Single Proton Exchange Membrane Research Articles

Biopolymeric electrolyte-based membrane on nanocrystalline cellulose/polyvinyl alcohol for a conceivable usage in proton exchange membrane fuel cell

In this study, we developed eco-friendly biopolymer electrolytes by blending nanocrystalline cellulose (NCC) with polyvinyl alcohol (PVA) and crosslinking them using glutaraldehyde. These membranes, denoted as NCC-x/PVA-y, were fabricated via the solution casting method. We thoroughly investigated the effects of different NCC to PVA ratios on various properties, including water uptake, swelling ratio, thermal and mechanical characteristics, proton conductivity, hydrogen permeation, and single Proton Exchange Membrane Fuel Cell (PEMFC) performances. Increasing the NCC concentration (ranging from 20 % to 60 %) led to enhanced surface roughness and compactness of ionic domains, resulting in improved dimensional stability and reduced hydrogen permeability across the membranes. Among the tested ratios, NCC-50/PVA-50 exhibited the highest proton conductivity, measuring 0.3 × 10−2 S cm−1. Notably, this ratio demonstrated a 60 % lower swelling ratio and lower hydrogen permeability (0.76 × 10−13 cm2/scmHg) compared to Nafion 117 (514 × 10−13 cm2/scmHg), indicating its superior performance. Furthermore, the NCC-50/PVA-50 membrane consistently maintained open-circuit voltages exceeding 0.9 V under all conditions, highlighting its effective proton transport capabilities and minimal fuel penetration. Density Functional Theory (DFT) analysis confirmed the successful cross-linking of NCC/PVA with glutaraldehyde, emphasizing its compatibility and potential for proton conductivity in PEMFC applications.

Constructing sandwich-like microstructure based on multi-nanofibers to accelerate proton conduction at subzero temperature

The well-ordered microstructure has been demonstrated to accelerate the proton conduction process through reducing proton conduction resistance. In this research, the proton exchange membranes (PEMs) with sandwich-like microstructure have been constructed based on Kevlar nanofibers and bifunctional nanofibers of chitosan (CS) with polyvinyl alcohol (PVA). The CS/PVA bifunctional nanofibers (CPNF) layer has been prepared with electrospinning process, which is stably adhered to the Kevlar nanofibers layer owing to compatible interfacial property. The fine structure stability without layer separation is achieved even with phosphoric acid (PA) molecules doping in the prepared PA doped composite membranes. The fibrous microstructure accelerats proton conduction through regulating proton conduction pathways. The objective of accelerating proton conduction at subzero temperature has been realized, reflecting in high and stable proton conductivities. For instance, the (Kevlar/CPNF/Kevlar)/PA membrane exhibits proton conductivities of 9.75 × 10−3 S/cm at −30 °C and 8.22 × 10−2 S/cm at 30 °C. Most importantly, the fine proton conductivity stability is identified by the results of the cycle test and long-term test. Specifically, the proton conductivities are respectively 8.62 × 10−3 S/cm at −30 °C and 8.07 × 10−2 S/cm at 30 °C after a five heating/cooling cycle process. The proton conductivities remain 2.97 × 10−2 S/cm at −25 °C and 7.19 × 10−2 S/cm at 30 °C after a 1032 h non-stop test. Additionally, the single proton exchange membrane fuel cell with the (Kevlar/CPNF/Kevlar)/PA membrane exhibits the peak power densities of 279.5 mW/cm2 at 100 °C and 352.7 mW/cm2 at 130 °C.

