High-performance proton exchange membrane fuel cell with ultra-low loading Pt on vertically aligned carbon nanotubes as integrated catalyst layer

Reducing a Pt loading with improved power output and durability is essential to promote the large-scale application of proton exchange membrane fuel cells(PEMFCs).To achieve this goal,constructing optimized structure of catalyst layers with efficient mass transportation channels plays a vital role.Herein,PEMFCs with order-structured cathodic electrodes were fabricated by depositing Pt nanoparticles by Ebeam onto vertically aligned carbon nanotubes(VACNTs)growth on Al foil via plasma-enhanced chemical vapor deposition.Results demonstrate that the proportion of hydrophilic Pt-deposited region along VACNTs and residual hydrophobic region of VANCTs without Pt strongly influences the cell performance,in particular at high current densities.When Pt nanoparticles deposit on the top depth of around 600 nm on VACNTs with a length of 4.6μm,the cell shows the highest performance,compared with others with various lengths of VACNTs.It delivers a maximum power output of 1.61 W cm^(-2)(H_(2)/O_(2),150 k Pa)and 0.79 W cm^(-2)(H_(2)/Air,150 k Pa)at Pt loading of 50μg cm^(-2),exceeding most of previously reported PEMFCs with Pt loading of<100μg cm^(-2).Even though the Pt loading is down to 30μg cm^(-2)(1.36 W cm^(-2)),the performance is also better than 100μg cm^(-2)(1.24 W cm^(-2))of commercial Pt/C,and presents better stability.This excellent performance is critical attributed to the ordered hydrophobic region providing sufficient mass passages to facilitate the fast water drainage at high current densities.This work gives a new understanding for oxygen reduction reaction occurred in VACNTs-based ordered electrodes,demonstrating the most possibility to achieve a substantial reduction in Pt loading<100μg cm^(-2) without sacrificing in performance.

In situ grown nanoscale platinum on carbon powder as catalyst layer in proton exchange membrane fuel cells(PEMFCs)

An extensive study has been conducted on the proton exchange membrane fuel cells （PEMFCs） with reducing Pt loading. This is commonly achieved by developing methods to increase the utilization of the platinum in the catalyst layer of the electrodes. In this paper, a novel process of the catalyst layers was introduced and investigated. A mixture of carbon powder and Nafion solution was sprayed on the glassy carbon electrode （GCE） to form a thin carbon layer. Then Pt particles were deposited on the surface by reducing hexachloroplatinic （IV） acid hexahydrate with methanoic acid. SEM images showed a continuous Pt gradient profile among the thickness direction of the catalytic layer by the novel method. The Pt nanowires grown are in the size of 3 nm （diameter） x l0 nm （length） by high solution TEM image. The novel catalyst layer was characterized by cyclic voltammetry （CV） and scanning electron microscope （SEM） as compared with commercial Pt/C black and Pt catalyst layer obtained from sputtering. The results showed that the platinum nanoparticles deposited on the carbon powder were highly utilized as they directly faced the gas diffusion layer and offered easy access to reactants （oxygen or hydrogen）.

Patterned catalyst layer boosts the performance of proton exchange membrane fuel cells by optimizing water management

Mass transport is crucial to the performance of proton exchange membrane fuel cells,especially at high current densities.Generally,the oxygen and the generated water share same transmission medium but move towards opposite direction,which leads to serious mass transfer problems.Herein,a series of patterned catalyst layer were prepared with a simple one-step impressing method using nylon sieves as templates.With grooves 100μm in width and 8μm in depth on the surface of cathode catalyst layer,the maximum power density of fuel cell increases by 10%without any additional durability loss while maintaining a similar electrochemical surface area.The concentration contours calculated by finite element analysis reveal that the grooves built on the surface of catalyst layer serve to accumulate the water nearby while oxygen tends to transfer through relatively convex region,which results from capillary pressure difference caused by the pore structure difference between the two regions.The separation of oxidant gas and generated water avoids mass confliction thus boosts mass transport efficiency.

