Oxygen Reduction Reaction Properties Research Articles

Metalation of functionalized benzoquinoline-linked COFs for electrocatalytic oxygen reduction and lithium-sulfur batteries

It is worthwhile to explore and develop multifunctional composites with unique advantages for energy conversion and utilization. Post-synthetic modification (PSM) strategies can endow novel properties to already excellent covalent organic frameworks (COFs). In this study, we prepared a range of COF-based composites via a multi-step PSM strategy. COF-Ph-OH was acquired by demethylation between anhydrous BBr3 and − OMe, and then, M@COF-Ph-OH was further obtained by forming the N − M − O structure. COF-Ph-OH exhibited a 2e−-dominated oxygen reduction reaction (ORR) pathway with high H2O2 selectivity, while M@COF-Ph-OH exhibited a 4e−-dominated ORR pathway with low H2O2 selectivity, which was due to the introduction of a metal salt with a d electron structure that facilitated the acquisition of electrons and changed the adsorption energy of the reaction intermediate (*OOH). It was proven that the d electron structure was effective at regulating the reaction pathway of the electrocatalytic ORR. Moreover, Co@COF-Ph-OH showed better 4e− ORR properties than Fe@COF-Ph-OH and Ni@COF-Ph-OH. In addition, compared with the other sulfur-impregnated COF-based composites examined in this study, S-Co@COF-Ph-OH had a larger initial capacity, a weaker impedance, and a stronger cycling durability in Li-S batteries, which was attributed to the unique porous structure ensuring high sulfur utilization, the loaded cobalt accelerating LiPS electrostatic adsorption and promoting LiPS catalytic conversion, and the benzoquinoline ring structure being ultra-stable. This work offers not only a rational and feasible strategy for the synthesis of multifunctional COF-based composites, but also promotes their application in electrochemistry.

In-situ synthesis strategy derived Nitrogen-doped carbon nanotubes embedded with Co nanoparticles active center to inspire oxygen reduction reaction

Developing efficient and stable non-precious metal electrocatalysts for oxygen reduction reaction (ORR) is challenging for metal-air batteries. Herein, active sites of Co nanoparticles embedded in nitrogen-doped carbon nanotubes (Co@N-CNTs-800) were prepared by pyrolysis transformation of precursors, using diphenylamine as carbon and nitrogen precursor. It discovered that the abundance of nitrogen species (pyridinic nitrogen and graphitic nitrogen) in the carbon skeleton, the unique carbon nanotube structure, and the synergistic interaction between carbon layers and Co nanoparticles are the main causes for the high ORR catalytic efficiency of the catalysts. As a result, the Co@N-CNTs-800 exhibits powerful electrocatalytic properties for ORR in 0.1 M KOH with half-wave potentials of 0.86 V and an ultimate current density of 5.70 mA cm−2. The zinc-air battery supplied with Co@N-CNTs-800 as the cathode exhibits an exceptional peak power density of 170 mW cm−2 and a specific capacity of 760 mAh gZn−1, demonstrating the enormous potential of novel Co@N-CNTs-800 catalyst in practical applications.

One−Step Synthesis of a Non−Precious−Metal Tris (Fe/N/F)−Doped Carbon Catalyst for Oxygen Reduction Reactions

Advancements in inexpensive, efficient, and durable oxygen reduction catalysts is important for maintaining the sustainable development of fuel cells. Although doping carbon materials with transition metals or heteroatomic doping is inexpensive and enhances the electrocatalytic performance of the catalyst, because the charge distribution on its surface is adjusted, the development of a simple method for the synthesis of doped carbon materials remains challenging. Here, a non-precious-metal tris (Fe/N/F)-doped particulate porous carbon material (21P2-Fe1-850) was synthesized by employing a one-step process, using 2-methylimidazole, polytetrafluoroethylene, and FeCl3 as raw materials. The synthesized catalyst exhibited a good oxygen reduction reaction performance with a half-wave potential of 0.85 V in an alkaline medium (compared with 0.84 V of commercial Pt/C). Moreover, it had better stability and methanol resistance than Pt/C. This was mainly attributed to the effect of the tris (Fe/N/F)-doped carbon material on the morphology and chemical composition of the catalyst, thereby enhancing the catalyst's oxygen reduction reaction properties. This work provides a versatile method for the gentle and rapid synthesis of highly electronegative heteroatoms and transition metal co-doped carbon materials.

