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.

The Preparation of Nanosized Pd/ZSM-23 Bifunctional Catalysts for n-Hexadecane Hydroisomerization by Employing PHMB as the Growth Modifi er

The development of highly effective metal-zeolite bifunctional catalysts for the hydroisomerization of n-alkanes is a paramount strategy to produce second-generation biofuels with high quality.In this study,polyhexamethylene biguanide hydrochloride(PHMB)is precisely added to the initial gel to synthesize nanosized ZSM-23 zeolites(Z23-x PH).Due to orientation adsorption and steric hindrance effects of PHMB,each sample of Z23-x PH demonstrates enhanced mesoporosity in comparison with the conventional Z23-C zeolite.Furthermore,the Bronsted acid density of the Z23-x PH samples is also signifi cantly reduced due to a reduction in the distribution of framework Al at T2-T5 sites.The corresponding Pd/23-C and Pd/Z23-x PH bifunctional catalysts with 0.5 wt%Pd loading for n-hexadecane hydroisomerization are prepared by incorporating ZSM-23 zeolites as acid supports.According to the catalytic test results,the suitable addition of PHMB can effectively promote the iso-hexadecane yield.The Pd/Z23-2PH catalyst with an n_(PHMB)/n(_Si)molar ratio of 0.002 demonstrates the highest maximum iso-hexadecane yield of 74.1%at an n-hexadecane conversion of 88.3%.Therefore,the employment of PHMB has provided a simple route for the development of highly effective Pd/ZSM-23 catalysts for n-alkane hydroisomerization.

FeCo alloy/N,S dual-doped carbon composite as a high-performance bifunctional catalyst in an advanced rechargeable zinc-air battery

The rational design and development of cost-effective,high-performance,and stable bifunctional oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)electrocatalysts are essential for rechargeable zinc-air batteries.Herein,a novel FeCo composite composed of alloy nanoparticles embedded in an N,S dual-doped carbon matrix(FeCo/NSC)was prepared via one-step carbonization of amphiphilic dodecanethiol-metal salts wrapped in carbon nitride(C_(3)N_(4)).The compact combination of dual metalalloys and dual-doped carbon endowed the composite with the active sites for the ORR and OER,achieving efficient electrical transmission and highly efficient bifunctional catalytic performance.The obtained FeCo-1/NSC catalyst exhibited excellent electrocatalytic activity with a half-wave potential of 0.82 V(vs.RHE)for the ORR and a low overpotential of 0.325 V at 10 mA cm^(-2) for the OER.The liquid Zn-air battery with FeCo-1/NSC as an air electrode displayed excellent charge-discharge performance,high power density,and robust charge-discharge stability for 150 h compared to the 20%Pt/C+RuO_(2) counterpart.Furthermore,the FeCo-1/NSC-based flexible solid-state Zn-air battery exhibited a higher power density and good charge-discharge stability over 10 h of operation.Thus,a promising strategy for bifunctional electrocatalyst development as part of rechargeable and wearable Zn-air batteries was provided.

Efficient conversion of benzene and syngas to toluene and xylene over ZnO-ZrO_(2)&H-ZSM-5 bifunctional catalysts

A series of ZnO-ZrO_(2) solid solutions with different Zn contents were synthesized by the urea coprecipitation method,which were coupled with H-ZSM-5 zeolite to form bifunctional catalysts.As a new benzene alkylation reagent,syngas was used instead of methanol to realize the efficient conversion of syngas and benzene into toluene and xylene.A suitable ratio of ZnO-ZrO_(2) led to the significant improvement in the catalytic performance,and a suitable amount of acid helped to increase the selectivity of toluene/xylene and reduce the selectivity of the by-products ethylbenzene and C^(9+) aromatics.The highest benzene conversion of 89.2%and toluene/xylene selectivity of 88.7%were achieved over 10%ZnO-ZrO_(2)&H-ZSM-5(Si/Al=23)at a pressure of 3 MPa and a temperature of 450℃.In addition,the effect of the zeolite framework structure on product distribution was examined.Similar to the molecular dynamics of aromatic hydrocarbons,H-ZSM-5 zeolites comprise 10-membered-ring pores,which are beneficial to the activation of benzene;hence,the conversion of benzene is higher.H-ZSM-35 and HMOR zeolites exhibited small eight-membered-ring channels,which were not conducive to the passage of benzene;hence,the by-product ethylbenzene exhibits a higher selectivity.The distance between the active centers of the bifunctional catalysts was the main factor affecting the catalytic performance,and the powder mixing method was more conducive to the conversion of syngas and benzene.