Fast design of catalyst layer with optimal electrical-thermal-water performance for proton exchange membrane fuel cells

The catalyst layer(CL)is the core component in determining the electrical-thermal-water performance and cost of proton exchange membrane fuel cell(PEMFC).Systemic analysis and rapid prediction tools are required to improve the design efficiency of CL.In this study,a 3D multi-phase model integrated with the multi-level agglomerate model for CL is developed to describe the heat and mass transfer processes inside PEMFC.Moreover,a research framework combining the response surface method(RSM)and artificial neural network(ANN)model is proposed to conduct a quantitative analysis,and further a rapid and accurate prediction.With the help of this research framework,the effects of CL composition on the electrical-thermal-water performance of PEMFC are investigated.The results show that the mass of platinum,the mass of carbon,and the volume fraction of dry ionomer has a significant impact on the electrical-thermal-water performance.At the selected points,the sensitivity of the decision variables is ranked:volume fraction of dry ionomer>mass of platinum>mass of carbon>agglomerate radius.In particular,the sensitivity of the volume fraction of dry ionomer is over 50%at these points.Besides,the comparison results show that the ANN model could implement a more rapid and accurate prediction than the RSM model based on the same sample set.This in-depth study is beneficial to provide feasible guidance for high-performance CL design.

Revealing the concentration of hydrogen peroxide in fuel cell catalyst layers by an in‐operando approach

To evaluate the H_(2)O_(2)‐tolerance of non‐Pt oxygen reduction reaction(ORR)catalysts as well as in‐vestigate the H_(2)O_(2)‐induced decay mechanism,the selection of an appropriate H_(2)O_(2) concentration is a prerequisite.However,the concentration criterion is still unclear because of the lack of in‐operando methods to determine the actual concentration of H_(2)O_(2) in fuel cell catalyst layers.In this work,an electrochemical probe method was successfully established to in‐operando monitor the H_(2)O_(2) in non‐Pt catalyst layers for the first time.The local concentration of H_(2)O_(2) was revealed to reach 17 mmol/L,which is one order of magnitude higher than that under aqueous electrodes test conditions.Powered by the new knowledge,a concentration criterion of at least 17 mmol/L is suggested.This work fills in the large gap between aqueous electrode tests and the real fuel cell working conditions,and highlights the importance of in‐operando monitoring methods.

Development and Challenges of Electrode Ionomers Used in the Catalyst Layer of Proton-Exchange Membrane Fuel Cells:A Review

The electrode ionomer plays a crucial role in the catalyst layer(CL) of a proton-exchange membrane fuel cell(PEMFC) and is closely associated with the proton conduction and gas transport properties,structural stability,and water management capability.In this review,we discuss the CL structural characteristics and highlight the latest advancements in ionomer material research.Additionally,we comprehensively introduce the design concepts and exceptional performances of porous electrode ionomers,elaborate on their structural properties and functions within the fuel cell CL,and investigate their effect on the CL microstructure and performance.Finally,we present a prospective evaluation of the developments in the electrode ionomer for fabricating CL,offering valuable insights for designing and synthesizing more efficient electrode ionomer materials.By addressing these facets,this review contributes to a comprehensive understanding of the role and potential of electrode ionomers for enhancing PEMFC performance.

Progress on Platinum-Based Catalyst Layer Materials for H_(2)-PEMFC

The constant increase in energy demand and related environmental issues have made fuel cells an attractive technology as an alternative to conventional energy technologies.Like any technology,fuel cells face drawbacks that scientific society has been focused on to improve and optimize the overall technology.Thus,the cost is the main inhibitor for this technology due to the significantly high cost of the materials used in catalyst layers.The current discussion mainly focuses on the fundamental electrochemical half-cell reaction of hydrogen oxidation reaction(HOR)and oxygen reduction reaction(ORR)that are taking place in the catalyst layers consisting of Platinum-based and Platinum-non noble metals.For this purpose,studies from the literature are presented and analyzed by highlighting and comparing the variations on the catalytic activity within the experimental catalyst layers and the conventional ones.Furthermore,an economic analysis of the main platinum group metals(PGMs)such as Platinum,Palladium and Ruthenium is introduced by presenting the economic trends for the last decade.

