Facile synthesis of metal-organic frameworks embedded in interconnected macroporous polymer as a dual acid-base bifunctional catalyst for efficient conversion of cellulose to 5-hydroxymethylfurfural

5-Hydroxymethylfurfural(5-HMF),as a key platform compound for the conversion of biomass to various biomass-derived chemicals and biofuels,has been attracted extensive attention.In this research,using Pickering high internal phase emulsions(Pickering HIPEs)as template and functional metal-organic frameworks(MOFs,UiO-66-SO;H and UiO-66-NH;)/Tween 85 as co-stabilizers to synthesis the dual acid-base bifunctional macroporous polymer catalyst by one-pot process,which has excellent catalytic activity in the cascade reaction of converting cellulose to 5-HMF.The effects of the emulsion parameters including the amount of surfactant(ranging from 0.5%to 2.0%(mass)),the internal phase volume fraction(ranging from 75%to 90%)and the acid/base Pickering particles mass ratio(ranging from 0:6 to 6:0)on the morphology and catalytic performance of solid catalyst were systematically researched.The results of catalytic experiments suggested that the connected large pore size of catalyst can effectively improve the cellulose conversion,and the synergistic effect of acid and base active sites can effectively improve the 5-HMF yield.The highest 5-HMF yield,about 40.5%,can be obtained by using polymer/MOFs composite as catalyst(Poly-P12,the pore size of(53.3±11.3)μm,the acid density of 1.99 mmol·g^(-1)and the base density of 1.13 mol·g^(-1))under the optimal reaction conditions(130℃,3 h).Herein,the polymer/MOFs composite with open-cell structure was prepared by the Pickering HIPEs templating method,which provided a favorable experimental basis and theoretical reference for achieving efficient production of high addedvalue product from abundant biomass.

Design Principles and Mechanistic Understandings of Non-Noble-Metal Bifunctional Electrocatalysts for Zinc-Air Batteries

Zinc-air batteries(ZABs)are promising energy storage systems because of high theoretical energy density,safety,low cost,and abundance of zinc.However,the slow multi-step reaction of oxygen and heavy reliance on noble-metal catalysts hinder the practical applications of ZABs.Therefore,feasible and advanced non-noble-metal elec-trocatalysts for air cathodes need to be identified to promote the oxygen catalytic reaction.In this review,we initially introduced the advancement of ZABs in the past two decades and provided an overview of key developments in this field.Then,we discussed the work-ing mechanism and the design of bifunctional electrocatalysts from the perspective of morphology design,crystal structure tuning,interface strategy,and atomic engineering.We also included theoretical studies,machine learning,and advanced characterization technologies to provide a comprehensive understanding of the structure-performance relationship of electrocatalysts and the reaction pathways of the oxygen redox reactions.Finally,we discussed the challenges and prospects related to designing advanced non-noble-metal bifunctional electrocatalysts for ZABs.

Defects and morphology engineering for constructing V_(s)-Ni_(3)S_(2)@V_(s)-Cu_(2)S nanotube heterojunction arrays toward efficient bifunctional electrocatalyst for overall water splitting

The development of highly active,stable and inexpensive electrocatalysts for hydrogen production by defects and morphology engineering remains a great challenge.Herein,S vacancies-rich Ni_(3)S_(2)@Cu_(2)S nan-otube heterojunction arrays were in-situ grown on copper foam(V_(s)-Ni_(3)S_(2)@V_(s)-Cu_(2)S NHAs/CF)for efficient electrocatalytic overall water splitting.With the merits of nanotube arrays and efficient electronic mod-ulation drived by the OD vacancy defect and 2D heterojunction defect,the resultant V_(s)-Ni_(3)S_(2)@V_(s)-Cu_(2)S NHAs/CF electrocatalyst exhibits excellent electrocatalytic activity with a low overpotential of 47 mV for the hydrogen evolution reaction(HER)at 10 mA cm^(-2) current density,and 263 mV for the oxygen evolution reaction(OER)at 50 mA cm^(-2) current density,as well as a cell voltage of 1.48 V at 10 mA cm^(-2).Moreover,the nanotube heterojunction arrays endows V_(s)-Ni_(3)S_(2)@V_(s)-Cu_(2)S NHAs/CF with outstanding stability in long-term catalytic processes,as confirmed by the continuous chronopotentiom-etry tests at current densities of 10 mA cm^(-2) for 100 h.

