Recent development of methanol electrooxidation catalysts for directmethanol fuel cell

Direct methanol fuel cells （DMFCs） are very promising power source for stationary and portable miniatureelectric appliances due to its high efficiency and low emissions of pollutants. As the key material, cata-lysts for both cathode and anode face several problems which hinder the commercialization of DMFCs.In this review, we mainly focus on anode catalysts of DMFCs. The process and mechanism of methanolelectrooxidation on Pt and Pt-based catalysts in acidic medium have been introduced. The influences ofsize effect and morphology on electrocatalytic activity are discussed though whether there is a size effectin MOP, catalyst is under debate. Besides, the non Pt catalysts are also listed to emphasize though Pt isstill deemed as the indispensable element in anode catalyst of DMFCs in acidic medium. Different cata-lyst systems are compared to illustrate the level of research at present. ome debates need to be verifiedwith experimental evidences.

Pyrochlore La_(2)Zr_(2-x)Ni_(x)O_(7)anodes for direct ammonia solid oxide fuel cells

Developing efficient anode catalysts for direct ammonia solid oxide fuel cells(NH_(3)-SOFCs)under intermediate-temperatures is of great importance,in support of hydrogen economy via ammonia utilization.In the present work,the pyrochlore-type La_(2)Zr_(2-x)Ni_(x)O_(7+δ)(LZN_(x),x=0,0.02,0.05,0.08,0.10)oxides were synthesized as potential anode catalysts of NH_(3)-SOFCs due to the abundant Frankel defect that contributes to the good conductivity and oxygen ion mobility capacity.The effects of different content of Ni^(2+)doping on the crystal structure,surface morphology,thermal matching with YSZ(Yttria-stabilized zirconia),conductivity,and electrochemical performance of pyrochlore oxides were examined using different characterization techniques.The findings indicate that the LZN_(x)oxide behaves as an n-type semiconductor and exhibits an excellent high-temperature chemical compatibility and thermal matching with the YSZ electrolyte.Furthermore,LZN_(0.05)exhibits the smallest conductive band potential and bandgap,making it have a higher power density as anode material for NH_(3)-SOFCs compared to other anodes.As a result,the maximum power density of the LZN_(0.05)-40YSZ composite anode reaches 100.86 mW/cm^(2)at 800℃,which is 1.8 times greater than that of NiO-based NH_(3)-SOFCs(56.75 mW/cm^(2))under identical flow rate and temperature conditions.The extended durability indicates that the NH_(3)-SOFCs utilizing the LZN_(0.05)-40YSZ composite anode exhibits a negligible voltage degradation following uninterrupted operation at 800℃for 100 h.

An Intermediate-temperature H_2S Fuel Cell with a Li_2SO_4-based Proton-conducting Membrane

A laboratory-scale intermediate-temperature H2S fuel cell with a configuration of H2S, (metal sulfide-based composite anode)/Li2SO4+Al2O3/(NiO-based composite cathode), air was developed and studied for production of power and for desulfurization of a fuel gas process stream. The cell was run at typical temperature (600—650℃) and ambient pressure, but its electrochemical performance may be limited by electrolyte membrane thickness. The membrane and its performance in cell have been characterized using scanning electron microscope (SEM) and electrochemical impedance spectrum (EIS) techniques. Composite anodes based on metal sulfides, Ag powder and electrolyte behaved well and stably in H2S stream, and composite cathodes based mainly on nickel oxide, Ag powder and electrolyte had superior per-formance to Pt catalyst. The maximum power density of up to 70mW?cm-2 and current density of as high as 250mA?cm-2 were obtained at 650℃. However, the long-term cell stability remains to be investigated.

CO耐受的单位点/纳米颗粒协同型质子交换膜燃料电池阳极催化剂

Nanosized Pt catalysts are the catalyst-of-choice for proton exchange membrane fuel cell(PEMFC)anode,but are limited by their extreme sensitivity to CO in parts per million(ppm)level,thereby making the use of ultrapure H_(2)a prerequisite to ensure acceptable performance.Herein,we confront the CO poisoning issue by bringing the Ir/Rh single atom sites to synergistically working with their metallic counterparts.In presence of 1000 ppm CO,the catalyst represents not only undisturbed H_(2)oxidation reaction(HOR)catalytic behavior in electrochemical cell,but also unparalleled peak power density at 643 mW cm^(-2)in single cell,27-fold in mass activity of the best PtRu/C catalysts available.Pre-poisoning experiments and surface-enhanced Raman scattering spectroscopy(SERS)and calculation results in combine suggest the presence of adjacent Ir/Rh single atom sites(SASs)to the nanoparticles(NPs)as the origin for this prominent catalytic behavior.The single sites not only exhibit superb CO oxidation performance by themselves,but can also scavenge the CO adsorbed on approximated NPs via supplying reactive OH*species.We open up a new route here to conquer the formidable CO poisoning issue through single atom and nanoparticle synergistic catalysis,and pave the way towards a more robust PEMFC future.

