Performance Comparison of Proton Exchange Membrane Fuel Cells with Nafion and Aquivion Perfluorosulfonic Acids with Different Equivalent Weights as the Electrode Binders

Short-Side-Chain Membranes with Stabilized Superacid on Graphitic Carbon Nitride for Polymer Electrolyte Fuel Cells under Low-Humidity Conditions

The integration of superacid-like heteropolyacids offers a promising route to develop highly proton-conducting membranes for energy storage and conversion. However, the inherent hydrophilicity of these acids can cause leaching, which undermines the fuel cell performance. In our research, we engineered a proton-conductive membrane with a facile hydrothermal synthesis approach to form stabilized hybrid superacids, namely, phosphotungstic acid (PTA), with graphitic carbon nitride (PCN) and its incorporation in a short-side-chain ionomer, namely, Aquivion. This unique approach via PCN nanohybrids enhances the proton transport within the membrane. These nanohybrids effectively combined the strong acidity of PTA with continuous 2D proton-transport pathways via a short side chain, resulting in a notable proton conductivity of 0.228 S cm-1 at 80 °C under 95% relative humidity. The real impact was evident in the performance of fuel cells using the Aquivion/PCN nanocomposite membrane, which demonstrated a significant improvement of 34% in the peak power density (1.0 W cm-2), and 44% cell performance (0.98 A cm-2) was retained for the nanocomposite membrane at a low relatively humidity (30% RH) at 0.6 V. This advancement represents a major leap in energy conversion and storage technologies at low-humidity conditions.

Understanding the infrared spectrum of the protic ionic liquid [DEMA][TfO] by atomistic simulations

Polymer-electrolyte fuel cells operating at a temperature above 100 °C would markedly reduce issues associated with water management in the cell and allow for a simplified system design. Available electrolytes such as fluoropolymers grafted with sulfonic acid groups or phosphoric acid either rely on the presence of water or they suffer from sluggish kinetics of the oxygen reduction reaction. Here, with experiments and atomistic simulations, we analysed vibrational spectra of the protic ionic liquid diethylmethylammonium triflate ([DEMA][TfO]) as an alternative electrolyte, with the aim to understand the statistical distribution of cations and anions in the electrolyte and the interaction of the H-bond with the surroundings. We present a comprehensive analysis of the infrared (IR) spectrum of [DEMA][TfO]. Special attention is given to understanding the high-frequency modes above 2500 cm-1, which exhibit a double peak feature in the experiment. While this feature can generally be attributed to the N-H vibrations of the cation, the precise mechanism behind the double peak was unclear. In this manuscript we managed to explain the nature of the double distribution, being influenced by different orientations between the DEMAs and TFOs. The correct assignment of observed vibrational modes is enabled by simulations of the ionic liquid as an infinitely extended fluid.

Solid-state electrochemical oxidation with polyelectrolyte membrane stamps for micro-/nanoscale pattern formation on Au surfaces

Nanoscale-patterned Au surfaces are promising for a wide range of applications from bio/chemical sensors to high-performance electrodes. However, pattern formation using conventional resist-based methods is complex, expensive, and environmentally unfriendly. Herein, we report a novel approach for pattern formation on Au surfaces using solid-state electrochemical treatment with polymer electrolyte membrane (PEM) stamps. During electrolysis, the patterned structure of the PEM stamp was transferred onto the Au surface to form micro- and nanoscale oxide patterns. X-ray analysis of the treated surface confirmed the formation of an oxide film on the Au surface, which was subsequently reduced to metallic Au after air exposure for several weeks. Although the pattern height decreased with air exposure, a patterned structure with a height of several hundred nanometers was maintained following oxide reduction. Reflectance spectroscopy revealed that the patterned Au surface exhibited sharp reflectance peaks, the intensities and positions of which strongly depended on the measurement angle, which are key characteristics of diffraction gratings. This fast and facile electrochemical treatment process is promising for the preparation of patterned Au surfaces that can be applied in optical gratings and localized surface plasmon resonance sensors.

Potential-Dependent Ionomer Rearrangement on the Pt Surface in Polymer Electrolyte Membrane Fuel Cells

The interface between the catalyst and the ionomer in the catalyst layer of polymer electrolyte membrane fuel cells (PEMFCs) has been a subject of keen interest, but its effect on durability has not been fully understood due to the complexity of the catalyst layer structure. Herein, we utilize a Pt nanoparticle (NP) array electrode fabricated using a block copolymer template as the platform for a focused investigation of the interfacial change between the Nafion thin film and the Pt NP under a constant potential. A set of analyses for the electrodes treated with various potentials reveals that the Nafion thin film becomes densely packed at the intermediate potentials (0.4 and 0.7 V), indicating an increased ionomer-catalyst interaction due to the positive charges formed at the Pt surface at these potentials. Even for a practical PEMFC single cell, we demonstrate that the potential holding at the intermediate potentials increases ionomer adsorption to the Pt surface and the oxygen transport resistance, negatively impacting its power performance. This work provides fresh insight into the mechanism behind the performance fade in PEMFCs caused by potential-dependent ionomer rearrangement.