The component-activity interrelationship of cobalt-based bifunctional electrocatalysts for overall water splitting:Strategies and performance

Cobalt-based electrocatalysts take advantage of potentially harmonizable microstructure and flexible coupling effects compared to commercial noble metal-based catalytic materials.However,conventional water electrolysis systems based on cobalt-based monofunctional hydrogen evolution reaction(HER)or oxygen evolution reaction(OER)catalysts have certain shortcomings in terms of resource utilization and universality.In contrast,cobalt-based bifunctional catalysts(CBCs)have attracted much attention in recent years for overall water splitting systems because of their practicality and reduced preparation cost of electrolyzer.This review aims to address the latest development in CBCs for total hydrolysis.The main modification strategies of CBCs are systematically classified in water electrolysis to provide an overview of how to regulate their morphology and electronic configuration.Then,the catalytic performance of CBCs in total-hydrolysis is summarized according to the types of cobalt-based phosphides,sulfides and oxides,and the mechanism of strengthened electrocatalytic ability is emphasized through combining experiments and theoretical calculations.Future efforts are finally suggested to focus on exploring the dynamic conversion of reaction intermediates and building near-industrial CBCs,designing advanced CBC materials through micro-modulation,and addressing commercial applications.

Interfacial modulation of bifunctional electrolyte additive engineering for dendrite-free and robust lithium metal anode

Anode materials for rechargeable electric car batteries are obtained from Li-metal owing to their extremely high specific capacity and low redox potential.Unfortunately,safety concerns related to dendrite formation on the anode surface caused by the uneven distribution of Li-ions during the discharge process interfere with the use of Li-metal in industrial batteries.In this study,methyl vinyl sulfone(MVS),a sulfone-based functional electrolyte additive,is used in an additive engineering strategy to control Lielectrolyte interactions and address the aforementioned problems.Li dendrite growth may be restricted,and transition metal degradation on the surface of the cathode can be reduced by the MVS-derived functional electrolyte additive interfacial layer.The electrochemical performance of an ethylene carbonate/dimethyl carbonate(EC/DMC)+1 wt% MVS Li-metal anode of a Li||Li symmetric cell exhibits remarkable cycle stability,maintaining a low overvoltage for over 750 h at 1 mA cm^(-2),and capacity of 1 mA h cm^(-2).Additionally,LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM811) full cells with the MVS additive exhibit enhanced electrochemical stability for 250 cycles at a current density of 100 mA g^(-1).This study provides an innovative approach for stabilizing the metal-electrolyte interfacial layer that may be used for practical applications in metal-based rechargeable batteries.

Wood-derived freestanding integrated electrode with robust interface-coupling effect boosted bifunctionality for rechargeable zinc-air batteries

Fabricating non-noble metal-based carbon air electrodes with highly efficient bifunctionality is big challenge owing to the sluggish kinetics of oxygen reduction/evolution reaction(ORR/OER).The efficient cathode catalyst is urgently needed to further improve the performance of rechargeable zinc-air batteries.Herein,an activation-doping assisted interface modification strategy is demonstrated based on freestanding integrated carbon composite(CoNiLDH@NPC)composed of wood-based N and P doped active carbon(NPC)and CoNi layer double hydroxides(CoNiLDH).In the light of its large specific surface area and unique defective structure,CoNiLDH@NPC with strong interfacecoupling effect in 2D-3D micro-nanostructure exhibits outstanding bifunctionality.Such carbon composites show half-wave potential of 0.85 V for ORR,overpotential of 320 mV with current density of 10 mA cm^(-2) for OER,and ultra-low gap of 0.70 V.Furthermore,highly-ordered open channels of wood provide enormous space to form abundant triple-phase boundary for accelerating the catalytic process.Consequently,zinc-air batteries using CoNiLDH@NPC show high power density(aqueous:263 mW cm^(-2),quasi-solid-state:65.8 mW cm^(-2))and long-term stability(aqueous:500 h,quasi-solid-state:120 h).This integrated protocol opens a new avenue for the rational design of efficient freestanding air electrode from biomass resources.

