Cathode Flow Research Articles

Determining the Influence of Catalyst Layer Architecture and Reactant Flow in an MEA for the Electrochemical Nitrogen Reduction Reaction Under Ambient Conditions

Ammonia (NH3) has been increasingly recognized as an advantageous energy/hydrogen carrier beyond agriculture use to assist in the achievement of net-zero and decarbonization goals. For over a century, NH3 production has been dominated by the thermochemical Haber-Bosch process which consumes significant fossil fuel-related energy and feedstocks with a heavy carbon footprint. By contrast, the electrochemical nitrogen reduction reaction (ENRR) presents a sustainable and modular approach to fit remote and small-scale NH3 needs, which has attracted growing interest in recent years. Rational design of electrocatalysts (e.g., introducing defects, size reduction, and heteroatom doping) has been the mainstream approach to address the bottlenecks in the ENRR, especially the low specific activity and poor faradaic efficiency. However, attempts to vary the ENRR electrolytic cell layout/design or the operating conditions have been scarce, and therefore present an opportunity to improve the NH3 electrosynthesis performance by well-thought-out reactor designs coupled with operating conditions.Our study aims to understand the influence of catalyst layer/electrode architectures and reactant mass transfer on the ENRR performance of model catalysts in a membrane electrode assembly (MEA) cell under different flow configurations. On the anode side, a platinum-coated membrane is used to oxidize the humidified H2, which provides sufficient protons for the cathode reactions. On the cathode side, electrocatalysts with commercial availability and reported ENRR activities are applied as the catalyst (e.g., noble metal, transition metal nitrides or dichalcogenides). The catalyst layer is deposited on the gas-diffusion layer and/or the proton-exchange membrane to construct a gas-diffusion electrode (GDE) and/or a catalyst-coated membrane (CCM). Subsequently, the NH3 electrosynthesis performances are evaluated under different cathode flow conditions for the varied catalyst layer architectures. Initially, the N2-saturated aqueous electrolyte (Na2SO4) is recirculated on the cathode side to flood the cathode surface constantly, which resembles the operating condition in the liquid-filled H-cell present in previous ENRR studies. In these cases, the catalytic sites are predominantly covered by proton donors (e.g., hydronium ions or water molecules) without accessing N2 molecules that only dissolve marginally (0.06 mmol/L) in aqueous media. Hence, in contrast with the “liquid-only” flow configuration, humidified N2 gas is supplied alone (“gas-only”) or in combination with the recirculated electrolyte solution (“gas-liquid”) to increase the presence of N2 near catalytic sites. When gaseous N2 is present, the gas outlet pressure (cell back pressure), as well as membrane drying, were observed to affect the current density and operational stability. Additionally, false positives are diligently recognized which arise from residual N-containing species in the MEA and environmental NH3 contamination. Linear scan voltammetry, the routine electrochemical characterization to distinguish potentially ENRR-active electrocatalysts, was found to be particularly susceptible and contribute significantly to erroneous ENRR performance. In short, This work demonstrates the challenge of getting authentic ammonia production in aqueous systems with improved electrolytic cell designs and operating conditions.

Enhancement effects of the side blockage arrangement in the flow channel on the performance of a proton exchange membrane fuel cell

Flow field configuration critically affects the heat and mass transfer process in a proton exchange membrane fuel cell (PEMFC), which is a key factor to ensure efficient and stable operation of fuel cells. Side blockages arranged in the cathode flow channel is proposed for performance improving of PEMFC. Conventional straight, side blockage alternating with straight, side blockage flow channels are studied to analyze the effects of side blockages arrangement on the distribution of velocity, temperature, reactant concentration and water content and the performance of PEMFC. Results show that the O2 mole concentration in the flow field could be increased by the presence of side blockages, thus the convective mass transfer coefficient and performance are both improved. At current density of 2.0 A cm−2, the performance of PEMFC increases by 9.5%. In comparison to the straight flow channel, flow channels installing side blockage present about 1.5 K lower of the maximum temperature, more uniform temperature distribution and increased Nusselt number, indicating the enhancement of heat transfer. Based on field synergy theory, it’s found that the average angles describing the synergetic effect of heat transfer and mass transfer decrease with the installation of side blockages. This reveals the enhancement of the synergetic degree in heat and mass transfer processes under the turbulence of side blockages, which coincides with the improved performance of PEMFC.