Pd nanoparticles immobilized on MIL-53(Al)as highly e ective bifunctional catalysts for oxidation of liquid methanol to methyl formate

A series of Pd/MIL-53(Al) heterogeneous bifunctional catalysts with di erent Pd contents were prepared by an impregnation method. The prepared metal–organic frameworks MIL-53(Al) and catalysts were characterized by XRD, SEM, HRTEM,FT-IR and N2 adsorption/desorption techniques. The results showed that MIL-53(Al) was synthesized successfully, and the structure was unchanged during and after the preparation of the catalysts. The Pd nanoparticles(NPs) with an average particle size of 4.6 nm were uniformly dispersed on the MIL-53(Al). The catalyst exhibited good catalytic activity in the selective oxidation of liquid methanol to methyl formate. Under the conditions of 150 °C, 2 MPa O2 and solvent-free for5 h, the conversion of methanol could reach 60.3%, and the selectivity of methyl formate was up to 62.2%. In addition, the Pd/MIL-53(Al) bifunctional catalyst exhibited excellent stability and maintained high catalytic activity after five cycles.

Co_(3)O_(4)/Mn_(3)O_(4) hybrid catalysts with heterointerfaces as bifunctional catalysts for Zn-air batteries

Zinc-air batteries(ZABs) with high energy density and safety are promising as next-generation energy storage systems, while their applications are severely hindered by the sluggish reaction kinetic of air cathodes. Developing a bifunctional catalyst with high activity and durability is an effective strategy to address the above challenges. Herein, a Co_(3)O_(4)/Mn_(3)O_(4) nanohybrid with heterointerfaces is designed as advanced cathode catalyst for ZABs. Density functional theory calculations show the heterogeneous interface between Co_(3)O_(4)/Mn_(3)O_(4) can improve the dynamics of carrier transport and thus enhancing the catalytic activity and durability. The Co_(3)O_(4)/Mn_(3)O_(4) catalyst anchored on reduced graphene oxide(rGO)exhibits high oxygen reduction reaction(ORR) activity with a half-wave potential of 0.86 V, and excellent oxygen evolution reaction(OER) activity with the potential of 1.59 V at 10 mA cm^(-2) , which are comparable to the commercial noble metal catalysts. The improved ORR/OER catalytic activity is ascribed to the synergistic effect of heterointerfaces between Co_(3)O_(4) and Mn_(3)O_(4)as well as the improved conductivity and contact area of oxygen/catalysts/electrolytes three-phase interface by r GO. Furthermore, a home-made ZAB based on Co_(3)O_(4)/Mn_(3)O_(4)/r GO shows a high open circuit voltage of 1.54 V, a large power density of 194.6 mW cm^(-2) and good long-term cycling stability of nearly 400 h at 5 mA cm^(-2) , which affords a promising bifunctional oxygen catalyst for rechargeable ZABs.

Interface-engineered MoS_(2)/CoS/NF bifunctional catalysts for highly-efficient water electrolysis

The utilization of non-noble metal catalysts with robust and highly efficient electrocatalytic activity for hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)are extremely important for the large-scale implementation of renewable energy devices.Integration of bifunctional electrocatalysts on both anode and cathode electrodes remains a significant challenge.Herein,we report on a novel and facile strategy to construct the ordered and aligned MoS_(2)nanosheet-encapsulated metal–organic frameworks(MOFs)derived hollow CoS polyhedron,in-situ grown on a nickel foam(NF).The starfish-like MoS_(2)/CoS/NF heterojunctions were formed due to the ordered growth of the material caused by NF substrate.The optimized 2-MoS_(2)/CoS/NF heterojunction exhibits robust bifunctional electrocatalytic activity with a low overpotential of 67 and 207 m V toward the HER and OER at 10 mA cm^(-2),and the long-term stability,which exceeds most of the reported bifunctional electrocatalysts.Such high electrocatalytic performance arises due to the synergistic effect between the MoS_(2)and CoS phases across the interface,the abundant active sites,as well as the hierarchical pore framework,which collectively enhance the mass and electron transfer during the reactions.The work provides a promising approach to fabricating bifunctional catalysts with custom-designed heterojunctions and remarkable performance for applications in electrochemical energy devices and related areas.

