Boost the Utilization of Dense FeN_(4) Sites for High-Performance Proton Exchange Membrane Fuel Cells

Iron-nitrogen-carbon(Fe-N-C)catalysts for the oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs)have seriously been hindered by their poor ORR performance of Fe-N-C due to the low active site density(SD)and site utilization.Herein,we reported a melamine-assisted vapor deposition approach to overcome these hindrances.The melamine not only compensates for the loss of nitrogen caused by high-temperature pyrolysis but also effectively etches the carbon substrate,increasing the external surface area and mesoporous porosity of the carbon substrate.These can provide more useful area for subsequent vapor deposition on active sites.The prepared 0.20Mela-FeNC catalyst shows a fourfold higher SD value and site utilization than the FeNC without the treatment of melamine.As a result,0.20Mela-FeNC catalyst exhibits a high ORR activity with a half-wave potential(E_(1/2))of 0.861 V and 12-fold higher ORR mass activity than the FeNC in acidic media.As the cathode in a H_(2)-O_(2)PEMFCs,0.20Mela-FeNC catalyst demonstrates a high peak power density of 1.30 W cm^(-2),outstripping most of the reported Fe-N-C catalysts.The developed melamine-assisted vapor deposition approach for boosting the SD and utilization of Fe-N-C catalysts offers a new insight into high-performance ORR electrocatalysts.

电化学与空间层选核磁共振波谱联用原位监测多碳醇氧化

醇类燃料电池具有环境友好、运输便利、反应温度低等优势,被认为是理想的能源替代品之一.含有两个碳原子以上的多碳醇,如正丁醇,在燃料电池应用中具有更高的能量密度和更低的质子膜穿透率等优点.然而,多碳醇的氧化反应通常涉及多种C-C化学键断裂,产生多种具有相似分子结构的产物和中间产物,从而增加了产物分析和反应机理研究的难度.原位电化学核磁共振联用(EC-NMR)技术将核磁共振波谱技术引入到原位电化学实验中,实时检测电化学反应过程中的谱学信息,对于深入理解液体燃料电池阳极反应的催化机理有重要应用.然而,原位电化学反应过程中磁场的时空变化通常会导致核磁共振谱峰展宽和谱图分辨率不足的问题,使其应用受到限制.本文将传统电化学方法与空间层选核磁共振波谱技术进行联用(EC-SPSENMR)以应对该挑战,实现多碳有机分子电催化过程的原位实时分析.该策略可以很好地克服原位电化学反应过程中磁场时空变化引起谱图分辨率不足等问题,在原位测量时能够记录具有清晰J偶合裂分结构的高分辨谱峰,实现对电化学反应进程中不同分子信息的直接识别,便于后续的定性和定量分析.此外,该策略还可直接在标准的商业核磁共振波谱仪器上使用,从中提取分辨率高且谱峰形状未失真的核磁共振信号用于电化学分析,且对电极材料和电极放置位置几乎没有特殊要求,因此可广泛适用于原位电化学研究.本文以正丁醇电氧化为例,探究了该技术应用于多碳醇氧化的原位监测以及相关机理研究的可行性和有效性.结果表明,相较于原位红外实验,EC-SPSENMR实验可直接观测和区分氧化产物中的正丁酸和乙酸.特别是当工作温度为60°C时,商业催化剂Pt/C在高电位下直接氧化正丁醇生成正丁酸的反应更显著,而随着电位降低,正丁醇氧化生成气态产物(主要是CO_(2))的比例升高.此外,在1.2 V电位(相对于SCE)下,相较于催化剂Pt Ru/C,采用商业催化剂Pt/C时正丁醇氧化生成气态产物的比例更高.说明在1.2 V的高电位下,相比于Pt Ru/C,Pt/C可能更倾向于辅助β-C–H键断裂过程.综上所述,相比于传统的EC-NMR实验,本文提出的EC-SPSENMR方案可以有效克服原位电化学反应过程中磁场变化引起的谱图分辨率低的问题,为实时监测电化学过程、研究氧化机理和评估催化特性提供了有效手段.此外,为液体燃料电池研究,尤其是多碳醇燃料电池的阳极电氧化反应研究,提供了一个有应用前景的范例,对进一步扩展核磁共振在电化学的应用提供参考.