Databionic Swarm Intelligence to Screen Wastewater Recycling Quality with Factorial and Hyper-Parameter Non-Linear Orthogonal Mini-Datasets

Electrodialysis (ED) may be designed to enhance wastewater recycling efficiency for crop irrigation in areas where water distribution is otherwise inaccessible. ED process controls are difficult to manage because the ED cells need to be custom-built to meet local requirements, and the wastewater influx often has heterogeneous ionic properties. Besides the underlying complex chemical phenomena, recycling screening is a challenge to engineering because the number of experimental trials must be maintained low in order to be timely and cost-effective. A new data-centric approach is presented that screens three water quality indices against four ED-process-controlling factors for a wastewater recycling application in agricultural development. The implemented unsupervised solver must: (1) be fine-tuned for optimal deployment and (2) screen the ED trials for effect potency. The databionic swarm intelligence classifier is employed to cluster the L9(34) OA mini-dataset of: (1) the removed Na+ content, (2) the sodium adsorption ratio (SAR) and (3) the soluble Na+ percentage. From an information viewpoint, the proviso for the factor profiler is that it should be apt to detect strength and curvature effects against not-computable uncertainty. The strength hierarchy was analyzed for the four ED-process-controlling factors: (1) the dilute flow, (2) the cathode flow, (3) the anode flow and (4) the voltage rate. The new approach matches two sequences for similarities, according to: (1) the classified cluster identification string and (2) the pre-defined OA factorial setting string. Internal cluster validity is checked by the Dunn and Davies–Bouldin Indices, after completing a hyper-parameter L8(4122) OA screening. The three selected hyper-parameters (distance measure, structure type and position type) created negligible variability. The dilute flow was found to regulate the overall ED-based separation performance. The results agree with other recent statistical/algorithmic studies through external validation. In conclusion, statistical/algorithmic freeware (R-packages) may be effective in resolving quality multi-indexed screening tasks of intricate non-linear mini-OA-datasets.

Characteristics of proton exchange membrane fuel cell considering “dot matrix” gas distribution zones and waveform staggered flow field with cooling channels

Conventional three-dimensional (3D) computational fluid dynamics (CFD) simulations of proton exchange membrane fuel cell (PEMFC) are limited to the single-channel scale, while the influence of gas distribution zone and complex flow structure with multiple channels is ignored and the role of cooling flow field is not considered. Therefore, a metal bipolar plate structure with “dot matrix” gas distribution zones and a waveform staggered flow field with small cathode size flow channels is proposed. The cooling flow fields are set up to analyze the effect on the output performance of the PEMFC. Firstly, the analysis of the gas and liquid distribution within the flow field reveals a maximum error of 10.36% for the cathode gas concentration, which is much larger than the anode (4.51%). The large pressure drop at the cathode leads to a small value for the liquid saturation. Secondly, the output parameters of the PEMFC are compared at different operating pressures, which results in a high operating pressure that clearly contributes to the improved performance of the fuel cell. Furthermore, when the reaction gas is counter-flow, the electrochemical reaction rate is faster and the water hydration level of the proton exchange membrane (PEM) is higher. The cooling flow field is most effective when it flows in the same direction as the oxygen flow. Finally, the effects of different thermal boundary conditions on the distribution of oxygen within the cathode flow field are compared and the results show that high local temperatures are also a major factor in the uneven distribution of oxygen concentration in the flow field.

A Feasibility Study of Placing a Heated Turbulence Grid in Front of an Air-Cooled Fuel Cell Stack in Freezing Conditions

This paper aims to better understand the temperature profile of a turbulence inducing grid if pre-heating of the incoming air in the cathode channel is required when the stack is operating under freezing conditions. The goal of this study is to design the grid by changing its thickness and the number of pores. A three-dimensional, steady-state computational fluid dynamic model was developed and validated for a baseline case of a single cathode channel of an air-cooled cell. The computational domain consists of the cathode flow channel, a gas diffusion layer, and the turbulence inducing grid. Four different grid designs were analyzed and compared, and in the best case heating of the turbulence grid was achieved where the temperature of the grid will be 236 °C and the power consumption will be around 30 % of the total power produced by the fuel cell stack. It is concluded that 2 mm thickness is not sufficient, leading to too high temperatures, and a multitude of staggered grids might be required.