Enhanced carbon monoxide tolerance of platinum nanoparticles synthesized through the Flash Joule Heating Method

Was employ the Flash Joule Heating Method (FJHM) to synthesize carbon-supported Pt nanoparticles. In this method, an aqueous solution of the Pt precursorH2PtCl6·6 H2O is introduced into a reactor containing Vulcan XC 72 carbon. Subsequently, the mixture undergoes 50 cycles of discharges at 100 coulombs per discharge. Comparative XRD analysis with a commercially prepared Pt/C BASF, utilizing a reduction deposition method, reveals an expansion in the interplanar spacing of the platinum crystal lattice in the FJHM-prepared Pt/C catalyst (FJHM-Pt/C). This expansion suggests the emergence of structural defects, a finding confirmed by TEM images displaying distinct step-like features on the FJHM-Pt/C surface. Cyclic voltammogram analysis demonstrates a noteworthy increase in the oxidation pre-peak at 0.5 V for FJHM-Pt/C compared to Pt/C BASF. When employing pure H2 as fuel, the single proton exchange membrane fuel cell (PEMFC) utilizing Pt/C BASF as the anode catalyst exhibits a higher maximum power density (MPD) than its FJHM-Pt/C counterpart. Conversely, in the presence of CO, the PEMFC with FJHM-Pt/C as the catalyst demonstrates a superior MPD compared to the cell equipped with commercial Pt/C as the anode. These findings underscore enhanced CO tolerance, highlighting the potential advantages of the FJHM preparation method.

Determination of an Optimal Parameter Combination for Single PEMFC Using the Taguchi Method and Orthogonal Array

In this study, the optimization of the operational parameters for a single proton exchange membrane fuel cell (PEMFC) was carried out using the Taguchi method and orthogonal array. The operating parameters were H2 stoichiometry, air stoichiometry, cell temperature, and back pressure of the anode∙cathode, each with three levels. The performance of the PEMFC, operated according to the L9 orthogonal arrangement, was evaluated through I–V curves at a step-up current loading ranging from 0.1 to 0.7 A/cm2. The results indicated that the anode∙cathode back pressure had the greatest sensitivity to the output voltage compared to the other operating parameters. Increasing the back pressure resulted in higher current output densities at higher values than those applied in the orthogonal arrangement. As the back pressure increased, the output voltage tended to increase at each current density. However, for operating conditions above 150 kPa, the improvement in cell performance was either not significant or tended to decrease. Therefore, it can be concluded that the Taguchi method and orthogonal array are effective tools for selecting the optimal operating conditions for PEMFC.

Numerical and Experimental Investigation of Performance and Flooding Phenomena of a PEM Fuel Cell with and without Micro-Porous Layers

This work presents the results of manufacturing a single Proton Exchange Membrane Fuel Cell (PEMFC) with Micro-Porous Layers (MPLs) and an active area of 25 cm2, and the experimental study required to build its polarization curve. Based on the physical model data, a numerical model of this PEMFC is created in the ANSYS PEM Fuel Cell module. Numerical simulations were performed with boundary conditions consistent with the experimental conditions on the test station. The calculation and experimental result comparison of the polarization curves for voltages ranging from 0.29 V to 0.94 V proved that the utilized numerical model is highly reliable. The simulation of PEMFC without MPLs was conducted according to other stable input parameters and boundary conditions. The results show that the PEMFC performance decreases significantly due to the flooding phenomenon inside PEMFC without MPLs compared to PEMFC with MPLs. Such phenomena are challenging to observe experimentally. Numerical modeling can be further used to optimize the fuel cell components.

Optimizing adhesive rheology for stencil printing of fuel cell sealings using supervised machine learning

In a single low-temperature proton exchange membrane fuel cell (LT-PEMFC) stack, the sealings are responsible for preventing leakages, providing electrical insulation and compensating assembly tolerances. This study investigates stencil printing to produce fuel cell sealings and aims to identify reliable conditions to print layer thicknesses of at least 500 μm, typically used for this application and substantially exceeding the current state-of-the-art. First, rheological and print experiments were conducted with 25 distinct adhesives, including ultraviolet (UV) curable acrylics and epoxies, to determine their printability. An adhesive was considered printable when it detached from the stencil without forming bubbles, a print defect that significantly diminishes the process stability. This had to be accomplished at two different squeegee speeds (40 and 160 mm/s), confirming the robustness of the adhesive for the print process. In addition, the impact of the aperture orientation, aperture aspect ratio (AR) and separation speed of the substrate from the stencil were evaluated. Here, it was detected that a multivariable criterion was necessary to reliably predict printability. Thus, classification models based on binary logistic regression, a simple supervised machine learning technique, were proposed using the thixotropy index TI (indicator for viscosity recovery ability), steady-state viscosity at 100 s−1, adhesive surface tension and aperture AR as predictors. The derived models achieved a prediction accuracy ≥88.2%, demonstrating adequate generalisation. Moreover, it was identified that increasing TI is the most effective approach to achieve printability. Finally, the driving physical mechanisms influencing the obtained print results were assessed, and it was shown that a TI value of about 50 Pa s/s is required to reach the minimum layer thickness.