Ru@RuO2 Core-Shell Nanorods: A Highly Active and Stable Bifunctional Catalyst for Oxygen Evolution and Hydrogen Evolution Reactions

Ru@RuO2 core-shell nanorods were successfully synthesized by heat-treating Ru nanorods with air oxidation through an accurate control of the temperature and time. The structure, composition, dimension, and adsorption property of the core-shell nanorods were well characterized with XRD and TEM. The catalytic activity and stability were electrochemically evaluated with a rotating disk electrode, a rotating ring-disk electrode, and chronopotentiometric methods. The Ru@RuO2 nanorods reveal excellent bifunctional catalytic activity and robust stability for both oxygen evolution reaction(OER) and hydrogen evolution reaction(HER). The overpotentials for OER and HER are 320 m V and 137 m V at the current density of10 m A cm-2, respectively. The catalytic activity of Ru@RuO2 nanorods for OER is 6.5 times higher than that of the state-of-the-art catalyst IrO2 according to the catalytic current density measured at 1.60 V(versus RHE).The catalytic activity of Ru@RuO2 nanorods for HER is comparable to 40%Pt/C by comparing the catalytic current densities at à0.2 V.

Environmentally Friendly Bifunctional Catalyst for ORR and OER from Coconut Shell Particles

Catalyst for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is at the heart of key renewable energy technologies such as water splitting and rechargeable batteries. But developing a low-cost oxygen electrode catalyst with high activity at low overpotential remains a great challenge. Coconut shells can be utilized as suitable raw material to produce activated carbon for enhanced adsorption capacity, bulk density, and hardness to be used as regenerative fuel cells running ORR and OER. The present work is designed to obtain an alternative to noble metal-based catalysts by synthesizing electroactive N-doped porous carbon from coconut shells;the use of biodegradable raw material through a single-step activation followed by nitrogen doping provides a more economical and environmentally friendly route to produce green catalysts for fuel cell applications. In valorization of biomass for the development of novel catalytic materials, our aim is also to reduce the use of hazardous chemicals. N-doped activated carbon shows promising bifunctional catalyst for ORR and OER as low-cost noble-metal-free and carbon-based oxygen catalysts.

Metal size effects over metal/zeolite bifunctional catalysts in the selective hydroalkylation of benzene

Bifunctional metal/zeolite materials are some of the most suitable catalysts for the direct hydroalkylation of benzene to cyclohexylbenzene.The overall catalytic performance of this reaction is strongly influenced by the hydrogenation,which is dependent on the metal sizes.Thus,systematically investigating the metal size effects in the hydroalkylation of benzene is essential.In this work,we successfully synthesized Ru and Pd nanoparticles on Sinopec Composition Materials No.1 zeolite with various metal sizes.We demonstrated the size-dependent catalytic activity of zeolite-supported Ru and Pd catalysts in the hydroalkylation of benzene,which can be attributed to the size-induced hydrogen spillover capability differences.Our work presents new insights into the hydroalkylation reaction and may open up a new avenue for the smart design of advanced metal/zeolite bi-functional catalysts.