Self-Sacrificing Template Synthesis of Carbon Nanosheets Assembled Hollow Spheres with Abundant Active Fe-N4 O1 Moieties for Electrocatalytic Oxygen Reduction.

Single-atom Fe-N-C (Fe1 -N-C) materials represent the benchmarked electrocatalysts for oxygen reduction reaction (ORR). However, single Fe atoms in the carbon skeletons cannot be fully utilized due to the mass transfer limitation, severely restricting their intrinsic ORR properties. Herein, a self-sacrificing template strategy is developed to fabricate ultrathin nanosheets assembled Fe1 -N-C hollow microspheres (denoted as Fe1 /N-HCMs) by rational carbonization of Fe3+ chelating polydopamine coated melamine cyanuric acid complex. The shell of Fe1 /N-HCMs is constructed by ultrathin nanosheets with thickness of only 2nm, which is supposed to be an ideal platform to isolate and fully expose single metal atoms. Benefiting from unique hierarchical hollow architecture with highly open porous structure, 2nm-thick ultrathin nanosheet subunits and abundant Fe-N4 O1 active sites revealed by X-ray absorption fine structure analysis, the Fe1 /N-HCMs exhibit high ORR performance with a positive half-wave potential of 0.88V versus the reversible hydrogen electrode and robust stability. When served as air-cathode catalysts with ultralow loading mass of 0.25mg cm-2 , Fe1 /N-HCMs based Zn-air batteries present a maximum power density of 187mW cm-2 and discharge specific capacity of 806mA h gZn -1 in primary Zn-air batteries, all exceeding those of commercial Pt/C.

PtRuFe/Carbon Nanotube Composites as Bifunctional Catalysts for Efficient Methanol Oxidation and Oxygen Reduction.

The design of bifunctional catalysts with high performance and low platinum for the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) is of significant implication to promote the industrialization of fuel cells. In our work, Pt/carbon nanotube (CNT), Pt3Ru/CNT, and PtRu/CNT catalysts were synthesized by plasma heat treatment, in which the pyrolysis reduction of organometallic salts and the dispersion of CNTs were achieved simultaneously, and catalytic nanoparticles with uniform particle size were anchored on the dispersed CNT surface. Later, Fe was further introduced, and PtFe/CNT, Pt3RuFe/CNT, and PtRuFe/CNT catalysts were synthesized by calcination, and the structure and electrochemical properties in both MOR and ORR of all as-synthesized catalysts were investigated. The results indicated that plasma thermal treatment has the advantage of rapidness and immediacy in the synthesis of catalysts, and the Pt/CNT, Pt3Ru/CNT, and PtRu/CNT catalysts exhibited better electrocatalytic properties than commercial platinum (JM-Pt/C) catalysts. Meanwhile, the introduction of Fe during the calcination further changed the surface electronic properties of catalytic nanoparticles and enhanced the graphitization degree of catalysts; the PtRuFe/CNT catalyst exhibited outstanding electrocatalytic properties with a mass activity of 834.3 mA mg-1 for MOR and a half-wave potential of 0.928 V in alkaline media for ORR. The combination of plasma thermal treatment and calcination puts forward a novel strategy for the optimization of catalysts, and the synthesis method based on plasma dispersion needs to be further optimized to achieve its large-scale promotion.

A facile mixed complex synthesis method for perovskite oxides toward electrocatalytic oxygen reduction.