Investigation of photoelectrocatalytic degradation mechanism of methylene blue by a-Fe_(2)O_(3) nanorods array

Efficiently and thoroughly degrading organic dyes in wastewater is of great importance and challenge.Herein,vertically oriented mesoporous a-Fe_(2)O_(3)nanorods array(a-Fe_(2)O_(3)-NA)is directly grown on fluorine-doped tin oxide(FTO)glass and employed as the photoanode for photoelectrocatalytic degradation of methylene blue simulated dye wastewater.The Ovsites on the a-Fe_(2)O_(3)-NA surface are the active sites for methylene blue(MB)adsorption.Electrons transfer from the adsorbed MB to Fe-O is detected.Compared with electrocatalytic and photocatalytic degradation processes,the photoelectrocatalytic(PEC)process exhibited the best degrading performance and the largest kinetic constant.Hydroxyl,superoxide free radicals,and photo-generated holes play a jointly leading role in the PEC degradation.A possible degrading pathway is suggested by liquid chromatography-mass spectroscopy analysis.This work demonstrates that photoelectrocatalysis by a-Fe_(2)O_(3)-NA has a remarkable superiority over photocatalysis and electrocatalysis in MB degradation.The in-depth investigation of photoelectrocatalytic degradation mechanism in this study is meaningful for organic wastewater treatment.

Elucidating electrochemical intercalation mechanisms of biomass-derived hard carbon in sodium-/potassium-ion batteries

Hard carbon materials are characterized by having rich resources,simple processing technology,and low cost,and they are promising as one of the anode electrodes for commercial applications of sodium-/potassium-ion batteries.Simultaneously,exploring the alkali metal ion storage mechanism is particularly important for designing high-performance electrode materials.However,the structure of hard carbon is more complex,and the description of energy storage behavior is quite controversial.In this study,the Magnolia grandiflora Lima leaf is used as a precursor,combined with simple pyrolysis and impurity removal processes,to obtain biomass-derived hard carbon material(carbonized Magnolia grandiflora Lima leaf[CMGL]).When it is used as an anode for sodium-ion batteries,it exhibits a high specific capacity of 315mAh/g,and the capacity retention rate is 90.0%after 100 cycles.For potassium-ion batteries,the charge specific capacity is 263.5mAh/g,with a capacity retention rate of 85.5%at the same cycling.Furthermore,different electrochemical analysis methods and microstructure characterization techniques were used to further elucidate the sodium/potassium storage mechanism of the material.All the results indicate that the high potential slope region represents the adsorption/desorption characteristics on the surface active sites,whereas the low-potential quasiplateau region belongs to the ion insertion/extraction in the graphitic microcrystallites interlayer.It is noteworthy that potassium ion is randomly intercalated between the graphitic microcrystallite layer without forming a segmented intercalation compound structure.

Fe,N,S-doped porous carbon as oxygen reduction reaction catalyst in acidic medium with high activity and durability synthesized using CaCl_2 as template

Proton exchange membrane fuel cells suffer from the sluggish kinetics of the oxygen reduction reaction(ORR)and the high cost of Pt catalysts.In the present work,a high‐performance ORR catalystbased on Fe,N,S‐doped porous carbon(FeNS‐PC)was synthesized using melamine formaldehyderesin as C and N precursors,Fe(SCN)3as Fe and S precursors,and CaCl2as a template via a two‐stepheat treatment without a harsh template removal step.The results show that the catalyst treated at900℃(FeNS‐PC‐900)had a high surface area of775m2/g,a high mass activity of10.2A/g in anacidic medium,and excellent durability;the half‐wave potential decreased by only20mV after10000potential cycles.The FeNS‐PC‐900catalyst was used as the cathode in a proton exchangemembrane fuel cell and delivered a peak power density of0.49W/cm2.FeNS‐PC‐900therefore hasgood potential for use in practical applications.

Graphene-nickel nitride hybrids supporting palladium nanoparticles for enhanced ethanol electrooxidation

Electrocatalysts for ethanol oxidation reaction(EOR)are generally limited by their poor durability because of the catalyst poisoning induced by the reaction intermediate carbon monoxide(CO).Therefore,the rapid oxidation removal of CO intermediates is crucial to the durability of EOR-based catalysts.Herein,in order to effectively avoiding the catalyst CO poisoning and improve the durability,the graphene-nickel nitride hybrids(AG-Ni_(3)N)were designed for supporting palladium nanoparticles(Pd/AG-Ni_(3)N)and then used for ethanol electrooxidation.The density functional theory(DFT)calculations demonstrated the introduction of AG-Ni_(3)N depresses the CO absorption and simultaneously promotes the adsorption of OH species for CO oxidation removal.The fabricated Pd/AG-Ni_(3)N catalyst distinctively exhibits excellent electroactivity with the mass catalytic activity of 3499.5 m A mg^(-1) on EOR in alkaline media,which is around 5.24 times higher than Pd/C(commercial catalyst).Notably,the Pd/AG-Ni_(3)N hybrids display excellent stability and durability after chronoamperometric measurements with a total operation time of 150,000 s.