Recent development of Au arched Pt nanomaterials as promising electrocatalysts for methanol oxidation reaction

The recent development of Aurum(Au)introduced Platinum(Pt)based nanomaterials is of great significance to direct methanol fuel cell as electrocatalysts for anode reactions,due to its stability and anti-poisoning features.Therefore,the performance of PtAu based catalysts with different elements,atomic ratio,and morphology was studied in methanol solution to further improve its electrocatalytic activity.Furthermore,the effects of Au have aroused the researchers'attention in Pt-based nanocatalysts.In this review,we summarize the controllable synthesis,mechanism,and catalytic performance of Au introduced Pt-based electrocatalysts such as PtAu core-shell nanostructures,PtAu dendrite,PtAu nanowires,self-supporting Au@Pt NPs,and Au@Pt star-like nanocrystals for the methanol oxidation reaction.Finally,the challenges and research directions for the future development of PtAu based catalysts are provided.

Anode Catalytic Dependency Behavior on Ionomer Content in Direct CO Polymer Electrolyte Membrane Fuel Cell

In this work,the effect of Nafion ionomer content on the structure and catalytic performance of direct CO polymer electrolyte membrane fuel cell(CO-PEMFC)by using Rh-N-C single-atom catalyst as the anode catalyst layers was studied.The ionic plaque and roughness of the anode catalyst layers increase with the increase of Nafion ionomer content.Furthermore,the contact angle measurement results show that the hydrophilicity of the anode catalyst layers also increases with the increase of Nafion ionomer content.However,when the Nafion ionomer content is too low,the binding between microporous layers,catalyst layers and membrane cannot meet the requirement for either electric conductivity or mass transfer.While Nafion ionomer content increased above 30%,the content of water in anode is difficult to control.Therefore,it was found that AN 30(30%Nafion ionomer content of anode)is the best level to effectively extend the three-phase boundary and improve CO-PEMFCs performance.

Electrochemical Characteristics of LaNi_(4.5)Al_(0.5) Alloy Used as Anodic Catalyst in a Direct Borohydride Fuel Cell

Fuel cells using borohydride as the fuel have received much attention because of high energy density and theoretical working potential.In this work,LaNi4.5Al0.5 hydrogen storage alloy used as the anodic material has been investigated.It was found that the increasing operation temperature was helpful to the open-circuit potential,the discharge potential and the power density,but showed a negative effect on the utilization of the fuel due to the accelerated hydrogen evolution.The high KOH concentration was favorable for high-rate discharge capability.The adsorption and transformation of hydrogen on LaNi4.5Al0.5 alloy electrode has been observed,but its contribution to the discharge capability during a high-rate discharge was small.

SnNi nanoneedles assembled 3D radial nanostructure loaded with SnNiPt nanoparticles： Towards enhanced electrocatalysis performance for methanol oxidation

A desirable methanol oxidation electrocatalyst was fabricated by metal atom diffusion to form an alloy of an assembled three-dimensional （3D） radial nanostructure of SnNi nanoneedles loaded with SnNiPt nanoparticles （NPs）.Herein,metal atom diffusion occurred between the SnNi support and loaded Pt NPs to form a SnNiPt ternary alloy on the catalyst surface.The as-obtained catalyst combines the excellent catalytic performance of the alloy and advantages of the 3D nanostructure;the SnNiPt NPs,which fused on the surface of the SnNi nanoneedle support,can dramatically improve the availability of Pt during electrocatalysis,and thus elevate the catalytic activity.In addition,the efficient mass transfer of the 3D nanostructure reduced the onset potential.Furthermore,the catalyst achieved a favorable CO poisoning resistance and enhanced stability.After atomic interdiffusion,the catalytic activity drastically increased by 45%,and the other performances substantially improved.These results demonstrate the significant advantage and enormous potential of the atomic interdiffusion treatment in catalytic applications.