The perovskite-type La(0.5+x)Sr(0.5-x)FeO3-δ (x = 0.00, 0.10, 0.20) oxides for the electrocatalytic oxygen reduction reaction (ORR) were synthesized by a facile reaction-EDTA/citric acid mixed complex sol-gel method. The cubic single-phase perovskite structure of the as-prepared oxides is demonstrated using powder X-ray diffraction (XRD). Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy/selected area electron diffraction (TEM-SAED), and X-ray photoelectron spectroscopy (XPS) characterizations were also conducted for the perovskite-type La(0.5+x)Sr(0.5-x)FeO3-δ (x = 0.00, 0.10, 0.20) oxides. Furthermore, the electrochemical ORR properties of the as-prepared oxides in alkaline media were studied, with the oxides exhibiting good electrocatalytic ORR performance.

Bimetallic zeolite imidazolium framework derived multiphase Co/HNC as pH-universal catalysts with efficient oxygen reduction performance for microbial fuel cells

Here, the metallic Co encapsulated in hierarchical porous nitrogen-doped carbon (Co/HNC) catalysts is synthesized by pyrolysis of bimetallic (Co, Zn) zeolite imidazolium framework (ZIF) precursors to facilitate oxygen reduction reaction (ORR) in microbial fuel cell (MFC). Importantly, the highly dispersed cobalt nanoparticles are completely encapsulated in the N-doped hierarchical porous carbon, with abundant metal-nitrogen active sites and high degree of graphitization, which is very favorable for the ORR process. As a result, the Co/HNC as pH-universal catalyst shows remarkable ORR properties in alkaline, acidic and neutral environments. More notably, the density functional theory (DFT) calculation demonstrates that the introduction of cobalt can reduce the ORR overpotential and improves the ORR catalytic activity. Furthermore, the assembled MFCs with Co/HNC as cathode catalysts also exhibit high power density of 1324.5 mWm−2, and an output voltage of 0.48 V. Consequently, the investigation provides a new perspective for preparing high-performance and stable electrocatalysts for MFC devices.

Electrocatalytic selectivity to H2O2 enabled by two-electron pathway on Cu-deficient Au@Cu2-xS-CNTs electrocatalysts

Electrochemical hydrogen peroxide (H2O2) production by two-electron oxygen reduction reaction (ORR) is an efficient and promising method to alternate industrial anthraquinone process. Herein, the Cu-deficient Au@Cu2-xS-CNTs core–shell electrocatalysts were synthesized for two-electron ORR, and composition, surface and structural properties were investigated using physicochemical characterizations. The Cu-defective Au@Cu2-xS-CNTs catalysts exhibit higher catalytic ORR activity and H2O2 specific productivity than Au@Cu2O-CNTs, indicating that the introduction of Cu defects effectively improves the two-electron transfer of ORR. The composition-optimized Au@Cu1.75S-CNTs sample with the abundant Cu defects exhibits high H2O2 selectivity (∼94 %) and good stability. Theoretical calculations reveal that the introduction of Cu defects can significantly lower the reaction energy barrier of the determinant intermediate OOH* formation of two-electron ORR pathway. This endows the synthesized catalysts with improved resistance to H2O generation. Our work deepens the fundamental understanding for guiding the optimization of H2O2 electrosynthesis catalysts to enhance selectivity and efficiency of two-electron pathway.

Aging effect on the structure formation of active sites in single-atomic catalysts and their electrochemical properties for oxygen reduction reaction

FeNC catalysts have attracted attention because of their superior oxygen reduction reaction (ORR) performance in alkaline media. However, there is a conflict between the active sites of FeNC catalysts, namely single-atomic Fe–Nx sites and dual active sites consisting of atomic sites/iron carbide nanoparticles. Herein, we synthesized catalysts with different types of active sites by controlling the facile aging process. The main active sites varied from single active sites to dual active sites when the aging time and Fe content was decreased and increased. A catalyst with 0.6 wt% Fe that is aged for 24 h (FeNC-24–0.6) has dual active sites, whereas a catalyst with 0.9 wt% Fe that is aged for 48 h (FeNC-48–0.9) consists mainly of single active sites. The catalysts showed outstanding ORR activity, exceeding the half-wave potential of the commercial 20 wt% Pt/C catalysts by 11 mV. Interestingly, the FeNC-48–0.9 catalyst exhibited a rare negative shift compared to the FeNC-24–0.6 catalyst in the durability tests. Therefore, it is believed that increasing the number of single-atomic Fe–Nx sites is an effective approach to enhance the ORR performance of FeNC catalyst in alkaline media.