Effect of Dispersing Solvents for an Ionomer on the Performance of Copper Catalyst Layers for CO2 Electrolysis to Multicarbon Products

To explore the effects of solvent-ionomer interactions in catalyst inks on the structure and performance of Cu catalyst layers (CLs) for CO2 electrolysis, we used a "like for like" rationale to select acetone and methanol as dispersion solvents with a distinct affinity for the ionomer backbone or sulfonated ionic heads, respectively, of the perfluorinated sulfonic acid (PFSA) ionomer Aquivion. First, we characterized the morphology and wettability of Aquivion films drop-cast from acetone- and methanol-based inks on flat Cu foils and glassy carbons. On a flat surface, the ionomer films cast from the Aquivion and acetone mixture were more continuous and hydrophobic than films cast from methanol-based inks. Our study's second stage compared the performance of Cu nanoparticle CLs prepared with acetone and methanol on gas diffusion electrodes (GDEs) in a flow cell electrolyzer. The effects of the ionomer-solvent interaction led to a more uniform and flooding-tolerant GDE when acetone was the dispersion solvent (acetone-CL) than when we used methanol (methanol-CL). As a result, acetone-CL yielded a higher selectivity for CO2 electrolysis to C2+ products at high current density, up to 25% greater than methanol-CL at 500 mA cm-2. Ethylene was the primary product for both CLs, with a Faradaic efficiency for ethylene of 47.4 ± 4.0% on the acetone-CL and that of 37.6 ± 5.5% on the methanol-CL at a current density of 300 mA cm-2. We attribute the enhanced C2+ selectivity of the acetone-CL to this electrode's better resistance to electrolyte flooding, with zero seepage observed at tested current densities. Our findings reveal the critical role of solvent-ionomer interaction in determining the film structure and hydrophobicity, providing new insights into the CL design for enhanced multicarbon production in high current densities in CO2 electrolysis processes.

Boosting Power Density of Proton Exchange Membrane Fuel Cell Using Artificial Intelligence and Optimization Algorithms

The adoption of Proton Exchange Membrane (PEM) fuel cells (FCs) is of great significance in diverse industries, as they provide high efficiency and environmental advantages, enabling the transition to sustainable and clean energy solutions. This study aims to enhance the output power of PEM-FCs by employing the Adaptive Neuro-Fuzzy Inference System (ANFIS) and modern optimization algorithms. Initially, an ANFIS model is developed based on empirical data to simulate the output power density of the PEM-FC, considering factors such as pressure, relative humidity, and membrane compression. The Salp swarm algorithm (SSA) is subsequently utilized to determine the optimal values of the input control parameters. The three input control parameters of the PEM-FC are treated as decision variables during the optimization process, with the objective to maximize the output power density. During the modeling phase, the training and testing data exhibit root mean square error (RMSE) values of 0.0003 and 24.5, respectively. The coefficient of determination values for training and testing are 1.0 and 0.9598, respectively, indicating the successfulness of the modeling process. The reliability of SSA is further validated by comparing its outcomes with those obtained from particle swarm optimization (PSO), evolutionary optimization (EO), and grey wolf optimizer (GWO). Among these methods, SSA achieves the highest average power density of 716.63 mW/cm2, followed by GWO at 709.95 mW/cm2. The lowest average power density of 695.27 mW/cm2 is obtained using PSO.

Effect of Blended Perfluorinated Sulfonic Acid Ionomer Binder on the Performance of Catalyst Layers in Polymer Electrolyte Membrane Fuel Cells

In this study, blended perfluorinated sulfonic acid (PFSA) ionomers with equivalent weights (EWs, g/mol) of ~1000, 980, and 830 are prepared. Catalyst layers (CLs), using blended PFSA ionomers, with different side chain lengths and EWs are investigated and compared to CLs using single ionomers. The ion exchange capacity results confirm that blended ionomers have the target EWs. As a result, blended ionomers exhibit higher ion conductivity than single ionomers at all temperatures due to the higher water uptake of the blended ionomers. This implies that blended ionomers have a bulk structure to form a competent free volume compared to single ionomers. Blended ionomers with short side chains and low EWs can help reduce the activation energy in proton conduction due to enhanced hydrophobic and hydrophilic segregation. In addition, when using the blended ionomer, the CLs form a more porous microstructure to help reduce the resistance of oxygen transport and contributes to lower mass transfer loss. This effect is proven in fuel cell operations at not a lower temperature (70 °C) and full humidification (100%) but at an elevated temperature (80 °C) and lower relative humidity (50 and 75%). Blended ionomer-based CLs with a higher water uptake and porous CL structure result in improved fuel cell performance with better mass transport than single ionomer-based CLs.