Positive direction of polarization-induced electric field improves formic acid electrooxidation on Pd

Adjusting the adsorption energy of adsorbates on catalyst can directly regulate the catalytic performance and reaction pathways of heterogeneous catalysis.Herein,we report a novel strategy,introducing polarization-induced electric field(PIEF)with different directions,to manipulate the adsorption energy of intermediates and reaction pathway of formic acid electrooxidation on Pd.Tourmaline nanoparticles are applied as the PIEF provider,of which the direction is successfully controlled via aligning the dipoles in tourmaline in a strong external electric field.Experimental and theoretical results systematically reveal that positive PIEF leads to an electron-deficient state of Pd,reduced adsorption energy of COad,enhanced adsorption energy of*HCOOH and*OH,and promoted formate pathway of formic acid electrooxidation.Pd/TNP+/FTO,with the aid of positive PIEF,shows three-fold enhancement in the formic acid electrooxidation(4.74 mA·cm^(−2))with high durability and anti-poisoning ability compared with pristine Pd.This study leads a new route to design formic acid electrocatalysts and provides an understanding on how to control the adsorption energy of adsorbates on electrocatalysts by an internal electric field.

Co3O4 nanocage derived from metal-organic frameworks: An excellent cathode catalyst for rechargeable Li-O2 battery

Rechargeable non-aqueous Li-O2 battery is regarded as one of the most promising energy-storage technologies on account of its high energy density.It is believed that the rational design of three-dimensional (3D) architecture for catalyst is a key factor for the remarkable performance.Metal-organic frameworks (MOFs) derived materials possess excellent architecture,which is beneficial for Li-O2 batteries.In this work,ZIF-67 is used as precursor template and calcinated under different temperature to produce Co3O4 crystals.When the anneal treatment is under 350℃,the derived Co3O4 nanocage holds the most complete skeleton,which provides better charge transfer ability as well as O2 and Li^+ diffusion.Meanwhile,the Co3O4 nanocage owns more oxygen vacancies,offering more active sites.With the synergistic effect of nanocage structure and active sites,the Co3O4 nanocage stably delivers a large specific capacity of 15,500 mAh·g^-1 as well as a long cycle-life of 132 cycles at limited discharge capacity of 1,000 mAh·g^-1 under discharge/charge current density of 0.5 A·g^-1.

Protection of Li metal anode by surface-coating of PVDF thin film to enhance the cycling performance of Li batteries

Lithium metal, the ideal anode material for next-generation high-energy batteries, suffers from the severe safety problem of Li dendrites. Herein, we report a simple approach to effectively maintain the morphology of Li-metal anode and enhance the cycling performance of Li batteries by surface coating of a porous polyvinylidene fluoride (PVDF) thin film. In symmetrical cells testing, the cells with the Li@PVDF electrode display stable cycling performance more than 1300 h (650 cycles) at the current density of 0.5 mA/cm^2 with a stripping/plating capacity of 0.5 mAh/cm^2. The results with full cells employing Li@PVDF anode and LiFePO_4 cathode show a good cycling ability with a capacity retention of 80.0% after 500 cycles at 4 C and an excellent rate capability with a high capacity of 78.4 mAh/g even at a high rate of 10 C.

Abnormal infrared effects of nanometer scale thin film material of PtPd alloy in CO adsorption

Nanometer scale thin film material of PtPd alloy supported on glassy carbon (nm-PtPd/GC) was prepared by the electrochemical codeposition method under cyclic voltammetric conditions. STM patterns demonstrated that the prepared thin films are composed of layered crystallites in elliptic form. Electrochemical in situ FTIRS studies explored the abnormal infrared effects (AIREs) of nm-PtPd/GC for CO adsorption, which are (i) the remarkable enhancement of IR absorption, (ii) the inversion of COad band direction, and (iii) notable increase in the full width at half maximum (FWHM) of COad bands. The results demonstrated also that the enhancement factor of IR absorption varies with the thickness of PtPd alloy film and has reached a maximum value of 38.3 under the experimental conditions.