Construction of Successive Proton Conduction Channels to Accelerate the Proton Conduction Process in Flexible Proton Exchange Membranes.

Successive proton conduction channels are constructed with the spin coating method in flexible proton exchange membranes (PEMs). In this research, phosphoric acid (PA) molecules are immobilized in the multilayered microstructure of Kevlar nanofibers and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) polymer molecular chains. As a result, successive proton conduction channels can accelerate the proton conduction process in the prepared membrane with the multilayered microstructure. Additionally, the microstructure fractures of the composite membranes from the external force of folding and stretching operations are modified by the inner PA molecules. Notably, numerous PA molecules are further combined through formed intermolecular hydrogen bonding. The stretched membrane absorbs more PA molecules owing to the arrangement of PA molecules, Kevlar nanofibers, and SEBS molecular chains. The stretched membrane thus exhibits the enhanced proton conduction ability, such as the through-plane proton conductivity of 1.81 × 10-1 S cm-1 at 160 °C and that of 4.53 × 10-2 S cm-1 at 120 °C lasting for 600 h. Furthermore, the tensile stress of PA-doped stretched membranes reaches (3.91 ± 0.40)-(6.15 ± 0.43) MPa. A single proton exchange membrane fuel cell exhibits a peak power density of 483.3 mW cm-2 at 120 °C.

Hf and Co Dual Single Atoms Co-Doped Carbon Catalyst Enhance the Oxygen Reduction Performance.

Single-atom metal-doped M-N-C (M═Fe, Co, Mn, or Ni) catalysts exhibit excellent catalytic activity toward oxygen reduction reactions (ORR). However, their performance still has a large gap considering the demand for their practical applications. This study reports a high-performance dual single-atom doped carbon catalyst (HfCo-N-C), which is prepared by pyrolyzing Co and Hf co-doped ZIF-8 . Co and Hf are atomically dispersed in the carbon framework and coordinated with N to form Co-N4 and Hf-N4 active moieties. The synergetic effect between Co-N4 and Hf-N4 significantly enhance the catalytic activity and durability of the catalyst. In an acidic medium, the ORRhalf-wave potential (E1/2) of the catalyst is up to 0.82V , which is much higher than that of the Co-N-C catalyst without Hf co-doping (0.80V). The kinetic current density of the catalyst is up to 2.49Acm-2 at 0.85V , which is 1.74 times that of the Co-N-C catalyst without Hf co-doping. Moreover, the catalyst exhibits excellent cathodic performance in single proton exchange membrane fuel cells and Zn-air batteries. Furthermore, Hf co-doping can effectively suppress the formation of H2O2, resulting in significantly improved stability and durability.

Supported-Ir Catalysts: The Impact of the Supports' Chemical Composition on the Oxygen Evolution Reaction

