Proton Exchange Research Articles

Optimizing efficiency of proton exchange membrane electrolyzer system based on multiphysics model and differential evolution strategy

This work focuses on a comprehensive performance enhancement considering hydrogen production, energy consumption of balance of plant (BOP), and thermal safety by optimizing the inlet water temperature and flow velocity. First, a multiphysics model is introduced to show that the inlet water temperature and flow velocity can affect the current density as well as the hydrogen production. An overall efficiency is defined to balance the hydrogen production and the energy consumption of BOP. After that, a surrogate model is established based on artificial neural network to replace the multiphysics model because of its huge computational effort. For the thermal safety and performance enhancement, an optimization problem with the maximum membrane temperature as a constraint and the overall efficiency as an objective function is proposed. The differential evolution (DE) strategy with the feasibility rule (FR) is adopted to solve this optimization problem. Finally, the DE-FR-based optimization algorithm is applied to three typical days in Chengdu of China representing summer, winter, and transitional seasons, respectively. Compared to the invariant inlet water flow velocity and temperature, the optimal and time-varying parameters improve their efficiency by relative percentages of 2.68%, 3.79%, and 3.29% for the three typical days, respectively.

Different functional groups cross-linked graphene oxide membranes for proton exchange membrane fuel cell

The graphene oxide (GO) membrane treated by ozone, GOL, exhibits a relatively high conductivity, but its mechanical strength cannot be maintained due to severe swelling. To further improve the conductivity while suppressing the swelling, the free-standing GO membrane was subjected to ozone treatment and subsequently modified by crosslinking agents with oxygen functional groups, i.e., glyoxal (GLX) and oxalic acid (OXA). The modified membranes, GLX/GOL and OXA/GOL, successfully reduced the swelling and increased the conductivity to provide an excellent power output of a fuel cell at 30 °C due to the increased oxygen functional groups and the carbon defects. Furthermore, OXA/GOL exhibited a significant stability at elevated temperatures. At 50 °C, the through-plane conductivity and power output increased to 23.5 mS cm−1 and 317 mW cm−2, respectively. This is considered to be due to the relatively high thermal stability of the carboxy group added by the OXA modification.

Thermodynamic performances of a power-to-X system based on solar concentrating photovoltaic/thermal hydrogen production

100% renewable power-to-X (fuel, power, and heat products) systems have great application potential for the achievement goal of carbon neutrality. However, the extensive chain of the power-to-X system could result in low energy utilization efficiency. A novel composite-parabolic-concentrating photovoltaic/thermal-collector-based power-to-X system utilizing 100% solar energy is proposed, which integrates proton exchange membrane electrolysis cells and proton exchange membrane fuel cells to provide heat, electricity, and hydrogen. Thermodynamic models for each subsystem are established, and energy and exergy efficiencies are assessed in the thermodynamic laws. Three operation modes are analyzed to adapt to the variations of solar radiation and a residential building is used as an application scenario to evaluate its thermodynamic and economic performances in dynamic variations of solar radiations and energy demands. The effects of key operating parameters, such as solar radiation intensity, photovoltaic coverage ratio, current density, and operating temperature, on the performances are investigated. The maximum exergy destruction of the concentrator photovoltaic/thermal collector is 93.20% at the rated operating conditions, and the system exergy and energy efficiencies are 9.11% and 48.97%, respectively. The economic results demonstrate that the levelized costs of solar power, hydrogen, and fuel cell power are 0.2936 $/kWh, 21.70 $/kg, and 2.1520 $/kWh, respectively.

Sulfonated Microporous Polyxanthene Binder for High-Temperature Hydrogen Fuel Cells.

High-temperature proton exchange membrane fuel cells based on phosphoric acid-doped polybenzimidazole (PBI) materials face challenges of low power output and low Pt utilization due to the lack of suitable electrode binders. We have developed a sulfonated microporous polymer material (namely, SPX, i.e., sulfonated polyxanthene) with excellent chemical stability, to be used as the electrode binder. The rigid and contorted polymer structure of SPX reduces the adsorption of the ionomer on the Pt catalyst surface, prevents phosphoric acid loss, and promotes the rapid transport of reactant gases and water molecules within the catalyst layer. The cell performance is thereby significantly improved, with a Pt utilization reaching 42.51%, and a peak power density approaching 805 mW cm-2 at 180 °C, surpassing the performance of cells using PBI as a binder.