Dual-Confined Bead-Like CoSe_(2)@NC@NCNFs Bifunctional Catalyst Boosting Rechargeable Zinc-Air Batteries

Rationally developing efficient and durable bifunctional catalysts toward oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)is critical for rechargeable zinc-air batteries(ZABs).Herein,a bead-like CoSe_(2)@NC@NCNFs bifunctional catalyst was designed and fabricated by confining cubic CoSe_(2)nanoparticles to three-dimensional(3D)porous MOFs-derived nitrogen-doped carbon(NC)and one-dimensional(1D)N-doped carbon nanofibers(NCNFs)through a facile encapsulate strategy.The 1D/3D continuous network structure contributes to the improvement of specific surface area and electronic conductivity,while the strong synergistic effect between CoSe_(2)sites and Co-Nx-C sites can effectively enhance electron/mass transfer and reduce the diffusion resistance.The as-constructed CoSe_(2)@NC@NCNFs catalyst exhibits high catalytic activity and stability toward ORR/OER with a high half-wave potential of 0.80 V(vs.RHE)in ORR and a low overpotential of 280 mV at 10 mA·cm^(−2)in OER.More encouragingly,the rechargeable ZABs with CoSe_(2)@NC@NCNFs cathode deliver high peak power densities(126.8 mW·cm^(−2)),large specific capacities(763.1 mA·h·g^(−1)),and robust charge-discharge cycling stability over 240 cycles.This study provides a facile strategy for designing efficient bifunctional catalysts for rechargeable energy conversion applications.

Research progress of transition metal compounds as bifunctional catalysts for zinc-air batteries

Zinc-air batteries(ZABs)are widely studied because of their high theoretical energy density,high battery voltage,environmental protection,and low price.However,the slow kinetics of oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)on the air electrode limits the further application of ZABs,so that how to develop a cheap,efficient,and stable catalyst with bifunctional catalytic activity is the key to solving the development of ZABs.Transition metal compounds are widely used as cathode materials for ZABs due to their low cost,high electrocatalytic activity,and stable structure.This review summarizes the research progress of transition metal compounds as bifunctional catalysts for ZABs.The development history,operation principle,and mechanism of ORR and OER reactions are introduced first.The application and development of transition metal compounds as bifunctional catalysts for ZABs in recent years are systematically introduced,including transition metal oxides(TMOs),transition metal nitrides(TMNs),transition metal sulfides(TMSs),transition metal carbides(TMCs),transition metal phosphates(TMPs),and others.In addition,the shortcomings of transition metal compounds as bifunctional catalysts for ZABs were summarized and reasonable design strategies and improvement measures were put forward,aiming at providing a reference for the design and construction of high-performance ZABs cathode materials.Finally,the challenges and future in this field are discussed and prospected.

Well-dispersed Mn/g-C_(3)N_(4)as bifunctional catalysts for selective epoxidation of olefins and carbon dioxide cycloaddition

Epoxidation is an important chemical process for the production of epoxides,key building blocks in chemical industry.Despite great efforts being made to facilitate this process,it remains a significant challenge to develop cost-effective,environmental-friendly,and selective catalysts.Herein,we reported a highly dispersed Mn supported by g-C_(3)N_(4)(Mn/g-C_(3)N_(4))with Mn loading up to 2.56 wt%.The Mn/g-CN_(4)exhibited satisfied catalytic performance for olefin epoxidation with excellent conversion(91%),high selectivity(93%)as well as outstanding recycling stability.Further analysis revealed the importance of Mn-N structure for the generation of active oxo-containing species and subsequent oxygen atom transfer.Besides,an efficient synthesis of cyclic carbonates from styrene epoxide and CO_(2)has been achieved(88%conversion,89%selectivity)based on the polar Mn-N coordinated characteristics of Mn/g-C_(3)N_(4)catalyst.

Manipulating oxygenate adsorption on N-doped carbon by coupling with CoSn alloy for bifunctional oxygen electrocatalyst

Highly active bifunctional oxygen electrocatalysts accelerate the development of high-performance Zn-air battery,but suffer from the mismatched activities of oxygen evolution reaction(OER)and oxygen reduced reaction(ORR).Herein,highly integrated bifunctional oxygen electrocatalysts,cobalt-tin alloys coated by nitrogen doped carbon(CoSn@NC)are prepared by MOFs-derived method.In this hybrid catalyst,the binary CoSn nanoalloys mainly contribute to highly active OER process while the Co(or Sn)-N-C serves as ORR active sites.Rational interaction between CoSn and NC donates more rapid reaction kinetics than Pt/C(ORR)and IrO_(2)(OER).Such CoSn@NC holds a promise as air-cathode electrocatalyst in Zn-air battery,superior to Pt/C+IrO_(2)catalyst.First-principles calculations predict that CoSn alloys can upgrade charge redistribution on NC and promote the transfer to reactants,thus optimizing the adsorption strength of oxygen-containing intermediates to boost the overall reactivity.The tuning of oxygenate adsorption by interactions between alloy and heteroatom-doped carbon can guide the design of bifunctional oxygen electrocatalysts.