In water electrolyzer cells, the anode electrode is one of the most important components, where the oxygen evolution reaction (OER) takes place. In this process, the water molecules split into oxygen ions, protons, and electrons, and the oxygen gas is produced on the anode surface [1]. The most suitable materials that catalyze OER are ruthenium, iridium, and their oxides, but their cost and scarcity require reduction and enhancement of their utilization [2]. One morphological strategy consists of the dispersion of the active nanoparticles in supportive nanoparticles made of less expensive materials to increase their mass activity. In addition, due to the high potential reached during operating conditions for water splitting, supportive materials have to possess a high corrosion resistance. Titanium oxides are good candidates because of their high thermal and chemical stability, low cost, and commercial availability [3]. But their poor electric conductivity (∼10−6 S cm−1) makes the design of an active and stable catalyst a complex task. In this work, Ir nanoparticles have been synthesized on the surface of several Ti-based nanoparticles and a complete analysis of their physicochemical properties have been carried out ( Fig. 1a-b ). In addition, electrochemical behaviour has been tested ex-situ in a half cell by the rotating disk electrode technique and after, the catalysts have been deposited in a polymer membrane for testing in-situ in a single cell proton exchange membrane water electrolyzer. The results show a successful performance of the supported Ir/TiO2 nanoparticles comparable to the pure Ir black nanoparticles but with an active metal loading five times lower. Differently, even though TiC showed excellent electrical conductivity during the ex-situ characterization, Ir/TiC nanoparticles had a poor activity after just one day of performance in the WE due to the complete oxidation of the TiC into TiO2 ( Fig. 1c-d ). Finally, Ir/TiB2 showed a balanced result in terms of activity and stability, showing promising properties as a catalyst for PEM-WE. Sadhasivam T., Ho-Young J. Chapter 3 - Nanostructured bifunctional electrocatalyst support materials for unitized regenerative fuel cells// Nanostructured, Functional, and Flexible Materials for Energy Conversion and Storage Systems- 2020.- 69-103. Antolini E. Iridium as Catalyst and Cocatalyst for Oxygen Evolution /Reduction in Acidic Polymer Electrolyte Membrane Electrolyzers and Fuel Cells // ACS Catal. - 2014.- 4, N 5.- P. 1426-1440. Van Pham C., Bühler M. IrO2 coated TiO2 core-shell microparticles advance performance of low loading proton exchange membrane water electrolyzers// Applied Catalysis B: Environmental-2020.- P 269.- P. 118762. Figure 1. TEM image of Ir/TIO2 (a), EDX mapping of Ir/TiO2(b), linear sweep voltammetry of catalysts (c), the current density at given potential 1.80 V (d). Figure 1

Investigating the Suitability of Printed Circuit Components for Fuel Cells

Flexible electrochemical energy sources using non-traditional cell materials and topologies have attracted growing attention because they offer unique design opportunities that are still being explored. They also offer potential advantages such as conformability, high power density, high specific power, and low cost through the adoption of electronics manufacturing techniques. This study examines the feasibility of using flexible printed circuits boards (PCBs) as the anode and cathode current collectors (CCs) of single cell Proton Exchange Membrane Fuel Cell (PEMFCs). In this work, we determine the best anode and cathode interfaces at which to embed flexible CCs to obtain the highest power, as illustrated in Figure 1. The flexible anode and cathode CCs are embedded A) inside the PEM|Catalyst Layer (CL) interface, B) between the CL|Micro Porous Layer (MPL) interface and C) between the Gas Diffusion Layer (GDL)| Flow field (FF) interface. The performance of the single cell PEMFC with the embedded flexible anode and cathode CCs at the different interfaces described in Figure 1 is investigated by using I-V polarization curves, electrochemical impedance spectroscopy (EIS), and thermal imaging. The performance of the cells tested with the embedded flexible CCs is compared to the performance of a standard cell. This study also investigates the effect of varying the anode and cathode CC geometry (square shape vs. circular) and opening ratio (20%, 30%, 40%, 50% and 60%) on the cell performance. Figure 1

ORR activity and stability of carbon supported Pt3Y thin films in PEMFCs

In order to investigate stability of oxygen reduction reaction (ORR) on a Pt3Y thin film under relevant fuel cell conditions, we performed an accelerated stress test (AST) consisting of 3600 potential cycles between 0.4 and 1.4 V at 1 V s−1 in a single proton exchange membrane fuel cell (PEMFC). The ORR activities were evaluated via polarization curves before and after the AST. Electrochemical active surface area (ECSA) was obtained by CO-stripping voltammetry whereas the morphological changes were monitored by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Variations in surface composition and electronic structures were evaluated by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). After AST, the polarization curves show loss of ORR activity in all voltages for both Pt and Pt3Y. Except at very high voltages (E > 0.85 VRHE), the ORR activity of Pt3Y after AST is very close to that of Pt before AST. This correlates well with the results from the deconvolution of Pt-4f XPS spectra where the binding energy of metallic Pt in Pt3Y is comparable to pure Pt (71.22 eV). SEM and TEM images demonstrate that the morphologies of the aged Pt3Y and as-sputtered Pt are similar, whereas EDX results confirm a steady bulk composition of Pt3Y thin films throughout the entire electrochemical test. By correlating all these results, we conclude that the loss of ORR activity for Pt3Y is due to an increase in the thickness of the Pt overlayer which induces a relaxation of the Pt overlayer decreasing the compressive strain effect. For pure Pt, the loss of ORR activity is associated with a growth of the Pt domains associated with Ostwald ripening process.