Flow flied inspired by sieve plate structure of plant leaf veins for proton exchange membrane fuel cells

Bionic flow fields have been applied in bipolar plates for proton exchange membrane fuel cells (PEMFCs) to significantly improve cell performance. This study, inspired by the vascular structure of plant leaf veins, proposes a bionic flow field that incorporates a sieve plate structure to enhance the distribution of reactants. To evaluate this design, a three-dimensional two-phase isothermal computational fluid dynamics (CFD) model was developed. The effect of hole parameters on the cell performance, such as opening ratio, hole number, and hole arrangement on the bionic sieve plate (BSP), was investigated and compared with a parallel flow field (PFF). The results showed that the peak power density of the bionic sieve plate flow field (BSPFF) was 0.991 W/cm2, 25.4% higher than that of the PFF, when the ratio of openings was 22.3%, the number of openings was 4, the sieve angle was 22.5°, and the number of sieves was 5. This BSPFF design provides insight into the development of bipolar plates to improve the performance of PEMFCs.

Variance-based global sensitivity analysis of the performance of a proton exchange membrane water electrolyzer

This study is threefold objective. First, a nonlinear one-dimensional steady-state simulation model for hydrogen production from proton exchange membrane water electrolyzer (PEMWE) is established. The model comprehensively addresses activation, diffusion overpotentials and ohmic potential drop, and particularly incorporating Nafion membrane properties in the presence of liquid water. The model is enhanced by analyzing the hydrogen crossover, introducing corresponding diffusion equations to evaluate Faraday efficiency. The model accurately quantifies voltage efficiency, hydrogen production rate and specific energy consumption, and it is validated with published experimental data found in the scientific literature. Second, a variance-based global sensitivity analysis (GSA) on the model, is employed as a metric to assess the impact of operating conditions and material characteristics on three objective functions: the hydrogen production rate; the voltage efficiency and the specific energy consumption. Third, to support the GSA analysis, genetic algorithm (GA) technique is performed to maximize hydrogen production rate while minimizing specific energy consumption. In the course of this novel investigation, it was discerned that the number of cells, the cross-sectional area of the electrolyzer, the current density and temperature all exerted a significant impact on the three objective functions. This combined approach GSA-GA provides a thorough exploration of parameter influences and an efficient optimization strategy for enhancing the model's performance. These findings provide valuable insights that can guide analysis of the performance and the optimization of the PEMWE system.

Adipic acid-mediated hydrogen bonding network allocation for efficient proton conduction in water-stabilized lamellar MOF membranes

The poor water-stability and cross-layer proton transfer property pose a challenge to the lamellar metal–organic frameworks (MOFs) membrane when acting as a promising proton exchange membrane. Herein, we report an adipic acid-mediated strategy to improve the water-stability and the cross-layer proton conductivity of CuTCPP lamellar MOF membrane, which achieves a maximum power density and current density of 112.6 mW cm−2 and 424.4 mA cm−2, respectively. Adipic acid with extra functional groups (–PO3H2, –COOH) stably bridges the adjacent crystal layers via the terminal carboxylic acid anchoring Cu sites. In particular, the extra functional groups introduced into the adipic acid regulate the allocation of hydrogen bonding networks in an umbrella-shape around adipic acid with copper-porphyrin structures as external margin, enriching the coherence of hydrogen bonding network on the proton transport path. Benefiting from the regular pore structure of MOF, the optimized hydrogen bonding networks in adjacent crystal layers construct a more abundant through-plane transfer pathway. The resultant through-plane proton conductivities of CuTCPP-PO3H2/–COOH membranes are up to 108/89 mS cm−1 at 80 °C and 100 % RH, which is ∼ 6-fold higher than that of the pristine CuTCPP membrane (13 mS cm−1), with a conductivity attenuation of < 5 % during a humidity cycling test for 12 times.