Performance improvement of air-breathing proton exchange membrane fuel cell (PEMFC) with a condensing-tower-like curved flow field

Air-breathing proton exchange membrane fuel cells (PEMFCs) are very promising portable energy with many advantages. However, its power density is low and many additional supporting parts affect its specific power. In this paper, we aim to improve the air diffusion and fuel cell performance by employing a novel condensing-tower-like curved flow field rather than an additional fan, making the fuel cell more compact and has less internal power consumption. Polarization curve test and galvanostatic discharge test are carried out and proved that curved flow field can strengthen the air diffusion into the PEMFC and improve its performance. With appropriate curved flow field, the fuel cell peak power can be 55.2% higher than that of planar flow field in our study. A four-layer stack with curved cathode flow field is fabricated and has a peak power of 2.35 W (120 W/kg).

Scaled up on direct methanol fuel cell under different operating conditions

A direct methanol fuel cell with an active area of 100 cm2 was tested experimentally under a variety of operating situations to determine its overall performance. Different operational parameters, such as anode flow rate (1–5 ml/min), cathode reactant (Air/Oxygen) and cathode flow rate (100–2000 ml/min) are the most influencing parameter, and the performance output of each parameter are compared. In addition, different cathode flow channels, such as serpentine and sinuous, are used to improve reactant supply, and their performance is compared with one another. Using sinuous flow field at the cathode and 3 ml/min of methanol and 500 ml/min of oxygen, the maximum power density of 24 mW/cm2 has been achieved.

Wastewater Quality Screening Using Affinity Propagation Clustering and Entropic Methods for Small Saturated Nonlinear Orthogonal Datasets

Wastewater recycling efficiency improvement is vital to arid regions, where crop irrigation is imperative. Analyzing small, unreplicated–saturated, multiresponse, multifactorial datasets from novel wastewater electrodialysis (ED) applications requires specialized screening/optimization techniques. A new approach is proposed to glean information from structured Taguchi-type sampling schemes (nonlinear fractional factorial designs) in the case that direct uncertainty quantification is not computable. It uses a double information analysis–affinity propagation clustering and entropy to simultaneously discern strong effects and curvature type while profiling multiple water-quality characteristics. Three water quality indices, which are calculated from real ED process experiments, are analyzed by examining the hierarchical behavior of four controlling factors: (1) the dilute flow, (2) the cathode flow, (3) the anode flow, and (4) the voltage rate. The three water quality indices are: the removed sodium content, the sodium adsorption ratio, and the soluble sodium percentage. The factor that influences the overall wastewater separation ED performance is the dilute flow, according to both analyses’ versions. It caused the maximum contrast difference in the heatmap visualization, and it minimized the relative information entropy at the two operating end points. The results are confirmed with a second published independent dataset. Furthermore, the final outcome is scrutinized and found to agree with other published classification and nonparametric screening solutions. A combination of modern classification and simple entropic methods which are offered through freeware R-packages might be effective for testing high-complexity ‘small-and-dense’ nonlinear OA datasets, highlighting an obfuscated experimental uncertainty.

PolyJet-Based 3D Printing against Micromolds to Produce Channel Structures for Microchip Electrophoresis.

In this work, we demonstrate the ability to use micromolds along with a stacked three-dimensional (3D) printing process on a commercially available PolyJet printer to fabricate microchip electrophoresis devices that have a T-intersection, with channel cross sections as small as 48 × 12 μm2 being possible. The fabrication process involves embedding removable materials or molds during the printing process, with various molds being possible (wires, brass molds, PDMS molds, or sacrificial materials). When the molds are delaminated/removed, recessed features complementary to the molds are left in the 3D prints. A thermal lab press is used to bond the microchannel layer that also contains printed reservoirs against another solid 3D-printed part to completely seal the microchannels. The devices exhibited cathodic electroosmotic flow (EOF), and mixtures of fluorescein isothiocyanate isomer I (FITC)-labeled amino acids were successfully separated on these 3D-printed devices using both gated and pinched electrokinetic injections. While this application is focused on microchip electrophoresis, the ability to 3D-print against molds that can subsequently be removed is a general methodology to decrease the channel size for other applications as well as to possibly integrate 3D printing with other production processes.