Strengthening absorption ability of Co-N-C as efficient bifunctional oxygen catalyst by modulating the d band center using MoC

Co-N-C is a promising oxygen electrochemical catalyst due to its high stability and good durability.However,due to the limited adsorption ability improvement for oxygen-containing intermediates,it usually exhibits inadequate catalytic activity with 2-electron pathway and high selectivity of hydrogen peroxide.Herein,the adsorption of Co-N-C to these intermediates is modulated by constructing heterostructures using transition metals and their derivatives based on d-band theory.The heterostructured nanobelts with MoC core and pomegranate-like carbon shell consisting of Co nanoparticles and N dopant(MoC/Co-N-C)are engineered to successfully modulate the d band center of active Co-N-C sites,resulting in a remarkably enhanced electrocatalysis performance.The optimally performing MoC/Co-N-C exhibits outstanding bi-catalytic activity and stability for the oxygen electrochemistry,featuring a high wave-half potential of 0.865 V for the oxygen reduction reaction(ORR)and low overpotential of 370 mV for the oxygen evolution reaction(OER)at 10 mA cm^(-2).The zinc air batteries with the MoC/Co-N-C catalyst demonstrate a large power density of 180 mW cm^(-2)and a long cycling lifespan(2000 cycles).The density functional theory calculations with Hubbard correction(DFT+U)reveal the electron transferring from Co to Mo atoms that effectively modulate the d band center of the active Co sites and achieve optimum adsorption ability with"single site double adsorption"mode.

Dimethyl ether synthesis from CO_2 hydrogenation on La-modified CuO-ZnO-Al_2O_3 /HZSM-5 bifunctional catalysts

A series of CuO-ZnO-Al2O3-La2O3/HZSM-5 biftmctional catalysts with various La loadings for dimethyl ether （DME） directly synthesized from CO2 hydrogenation were prepared. The catalysts were characterized with N2 adsorption-desorption, X-ray diffraction （XRD）, H2 temperature-programmed reduction （H2-TPR）, NH3 temperature-programmed desorption （NH3-TPD） and N2O titration techniques, and tested for the synthesis of DME directly from CO2 hydrogenation in a fixed-bed reactor. The results showed that the reducibility, dispersion ofbifunctional catalysts were strongly dependent on the addition of La. With the addition of appropri- ate amount of La, the crystaUite size of CuO was decreased and the dispersion of Cu on the surface was enhanced, which resulted in the increased conversion of CO2. It was also found that the selectivity to DME was related to the intensity and amount of strong acid site on the catalyst surface. The presence of La favored the production of DME, and the optimum catalytic activity was obtained when the amount of La was 2.0 wt.%.

Biomass-derived bifunctional electrocatalysts for oxygen reduction and evolution reaction: A review

Oxygen electrode catalysts are important as inter-conversion of O_(2) and H_(2)O is crucial for energy technologies.However,the sluggish kinetics of oxygen reduction and evolution reactions(ORR and OER)are a hindrance to their scalable production,whereas scarce and costly Pt and Ir/Ru-based catalysts with the highest electrocatalytic activity are commercially unviable.Since good ORR catalysts are not always efficient for OER and vice versa,so bifunctional catalysts on which OER and ORR occurs on the same electrode are very desirable.Alternative catalysts based on heteroatom-doped carbon nanomaterials,though showed good electrocatalytic activity yet their high cost and complex synthesis is not viable for scalable production.To overcome these drawbacks,biomass-derived heteroatom-doped porous carbons have recently emerged as low-cost,earth-abundant,renewable and sustainable environment-friendly materials for bifunctional oxygen catalysts.The tunable morphology,mesoporous structure and high concentration of catalytic active sites of these materials due to heteroatom(N)-doping could further enhance their ORR and OER activity,along with tolerance to methanol crossover and good durability.Thus,biomassderived heteroatom-doped porous carbons with large surface area,rich edge defects,numerous micropores and thin 2 D nanoarchitecture could be suitable as efficient bifunctional oxygen catalysts.In the present article,synthesis,N-doping,ORR/OER mechanism and electrocatalytic performance of biomassderived bifunctional catalysts has been discussed.The selected biomass(chitin,eggs,euonymus japonicas,tobacco,lysine and plant residue)except wood,act as both C and N precursor,resulting in N selfdoping of porous carbons that avoids the use of toxic chemicals,thus making the synthesis a facile and environment-friendly green process.The synthetic strategy could be further optimized to develop future biomass-based N self-doped porous carbons as metal-free high performance bifunctional oxygen catalysts for commercial energy applications.Recent advances and the importance of biomass-based bifunctional oxygen catalysts in metal-air batteries and fuel cells has been highlighted.The material design,perspectives and future directions in this field are also provided.