Visible Light-Induced Photocatalysis:Self-Fenton Degradation of p-CIPhOH Over Graphitic Carbon Nitride by a Polyethylenimine Bifunctional Catalyst

Deep degradation of organic pollutants by sunlight-induced coupled photocatalytic and Fenton (photo-Fenton) reactions is of immense importance for water purification. In this work, we report a novel bifunctional catalyst (Fe-PEI-CN) by codoping graphitic carbon nitride (CN) with polyethyleneimine ethoxylated (PEI) and Fe species, which demonstrated high activity during p-chlorophenol (p-ClPhOH) degradation via H_(2)O_(2) from the photocatalytic process. The relationship between the catalytic efficiency and the structure was explored using diff erent characterization methods. The Fe modification of CN was achieved through Fe-N coordination, which ensured high dispersion of Fe species and strong stability against leaching during liquid- phase reactions. The Fe modification initiated the Fenton reaction by activating H_(2)O_(2) into ·OH radicals for deep degradation of p-ClPhOH. In addition, it eff ectively promoted light absorption and photoelectron-hole (e-h ^(+) ) separation, corresponding to improved photocatalytic activity. On the other hand, PEI could significantly improve the ability of CN to generate H_(2)O_(2) through visible light photocatalysis. The maximum H_(2)O_(2) yield reached up to 102.6 μmol/L, which was 22 times higher than that of primitive CN. The cooperation of photocatalysis and the self-Fenton reaction has led to high-activity mineralizing organic pollutants with strong durability, indicating good potential for practical application in wastewater treatment.

Intermolecular Acid-Base-Pairs Containing Poly(p-Terphenyl-co-lsatin Piperidinium)for High Temperature Proton Exchange Membrane Fuel Cells

How to optimize and regulate the distribution of phosphoric acid in matrix,and pursuing the improved electrochemical performance and service lifetime of high temperature proton exchange membrane(HT-PEMs)fuel cell are significant challenges.Herein,bifunctional poly(p-terphenyl-co-isatin piperidinium)copolymer with tethered phosphonic acid(t-PA)and intrinsic tertiary amine base groups are firstly prepared and investigated as HT-PEMs.The distinctive architecture of the copolymer provides a well-designed platform for rapid proton transport.Protons not only transports through the hydrogen bond network formed by the adsorbed free phosphoric acid(f-PA)anchored by the tertiary amine base groups,but also rely upon the proton channel constructed by the ionic cluster formed by the t-PA aggregation.Thorough the design of the structure,the bifunctional copolymers with lower PA uptake level(<100%)display prominent proton conductivities and peak power densities(99 mS cm^(-1),812 mW cm^(-2)at 160℃),along with lower PA leaching and higher voltage stability,which is a top leading result in disclosed literature.The results demonstrate that the design of intermolecular acid-base-pairs can improve the proton conductivity without sacrificing the intrinsic chemical stability or mechanical property of the thin membrane,realizing win-win demands between the mechanical robustness and electrochemical properties of HT-PEMs.