Oxygen Reduction Reaction of Pt and Non-PGM Transition Metal High Entropy Alloys Single Crystal Stacking Structures

Introduction Nanoparticles of Pt as well as Pt-based alloys are widely used as cathode catalyst materials for proton exchange membrane fuel cells (PEMFC). However, electrochemical stability of the materials is rather low under practical operating conditions of PEMFC cathode, resulting in severe deactivation of oxygen reduction reaction (ORR). Therefore, further material’s developments are required for next-generation PEMFC cathode catalysts, i.e., more enhanced ORR durability with low platinum group metal (PGM) usage.High entropy alloys (HEAs), defined as single phase solid solutions of five or more elements in equal composition ratios, are known as thermodynamically stable, in comparison to conventional binary alloys. Furthermore, complex atomic-level local structures bring about unique electronic as well as (electro-)chemical properties that originating from lattice strains induced by specific local structures and/or so-called sluggish diffusion of the constituent elements. [1] However, to our best knowledge, no study has been made for ORR properties of Pt alloying with non-PGM Cantor alloy (fcc structure HEA with equi-atomic ratio of Cr-Mn-Fe-Co-Ni [2]) elements in strong acid condition.In this study, we synthesized lattice stacking structures of Pt/HEA(hkl) (hkl = (111), (110), (100)) through arc-plasma deposition (APD) of the Cantor alloy layer on Pt(hkl) substrate surfaces, followed by deposition of the surface Pt layer in ~10-7 Pa. Then, we performed cross-sectional STEM-EDS observations for Pt/HEA/Pt(hkl) stacking structures with atomic-level resolution and evaluated the ORR properties (initial activity and structural stability). Experimental An APD target of Cr-Mn-Fe-Co-Ni (Cantor alloy) was fabricated by sintering of equal quantity corresponding elements. 10 ML(monolayer)-thick (1 ML = ca. 0.3 nm) Cantor alloy layer (as HEA) was vacuum-deposited by APD on surface cleaned Pt(hkl) substrate surfaces at 300 K, and subsequently annealed in vacuum at 773 K for 30 minutes. Then, 4ML-thick Pt layer was deposited on the pre-deposited Cantor alloy layer at 300 K and annealed at 623 K. The samples thus prepared are designated as Pt/HEA/Pt(hkl). The atomic-level micro-structures and chemical bonding states of Pt/HEA/Pt(hkl) surfaces were characterized by cross-sectional STEM-EDS, RHEED, XPS etc. CV and LSV with the RDE method were conducted in N2-purged and O2-saturated 0.1 M HClO4. ORR activity was evaluated from j k values at 0.9 V vs. RHE by using Koutecky-Levich equation and structural stability (ORR durability) was discussed based upon activity transitions during applying the potential cycles (PCs) of 0.6(3s)‐1.0(3s) V vs. RHE in O2 saturated 0.1 M HClO4 at room temperature. Results and Discussion Atomically-resolved, cross-sectional HAADF-STEM images for Pt/HEA/Pt(hkl) (a) and EDS line profiles of elemental distributions at corresponding yellow arrows (b) are presented in Figure 1. As clearly shown in (a), irrespective of the Pt surface indices, (hkl), HEA (Cantor alloy) and surface Pt layers are epitaxially grown on the substrates. By contrast, elemental distributions in each surface normal (b) seriously depend on the substrate Pt lattice indices. Notably, severe thermal diffusion of the constituent elements including Pt is confirmed by (a) and (b) for both Pt/HEA/Pt(110) and (100). Figure 2 summarizes electrochemical results. 4ML-thick-Pt/10ML-thick-Co/Pt(hkl) that prepared under the same preparation condition of Pt/HEA/Pt(hkl), and clean Pt(hkl) (light blue and gray, respectively) are also shown as references. As shown in the figure, the Pt/HEA and Pt/Co fabricated on Pt(111) substrate (top) show quite similar CV characteristics (shrink in hydrogen adsorption charges (0 – 0.3 V) and higher potential shifts in oxygen-related species adsorption (0.6 – 1.0 V)), in comparison to clean Pt(111), and almost the same initial ORR activity. Meanwhile, the Pt/HEA fabricated on Pt(110) and (100) substrates show more reduced hydrogen absorption charges, compared with corresponding Pt/Co samples. Particularly, distinctive redox features for clean Pt(110) at 0.12 V and for Pt(100) at 0.35 V are absent for corresponding CVs, suggesting specific topmost surface atomic-structures might be formed in the electrolyte, that probably resulting from significant electronic interactions between surface Pt and HEA constituent elements (Cr, Mn, Fe, Co, Ni) and/or local strain of the surface Pt layer induced by distorted Pt-HEA lattices located nearby. One might notice that Pt/HEA/Pt(110) reveals remarkable ORR activity enhancement compared with corresponding Pt/Co/Pt(110), while the activities for Pt/HEA and corresponding Pt/Co surfaces fabricated on Pt(100) are almost the same value. At the meeting, correlations between surface atomic-level micro-structures of Pt/HEA/Pt(hkl) and ORR properties will be discussed in detail. Acknowledgement This study was supported by new energy and industrial technology development organization (NEDO) of Japan and JST SPRING, Grant Number JPMJJSP2114.Reference[1] J. Yeh, JOM, 65, 1759 (2013).[2] B. Cantor et al., Mater. Sci. Eng. A, 375, 213 (2004). Figure 1