Overpotential-dependent shape evolution of gold nanocrystals grown in a deep eutectic solvent

This paper reports an overpotential-dependent shape evolution of gold nano-crystals （Au NCs） in a choline chloride-urea （ChCl-urea） based deep eutectic solvent （DES）. It was found that the growth overpotentials play a key role in tuning the shape of Au NCs. The shape evolution of Au NCs successively from concave rhombic dodecahedra （RD） to concave cubes, octopods, cuboctahedral boxes, and finally, to hollow octahedra （OH） was achieved by carefully controlling the growth overpotentials in the range from -0.50 to -0.95 V （vs. Pt quasi-reference electrode）. In addition, the presence of urea was important in the shape evolution of Au NCs. The surface structure of the as-prepared Au NCs was comprehensively characterized by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and electrochemical studies. It was demonstrated that the electrocatalytic activity of the as-prepared Au NCs for D-glucose electrooxidation was sensitively dependent on their morphologies. The results illustrated that the dehydrogenated glucose adsorbed on concave RD and concave cubic Au NCs was preferentially transformed to gluconolactone at low electrode potentials. Subsequent gluconolactone oxidation occurred favorably on octopods with {111}-truncated arms and hollow OH at high electrode potential. This study opens up a new approach to develop the surface-structure-controlled growth of Au NCs by combining DES with electrochemical techniques. In addition, it is significant for the tuning of the electrocatalytic properties of NCs.

Controllable CO adsorption determines ethylene and methane productions from CO_(2) electroreduction

Among all CO2 electroreduction products,methane(CH4)and ethylene(C_(2)H_(4))are two typical and valuable hydrocarbon products which are formed in two different pathways:hydrogenation and dimerization reactions of the same CO intermediate.Theoretical studies show that the adsorption configurations of CO intermediate determine the reaction pathways towards CH4/C_(2)H_(4).However,it is challenging to experimentally control the CO adsorption configurations at the catalyst surface,and thus the hydrocarbon selectivity is still limited.Herein,we seek to synthesize two well-defined copper nanocatalysts with controllable surface structures.The two model catalysts exhibit a high hydrocarbon selectivity toward either CH4(83%)or C_(2)H_(4)(93%)under identical reduction conditions.Scanning transmission electron microscopy and X-ray absorption spectroscopy characterizations reveal the low-coordination Cu^(0)sites and local Cu^(0)/Cu^(+)sites of the two catalysts,respectively.CO-temperature programed desorption,in-situ attenuated total reflection Fourier transform infrared spectroscopy and density functional theory studies unveil that the bridge-adsorbed CO(CO_(B))on the low-coordination Cu^(0)sites is apt to be hydrogenated to CH4,whereas the bridge-adsorbed CO plus linear-adsorbed CO(CO_(B)+CO_(L))on the local Cu^(0)/Cu^(+)sites are apt to be coupled to C_(2)H_(4).Our findings pave a new way to design catalysts with controllable CO adsorption configurations for high hydrocarbon product selectivity.

In situ FTIR spectroscopic studies of CO adsorption on electrodes of nanometer-thin layer of Pt-Ru and Pt-Pd surface alloys

CO adsorption on nanometer-thin layer of surface alloys of Pt-Ru and Pt-Pd prepared by electrochemical codeposition has been studied using in situ FTIR spectroscopy. Abnormal infrared effects (AIREs) that consist of the enhancement of IR absorption by adsorbed CO on different surface sites and the inversion of IR band direction have been observed on the thin-layer prepared. The results also demonstrate the considerable significance of Pt-Ru and Pt-Pd surface alloys in electrocatalysis applications.

Study of pyrolyzed hemin/C as non-platinum cathodic catalyst for direct methanol fuel cells

Biological reduction of O2 to H2O justifies a serious look at heme as a potential O2 reduction reaction(ORR) catalyst for low temperature fuel cells.In this study,a novel non-platinum electrocatalyst for ORR was prepared through hemin,which is hydrochloride of heme,supported on Black Pearls 2000 carbon black(Hm-BP) pyrolyzed at 700-900℃ in Ar atmosphere.The physical and electrocatalytic properties of as-prepared catalysts were characterized by TGA,XRD,XPS,TEM,rotating disk electrode(RDE) and rotating ring disk electrode(RRDE).It has found that the catalyst treated at 750℃(Hm-BP-750) exhibits the best property among the Hm-BP catalysts prepared.The onset potential of ORR on the Hm-BP-750 at 30℃ was measured ca.0.90 V(vs.RHE) in 0.1 M H2SO4,and mass current density was reached 15.3 mA mg-1 at 0.75 V.It has revealed that O2 could be reduced directly to water in a 4e process between 0.9 and 0.83V,and the yield of H2O2 was 0-18% in the potential range of 0.83-0.63 V.This methanol-tolerant catalyst also presents excellent stability in medium-term test of direct methanol fuel cell at 80℃.