Investigation on electrical and electrochemical behaviour of cellulose acetate: Ammonium iodide: Silica composite biopolymer electrolyte for proton exchange membrane (PEM) fuel cell performance

Cellulose acetate (CA): ammonium iodide (NH4I) solid biopolymer electrolyte and cellulose acetate (CA): ammonium iodide (NH4I): silica (SiO2) particle composite-based biopolymer electrolytes were developed via solution casting route for single proton-exchange membrane fuel cells (PEMFC) applications. X-ray diffraction (XRD) analysis was used to identify the diffraction peaks and their corresponding angles, which led to the confirmation of the aforementioned biopolymer. The admixture of SiO2 into the 50CA:50NH4I improves the amorphous nature than 50CA:50NH4I in the XRD pattern. Using electrochemical impedance spectroscopy (EIS) analysis, the CA:NH4I:SiO2 has found higher ionic conductivity, lower electrical resistance, and a lesser CPE value than the CA and CA:NH4I. The highest-conducting CA:NH4I:SiO2 and CA:NH4I developed were used in the construction of a single PEMFC, where the obtained power density values were 122.4 and 106.4 mWcm−2. The introduction of SiO2 admixtures with CA:NH4I has found relatively higher power density value than CA:NH4I.

Morphological and microstructural engineering of Mn-N-C with strengthened Mn-N bond for efficient electrochemical oxygen reduction reaction

Revealing the correlation between the micro–macro structures and active sites of transition metal-nitrogen-carbon (M−N−C) for electrochemical oxygen reduction reaction (ORR) is essential to develop non-precious metal catalyzed fuel cells and metal-air batteries. Herein, Mn-N-C catalysts with various morphologies and microstructures were prepared using Mn2+ coordinated bis(imino)-pyridine-based polymer with N-rich content as a new platform of precursor, which was synthesized via a condensation reaction of 1H-1, 2, 4-Triazole-3, 5-Diamine and 2, 6-Diacetylpyridine. Results demonstrate that morphologies and fine structures (pore structure, N dopants, surface area, and atomic Mn-N bond length, etc.) of Mn-N-C catalysts are strongly dependent on the growth of the specific precursor with and without NaCl as a template and the secondary calcination temperature can further optimize the bond length of Mn-Nx moieties, resulting in significant activity differences between correspondingly derived Mn-N-C catalysts for ORR. Compared to Mn-N-C derived from the synthesized precursor without NaCl, Mn-N-C obtained by the precursor grown directly on NaCl features an ultra-thin nanosheet-like structure with a hierarchical pore distribution and a shorter Mn-N bond, presenting high ORR performance with a half-wave potential of 0.88 V in 0.1 M KOH and a tiny potential loss of 11 mV after 30 K cycles, which is also proved by high-performance practical single Zn-Air battery (139 mW·cm−2) and proton exchange membrane fuel cell (400 mW·cm−2). This work provides a new understanding of the critical role of morphology and Mn-N bonding length of M−N−C for enhancing ORR and a new route of developing non-Fe/Co-based M−N−C catalysts for electrocatalysis.