3D Flower‐Like Carbon Spheres with Hierarchical Pore Structure: An Efficient Asphaltene‐Based Metal‐Free Catalyst for ORR

Abstract3D carbon superstructures assembled from low‐dimensional segments can inherit the specific properties of their building blocks and gain certain unconventional advantages that make them attractive candidates for electrocatalysts. Furthermore, hierarchical pores and nitrogen doping are effective strategies to enhance carbon‐based metal‐free catalysts. Based on this, 3D flower‐like carbon spheres with a micro‐meso‐macroporous hierarchical pore structure constructed from 2D porous nanosheets are designed and developed using asphaltene as carbon precursor in this work. The high specific surface area and hierarchical pore structure of the prepared catalyst maximize exposure of the active sites and facilitate the penetration of electrolytes and the rapid transport of ions and O2, thus improving its oxygen reduction reaction (ORR) activity. It shows good ORR properties in both acid and alkaline electrolyte with Eon of 0.77 and 0.98 V, and E1/2 of 0.60 and 0.833 V, respectively. When the catalyst is assembled into zinc–air battery, it shows a specific capacity of 797 mAh g–1 and an open‐circuit voltage of 1.544 V. Furthermore, the assembled battery displays good cyclic stability with stable charge and discharge exceeding 150 h at 5 mA cm–2.

