One-Pot Synthesis of Co/CoFe₂O₄ Nanoparticles Supported on N‑Doped Graphene for Efficient Bifunctional Oxygen Electrocatalysis

We herein report a facile strategy to synthesize transition metal/spinel oxide nanoparticles coupled with nitrogen-doped graphene (Co/CoFe₂O₄@N-graphene) as an efficient bifunctional electrocatalyst toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). This approach involves a spontaneous solution-polymerization of polydopamine (PDA) film on graphene oxide (GO) sheets in the presence of Fe³⁺ and Co²⁺ to form the Fe/Co-PDA-GO precursor, followed by pyrolysis at 800 °C in argon (Ar) atmosphere. During the calcination process, Co/CoFe₂O₄ nanoparticles are in situ formed via high-temperature solid state reaction and are further entrapped by the PDA-derived N-doped carbon layer. As-prepared Co/CoFe₂O₄@N-graphene exhibits highly efficient catalytic activity and excellent stability for both ORR and OER in alkaline solution. This work reports a facile synthetic approach to develop highly active electrocatalysts while offering great flexibility to tailor their components and morphologies and thus provides a useful route to the design and synthesis of a broad variety of electrocatalysts

Ru₂P Nanoparticle Decorated P/N-Doped Carbon Nanofibers on Carbon Cloth as a Robust Hierarchical Electrocatalyst with Platinum-Comparable Activity toward Hydrogen Evolution

It is desirable yet challenging to develop highly active and durable hydrogen evolution reaction (HER) electrocatalysts with Pt-comparable activity for future energy devices. In this work, we report Ru₂P nanoparticle decorated P/N dual-doped carbon nanofibers on carbon cloth (Ru₂P@PNC/CC-900) as a highly efficient and durable hierarchical HER electrocatalyst in both acidic and alkaline media. Electrochemical tests show that this Ru₂P@PNC/CC-900 possesses Pt-comparable HER activity to support 10 mA cm^–2 HER current density at low overpotential of 15 and 50 mV in acidic and alkaline condition, respectively. Density functional theory calculations reveal that coupling Ru₂P nanoparticles with heteroatom-doped carbon fibers leads to enhanced intrinsic HER activity. The integrative hierarchical architecture further endows high surface areas with good mechanical robustness to support abundant catalytically active sites and possesses excellent electrical conductivity and efficient access for mass transportation to facilitate the HER process

Manganese/Cobalt Bimetal Nanoparticles Encapsulated in Nitrogen-Rich Graphene Sheets for Efficient Oxygen Reduction Reaction Electrocatalysis

It is of vital importance to search for a nonprecious metal based sustainable and efficient oxygen reduction reaction (ORR) electrocatalyst for the next generation of energy conversion and storage technology. We herein report a hybrid bimetal material composed of MnO/Co nanoparticles encapsulated in nitrogen-rich graphene nanosheets (MnO/Co–N–G) as a high performance ORR catalyst in alkaline electrolyte. The MnO/Co–N–G catalyst is derived from Mn²⁺, Co²⁺ incorporated polydopamine (PDA) coated graphene oxide (GO) sheets via a carbonization process. The morphology, structure, and composition properties of as-prepared MnO/Co–N–G catalyst are systematically investigated. Electrochemical measurements show that the MnO/Co–N–G catalyst exhibits excellent ORR activity superior to commercial Pt/C, featuring higher limiting current density, better methanol resistance, and excellent long-term durability in alkaline solution. The bimetal nanoparticles are believed to be responsible for the impressive ORR activity of the catalyst

Mesoporous Hollow Nitrogen-Doped Carbon Nanospheres with Embedded MnFe₂O₄/Fe Hybrid Nanoparticles as Efficient Bifunctional Oxygen Electrocatalysts in Alkaline Media

Exploring sustainable and efficient electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is necessary for the development of fuel cells and metal–air batteries. Herein, we report a bimetal Fe/Mn–N–C material composed of spinel MnFe₂O₄/metallic Fe hybrid nanoparticles encapsulated in N-doped mesoporous hollow carbon nanospheres as an excellent bifunctional ORR/OER electrocatalyst in alkaline electrolyte. The Fe/Mn–N–C catalyst is synthesized via pyrolysis of bimetal ion-incorporated polydopamine nanospheres and shows impressive ORR electrocatalytic activity superior to Pt/C and good OER activity close to RuO₂ catalyst in alkaline environment. When tested in Zn–air battery, the Fe/Mn–N–C catalyst demonstrates excellent ultimate performance including power density, durability, and cycling. This work reports the bimetal Fe/Mn–N–C as a highly efficient bifunctional electrocatalyst and may afford useful insights into the design of sustainable transition-metal-based high-performance electrocatalysts

Efficient Production of Coaxial Core–Shell MnO@Carbon Nanopipes for Sustainable Electrochemical Energy Storage Applications

Adverse structural changes and poor intrinsic electrical conductivity as well as the lack of an environmentally benign synthesis for MnO species are major factors to limit their further progress on electrochemical energy storage applications. To overcome the above constraints, the development of reliable and scalable techniques to confine MnO within a conductive matrix is highly desired. We herein propose an efficient and reliable way to fabricate coaxial core–shell hybrids of MnO@carbon nanopipes merely via simple ultrasonication and calcination treatments. The evolved MnO nanowires disconnected/confined in pipe-like carbon nanoreactors show great promise in sustainable supercapacitors (SCs) and Li-ion battery (LIB) applications. When used in SCs, such core–shell MnO@carbon configurations exhibit outstanding positive and negative capacitive behaviors in distinct aqueous electrolyte systems. This hybrid can also function as a prominent LIB electrode, demonstrating a high reversible capacity, excellent rate capability, long lifespan, and stable battery operation. The present work may shed light on effective and scalable production of Mn-based hybrids for practical applications, not merely for energy storage but also in other broad fields such as catalysts and biosensors