Effects of anode flow channel on performance of air-cooled proton exchange membrane fuel cell

The cathode channel of an air-cooled proton exchange membrane fuel cell (PEMFC) adopts a straight flow channel for air supply and heat dissipation. Considering the present cathode flow channel, the type of the anode flow channel has an impact on the water and heat management of air-cooled PEMFCs. In this study, we established three-dimensional (3D) multi-physics field models to investigate the performance of three types of anode flow channels: straight flow channel, improved straight flow channel, and serpentine flow channel. Among the three flow channel types under the same voltage condition, the straight flow channel exhibited the best temperature control ability, smallest cathode stoichiometric ratio at the peak power density output, and highest power density. Moreover, the temperature distribution of membrane electrode assembly in the straight flow channel was the most uniform. The coupling of the high cathode air speed and electro-osmotic drag (EOD) easily caused the water loss of anode and cathode membrane electrodes and had an adverse effect on the performance of the fuel cell. The straight flow channel demonstrated the optimal performance with the highest water content.

Quantitative investigation of oxygen transport in proton exchange membrane fuel cell: Considering cross-flow

Oxygen transport is a key factor limiting fuel cell performance. To quantitatively analyze the dominant mechanism of oxygen transport. In particular, the cross-flow under the rib (x-direction), as well as the effect of cathode flow field and spatially variable properties of gas diffusion layer (GDL). A three-dimensional (3D), multiphase and non-isothermal model which considers Forchheimer's effect is described. And the oxygen flux under different mechanisms and directions is numerically researched. The results demonstrate that in membrane electrode assembly (MEA), under high current density, the main direction of oxygen transport is y-direction (through-plane). However, x-direction also accounts for a large proportion, especially in GDL and under low current density. Diffusion is the dominant mechanism in MEA, at 0.6 V output voltage, it accounts for more than 50% in GDL and 80% in microporous layer (MPL) and catalyst layer (CL). The 3D and serpentine flow field could enhance the oxygen convection in y-direction and x-direction, respectively, and then improve the performance. The spatially variable properties of GDL also change the oxygen flux distribution. Oxygen diffusive mass flux gradually decreases from gas channel side to MPL side rather than gradually increase. In addition, the age of reactant gas is introduced to quantitatively study the oxygen and hydrogen response speed. The results show that, in general, the age of oxygen decreases as current density increases and the situation is just opposite for hydrogen. The change rate for these two is almost a constant about 3 ms/(A cm−2) and 10 ms/(A cm−2), respectively. The “age-flux” diagram is also proposed to evaluate the reactant gas transport quality. This research provides a new approach and evaluation method for optimizing fuel cell design from the perspectives of oxygen transport quantification and the age of reaction gas.

Transient temperature heterogeneous distribution analysis in three-dimensional passive µDMFC

In this paper, the transient temperature heterogeneous distribution analysis in three-dimensional passive micro Direct Methanol Fuel Cell (µDMFC) is presented in detail. The metal-based µDMFC with the effective area of 1.0 cm2 is fabricated to verify the correctness of the model. By coupling the mass transport, momentum transport, electron-proton conduction and heat transfer mechanisms, the models of the whole cell and a single flow channel are established, and the non-uniform temperature changes in different stages of the cell are analyzed. Simulation results manifest that the temperature of collector and channel is in heterogeneous distribution state during the process of the fuel cell from starting work to reaching a stable trend. Due to the different fluids in the cathode and anode flow channels, the inside of flow channels also presents different heating trends. In addition, the temperature-increasing rate of each part of the cell after starting work is also simulated. The results can be used as a reference for the inner heterogeneous transfer and startup phase optimization of fuel cells.

Improvement of thermal and water management of air-cooled polymer electrolyte membrane fuel cells by adding porous media into the cathode gas channel

In air-cooled polymer electrolyte membrane fuel cells (PEMFCs), the contradiction between cooling and water retention renders the improvement of cell performance really challenging. In the present study, cathode flow field is designed by inserting porous media into the gas channel to properly distribute flow rate between gas channel and cooling channel. A three dimensional two-phase non-isothermal model of PEMFCs is adopted to investigate the reactive transport processes in air-cooled PEMFCs. The results show that by inserting porous media into the outlet of the gas channel, the current density can be improved by 18.2% compared with the conventional parallel flow field. Then, effects of permeability of the porous media and the cathode outlet set-point temperature on the performance of PEMFC are examined, which both show a nonmonotonic influence on fuel cell performance. The reason can be attributed to the complex trade-off between cooling, water retention and reactant supply. Finally, effects of the altitude are explored, and it is found that the proposed novel design also shows advantage in alleviating the performance reduction due to the increase of altitude. The proposed design is proved to be a promising scheme to alleviate the contradiction between cooling and water retention in air-cooled PEMFCs.