Alleviated surface calcium segregation and improved electrocatalytic properties of La0.3Ca0.7Fe0.7Cr0.3O3-δ cathode: A demonstration of A-site deficiency effect

The crystal structure, electrical conductivity, thermal expansion behavior and electrocatalytic properties for oxygen reduction reaction of A-site deficient (La0.3Ca0.7)1−xFe0.7Cr0.3O3-δ (x = 0.01–0.05) perovskites were investigated in comparison with their stoichiometric counterpart (x = 0). The tolerance limit of the perovskite structure for A-site deficiency was x = 0.04 or so. The unit cell parameters decreased and oxygen nonstoichiometry (δ) increased with increasing A-site deficiency. The electrocatalytic activity was appreciably improved by introducing an A-site deficiency of x = 0.04, concomitant with a slight decrease of the electrical conductivity and thermal expansion coefficient. The porous electrode with x = 0.04 exhibited a polarization resistance of 0.044 Ω·cm2 at 800 °C, lowered by about 42% compared with the electrode with x = 0. Moreover, the introduction of the A-site deficiency enhanced the stability of the perovskite structure and electrocatalytic activity relative to cathodic polarization. The electrode with x = 0 showed segregation of calcium onto the surface and an increase of the polarization resistance by 0.106 Ω·cm2 after being cathodically polarized under 250 mA·cm-2 at 800 °C for 6 h. In contrast, surface calcium segregation was undetected for the electrode with x = 0.04 after being likewise polarized and the electrocatalytic activity of the polarized A-site deficient electrode was virtually undegraded. The improved stability of the structure and electrocatalytic activity of the A-site deficient electrode was tentatively explained with respect to its defect chemistry.

Electric Field Polarized Fe−N Functionalized Graphene Oxide Nanosheet Catalyst for Efficient Oxygen Reduction Reaction

AbstractLow‐cost noble‐metal‐free electrocatalysts for oxygen reduction reaction (ORR) are useful for future energy storage and conversion devices, and other technologies. In this work, iron (Fe)‐nitrogen (N) functionalized graphene oxide (Fe−N−GO) nanosheets have been synthesized and studied for ORR properties in alkaline solution. We utilized a multi‐layer/multi‐polarization method to study the DC electric field polarization effect on the electrocatalytic properties of the Fe−N−GO catalyst. The poling effect with DC electric field was created on the catalyst ink drop‐casted on a polished glassy carbon working electrode, resulting in more compact electrocatalyst electrode. Compared to the commercial Pt/C catalyst, the polarized Fe−N−GO catalyst exhibited similar ORR catalytic activity along with superior stability in alkaline media.

Introduction of a new active and stable cathode catalyst based on bimetal-organic frameworks/PPy-sheet for alkaline direct ethanol fuel cell

For the first time, the polypyrrole (PPy) with a sheet-like structure was synthesized by a high-efficiency and facile chemical reaction process. A new composite with the growth of bimetallic zeolitic imidazolate frameworks on polypyrrole sheet-like (BMZIF@PPy) was synthesized. Then, the BMZIF@PPy composite by different heat-treatment temperatures is applied to make oxygen reduction reaction (ORR) electrocatalysts. Electrochemical measurements perform to investigate the ORR properties in both acidic and alkaline media. The onset potential and the limiting current density for the Cobalt/Zinc-nanocarbon@polypyrrole pyrolysis at 800 °C (Co/Zn-NC@PPy-800) were 0.977 VRHE and 4.99 mA cm−2 in 0.1 M KOH and 0.85VRHE and 5.48 mA cm−2 in 0.5 M H2SO4. Finally, due to the good activity and stability in alkaline media, the Co/Zn-NC@PPy-800 electrocatalyst is used as the cathode in an alkaline direct ethanol fuel cell. The maximum power of the Co/Zn-NC@PPy-800 cathode catalyst was 77% higher than that of the commercial Pt/C electrocatalyst.

Mn 2 V 2 O 7 spiked ball‐like material as bifunctional oxygen catalyst for zinc‐air batteries