Ternary NiCoP nanosheet arrays： An excellent bifunctional catalyst for alkaline overall water splitting

Exploring bifunctional catalysts for the hydrogen and oxygen evolution reactions （HER and OER） with high efficiency, low cost, and easy integration is extremely crucial for future renewable energy systems. Herein, ternary NiCoP nanosheet arrays （NSAs） were fabricated on 3D Ni foam by a facile hydrothermal method followed by phosphorization. These arrays serve as bifunctional alkaline catalysts, exhibiting excellent electrocatalytic performance and good working stability for both the HER and OER. The overpotentials of the NiCoP NSA electrode required to drive a current density of 50 mA/cm2 for the HER and OER are as low as 133 and 308 mV, respectively, which is ascribed to excellent intrinsic electrocatalytic activity, fast electron transport, and a unique superaerophobic structure. When NiCoP was integrated as both anodic and cathodic material, the electrolyzer required a potential as low as -1.77 V to drive a current density of 50 mA/cm2 for overall water splitting, which is much smaller than a reported electrolyzer using the same kind of phosphide-based material and is even better than the combination of Pt/C and Ir/C, the best known noble metal-based electrodes. Combining satisfactory working stability and high activity, this NiCoP electrode paves the way for exploring overall water splitting catalysts.

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.

Self-supporting and hierarchically porous Ni_(x)Fe-S/NiFe_(2)O_(4) heterostructure as a bifunctional electrocatalyst for fluctuating overall water splitting

Stable non-noble metal bifunctional electrocatalysts are one of the challenges to the fluctuating overall water splitting driven by re-newable energy.Herein,a novel self-supporting hierarchically porous Ni_(x)Fe-S/NiFe_(2)O_(4) heterostructure as bifunctional electrocatalyst was constructed based on porous Ni-Fe electrodeposition on three-dimensional(3D)carbon fiber cloth,in situ oxidation,and chemical sulfuration.Results showed that the Ni_(x)Fe-S/NiFe_(2)O_(4) heterostructure with a large specific surface area exhibits good bifunctional activity and stability for both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)because of the abundance of active sites,synergistic effect of the heterostructure,superhydrophilic surface,and stable,self-supporting structure.The results further confirmed that the Ni_(x)Fe-S phase in the heterostructure is transformed into metal oxides/hydroxides and Ni_(3)S_(2) during OER.Compared with the commercial 20wt%Pt/C||IrO_(2)-Ta_(2)O_(5) electrolyzer,the self-supporting Ni1/5Fe-S/NiFe_(2)O_(4)||Ni1/2Fe-S/NiFe_(2)O_(4) electrolyzer exhibits better stability and lower cell voltage in the fluctu-ating current density range of 10-500 mA/cm^(2).Particularly,the cell voltage of Ni1/5Fe-S/NiFe_(2)O_(4)||Ni1/2Fe-S/NiFe_(2)O_(4) is only approximately 3.91 V at an industrial current density of 500 mA/cm^(2),which is lower than that of the 20wt%Pt/C||IrO_(2)-Ta_(2)O_(5) electrolyzer(i.e.,approximately 4.79 V).This work provides a promising strategy to develop excellent bifunctional electrocatalysts for fluctuating overall water splitting.