Catalytic hydrogenolysis of organosolv lignin: Cleaving C–O bonds over CuMgAlO_(x)-layered porous metal oxide catalysts for oriented monophenols production

To understand the catalytic conversion of lignin into high-value products,lignin depolymerization was performed using a layered polymetallic oxide(CuMgAlO_(x))catalyst.The effects of the conversion temperature,hydrogen pressure,and reaction time were studied,and the ability of CuMgAlO_(x)to break the C–O bond was evaluated.The CuMgAlO_(x)(Mg/Al=3:1)catalyst contained acidic sites and had a relatively homogeneous elemental distribution with a high pore size and specific surface area.Theβ-O-4 was almost completely converted by disassociating the C–O bond,resulting in yields of 14.74%ethylbenzene,47.58%α-methylphenyl ethanol,and 36.43%phenol.The highest yield of lignin-derived monophenols was 85.16%under reaction conditions of 280℃ and 3 Mpa for 4 h.As the reaction progressed,depolymerization and condensation reactions occurred simultaneously.Higher temperatures(>280℃)and pressures(>3 Mpa)tended to produce solid char.This study establishes guidelines for the high-value application of industrial lignin in the catalytic conversion of polymetallic oxides.

Optimizing the nickel boride layer thickness in a spectroelectrochemical ATR-FTIR thin-film flow cell applied in glycerol oxidation

The influence of the drop-casted nickel boride catalyst loading on glassy carbon electrodes was investigated in a spectroelectrochemical ATR-FTIR thin-film flow cell applied in alkaline glycerol electrooxidation.The continuously operated radial flow cell consisted of a borehole electrode positioned 50μm above an internal reflection element enabling operando FTIR spectroscopy.It is identified as a suitable tool for facile and reproducible screening of electrocatalysts under well-defined conditions,additionally providing access to the selectivities in complex reaction networks such as glycerol oxidation.The fast product identification by ATR-IR spectroscopy was validated by the more time-consuming quantitative HPLC analysis of the pumped electrolyte.High degrees of glycerol conversion were achieved under the applied laminar flow conditions using 0.1 M glycerol and 1 M KOH in water and a flow rate of 5μL min^(–1).Conversion and selectivity were found to depend on the catalyst loading,which determined the catalyst layer thickness and roughness.The highest loading of 210μg cm^(–2)resulted in 73%conversion and a higher formate selectivity of almost 80%,which is ascribed to longer residence times in rougher films favoring readsorption and C–C bond scission.The lowest loading of 13μg cm^(–2)was sufficient to reach 63%conversion,a lower formate selectivity of 60%,and,correspondingly,higher selectivities of C_(2)species such as glycolate amounting to 8%.Thus,only low catalyst loadings resulting in very thin films in the fewμm thickness range are suitable for reliable catalyst screening.

Modeling development on the meso-scale reacting transport phenomena in proton exchange membrane fuel cells

The catalyst layer （CL） of proton exchange mem-brane fuel cell （PEMFC） involves various particles and pores in meso-scale, which has an important effect on the mass, charge （proton and electron） and heat transport coupled with the electrochemical reactions. The coarse-grained molecular dynamics （CG-MD） method is employed as a meso-scale structure reconstruction technique to mimic the self-organization phenomena in the fabrication steps of a CL. The meso-scale structure obtained at the equilibrium state is further analyzed by molecular dynamic （MD） software to provide the necessary microscopic parameters for understanding of multi-scale and-physics processes in CLs. The primary pore size distribution （PSD） and active platinum （Pt） surface areas are also calculated and then compared with the experiments. In addition, we also highlight the implementation method to combine microscopic elementary kinetic reaction schemes with the CG-MD approaches to provide insight into the reactions in CLs. The concepts from CG modeling with particle hydrodynamics （SPH） and the problems on coupling of SPH with finite element modeling （FEM） methods are further outlined and discussed to understand the effects of the meso-scale transport phenomena in fuel cells.

