reported previously and even close to those of the commercial Pt/C (the ORR onset and half-wave potential of the Pt/C are 0.962 and 0.861 V vs. RHE, respectively). This, together with its high stability, strongly suggests that the Co–CoO@NC/NC could be used as an efficient catalyst for the ORR.

A simple method has been developed for the synthesis of Co–CoO@NC/NC, which exhibits high and stable performance for the ORR.

Nitrogen-Doped Co3 O4 Mesoporous Nanowire Arrays as an Additive-Free Air-Cathode for Flexible Solid-State Zinc-Air Batteries

The kinetically sluggish rate of oxygen reduction reaction (ORR) on the cathode side is one of the main bottlenecks of zinc-air batteries (ZABs), and thus the search for an efficient and cost-effective catalyst for ORR is highly pursued. Co₃ O₄ has received ever-growing interest as a promising ORR catalyst due to the unique advantages of low-cost, earth abundance and decent catalytic activity. However, owing to the poor conductivity as a result of its semiconducting nature, the ORR activity of the Co₃ O₄ catalyst is still far below the expectation. Herein, we report a controllable N-doping strategy to significantly improve the catalytic activity of Co₃ O₄ for ORR and demonstrate these N doped Co₃ O₄ nanowires as an additive-free air-cathode for flexible solid-state zinc-air batteries. The results of experiments and DFT calculations reveal that the catalytic activity is promoted by the N dopant through a combined set of factors, including enhanced electronic conductivity, increased O₂ adsorption strength and improved reaction kinetics. Finally, the assembly of all-solid-state ZABs based on the optimized cathode exhibit a high volumetric capacity of 98.1 mAh cm^-3 and outstanding flexibility. The demonstration of such flexible ZABs provides valuable insights that point the way to the redesign of emerging portable electronics.

A novel composite of W18O49 nanorods on reduced graphene oxide sheets based on in situ synthesis and catalytic performance for oxygen reduction reaction

A novel composite catalyst based on in situ synthesis of W₁₈O₄₉ nanorods on reduced graphene oxide sheets was successfully fabricated through a one-pot solvothermal route.

Nitrogen Doping in Oxygen-Deficient Ca2Fe2O5: A Strategy for Efficient Oxygen Reduction Oxide Catalysts

Oxygen reduction reaction (ORR) is increasingly being studied in oxide systems due to advantages ranging from cost effectiveness to desirable kinetics. Oxygen-deficient oxides like brownmillerites are known to enhance ORR activity by providing oxygen adsorption sites. In parallel, nitrogen and iron doping in carbon materials, and consequent presence of catalytically active complex species like C-Fe-N, is also suggested to be good strategies for designing ORR-active catalysts. A combination of these features in N-doped Fe containing brownmillerite can be envisaged to present synergistic effects to improve the activity. This is conceptualized in this report through enhanced activity of N-doped Ca₂Fe₂O₅ brownmillerite when compared to its oxide parents. N doping is demonstrated by neutron diffraction, UV-vis spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Electrical conductivity is also found to be enhanced by N doping, which influences the activity. Electrochemical characterization by cyclic voltammetry, rotating disc electrode, and rotating ring disk electrode (RRDE) indicates an improved oxygen reduction activity in N-doped brownmillerite, with a 10 mV positive shift in the onset potential. RRDE measurements show that the compound exhibits 4-electron reduction pathways with lower H₂O₂ production in the N-doped system; also, the N-doped sample exhibited better stability. The observations will enable better design of ORR catalysts that are stable and cost-effective.

Defective-Activated-Carbon-Supported Mn-Co Nanoparticles as a Highly Efficient Electrocatalyst for Oxygen Reduction

A highly active and durable cathodic oxygen reduction reaction (ORR) catalyst is synthesized by introducing a small amount of Mn-Co spinel into a kind of defective activated-carbon (D-AC) support. It is assumed that the synergetic coupling effects between the unique defects in the D-AC and the loaded Mn-Co spinel facilitate the ORR and enhance its durability.

Electrocatalytic study of a 1,10-phenanthroline–cobalt(ii) metal complex catalyst supported on reduced graphene oxide towards oxygen reduction reaction

1,10-Phenanthroline–cobalt(ii) metal-complex supported on rGO exhibited a high efficient four-electron catalytic activity towards ORR.

Cobalt-embedded nitrogen doped carbon nanotubes: a bifunctional catalyst for oxygen electrode reactions in a wide pH range

Electrocatalysts for the oxygen reduction and evolution reactions (ORR/OER) are often functionally separated, meaning that they are only proficient at one of the tasks. Here we report a high-performance bifunctional catalyst for both ORR and OER in both alkaline and neutral media, which is made of cobalt-embedded nitrogen doped carbon nanotubes. In OER, it shows an overpotential of 200 mV in 0.1 M KOH and 300 mV in neutral media, while the current density reaches 50 mA cm(-2) in alkaline media and 10 mA cm(-2) in neutral media at overpotential of 300 mV. In ORR, it is on par with Pt/C in both alkaline and neutral media in terms of overpotential, but its stability is superior. Further study demonstrated that the high performance can be attributed to the coordination of N to Co and the concomitant structural defects arising from the transformation of cobalt-phthalocyanine precursor.

An in situ vapour phase hydrothermal surface doping approach for fabrication of high performance Co3O4 electrocatalysts with an exceptionally high S-doped active surface

A vapour phase hydrothermal doping approach is developed to fabricate highly S-doped Co₃O₄ nanosheets as electrocatalysts for triiodide reduction in DSSCs.