CuO/Co_(3)O_(4)Bifunctional Catalysts for Electrocatalytic 5-Hydroxymethylfurfural Oxidation Coupled Cathodic Ammonia Production

The electrochemical coupling of biomass oxidation and nitrogen conversion presents a potential strategy for high value-added chemicals and nitrogen cycling.Herein,in this work,CuO/Co_(3)O_(4)with heterogeneous interface is successfully constructed as a bifunctional catalyst for the electrooxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid and the electroreduction of nitrate to ammonia(NH_(3)).The open-circuit potential spontaneous experiment shows that more 5-hydroxymethylfurfural molecules are adsorbed in the Helmholtz layer of the CuO/Co_(3)O_(4)composite,which certifies that the CuO/Co_(3)O_(4)heterostructure is conducive to the kinetic adsorption of 5-hydroxymethylfurfural.In situ electrochemical impedance spectroscopy further shows that CuO/Co_(3)O_(4)has faster reaction kinetics and lower reaction potential in oxygen evolution reaction and 5-hydroxymethylfurfural electrocatalytic oxidation.Moreover,CuO/Co_(3)O_(4)also has a good reduction effect on NO_(3)^(-).The ex-situ Raman spectroscopy shows that under the reduction potential,the metal oxide is reduced,and the generated Cu_(2)O can be used as a new active site for the reaction to promote the electrocatalytic conversion of NO_(3)^(-)to NH_(3) synthesis.This work provides valuable guidance for the synthesis of value-added chemicals by 5-hydroxymethylfurfural electrocatalytic oxidation coupled with NO_(3)^(-)while efficiently producing NH_(3).

Enhanced bifunctional oxygen electrochemical catalytic performance using La-doped CoFe_(2)O_(4)spinel supported by 3D-G for Zn-air batteries

The preparation of bifunctional catalysts for oxygen reduction(ORR)and oxygen evolution(OER)is crucial for Zn-air batteries.Here,we report a La doped CoFe_(2)O_(4) spinel catalyst supported on threedimensional graphene(3D-G),where La can facilitate electron transfer from Co to Fe,leading to increased electron cloud density in Fe and improved catalytic performance.The redshift of the G peak in the Raman spectra indicates the interaction between theπbond of 3D-G and d orbitals in La_(0.2)CoFe_(1.8)O_(4).La_(0.2)CoFe_(1.8)/3D-G exhibits superior ORR performance(E_(1/2)=0.86 V vs.RHE)and OER performance(E_(j=10)=1.55 V vs.RHE)to CoFe_(2)O_(4)/3D-G(E_(1/2)=0.831 V vs.RHE,E_(j=10)=1.603 V vs.RHE).Furthermore,it demonstrates excellent bifunctional oxygen catalytic performance while maintaining high power density and stability in liquid zinc-air batteries(ZABs)and flexible ZABs(F-ZABs).This work presents a viable strategy for utilizing rare earth element doped spinels to enhance oxygen catalyst and ZABs performance.

Conversion of Bio-syngas to Liquid Hydrocarbon over CuCoMn-Zeolite Bifunctional Catalysts

A series of bifunctional catalysts composed of a component for higher alcohol synthesis （Cu-CoMn oxides, CCM） and an acidic zeolite （SAPO-34, ZSM-5, Y, MCM-41） were prepared for production of liquid hydrocarbon directly from a bio-syngas through a one-stage pro-cess. The effects of zeolite type, zeolite content, Si/Al ratio and preparation method on catalyst texture and its reaction performance were investigated. Higher selectivities and yields of liquid products were obtained by using bifunctional catalysts. The yields of liquid hydrocarbons decreased in the order CCM-ZSM-5〉CCM-SAPO-34〉CCM-Y〉CCM-MCM-41. CCM-ZSM-5 （20wt%, Si/Al=100） prepared by coprecipitation method displayed the optimal catalytic performance with the highest CO conversion （76%） and yield of liquid products （30%）. The catalysts were characterized by N2 adsorption/desorption, NH3-TPD, XRD, and H2-TPR analysis. The results showed that higher speci c surface areas and pore volumes of bifunctional catalysts were achieved by adding zeolites into CuCoMn precursors. Medium pore dimension and moderate acidity in CCM-ZSM-5 were observed, which proba-bly resulted in its excellent reaction performance. Additionally, a higher number of weaker acid sites （weak and/or medium acid sites） were formed by increasing ZSM-5 content in CCM-ZSM-5 or decreasing Si/Al ratio in ZSM-5. It was also seen that metal dispersion was higher and reducibility of metal ions was easier on the CCM-ZSM-5 catalyst prepared by coprecipitation. The higher alcohols-to-hydrocarbon process provides a promising route to hydrocarbon fuels via higher alcohols from syngas or biobased feedstocks.

