Boosted activity of graphene encapsulated CoFe alloys by blending with activated carbon for oxygen reduction reaction

Iron/cobalt-decorated nitrogen-rich 3D layer-stacked porous biochar as high-performance oxygen reduction air-cathode catalyst in microbial fuel cell

Developing low-cost and high-efficiency oxygen reduction reaction (ORR) catalysts is crucial to the commercial application of microbial fuel cell (MFC). Herein, Fe/Co-decorated nitrogen-rich three-dimensional (3D) layer-stacked porous biochar (Fe/Co-NC-x) have been synthesized from silk gel through secondary carbonization of activated carbons which firstly adsorbed metal ions. The multilayer porous structure of Fe/Co-NC-3 contributes to construction of high specific surface area (576 m² g^-1), large pore volume (1.27 cm³ g^-1) and many defect structure (I_D/I_G = 1.004). As expected, with Fe/Co synergistic effect, Fe/Co-NC-3 exhibits excellent ORR performance through 4e^- pathway with good methanol resistance. In addition, the performance of MFC using Fe/Co-NC-3 as air-cathode catalyst is more prominent with higher maximum power density (1059.62 ± 30.00 mW m^-2) compared to that using NC (668.19 ± 9.84 mW m^-2) and commercial Pt/C catalyst (957.33 ± 10.50 mW m^-2). Therefore, Fe/Co-NC-3 should be a prospective catalyst in the practical application of fuel cells and other energy devices.

B, P-co-doped PdCu nanothorn assemblies for enhanced oxygen reduction electrolysis

Nonmetal doping is a promising strategy to improve electrocatalytic performance of noble metal based catalysts for oxygen reduction reaction (ORR). Herein, we report a facile method to fabricate PdCuBP nanothorn assemblies (PdCuBP NTAs) by co-doping B and P into pre-synthesized PdCu NTAs using NaBH₄and NaH₂PO₂as B source and P source, respectively. The metal-nonmetal structure and multi-branched morphology can optimize oxygen adsorption energy and avoid catalyst migration, agglomeration and Ostwald ripening. As such, the obtained PdCuBP NTAs exhibit efficient activity and excellent long-term stability for ORR. This research offers an excellent strategy for co-doping nonmetal elements into metal nanocrystals with controllable composition and structure to improve electrocatalytic ORR performance.

FeCo/Fe3C-cross-linked N-doped carbon via synergistic confinement and efficient catalyst to enable high-performance Li-S batteries

Lithium-sulfur batteries (LSB) with high specific energy capacity and low material costs promise to be the next generation of energy storage devices. However, their commercialization is holding back by the poor cycling stability and fast capacity fading resulting from the shuttle effect and slow redox reaction. In this work, the FeCo/Fe₃C-CNC composite was prepared by anchoring FeCo/Fe₃C nanoparticles onto the crosslinked N-doped Carbon (CNC). The results showed that the addition of Co element improved the electrochemical activity of Co-Fe alloy through tuning the electronic structure of Fe atoms. The carbon nanotubes (CNTs) grown around Co-Fe alloy and Fe₃C nanoparticles exhibited a strong affinity to polysulfide species and superior catalytic capability as nano-reactors. The N-doping CNTs/carbon sheets (CS) facilitated the formation of Li₂S compound by promoting the Li⁺ ions transport while hindering the polysulfide shuttle effect. Hence, the issues of slow redox reactions and loss of polysulfide species were effectively rectified. As a result, the composite cathode FeCo/Fe₃C-CNC-based LSB delivered a good specific capacity of 1401 mAh g^-1 at 0.1C, and a low apacity fading rate of 0.029% per cycle at 1C. Besides, the structural stability of the FeCo/Fe₃C-CNC composite confirms its potential for the deployment in LSB applications.