Approaches to the Modification of Perfluorosulfonic Acid Membranes

Polymer ion-exchange membranes are featured in a variety of modern technologies including separation, concentration and purification of gases and liquids, chemical and electrochemical synthesis, and hydrogen power generation. In addition to transport properties, the strength, elasticity, and chemical stability of such materials are important characteristics for practical applications. Perfluorosulfonic acid (PFSA) membranes are characterized by an optimal combination of these properties. Today, one of the most well-known practical applications of PFSA membranes is the development of fuel cells. Some disadvantages of PFSA membranes, such as low conductivity at low humidity and high temperature limit their application. The approaches to optimization of properties are modification of commercial PFSA membranes and polymers by incorporation of different additive or pretreatment. This review summarizes the approaches to their modification, which will allow the creation of materials with a different set of functional properties, differing in ion transport (first of all proton conductivity) and selectivity, based on commercially available samples. These approaches include the use of different treatment techniques as well as the creation of hybrid materials containing dopant nanoparticles. Modification of the intrapore space of the membrane was shown to be a way of targeting the key functional properties of the membranes.

Suppression of Membrane Degradation Accompanied with Increased Output Performance in Fuel Cells by Use of Silica-Containing Anode Catalyst Layers

Polymer electrolyte membranes (PEMs) for fuel cells are chemically degraded by the attack of ·OH radicals generated from the decomposition of H2O2, which is predominantly produced at the Pt/C hydrogen anode. The incorporation of conventional radical scavengers into the PEM suffers from a decrease in the output performance. We, for the first time, demonstrate that the addition of hygroscopic silica nanoparticles (NPs) to the Pt/C anode catalyst layer provides a remarkably prolonged (ca. 4 times) lifetime of a Nafion membrane in an accelerated stress test and open circuit voltage (OCV) holding at 90 °C, accompanied by improved output (I-E) performances at low relative humidity. It has been found that the use of silica NPs decreases H2O2 formation rate from the OCV to a practical H2 oxidation potential in a half-cell using 0.1 M HClO4 at 90 °C and provides reduced ohmic resistance (increase in water content) and effective utilization of Pt cathode catalyst in a single cell, by which the improvement of the durability of the PEM and increased output performance are explained rationally.

Facile and controllable synthesis of monodisperse gold nanoparticle bipyramid for electrochemical dopamine sensor

We demonstrated potential features of gold nanoparticle bipyramid (AuNB) for an electrochemical biosensor. The facile synthesis method and controllable shape and size of the AuNB are achieved through the optimization of cetyltrimethylammonium chloride (CTAC) surfactant over citric acid (CA) ratio determining the control of typically spherical Au seed size and its transition into a penta-twinned crystal structure. We observe that the optimized ratio of CTAC and CA facilitates flocculation control in which Au seeds with size as tiny as ∼14.8 nm could be attained and finally transformed into AuNB structures with an average length of ∼55 nm with high reproducibility. To improve the electrochemical sensing performance of a screen-printed carbon electrode, surface modification with AuNB via distinctive linking procedures effectively enhanced the electroactive surface area by 40%. Carried out for the detection of dopamine, a neurotransmitter frequently linked to the risk of Parkinson's, Alzheimer's, and Huntington's diseases, the AuNB decorated-carbon electrode shows outstanding electrocatalytic activity that improves sensing performance, including high sensitivity, low detection limit, wide dynamic range, high selectivity against different analytes, such as ascorbic acid, uric acid and urea, and excellent reproducibility.

High Proton Conductivity of 3D Graphene Oxide Intercalated with Aromatic Sulfonic Acids

The development of efficient proton conductors that are capable of high power density, sufficient mechanical strength, and reduced gas permeability is challenging. Herein, we report the development of a series of aromatic sulfonic acid/graphene oxide hybrid membranes incorporating benzene sulfonic acid (BS), naphthalene sulfonic acid (NS), naphthalene disulfonic acid (DS) or pyrene sulfonic acid (PS) using a facile freeze dried method. For out-of-plane proton conductivity, the 3DGO-BS and 3DGO-NS yielded proton conductivities of 4.4×10-2  S cm-1 and 3.1×10-2  S cm-1 , respectively; this represents a two-times higher value than that which occurs for three dimensional graphene oxide (3DGO). Additionally, the respective prepared films as membranes in a proton exchange membrane fuel cell (PEMFC) show maximum power density of 98.76 mW cm-2 for 3DGO-NS while it is 92.75 mW cm-2 for 3DGO-BS which are close to double that obtained for 3DGO (50 mW cm-2 ).