Ionic liquids in electrocatalysis

The performance of an electrocatalyst, which is needed e.g. for key energy conversion reactions such as hydrogen evolution, oxygen reduction or CO2 reduction, is determined not only by the inherent structure of active sites but also by the properties of the interfacial structures at catalytic surfaces. Ionic liquids（ILs）, as a unique class of metal salts with melting point below 100 ℃, present themselves as ideal modulators for manipulations of the interfacial structures. Due to their excellent properties such as good chemical stability, high ionic conductivity, wide electrochemical windows and tunable solvent properties the performance of electrocatalysts can be substantially improved through ILs. In the current minireview, we highlight the critical role of the IL phase at the microenvironments created by the IL, the liquid electrolyte, catalytic nanoparticles and/or support materials, by detailing the promotional effect of IL in electrocatalysis as reaction media, binders, and surface modifiers. Updated exemplary applications of IL in electrocatalysis are given and moreover, the latest developments of IL modified electrocatalysts following the ＂Solid Catalyst with Ionic Liquid Layer（SCILL）＂ concept are presented.

Feasibility Assessment of Fast Numerical Simulations for Real-Time Monitoring and Control of PEM Fuel Cells

Computational models that ensure accurate and fast responses to the variations in operating conditions,such as the cell tem-perature and relative humidity(RH),are essential monitoring tools for the real-time control of proton exchange membrane(PEM)fuel cells.To this end,fast cell-area-averaged numerical simulations are developed and verifi ed against the present experiments under various RH levels.The present simulations and measurements are found to agree well based on the cell voltage(polarization curve)and power density under variable RH conditions(RH=40%,RH=70%,and RH=100%),which verifi es the model accuracy in predicting PEM fuel cell performance.In addition,computationally feasible reduced-order models are found to deliver a fast output dataset to evaluate the charge/heat/mass transfer phenomena as well as water production and two-phase fl ow transport.Such fast and accurate evaluations of the overall fuel cell operation can be used to inform the real-time control systems that allow for the improved optimization of PEM fuel cell performance.

Structure,Property,and Performance of Catalyst Layers in Proton Exchange Membrane Fuel Cells

Catalyst layer(CL)is the core component of proton exchange membrane(PEM)fuel cells,which determines the performance,durability,and cost.However,difficulties remain for a thorough understanding of the CLs’inhomogeneous structure,and its impact on the physicochemical and electrochemical properties,operating performance,and durability.The inhomogeneous structure of the CLs is formed during the manufacturing process,which is sensitive to the associated materials,composi-tion,fabrication methods,procedures,and conditions.The state-of-the-art visualization and characterization techniques are crucial to examine the CL structure.The structure-dependent physicochemical and electrochemical properties are then thoroughly scrutinized in terms of fundamental concepts,theories,and recent progress in advanced experimental techniques.The relation between the CL structure and the associated effective properties is also examined based on experimental and theoretical findings.Recent studies indicated that the CL inhomogeneous structure also strongly affects the performance and degradation of the whole fuel cell,and thus,the interconnection between the fuel cell performance,failure modes,and CL structure is comprehensively reviewed.An analytical model is established to understand the effect of the CL structure on the effective properties,performance,and durability of the PEM fuel cells.Finally,the challenges and prospects of the CL structure-associated studies are highlighted for the development of high-performing PEM fuel cells.