Facile synthesis of V-doped CoP nanoparticles as bifunctional electrocatalyst for efficient water splitting

Adjusting the intrinsic activity and conductivity of electrocatalysts may be a crucial way for excellent performance for water splitting.Herein,the rational design of vanadium element doped cobalt phosphide(V-doped CoP)nanoparticles has been investigated through a facile gaseous phosphorization using cobalt vanadium oxide or hydroxide(Co-V hydr(oxy)oxide)as precursor.The physical characterization shows that the homogeneous dispersion of V element on V-doped CoP nanoparticles have obtained,which may imply the enhanced electrocatalytic activity for hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).The electrochemical measurements of the prepared V-doped CoP in alkaline electrolyte demonstrate the superior electrocatalytic activity for both HER(overpotential of 235 mV@10 mA cm^-2)and OER(overpotential of 340 mV@10 mA cm^-2).Further,V-doped CoP nanoparticles used as anode and cathode simultaneously in a cell require only 370 mV to achieve a current density of 10 mA cm^-2.The outstanding electrocatalytic activity may be ascribed to the improved conductivity and intrinsic activity owing to phosphating and the doping of V element.In addition,the long-term stability of V-doped Co P has been obtained.Therefore,metal doping into transition metal-based phosphides may be a promising strategy for the remarkable bifunctional electrocatalyst for water splitting.

In Situ Coupling Strategy for Anchoring Monodisperse Co_9S_8 Nanoparticles on S and N Dual?Doped Graphene as a Bifunctional Electrocatalyst for Rechargeable Zn–Air Battery

An in situ coupling strategy to prepare Co_9S_8/S and N dual?doped graphene composite(Co_9S_8/NSG) has been proposed. The key point of this strategy is the function?oriented design of organic compounds. Herein, cobalt porphyrin derivatives with sulfo groups are employed as not only the coupling agents to form and anchor Co_9S_8 on the graphene in situ, but also the heteroatom?doped agent to generate S and N dual?doped graphene. The tight coupling of multiple active sites endows the composite materials with fast electrochemical kinetics and excellent stability for both oxygen reduction reaction(ORR) and oxygen evolution reaction(OER). The obtained electrocatalyst exhibits better activity parameter(ΔE = 0.82 V) and smaller Tafel slope(47.7 mV dec^(-1) for ORR and 69.2 mV dec^(-1) for OER) than commercially available Pt/C and RuO_2. Most importantly, as electrocatalyst for rechargeable Zn–air battery, Co_9S_8/NSG displays low charge–discharge voltage gap and outstanding long?term cycle stability over 138 h compared to Pt/C–RuO_2. To further broaden its application scope, a homemade all?solid?state Zn–air battery is also prepared, which displays good charge–discharge performance and cycle performance. The function?oriented design of N_4?metallomacrocycle derivatives might open new avenues to strategic construction of high?performance and long?life multifunctional electrocatalysts for wider electro?chemical energy applications.