Emerging carbon shell-encapsulated metal nanocatalysts for fuel cells and water electrolysis

The development of low-cost, high-efficiency electrocatalysts is of primary importance for hydrogen energy technology. Noble metal-based catalysts have been extensively studied for decades; however, activity and durability issues still remain a challenge. In recent years, carbon shell-encapsulated metal (M@C) catalysts have drawn great attention as novel materials for water electrolysis and fuel cell applications. These electrochemical reactions are governed mainly by interfacial charge transfer between the core metal and the outer carbon shell, which alters the electronic structure of the catalyst surface. Furthermore, the rationally designed and fine-tuned carbon shell plays a very interesting role as a protective layer or molecular sieve layer to improve the performance and durability of energy conversion systems. Herein, we review recent advances in the use of M@C type nanocatalysts for extensive applications in fuel cells and water electrolysis with a focus on the structural design and electronic structure modulation of carbon shell-encapsulated metal/alloys. Finally, we highlight the current challenges and future perspectives of these catalytic materials and related technologies in this field.

The cobalt carbide/bimetallic CoFe phosphide dispersed on carbon nanospheres as advanced bifunctional electrocatalysts for the ORR, OER, and rechargeable Zn-air batteries

It is very important, but also challenging to produce high-activity, high durability and affordable non-noble-metal-bifunctional-electrocatalysts for sustainable energy application. Here, one-pot synthesized iron covalent porphyrin polymers (FePor-CPP), with carefully placed Fe, N atoms, a regular porous structure, Co₃[Co(CN)₆]₂ and NaH₂PO₂ precursors were carbonized into N,P-doped carbon nanospheres with the active species of both bimetallic CoFe phosphides and CoC_x nanoparticles (denoted as CoC_x/(Co_0.55Fe_1.945)₂P@C). By employing the CoC_x/(Co_0.55Fe_1.945)₂P@C as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrode catalysts, superior catalytic activity is achieved with E_1/2 of 0.84 V for ORR, and overpotential of 0.39 V at 10 mA cm^-2 for OER in an alkaline medium, respectively. Furthermore, CoC_x/(Co_0.55Fe_1.945)₂P@C as air electrode for rechargeable Zn-air battery shows power density as high as 131 mW cm^-2 and charge-discharge cycle stability, and this suggests the potential application of CoC_x/(Co_0.55Fe_1.945)₂P@C in energy transformation systems. The high electrocatalytic performances are revealed to originate from the change of electronic structure of bimetallic (Co_0.55Fe_1.945)₂P via introducing P into the Co_0.55Fe_1.945 alloy, resulting in a decreased energy gap of CoC_x/(Co_0.55Fe_1.945)₂P@C relative to that of CoC_x/Co_0.55Fe_1.945@C. This work proposes a versatile strategy to develop multifunctional non-precious catalysts for this kind of energy-related electrocatalytic reactions.

Hematite/M (M = Au, Pd) Catalysts Derived from a Double-Hollow Prussian Blue Microstructure: Simultaneous Catalytic Reduction of o- and p-Nitrophenols

Present study deals with hematite/M (M = Au, Pd) catalysts converted from a double-hollow Prussian blue microstructure (DHPM). The unique Prussian blue (PB) microstructure (MS) is prepared by a template-free solvothermal synthetic route in a single-step reaction. An amine-functionalized silicate sol-gel matrix (SSG) has served as the structure-directing agent cum stabilizer for making DHPM. Synthesized DHPM is having a unique structure: a hollow core and an in situ etched porous surface. Growth mechanism is explored and revealed by analyzing several experimental parameters such as HCl concentration, Fe source, effect of the added EtOH, silane concentration, and role of silanes' amine groups. It is identified that the superstructure consisted of well-aligned PB cubes growing radially from the core of the superstructure. Metal (Au and Pd) nanoparticles (NPs) are deposited on both interior and exterior of the PB MS through galvanic displacement reaction, and thus metal NP-loaded hematite phase iron oxide (α-Fe₂O₃) nanomaterials were derived by annealing them in air. Catalytic activities of the hematite/M(M = Au, Pd) MS are investigated toward simultaneous catalytic reduction of o-nitrophenol and p-nitrophenol. The resultant hematite/Pd MS showed high structural stability and catalytic active sites than the hematite/Au MS, which enhances the catalytic properties for the simultaneous catalytic reduction of both nitrophenols.