A comparative analysis of single and modular proton exchange membrane water electrolyzers for green hydrogen production- a case study in Trois-Rivières

Proton Exchange Membrane Water Electrolyzers demonstrate significant potential for hydrogen production from renewable energy sources. Addressing the inherent intermittency of these sources, a modular design for the electrolyzers emerges as an essential avenue of research. This study delves into potential solutions and strategies for harnessing renewable energy efficiently to fuel these electrolyzers and presents a comparative analysis between single-stack and modular designs based on a hypothetical scenario. Using experimental data, the research projects the hydrogen output derived from solar energy in Trois-Rivières. Machine learning techniques are employed to forecast available energy from photovoltaic panel datasets. A strategic power allocation mechanism is introduced to regulate input current across each electrolyzer, aiming to optimize system performance. Experimental evaluations on a purpose-built test bench validate the conversion efficiency of the electrolyzer. Notably, the results suggest that embracing a modular design can amplify hydrogen production by over 33% annually while concurrently minimizing system degradation.

Experimental investigation on PEM fuel cell flooding mitigation under heavy loading condition

Water flooding is a crucial factor affecting the lifetime of a proton exchange membrane (PEM) fuel cell. In this paper, A laboratory-scale (25 cm2) single PEM fuel cell was tested to investigate the characteristics of fuel cell under a load shedding process with various air flow rates. The performance was assessed using output power and electrochemical impedance spectroscopy, while the cathode flooding was identified using voltage and cathode pressure drop. The results show that reducing the load within a specific range can lower the impedance and lessen floods. The results also demonstrate that there is an optimal inlet flow rate interval considering its effect on system efficiency, durability, and water flooding. In addition, a stepped load shedding pattern was proposed to solve the flooding problem of a fuel cell while taking the power demand into account. The effect of load shedding cycle and air inlet flow rate on flooding was evaluated by comparing the flooding severity coefficient and output power. The results prove that a longer current reduction cycle is more favorable in alleviating flooding problems. The optimal mode for the fuel cell in this paper was determined according to the flooding situation and power variation. Finally, the approach to obtaining the optimal load shedding pattern for other PEM fuel cells system was summarized. The flooding mitigation approach proposed in this paper can be utilized as a guide for developing strategies to extend the life of PEM fuel cells.

Experimental and simulation of PEM water electrolyser with Pd/PN-CNPs electrodes for hydrogen evolution reaction: Performance assessment and validation

Water electrolysis using a proton exchange membrane (PEM) offers a sustainable solution for green hydrogen production from intermittent renewable energy sources. However, the utilization of costly electrode materials and cell components has resulted in expensive hydrogen production costs and limited its commercial applications. Furthermore, the management of gas-liquid flow and thermal distributions presents significant challenges in the operation of PEM water electrolysers. In this study, a COMSOL Multiphysics model was developed for a 25 cm2 single cell PEM water electrolyser with parallel flow field configurations to investigate its performance including operating principles, mechanisms, and ion transport properties. Subsequently, the model was validated with in-house experimental data at different operating conditions. Impressively, it effectively predicted the current-voltage polarization curves, demonstrating strong correlation with the experimental data. For a more rigorous comparison between experimental and numerical simulation, the normalized root mean square deviation was calculated for current-voltage polarization curves at various temperatures, ranging from 30 °C to 80 °C. The deviation was observed to be around 1.1% across all the temperatures, an acceptably low error value. In addition, the model was used to analyze the reactant flow and thermal distributions. This work can provide both experimental and simulation support for the selection and optimization of operating conditions, including flow fields in PEM water electrolysers.

High-performance sandwich-structure PI/SPEEK+HPW nanofiber composite membrane with balanced proton conductivity and stability

Due to its uncomplicated manufacturing procedure for large-scale industrialization and adaptable conductivity, the competitive proton exchange membrane (PEM) matrix employed is sulfonated poly (ether ether ketone). However, the conflict between the strong proton conductivity and high stability of SPEEK-based PEM constantly upsets the equilibrium; the primary chain of SPEEK will conduct more protons if additional sulfonic acid is introduced, but it also causes a high swelling ratio and lowers stability. To tackle this challenging issue, we coupled the high intrinsic proton conductivity of phosphotungstic acid (HPW) and the excellent stability of polyimide (PI) nanofibers in a single PEM. In particular, sandwich-structure hybrid membranes (PI/SPEEK + HPW) were created to reduce HPW loss under operational conditions, further improving stability. Consequently, the swelling ratio and conductivity of the premium sandwich-structure PI/SPEEK + HPW-20 were 29% and 223.4 mS cm−1 under 60 °C and 100% RH, their respective values were 8% larger than those of SPEEK. Its proton conductivity reached 170.9 mS cm−1 during 13 days of exposure under 60 °C and 100% RH, which would be 30% better than that of SPEEK over the same treatment. Protons in these membranes were transported through Grotthus and vehicle mechanism, and the establishment of an acid-rich layer at the surface among PI nanofiber with HPW/SPEEK, which was confirmed by FTIR, XPS, and TEM, is responsible for these superior performances. From our point of view, our findings might encourage more studies into the creation of high-performance PEM.