Hierarchical micro/nanostructures are believed to be magnificent electrocatalyst materials capable of competing with noble metals and the most expensive catalyst materials for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, Mn2V2O7-based hierarchical spiked ball structures (MVO SBs) were synthesized using a simple hydrothermal technique as a bifunctional oxygen catalyst for rechargeable Zn-air batteries. The linear sweep voltammetry by a rotating disc electrode was used to investigate the ORR and OER properties and their mechanisms, and the charge transfer mechanism was also studied by electrochemical impedance spectroscopy analysis. When compared with platinum with carbon black (Pt/C), the MVO SB catalyst material exhibited comparable ORR and OER properties. Furthermore, the MVO SB material revealed a 4e− transfer pathway in an electrolyte solution. Furthermore, the prepared MVO SB material demonstrated a lower charge-discharge voltage gap when compared with Pt/C material, which is lower than 180 mV at 45 mA cm−2. The cycling test result of MVO SB catalyst sample revealed excellent cycling stability over 50 charging and discharging cycles (~800 min) than the Pt/C sample (30 cycles [~520 min]). The good catalytic activity and excellent structural stability of the MVO SB material are especially due to the more active sites enhanced by the unique spiked ball-like morphology and high specific surface area (11.70 m2 g−1) properties. The achieved results suggest that the synthesized catalyst material could be employed as an oxygen catalyst material for rechargeable Zn-air batteries.

Salt-Assisted Pyrolysis of Covalent Organic Framework for Controlled Active Nitrogen Functionalities for Oxygen Reduction Reaction

Abstract The development of defect-containing metal-free carbon materials is an exciting challenge, as it could contribute greatly to the emergence of more sustainable fuel cells and metal–air batteries. Here we report the combination of a covalent organic framework (COF) as a host material and potassium carbonate as an activator to synthesize, from relatively low temperature and with good control, hierarchical mesoporous/microporous structures, high-porosity (up to 2053 m2 g−1) and nitrogen-doped carbon materials with oxygen reduction reaction (ORR) activity. Indeed, the formation of large sp2 domains and the nature of heteroatom catalytic active sites, ranging from a large content of pyridinic (N-6) to quaternary (N-Q) functionalities, could be simply controlled within a range of pyrolysis temperatures from 625 °C to 775 °C. The resulting ORR properties of carbon material exhibit systematic behaviour regarding the pyrolysis temperature, testifying good control upon carbon material nature. Thus, this work opens new ways to explore COF capabilities to efficiently synthesize metal-free carbon materials for electrochemical energy storage and conversion systems.

Three-dimensional PdAuRu nanospines assemblies for oxygen reduction electrocatalysis

Tailoring morphology and composition of electrocatalysts has a substantial impact on catalytic properties for oxygen reduction reaction (ORR). In this work, trimetallic PdAuRu nanospine assemblies (PdAuRu NSAs) are fabricated via a simple one-step reduction route using DM-970 and KBr used as surfactant and structure directing agent, respectively. The hyperbranched structure has the characteristics of sufficient active sites, accessible transfer channels, and the excellent tolerance towards Ostwald ripening, migration and agglomeration of catalysts. Furthermore, the synergistic effect of Pd, Au and Ru atoms can alter the d-band energy of Pd, weaken the bond energy between the catalyst surface and the adsorbed species, thus changing the electronic structure and optimize the adsorption of oxygen on Pd. When explored for ORR in alkaline solution, the PdAuRu NSAs display superior catalytic activity and stability to commercial Pt/C. This synthesis tactic delivers a feasible route for the preparation of hyperbranched multi-metallic nanomaterials towards various electrocatalytic applications.

Electrocatalytic activity of calcined manganese ferrite solid nanospheres in the oxygen reduction reaction.

In this study, we synthesized MnFe2O4 solid nanospheres (MSN) calcined at different temperatures (200-500°C) and MSN-based materials mixed with carbon black, for their use as electrocatalysts in the oxygen reduction reaction (ORR) in alkaline medium (0.1M KOH). It was demonstrated that the calcination temperature of MSN material determined its chemical surface composition and microstructure and it had an important effect on the electrocatalytic properties for ORR, which in turn was reflected in the performance of MSN/CB-based electrocatalysts. The study revealed that the presence of Mn species plays a key role in the ORR activity. Among tested, MSN200/CB and MSN350/CB exhibited the best electrochemical performances together with outstanding stability.