The Controllable Design of Catalyst Inks to Enhance PEMFC Performance:A Review

Typical catalyst inks in proton exchange membrane fuel cells(PEMFCs)are composed of a catalyst,its support,an ionomer and a solvent and are used with solution processing approaches to manufacture conventional catalyst layers(CLs).Because of this,catalyst ink formulation and deposition processes are closely related to CL structure and performance.However,catalyst inks with ideal rheology and optimized electrochemical performances remain lacking in the large-scale application of PEMFCs.To address this,this review will summarize current progress in the formulation,characterization,modeling and deposition of catalyst inks.In addition,this review will highlight recent advancements in catalyst ink materials and discuss corresponding complex interactions.This review will also present various catalyst ink dispersion methods with insights into their stability and introduce the application of small-angle scattering and cryogenic transmission electron microscopy(cryo-TEM)technologies in the characterization of catalyst ink microstructures.Finally,recent studies in the kinetic modeling and deposition of catalyst inks will be analyzed.

Modeling nanostructured catalyst layer in PEMFC and catalyst utilization

A lattice model of the nanoscaled catalyst layer structure in proton exchange membrane fuel cells(PEMFC)was established by Monte Carlo method.The model takes into account all the four components in a typical PEMFC catalyst layer:platinum(Pt),carbon,ionomer and pore.The elemental voxels in the lattice were setfine enough so that each average sized Pt particulate in Pt/C catalyst can be represented.Catalyst utilization in the modeled catalyst layer was calculated by counting up the number of facets of Pt voxels where“three phase contact”are met.The effects of some factors,including porosity,ionomer content,Pt/C particle size and Pt weight percentage in the Pt/C catalyst,on catalyst utilization were investigated and discussed.

Nano-Morphology of a Polymer Electrolyte Fuel Cell Catalyst Layer Imaging, Reconstruction and Analysis

The oxygen reduction reaction （ORR） in the cathode catalyst layer （CCL） of polymer electrolyte fuel cells （PEFC） is one of the major causes of performance loss during operation. In addition, the CCL is the most expensive component due to the use of a Pt catalyst. Apart from the ORR itself, the species transport to and from the reactive sites determines the performance of the PEFC. The effective transport properties of the species in the CCL depend on its nanostructure. Therefore a three-dimensional reconstruction of the CCL is required. A series of two-dimensional images was obtained from focused ion beam- scanning electron microscope （FIB-SEM） imaging and a segmentation method for the two-dimensional images has been developed. The pore size distribution （PSD） was calculated for the three-dimensional geometry. The influence of the alignment and the anisotropic pixel size on the PSD has been investigated. Pores were found in the range between 5 nm and 205 nm. Evaluation of the Knudsen number showed that gas transport in the CCL is governed by the transition flow regime. The liquid water transport can be described within continuum hydrodynamics by including suitable slip flow boundary conditions.

Functional ceramic support as an independent catalyst layer for direct liquid fuel solid oxide fuel cells

A porous ceramic support is designed as a multi-functional independent catalyst layer for solid oxide fuel cells(SOFCs)running on liquid hydrocarbon fuel.The layer consists of a highly porous Ce_(0.9)Ca_(0.1)O_(2−δ)ceramic backbone and active NiMo catalysts,which could be integrated into the conventional Ni metal containing the anode for internal reforming of the hydrocarbon fuel.Compared to conventional catalyst layers sintered on the anodes,this independent catalyst layer could be simply assembled on top of the anode without additional sintering,thereby avoiding the mismatch of the thermal expansion coefficient between the catalyst layer and the anode and improving stability of a single cell.Moreover,a current collector layer could be inserted between the catalyst and the anode to enhance current collection efficiency and electrochemical performance of the single cell.At 750℃,the independent catalyst layer displays high activity towards the catalytic decomposition of methanol,and the single cell could achieve the maximum power density of 400–500 mW·cm^(−2)in dry methanol.Furthermore,by employing the independent catalyst layer,the single cell offers additional in-situ catalyst regeneration capability under the methanol operation mode.Feeding 10 mL·min−1 air into an anode channel for 5 min is found to be effective to burn out carbon species in the catalyst layer,which reduces the degradation rate of the cell voltage by orders of magnitude from 2.6 to 0.024 mV·h−1 during the operation of 360 h in dry methanol.The results demonstrate the significance of the independent catalyst layer design for direct internal reforming methanol fuel cells.