Platinum-dependent 2H-to-1T phases conversion of MoS2 nanosheets growing on cross-interlocking porous carbon for boosting hydrogen evolution reaction

Proton exchange membrane water electrolysis (PEMWE) coupled with renewable energy is regarded as a sustainable approach for green hydrogen production. However, the low reserve and high cost of platinum cathode electrocatalysts greatly limit its widespread deployment. Herein, we report a phase conversion strategy to obtain an efficient low-Pt loading electrocatalyst composed of multi-atomic Pt substituted 1T-MoS2 nanosheet grown on a cross-interlocking porous carbon matrix (Pt@1T-MoS2/C). In combination with experimental and theoretical results, the 2H-to-1T phase conversion of MoS2 induced by the Pt substitution is investigated, and the as-formed Pt-S-Mo active site accounts for the excellent hydrogen evolution reaction (HER) performance. Benefiting from the improved electron transfer efficiency and Pt-S-Mo active sites, the Pt@1T-MoS2/C delivers a high mass HER activity of ∼58.9 A·mgPt−1, and an excellent stability of 200 h at 1000 mA∙cm−2 in a practical PEMWE device.

Ultrastable monolithic electrodes with single-atom platinum-oxygen sites for efficient hydrogen evolution in acidic conditions

PtNC single-atom catalysts (SACs) single-atom catalysts (SACs) are promising for acidic hydrogen evolution reaction (HER) but suffer from instability at high current densities, limiting their large-scale application. Herein, PtO bonds are constructed to securely anchor atomically dispersed Pt for single-atom (SA) catalysis, utilizing etched vertical graphene (EVG) nanosheets as monolithic supports (Pt-SAs/EVG). Compared to PtNC, the resultant PtO4 coordination demonstrates improved stability while maintaining significant catalytic activity. When applying this catalyst in the acidic HER, a high turnover frequency (34.6 s−1) is achieved at 70 mV, accompanied by exceptional durability exceeding 100 h at −100 mA cm−2. Theoretical analyses indicate that the PtO bonds confer stability to the Pt atoms, facilitating the efficient adsorption of protons and the subsequent desorption of hydrogen. The prepared Pt-SAs/EVG can also be directly employed as the cathode to afford stable operation at 0.5 A cm−2 in a proton exchange membrane electrolyzer cell. This study offers novel insights into enhancing the performance of SACs for industrial applications in electrocatalysis.

Effect of defective cells on the temperature distribution of a proton exchange membrane fuel cell stack

Proton exchange membrane fuel cell (PEMFC) stacks may encounter performance degradation or even damage during long-term operations, while the influence of defective cells on the stack performance still remains inadequately understood. In this study, the effect of defective cells on the stack temperature distribution was experimentally investigated. Two defective cells of different defect degrees were prepared by controlling hydrogen starvation time and quantitively characterized by the polarization curves, electrochemical impedance spectroscopy (EIS), and galvanostatic charge method (GCM) tests. Results show that the presence of defective cells reduces the stack performance and the temperature distribution uniformity. The increment of stack temperature and decrement of stack temperature uniformity is more prominent (with 0.9 °C and 0.31 °C at 0.8 A cm−2, respectively) when the defective cell is located at central stack. The peak sub-cell regional temperature rise can even reach 2.9 °C. For defective cells with a relatively low degree of defect, the reverse current density is high, thus leading to an increased heat generation with the average sub-cell regional temperature increment of 0.5 °C and causing adjacent normal cells to operate at higher temperature. For defective cells with an excessive degree of defect, polarization reverse occurs at low current densities, resulting in significant voltage losses and reduced performance of the stack. The present results are insightful for developing thermal management strategies for the long-term operation of PEMFC stacks.