Co9S8 nanoparticles encapsulated in N,S co-doped hierarchical carbon as an efficient oxygen reduction electrocatalyst for microbial fuel cells

• Co 9 S 8 @HN/S-C (Co 9 S 8 encapsulated in N/S co-doped porous carbon) is successfully synthesized. • Co 9 S 8 @HN/S-C exhibits high ORR electrocatalytic in alkaline and neutral media. • MFCs with Co 9 S 8 @HN/S-C show high power density of 1436.5mWm −2. • Outstanding chemical oxygen demand (COD) removal rate (80%) The Co 9 S 8 nanoparticles encapsulated in a N/S co-doped hierarchical porous carbon (Co 9 S 8 @HN/S-C) is successfully synthesized to accelerate oxygen reduction reaction (ORR) of microbial fuel cell (MFC). Herein, we prepared the Co 9 S 8 @HN/S-C catalyst using a bimetallic (Zn, Co) zeolite imidazolium salt framework as the precursor, which is carbonized at high temperature and then treated with thiourea pyrolysis. The Co 9 S 8 @HN/S-C catalyst exhibits an abundant porous structure (pore volume ≈ 0.46 cm 3 g −1 ) and high specific surface area (485 m 2 g −1 ). Benefiting from the active Co 9 S 8 species and N/S co-doped hierarchical porous carbon (HN/S-C), the Co 9 S 8 @HN/S-C exhibits excellent ORR properties in alkaline solution. The half-wave potential (E 1/2 ) and an onset potential are 0.91 V and 1.01 V (vs. RHE), respectively, which outperforms most previously reported non-precious metal catalysts. In addition, the assembled MFC with Co 9 S 8 @HN/S-C as cathode catalyst also exhibits excellent electrical performance and stability, with the maximum output power density of 1436.5 mW m −2 and a stable output voltage of 0.59 V, which is better than the most recently reported MFC cathode materials, such as Co 9 S 8 /NHCS (704 mW m −2 , 0.5 V) and Co/Co 9 S 8 /NPG (1156 mW m −2 , 0.562 V), etc. More notably, the outstanding chemical oxygen demand (COD) removal rate can reach 80%, and the coulomb efficiency of Co 9 S 8 @HN/S-C based MFC is also better than that of commercial Pt/C. This universal method can be widely used to prepare high-performance electrocatalysts for MFC in wastewater treatment and recovery of electricity.

Three-dimensional hierarchical graphitic carbon encapsulated CoNi alloy/N-doped CNTs/carbon nanofibers as an efficient multifunctional electrocatalyst for high-performance microbial fuel cells

A novel Co/Ni metal-organic framework (MOF)-derived three-dimensional (3D) nanoarchitecture in which graphene carbon-coated CoNi alloy nanoparticles grow on the tips of N-doped carbon nanotubes that are vertically-aligned on carbon nanofibers (Co/Ni@GC/NCNTs/CNFs) is fabricated. The Co/Ni@GC/NCNTs/CNFs electrode has a half-wave oxygen reduction reaction (ORR) potential of 0.80 V, a superior standing stability with 84.8% current retention after 175 000 s. The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) reach a lower overpotential of 0.395 V and 0.15 V, respectively. Moreover, the resultant sample is an air cathode catalyst in a microbial fuel cell and indicates an utmost power density of 2100 ± 45 mW cm −2 , which is much better than that of the Pt/C electrode (1334 ± 61 mW m −2 ). The density functional theory calculation demonstrates that the designed Co/Ni@GC/NCNTs/CNFs catalyst can remarkably promote OER, ORR, and HER performance. • Co/Ni MOF-derived graphene carbon-coated CoNi alloy/NCNTs/CNFs was fabricated. • Co/Ni@GC/NCNTs/CNFs endows excellent ORR, OER and HER properties. • The as-prepared electrode exhibits high power density of 2100 ± 45 mW cm −2 in MFCs. • Superior property is due to the synergy of abundant active sites and 3D structure.