The effect of catalyst layer design on catalyst utilization in PEMFC studied via stochastic reconstruction method

Catalyst utilization is an important determinant of proton exchange membrane fuel cell performance,and increasing the catalyst utilization is one of the most critical approaches to reducing the catalyst loading in PEMFC.4-phase stochastic reconstruction method based on the variable-resolution Quartet Structure Generation Set(QSGS)algorithm is utilized to elucidate the influence of different parameters of electrode preparation,including the porosity,the dispersion degree of carbon agglomerate,ionomer content,and carbon support size,on the catalyst utilization in the catalyst layer.It was found that there exist optimal values for the porosity,dispersion degree of carbon agglomerate,ionomer content,and carbon support sizes in CLs and any deviations from these optimal values would lead to transport issues of electron,proton and mass within CLs.Taking electron,proton and mass transport into consideration simultaneously,the optimal Pt utilization is 46.55%among 48 cases in this investigation,taken at the carbon support diameter of 40 nm,the porosity of 0.4,the agglomerate spatial density of 25μm^(−3) and I/C at 0.7.The selection of porosity,ultrasonic dispersion technique and ionomer content for conventional electrode preparation requires compromises on mass,electron and proton transport,leading to catalyst utilization in CLs hardly exceeding 50%.Therefore,the next generation of catalyst layer design and preparation technology is desired.

Improved performance of direct methanol fuel cells with the porous catalyst layer using highly-active nanofiber catalyst

PtRu supported on TiO2-embedded carbon nanofibers(PtRu/TECNF),which was recently reported as a highly-active catalyst for methanol oxidation,was applied to a direct methanol fuel cell(DMFC),and the power generation performance was compared to that using the commercial PtRu/C.Before the comparison,the effect of the catalyst loading on the power density of the DMFC was investigated using PtRu(18 wt%)/TECNF.The DMFC power density showed a maximum at about a 1.5 mg cm
2 PtRu loading that corresponds to about an 80 mm layer thickness.A catalyst layer thicker than this value reduced the power density probably due to the concentration overvoltage.The PtRu content in the PtRu/TECNF was then increased to 30 wt%or more to reduce the layer thickness and to increase the power density.The DMFC performance was compared to that of different anode catalysts at a 1 mg cm
2 PtRu loading.The power density was maximized using the PtRu30 wt%/TECNF,which showed a 173 mW cm
2 at 353 K and had 66 mm layer thick,that was 26%higher than that of commercial PtRu/C.The current–voltage curve of the DMFC with the PtRu/TECNF suggested an improved mass transport overvoltage,but a little improvement in the activation one despite using the catalyst with about a 2 times higher activity compared to that of the commercial PtRu/C.This was attributed to the lower Pt utilization of the nanofiber catalyst layer.

Monte Carlo simulation of the PEMFC catalyst layer

The performance of the polymer electrolyte membrane fuel cell(PEMFC)is greatly controlled by the structure of the catalyst layer.Low catalyst utilization is still a significant obstacle to the commercialization of the PEMFC.In order to get a fundamental understanding of the electrode structure and to find the limiting factor in the low catalyst utilization,it is necessary to develop the mechanical model on the effect of catalyst layer structure on the catalyst utilization and the performance of the PEMFC.In this work,the structure of the catalyst layer is studied based on the lattice model with the Monte Carlo simulation.The model can predict the effects of some catalyst layer components,such as Pt/C catalyst,electrolyte and gas pores,on the utiliza-tion of the catalyst and the cell performance.The simulation result shows that the aggregation of conduction grains can greatly affect the degree of catalyst utilization.The better the dispersion of the conduction grains,the larger the total effective area of the catalyst is.To achieve higher utilization,catalyst layer components must be distributed by means of engineered design,which can prevent aggregation.