Efficient oxygen electrocatalysts with highly-exposed Co-N4 active sites on N-doped graphene-like hierarchically porous carbon nanosheets enhancing the performance of rechargeable Zn-air batteries

Designing bifunctional oxygen electrocatalysts with high activity,lasting stability,and low-cost for rechargeable zinc-air batteries(RZABs)is a tough challenge.Herein,an advanced electrocatalyst is prepared by anchoring atomically dispersed Co atoms on Ndoped graphene-like hierarchically porous carbon nanosheets(SA-Co-N4-GCs)and thereby forming Co-N4-C architecture.Its unique structure with excellent conductivity,large surface area,and three dimensional(3D)interconnected hierarchically porous architecture exposes not only more Co-N4 active sites to accelerate the kinetics of both oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),but also provides an efficient charge/mass transport environment to reduce diffusion barrier.Consequently,SA-Co-N4-GCs exhibits excellent ORR/OER bifunctional activities and durability,surpassing noble-metal catalysts.Liquid RZABs using SA-Co-N4-GCs cathodes display a high open-circuit voltage of 1.51 V,a remarkable power density of 149.3 mW·cm−2,as well as excellent stability and rechargeability with faint increase in polarization even at a large depth of charge–discharge cycle with 16 h per cycle over an entire 600 h long-term test.Moreover,flexible quasi-solid-state RZABs with SA-Co-N4-GCs cathodes also deliver a considerable power density of 124.5 mW·cm−2,which is even higher than that of liquid batteries using noble-metal catalysts.This work has thrown new insight into development of high-performance and low-cost electrocatalysts for energy conversion and storage.

RuO_(2) nanoparticles supported on Ni and N co-doped carbon nanotubes as an efficient bifunctional electrocatalyst of lithium-oxygen battery

Li_(2)O_(2),as the discharge product of Li-O_(2) batteries on cathode,is difficult to be electrochemically decomposed,which will lead to short cycling lifespan of the batteries.In this study,the cycling lifespan of Li-O_(2)battery was prolonged significantly by an efficient bifunctional catalyst.The Ni and N co-doped carbon nanotubes(Ni NCs)were synthesized firstly,and then RuO_(2) nanoparticles were deposited on Ni NCs by a hydrothermal route to synthesize RuO_(2)/Ni NC catalysts.Transmission electron microscopy and X-ray diffraction characterizations demonstrated that part of metallic Ni was converted into NiO and Ni(OH)2 after loading RuO_(2),and the existence of Ni O layer can prevent further oxidation of metallic Ni.The Li-O_(2)battery with RuO_(2)/Ni NC as the cathode catalyst exhibits an overpotential of 0.43 V,which is much lower than the value of 1.03 V measured with the Li-O_(2) battery using Ni NC as the cathode catalyst.At a rate of 200 mAg^(-1),the Li-O_(2) battery with the RuO_(2)/Ni NC cathode can maintain a reversible capacity of 500 mAhg^(-1)for 260 cycles,and 117 cycles with a higher reversible capacity of 1000 m A h g^(-1).The superior property of the RuO_(2)/NiNC bifunctional catalyst could be ascribed to the high activity of RuO_(2) and the rich carbon nanotube structure of NiNC for deposition and decomposition of Li_(2)O_(2).

Microscope in situ FTIRS studies of CO adsorption on an array of platinum micro-electrodes

An array of platinum microelectrodes was designed and fabricated. The adsorption of CO on such a Pt microelectrode (μ-Pt) was investigated by employing microscope in situ FTIR spectroscopy. A nanostructured film is formed at the surface of μ-Pt (denoted as μ-Pt(R)) when it has been subjected to a treatment of fast potential cycling. Abnormal infrared effects (AIREs) were observed in CO adsorption on the surface of μ-Pt(R), consisting of the inversion of the IR bipolar CO band and the extensively enhanced IR adsorption of COad species.