Experimental study of key operating parameters effects on the characteristics of proton exchange membrane fuel cell with anode recirculation

Water management is essential to ensure high performance and stable operation of the proton exchange membrane fuel cell (PEMFC). However, little is known about water management in the hydrogen circulation anode (HCA) mode which can achieve high hydrogen utilization. In this work, the effects of hydrogen circulation rate, a key parameter of HCA mode, on water management and cell performance are experimentally investigated. In particular, transparent fuel cell and printed circuit board segmented fuel cell technologies are used to study the water distribution and the local current density distribution, respectively. Furthermore, the electrochemical properties and PEMFC stability at different hydrogen circulation rates are discussed in detail. The experimental results indicate that increasing the hydrogen circulation rate reduces liquid water in the cathode and anode flow channels, which can effectively alleviate the adverse effects of flooding on overall performance and cell stability. However, subsequent drying of the membrane and catalyst layer results in an increase in ohmic resistance and a decline in cell performance, especially at low current densities. The current density distribution shows that severe local flooding is likely to occur in the hydrogen and air outlet regions at a low hydrogen circulation rate. For a high hydrogen circulation rate, membrane drying will occur in some areas, especially near the hydrogen inlet. To achieve uniform current density distribution and high fuel cell performance, the hydrogen circulation rate should be increased with the load current.

Three-dimensional numerical study of a cathode gas diffusion layer with a through/in plane synergetic gradient porosity distribution for PEM fuel cells

This study proposes a through-plane (TP) and in-plane (IP) synergetic (SYN) gradient porosity distribution (GPD) in the cathode gas diffusion layer (CGDL) to enhance the mass transfer and water removal of a polymer electrolyte membrane (PEM) fuel cell. The novel SYN-GPD CGDL is comparatively evaluated with TP-GPD, IP-GPD and uniform porosity distribution (UPD) CGDL by implementing a three-dimensional multiphase fuel cell model. The results show that a higher porosity within CGDL near the cathode flow channel (CFC) for TP-GPD CGDL, however, a higher or lower porosity near the cathode outlet for IP-GPD CGDL improves the mass transfer and water removal within fuel cell, which benefitting the uniform distributions of oxygen and current density, and the cell performance. Additionally, as compared with the TP-GPD, IP-GPD and UPD CGDL, the SYN-GPD CGDL has a greater advantage in the enhancement of mass transfer and water removal, consequently resulting in much more homogeneous internal physical quantity profiles and a higher overall cell performance. Ultimately, the optimal SYN-GPD CGDL improves the maximum power density by 6.73%, while reducing the coefficient variations (CVs) of the oxygen mass fraction and current density by approximately 10.24% and 40.69%, respectively, compared with those of the UPD CGDL.

Performance study on a large-scale proton exchange membrane fuel cell with cooling

The output performance of PEMFC (proton exchange membrane fuel cell) is limited by the operating conditions of the fuel cell, including the control temperature, gas concentration distribution and working pressure. In order to simplify the calculation process, the existing literatures mostly use single channel to study the output indexes of batteries. Initially, based on 3D (three-dimensional) CFD (computational fluid dynamics) simulation, a method to optimize the gas distribution in the flow field by using the distribution area is proposed for a commercial large-scale PEMFC with an activation area of 107.44 cm2. The uniformity of gas concentration distribution in anode and cathode flow field is taken into consideration to test the influence of flow field. The relationship between liquid saturation and gas velocity in the flow field is also analyzed. Furthermore, the effects of anode and cathode gas flow direction on gas concentration in CL (catalytic layer) and water content in PEM (proton exchange membrane) is studied, and both methods have little effect on PEMFC. Additionally, the performance of PEMFC is obviously improved by increasing operating pressure, and the reactant gas molar concentration and membrane water content are increased significantly. Finally, study proves that it is more beneficial to the performance of PEMFC when cooling flow direction is consistent with oxygen.