Superior Proton Exchange Membrane Fuel Cell (PEMFC) Performance Using Short-Side-Chain Perfluorosulfonic Acid (PFSA) Membrane and Ionomer

Optimization of the ionomer materials in catalyst layers (CLs) which sometimes is overlooked has been equally crucial as selection of the membranes in membrane electrode assembly (MEA) for achieving a superior performance in proton exchange membrane fuel cells (PEMFCs). Four combinations of the MEAs composed of short-side-chain (SSC) and long-side-chain (LSC) perfluorosulfonic acid (PFSA) polymers as membrane and ionomer materials have been prepared and tested under various temperatures and humidity conditions, aiming to investigate the effects of different side chain polymer in membranes and CLs on fuel cell performance. It is discovered that SSC PFSA polymer used as membrane and ionomer in CL yields better fuel cell performance than LSC PFSA polymer, especially at high temperature and low RH conditions. The MEA with the SSC PFSA employed both as a membrane and as an ionomer in cathode CL demonstrates the best cell performance amongst the investigated MEAs. Furthermore, various electrochemical diagnoses have been applied to fundamentally understand the contributions of the different resistances to the overall cell performance. It is illustrated that the charge transfer resistance (R_ct) made the greatest contribution to the overall cell resistance and then membrane resistance (R_m), implying that the use of the advanced ionomer in CL could lead to more noticeable improvement in cell performance than only the substitution as the membrane.

Influence of Ionomer Content in the Catalytic Layer of MEAs Based on Aquivion® Ionomer

Perfluorinated sulfonic acid (PFSA) polymers such as Nafion^® are widely used for both electrolyte membranes and ionomers in the catalytic layer of membrane-electrode assemblies (MEAs) because of their high protonic conductivity, σ_H, as well as chemical and thermal stability. The use of PFSA polymers with shorter side chains and lower equivalent weight (EW) than Nafion^®, such as Aquivion^® PFSA ionomers, is a valid approach to improve fuel cell performance and stability under drastic operative conditions such as those related to automotive applications. In this context, it is necessary to optimize the composition of the catalytic ink, according to the different ionomer characteristics. In this work, the influence of the ionomer amount in the catalytic layer was studied, considering the dispersing agent used to prepare the electrode (water or ethanol). Electrochemical studies were carried out in a single cell in the presence of H₂-air, at intermediate temperatures (80-95 °C), low pressure, and reduced humidity ((50% RH). %). The best fuel cell performance was found for 26 wt.% Aquivion^® at the electrodes using ethanol for the ink preparation, associated to a maximum catalyst utilization.

Differences in the Electrochemical Performance of Pt-Based Catalysts Used for Polymer Electrolyte Membrane Fuel Cells in Liquid Half- and Full-Cells

A substantial amount of research effort has been directed toward the development of Pt-based catalysts with higher performance and durability than conventional polycrystalline Pt nanoparticles to achieve high-power and innovative energy conversion systems. Currently, attention has been paid toward expanding the electrochemically active surface area (ECSA) of catalysts and increase their intrinsic activity in the oxygen reduction reaction (ORR). However, despite innumerable efforts having been carried out to explore this possibility, most of these achievements have focused on the rotating disk electrode (RDE) in half-cells, and relatively few results have been adaptable to membrane electrode assemblies (MEAs) in full-cells, which is the actual operating condition of fuel cells. Thus, it is uncertain whether these advanced catalysts can be used as a substitute in practical fuel cell applications, and an improvement in the catalytic performance in real-life fuel cells is still necessary. Therefore, from a more practical and industrial point of view, the goal of this review is to compare the ORR catalyst performance and durability in half- and full-cells, providing a differentiated approach to the durability concerns in half- and full-cells, and share new perspectives for strategic designs used to induce additional performance in full-cell devices.

Tuning Proton Exchange and Transport in Protic Ionic Liquid Solution through Anion Chemistry

Herein, we demonstrate that the potential difference of proton reduction and hydrogen gas oxidation of protic ionic liquids is closely related to the proton exchange rate in the electrolyte. Through a careful design of anion chemistry, the proton exchange rate can be boosted by several orders of magnitude, reaching 200 kHz at 100 °C. It is found that the enhanced proton exchange rate can effectively decrease the potential loss at the electrode, most likely through alleviating the H⁺ concentration gradient incurred by electrochemical reactions at the electrode surfaces. This research therefore highlights the strategy of using anions of medium-strength acids, such as H₂PO₄^-, for protic ionic liquids with enhanced proton exchange capability.