High-performance atomic Co/N co–doped porous carbon catalysts derived from Co–doped metal–organic frameworks for oxygen reduction

Improving the activity and durability of carbon-based catalysts is a key challenge for their application in fuel cells. Herein, we report a highly active and durable Co/N co-doped carbon (CoNC) catalyst prepared via pyrolysis of Co–doped zeolitic–imidazolate framework–8 (ZIF–8), which was synthesized by controlling the feeding sequence to enable Co to replace Zn in the metal–organic framework (MOF). The catalyst exhibited excellent oxygen reduction reaction (ORR) performance, while the half-wave potential decreased by only 8 mV after 5,000 accelerated stress test (AST) cycles in an acidic solution. Furthermore, the catalyst exhibited satisfactory cathodic catalytic performance when utilized in a hydrogen/oxygen single proton exchange membrane (PEM) fuel cell and a Zn-air battery, yielding maximum power densities of 530 and 164 mW cm−2, respectively. X-ray absorption spectroscopy (XAS) and high-angle annular dark field-scanning transmission electron microscopy (HAAD–STEM) analyses revealed that Co was present in the catalyst as single atoms coordinated with N to form Co–N moieties, which results in the high catalytic performance. These results show that the reported catalyst is a promising material for inclusion into future fuel cell designs.

Tuning synthesis parameters and support composition for high-performing and durable core-shell Pt–Ni carbon nitride electrocatalysts for the oxygen reduction reaction

This report presents the interplay between the synthesis parameters, physicochemical properties, and electrochemical performance of core-shell low-Pt electrocatalysts (ECs) for the oxygen reduction reaction (ORR) based on PtxNi active sites stabilized on a carbon nitride shell. The impact of the pyrolysis temperature (Tf), of the support core (H) composition and of an electrochemical dealloying-activation step on the EC morphology and on the accessibility and stability of the active sites are studied in detail. Three supports are employed based on carbon nanoparticles and/or graphene platelets. The ORR performance of activated ECs measured by cyclic voltammetry with the thin-film rotating ring-disk electrode approach is strongly affected by Tf and H. The best performing ECs are tested in single proton exchange membrane fuel cells under operating conditions. The simultaneous presence of graphene and carbon in H improves the dispersion of active sites, resulting in a vastly improved mass activity and durability in comparison with a benchmark state-of-the-art Pt/C EC.

Multiple effects of non-uniform channel width along the cathode flow direction based on a single PEM fuel cell: An experimental investigation

Proton exchange membrane (PEM) fuel cell is considered to be one of the promising alternatives to conventional engines in the future as on-board vehicle energy conversion device. In this paper, three single PEM fuel cells with different cathode flow field plates (FFPs), which vary from each other on the channel width along the cathode flow direction, are assembled. Polarization and power density curves, electrochemical impedance spectroscopy (EIS) fitting results are utilized to evaluate the output performance. Moreover, the economic characteristic of three single cells is calculated based on the assumption of parasitic pumping power generated by air compressor. Finally, the durability of three single cells is assessed based on comparison of electrochemical surface area (ECSA) obtained from analysis of cyclic voltammetry (CV) method. The comprehensive experimental results reveal that cell 0.8-1.0-1.2 exhibits better performance under high RH conditions and cell 1.0-1.0-1.0 is more favorable under a low RH condition. The mechanism behind the phenomenon of performance variation is analyzed and attributed to the switching of dominating factor from two-phase flow velocity to spatial availability degree under various conditions of RH.