Design, fabrication and testing of a direct methanol fuel cell stack

The present paper reports the results of an experimental work done on a direct methanol fuel cell (DMFC) stack. The two cell DMFC stack of active area 16 cm2 is designed, fabricated and tested. The studies are focused on determining the performance characteristics of two cell DMFC stack at various operating conditions and oxygen flow rates. In order to investigate the effect of various operating parameters on DMFC stack performance, experiments are performed at cell temperatures of 50 °C, 60 °C, 70 °C, 75 °C and 80 °C. The methanol concentration varied from 2 M to 5 M in steps of 1 M and cathode (oxygen) flow rate considered are 100 –300 cc/min in steps of 100 cc/min. The membrane electrode assembly (MEA) used is Nafion 117, by loading a Platinum-Ruthenium (Pt-Ru) catalyst at the anode and Pt-black catalyst at the cathode side. Results revealed that the performance of the DMFC was enhanced by increasing the cell temperature, cathode flow rate and methanol concentration. The present DMFC stack shows a peak power density of 0.1 W/cm2 with a cell voltage of 0.4 V and a current density of 0.25 A/cm2 at methanol concentration of 4 M, temperature of 75 °C and oxygen flow rate of 200 cc/min. Comparison study between the stack and single cell of the same stack with 4 M methanol solution under the operating conditions of 200 cc/min and 70 °C is also carried out in which maximum power density of single cell is obtained as 0.04 W/cm2.

Non-Dimensional Analysis of Diffusion Characteristics in Polymer Electrolyte Membrane Fuel Cells with Mismatched Anodic and Cathodic Flow Channels

Polymer electrolyte membrane fuel cells were analyzed to investigate changes in the structure of the flow field and operating conditions. The cell performance, which was controlled by adjusting the width of the cathodic channel, improved as the backpressure increases. With the anodic and cathodic flow channels mismatched, the maximum power densities at 3.0 bar for a narrow cathodic channel were 1115 and 1024 mW/cm2, and those for a wide cathodic channel were 959 and 868 mW/cm2, respectively. The diffusion characteristics were investigated using the non-dimensional numbers Re (Reynolds), Sc (Schmidt), and Sh (Sherwood) to confirm the improvement of mass transport. The narrower the channel or the higher the operating pressure, the larger Re was and the smaller Sc and Sh became. In particular, the wider the anodic channel, the larger the value of Sh.

Disclosure of the internal transport phenomena in an air-cooled proton exchange membrane fuel cell—part III: Performance research based on qualitative comparisons between modeling and experimental results

The validation of a computational fluid dynamics model for a proton exchange membrane fuel cell (PEMFC) is normally conducted by the experimental I–V performance curve. However, it seems this method is not solid enough. In the meantime, it's difficult to conduct the item-to-item quantitative comparisons between the internal distributions acquired from numerical and testing results. Therefore, in this paper, as the first attempt, qualitative comparisons between the modeling and experimental results are conducted based on the three important parameters of an air-cooled PEMFC (air stoichiometric ratio, air relative humidity, cathode flow field design) to explore the trends of the related fuel cell I–V performance curves and internal resistances. The internal resistances are tested using the EIS technique and differentiated by an equivalent circuit model. Conclusions show that the qualitative comparisons between the numerical and testing results support each other well and new results are found based on the comparisons. Finally, discussions on the sensitivity based on the experimental EIS results are conducted to explore the response degree of the total resistance to the air stoichiometric ratio, the air relative humidity and the cathode flow field design.

Optimization of graded catalyst layer to enhance uniformity of current density and performance of high temperature-polymer electrolyte membrane fuel cell

The optimal use of catalyst materials is essential to improve the performance, durability and reduce the overall cost of the fuel cell. The present study is related to spatial distributions of current and overpotential for various graded catalyst structures in a high temperature-polymer electrolyte membrane fuel cell (HT-PEMFC). The effect of catalyst gradient across the catalytic layer (CL) thickness and along the channel and their combination on cell performance and catalyst utilization is investigated. The graded catalytic structure comprises two, three, or multiple layers of catalyst distribution. For a total cathode catalyst loading of 0.35 mg/cm2, higher loading near the membrane presents improved cell performance and catalyst utilization due to reduced limitations caused by oxygen and ion diffusions. However, non-uniformity in the current distribution is significantly increased. The increase in the catalyst loading along the reactant flow provides a substantially uniform current density but lower cell performance. The synergy of varying catalytic profiles across the CL thickness and along the cathode flow direction is investigated. The results emphasize the importance of a rational design of cathode structure and mathematical functions as a strategic tool for functional grading of a CL towards improved uniform current distribution and catalyst utilization.