Bifunctional Electrocatalysts Based on Mo-Doped NiCoP Nanosheet Arrays for Overall Water Splitting

Rational design of efficient bifunctional electrocatalysts is highly imperative but still a challenge for overall water splitting.Herein,we construct novel freestanding Mo-doped NiCoP nanosheet arrays by the hydrothermal and phosphation processes,serving as bifunctional electrocatalysts for overall water splitting.Notably,Mo doping could effectively modulate the electronic structure of NiCoP,leading to the increased electroactive site and improved intrinsic activity of each site.Furthermore,an electrochemical activation strategy is proposed to form Mo-doped(Ni,Co)OOH to fully boost the electrocatalytic activities for oxygen evolution reaction.Benefiting from the unique freestanding structure and Mo doping,Mo-doped NiCoP and(Ni,Co)OOH show the remarkable electrochemical performances,which are competitive among current researches.In addition,an overall water splitting device assembled by both electrodes only requires a cell voltage of 1.61 V to reach a current density of 10 mA cm?2.Therefore,this work opens up new avenues for designing nonprecious bifunctional electrocatalysts by Mo doping and in situ electrochemical activation.

Hierarchical sulfur and nitrogen co-doped carbon nanocages as efficient bifunctional oxygen electrocatalysts for rechargeable Zn-air battery

Exploring inexpensive and efficient bifunctional electrocatalysts for oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) is critical for rechargeable metal-air batteries. Herein, we report a new 3D hierarchical sulfur and nitrogen co-doped carbon nanocages(hSNCNC) as a promising bifunctional oxygen electrocatalyst by an in-situ MgO template method with pyridine and thiophene as the mixed precursor. The as-prepared h SNCNC exhibits a positive half-wave potential of 0.792 V(vs. reversible hydrogen electrode, RHE) for ORR, and a low operating potential of 1.640 V at a 10 mA cm-2 current density for OER. The reversible oxygen electrode index is 0.847 V, far superior to commercial Pt/C and IrO2,which reaches the top level of the reported bifunctional catalysts. Consequently, the hSNCNC as air cathodes in an assembled Zn-air battery features low charge/discharge overpotential and long lifetime. The remarkable properties arises from the introduced multiple heteroatom dopants and stable 3D hierarchical structure with multi-scale pores, which provides the abundant uniform high-active S and N species and efficient charge transfer as well as mass transportation. These results demonstrate the potential strategy in developing suitable carbon-based bi-/multi-functional catalysts to enable the next generation of the rechargeable metal-air batteries.

Extraction Kinetics of Lanthanum in Chloride Medium by Bifunctional Ionic Liquid [A336][CA-12] Using a Constant Interfacial Cell with Laminar Flow

The extraction kinetics of La(III) from aqueous chloride solutions into n-heptane solutions of bifunctional ionic liquid extractant [A336][CA-12](tricaprylmethylammonium sec-octylphenoxy acetic acid) was investigated using a constant interfacial cell with laminar flow. The effects of stirring speed, temperature and specific interfacial area on the extraction rate were examined. The results indicate that mass transfer kinetics of La(III) is a mixed-controlled process influenced by interfacial reaction. On the basis of mass transfer kinetic results in the extraction of La(III) by [A336][CA-12], the extraction rate equation of La(III) is proposed in terms of pseudo-firstorder constants, which is supported by the measured thermodynamic equations. The mass-transfer kinetic model deduced from the rate controlling step is adequate to interpret the experimental data qualitatively.

In-situ emb e dding zeolitic imidazolate framework derived Co–N–C bifunctional catalysts in carbon nanotube networks for flexible Zn–air batteries

Recently, the development of high-performance bifunctional oxygen catalysts integrated with flexible conductive scaffolds f or rechargeable metal-air batteries has attracted considerable interest, driving by fastgrowing wearable electronics. Herein, we report a flexible bifunctional oxygen catalyst thin film consisting of Co–N–C bifunctional catalysts embedding in carbon nanotube(CNT) networks. The catalyst is readily prepared by pyrolysis of cobalt-based zeolitic imidazolate frameworks(ZIF-67) that are in-situ synthesized in CNT networks. Such catalyst film demonstrates very high catalytic activities for oxygen reduction(onset potential: 0.91 V, and half-wave potential: 0.87 V vs. RHE) and oxygen evolution(10 m Acm^-2 at 1.58 V) reactions, high methanol tolerance property, and long-term stability(97% current retention). Moreover, our integrated catalyst film shows very good structure flexibility and robustness. Based on the obtained film air electrodes, flexible Zn–air batteries demonstrate low charging and discharging overpotentials(0.82 V at 1 m A cm^-1) and excellent structure stability in the bending tests. These results indicate that presently reported catalyst films are potential air electrodes for flexible metal–air batteries.

