Molten-Salt Media Synthesis of N-Doped Carbon Tubes Containing Encapsulated Co Nanoparticles as a Bifunctional Air Cathode for Zinc-Air Batteries.

Cost efficient bifunctional air cathodes possessing high electrocatalytic activity are of great importance for the development of secondary Zn-air batteries. In this work, cobalt nanoparticles are encapsulated within a 3D N-doped open network of carbon tubes (Co@N-CNTs) by a molten-salt synthesis procedure conducted at a high temperature. Physical characterization demonstrates that Co@N-CNTs are comprised of Co particle inserted carbon tubes with mesoporous tube walls, providing significant active surface area for electrochemical reactions. High electrocatalytic activity of Co@N-CNTs towards both oxygen evolution and oxygen reduction reactions is due to its well-developed active surface and a synergistic effect between N-doped carbon and Co nanoparticles. Both primary and secondary Zn-air battery cells assembled using Co@N-CNTs as an air cathode show higher electrochemical performance than similar cells containing commercial Pt/C and Pt/C +RuO2 , making the newly developed material a promising alternative to existing metal-based air cathodes.

Enhanced Methanol Electrooxidation and Supercapacitive Performance via Compositional Engineering of Colloidal Ni-Co Alloying Nanoparticles.

Among renewable energy technologies, particular attention is paid to electrochemically transforming methanol into valuable formate and storing energy into supercapacitors. In this study, we detailed a simple colloidal-based protocol for synthesizing a series of alloy nanoparticles with tuned Ni/Co atomic ratios, thereby optimizing their electrochemical performance. With the addition of 1 M methanol in 1 M KOH, the optimized composition was able to electrochemically produce formate at 0.149 mmol cm-2 h-1 with a Faradaic efficiency up to 95.1% at 0.6 V versus Hg/HgO within a 22-hour testing period. In 1 M KOH solution without methanol, the supercapacitive performance was achieved at a specific capacitance of over 1500 F g-1, and outstanding cycling stability with only approximately 20% decay after continuous 10000 charging-discharging cycles. These results underscore that the prepared Ni-Co alloy nanoparticles serve as multi-functional electrodes for electrochemical energy conversion and storage, particularly in the MOR and supercapacitors applications.

Ligand-induced hollow binary metal-organic framework derived Fe-doped cobalt-carbon nanomaterials for oxygen evolution.

There is significant anticipation for high-efficiency and cost-effective non-precious metal-based catalysts to advance the industrial application of the anodic oxygen evolution reaction (OER) for hydrogen production. This study introduces an efficient strategy that utilizes ligand-induced metal-organic framework (MOF) building blocks for the synthesis of hollow binary zeolitic imidazolate frameworks 67 (ZIF-67) and Prussian blue analogues (PBAs) (ZIF-67@PBA) heterostructures through a hybrid MOF-on-MOF approach. Manipulating the Co2+/Zn2+ ratio in the precursor ZIF-67 allows for the convenient synthesis of the final product, denoted as CoxFe-ZP, after pyrolysis, where the inclusion of Zn effectively modulates the distribution of Co in the catalyst. The resulting CoxFe-ZP catalysts exhibit a positive synergistic effect between hollow graphitic carbon nanomaterials and Fe-doped Co nanoparticles. The optimal Co0.3Fe-ZP catalyst demonstrates satisfactory OER performance, achieving an overpotential of 302 mV at 10 mA cm-2 and a small Tafel slope of 60.0 mV dec-1. Further analysis of the activation energy confirms that the enhanced OER activity of Co0.3Fe-ZP can be reasonably attributed to the combined influence of its morphology and composition. This study demonstrates a ligand-induced method for examining the morphology and electrochemical properties of grown binary MOF-on-MOF heterostructures for OER applications.

Co-entrapped, N-doped mesoporous carbons prepared from melamine formaldehyde resins with CoCl2 as template for hydrogen evolution.

Cobalt-entrapped, nitrogen-doped mesoporous carbon materials have been prepared using melamine formaldehyde resin (MF resin) as precursor and CoCl2 as template. A fraction of CoCl2 can be reduced to Co nanoparticles and wrapped by the nitrogen doped carbon. Meanwhile, the ratio of MF resin to CoCl2 is an important parameter determining the mesoporous structures of the final products. The surface area of the obtained material decreases with the increase in the ratio of MF resin to CoCl2. Electrocatalytic tests show that the obtained catalysts are highly active for hydrogen evolution reaction in both acidic and basic media, achieving a current density of 10 mA cm-2 at 171 and 186 mV under acidic and alkaline conditions, respectively. Additionally, these catalysts also show good long-term stabilities.