Synthesis of 3D Hexagram-Like Cobalt–Manganese Sulfides Nanosheets Grown on Nickel Foam: A Bifunctional Electrocatalyst for Overall Water Splitting

The exploration of low-cost and efficient bifunctional electrocatalysts for oxygen evolution reaction and hydrogen evolution reaction through tuning the chemical composition is strongly required for sustainable resources. Herein, we developed a bimetallic cobalt–manganese sulfide supported on Ni foam(CMS/Ni) via a solvothermal method. It has discovered that after combining with the pure Co_9S_8 and Mn S, the morphologies of CMS/Ni have modulated. The obtained three-dimensionally hexagram-like CMS/Ni nanosheets have a significant increase in electrochemical active surface area and charge transport ability. More than that, the synergetic effect of Co and Mn has also presented in this composite. Benefiting from these, the CMS/Ni electrode shows great performance toward hydrogen evolution reaction and oxygen evolution reaction in basic medium, comparing favorably to that ofthe pure Co_9S_8/Ni and Mn S/Ni. More importantly, this versatile CMS/Ni can catalyze the water splitting in a twoelectrode system at a potential of 1.47 V, and this electrolyzer can be efficiently driven by a 1.50 V commercial dry battery.

The influence of the type of N dopping on the performance of bifunctional N-doped ordered mesoporous carbon electrocatalysts in oxygen reduction and evolution reaction

To develop more ideal bifunctional heteroatom-doped carbon electrocatalysts toward the oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) for regenerative fuel cells and rechargeable metal–air batteries, herein, tobacco-derived N-containing ordered mesoporous carbon(N-OMC) electrocatalysts with different N species distributions are designed. Results indicate that the as-prepared N-OMC with more pyrrolic and pyridinic Ns exhibits much higher activities for the ORR and OER than N-OMC with more graphitic N in both acidic and alkaline media, suggesting that the increase of pyrrolic and pyridinic Ns favors the improvement of ORR and OER activities of the N-containing carbon catalysts, and showing a great potential for the designing of more effective, lower-cost ORR and OER bifunctional electrocatalysts for future regenerative fuel cells and rechargeable metal–air batteries.

Gold-iridium bifunctional electrocatalyst for oxygen reduction and oxygen evolution reactions

Carbon supported gold-iridium composite(Au Ir/C) was synthesized by a facile one-step process and was investigated as the bifunctional catalyst for oxygen reduction reaction(ORR) and oxygen evolution reaction(OER). The physical properties of the Au Ir/C composite were characterized by transmission electron microscopy(TEM), X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS). Although the Au and Ir in the Au Ir/C did not form alloy, it is clear that the introduction of Ir decreases the average Au particle size to 4.2 nm compared to that in the Au/C(10.1 nm). By systematical analysis on chemical state of metal surface via XPS and the electrochemical results, it was found that the Au surface for the Au/C can be activated by potential cycling from 0.12 V to 1.72 V, resulting in the increased surface roughness of Au,thus improving the ORR activity. By the same potential cycling, the Ir surface of the Ir/C was irreversibly oxidized, leading to degraded ORR activity but uninfluenced OER activity. For the Au Ir/C, Ir protects Au against being oxidized due to the lower electronegativity of Ir. Combining the advantages of Au and Ir in catalyzing ORR and OER, the Au Ir/C catalyst displays an enhanced catalytic activity to the ORR and a comparable OER activity. In the 50-cycle accelerated aging test for the ORR and OER, the Au Ir/C displayed a satisfied stability, suggesting that the Au Ir/C catalyst is a potential bifunctional catalyst for the oxygen electrode.