Model-based humidity observer for vehicle proton exchange membrane fuel cell based on a new sliding mode observer estimation technique

ABSTRACT The internal water content of the proton exchange membrane fuel cell (PEMFC) stack significantly affects its performance and duration. To achieve optimal humidity level, real-time monitoring of the humidity of the cathode and the anode is crucial for the PEMFC. As far as we know, the relative humidity of the PEMFC can be estimated via an observer based on the measurable output voltage. However, the rapid changes in vehicle operating conditions pose a challenge to the estimation accuracy. Different from the existing sliding mode observers (SMOs), this study pays more attention to the testing noise of voltage measuring sensor. To reduce the noise influence and improve the estimation accuracy, a new sliding mode observer (NSMO) combined with an online Kalman filter is presented based on the dimensionless model of the PEMFC in this study. The applicability of the proposed NSMO in estimating the cathode relative humidity and the anode relative humidity is illustrated by the simulation results. At the same time, comparisons between the NSMO and the online Kalman filter are provided which show a substantially higher estimation accuracy and lower cost for the NSMO. Furthermore, the final results indicate the mean absolute deviations of the cathode and the anode relative humidity for the NSMO are, respectively, reduced to 0.39% and 0.28%.

Carbone-neutral oriented methanol-reforming HT-PEMFC cogeneration based on absorption power refrigeration cycle

Methanol is considered as a promising hydrogen carrier in accelerating the carbon-neutral applications of fuel cell cogeneration. However, the methanol reforming process emits CO2 whose efficient recycling is challenging due to the inevitable power and cooling consumption. To this end, this paper considers the methanol reforming based high-temperature proton exchange membrane fuel cells (HT-PEMFC) cogeneration system, equipped with ammonia absorption power-refrigeration cycle (APRC). The waste heat in the integrated system is utilized for the fuel preheating, evaporation and reforming, driving APRC, and water heating, achieving a cascaded utilization of thermal energy. By building the mathematical models for each subsystem, thermodynamic and economic assessments are investigated. The results confirm that the waste heat of HT-PEMFC is sufficient to drive both methanol reforming and APRC, with additional electricity output from APRC. At a current density of 0.53 A/cm2, the exergy efficiency of the integrated system under the design condition is 0.525 and reaches a maximum value of 0.565 at a reaction temperature of 180 °C and pressure of 1.2 bar. The techno-economic analysis reveals a dynamic payback period of 5.2 years and net present value of 1.14 M$ with a 20-year lifespan of the integrated system.

Rough-surfaced polybenzimidazole membranes incorporating sulfonated porous aromatic frameworks for simultaneous enhancement of proton conduction and membrane electrode assembly optimization

The interface between the proton exchange membrane (PEM) and the catalyst layer (CL) has a substantial impact on the performance of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, studies on the interface in HT-PEMFCs have been rarely reported. In this work, an effective strategy to mitigate interface problems was designed. A rough-surfaced membrane was successfully constructed by depositing high-surface-area sulfonated porous aromatic frameworks (SPAFs) in poly[2,2′ −(p-oxydiphenylene)-5,5′ −benzimidazole (OPBI) to achieve a dual goal. The catalyst was sprayed on the rough-surfaced side of the composite membranes, and the surface area was significantly increased. Meanwhile, an efficient proton transport pathway within the rough-surfaced membrane was constructed based on hydrophilic nanochannels in SPAFs. As a result, a substantial increase of 1.7 times in the electrochemical surface area (ECSA) of the membrane electrode assembly (MEA) was achieved relative to that of a flat membrane. Compared to a pristine OPBI membrane, the membrane with a high content of 20 wt% SPAFs exhibits a 236% increase in proton conductivity at 170 °C and a considerable 1.82-fold enhancement in fuel cell performance under analogous circumstances. This strategy, which simultaneously enhances the proton conductivity of the membrane and strengthens the interface between the membrane and the catalyst layer, provides a new approach to improving the performance of HT-PEMFC.

Performance prediction of experimental PEM electrolyzer using machine learning algorithms

Proton exchange membrane water electrolyzer (PEMWE) is a sustainable energy conversion device that uses electrical energy to oxidize water and convert it into chemical energy (hydrogen and oxygen) and heat. Despite their numerous advantages, such as high current density, efficiency, high-purity hydrogen production, compatibility with renewable energy sources, and compact design, they have not yet matured due to durability, cost, and electrochemical performance deficiencies. Effective assessment of performance and durability is crucial for electrolyzer design and optimization. This study analyzes the electrochemical performance of PEMWE with artificial intelligence approaches using experimental data. Three different machine learning (ML) techniques − Multilayer Perceptron (MLP), Support Vector Machine (SVM), and Random Forest (RF) were trained and tested for predicting the hydrogen flowrate and current density for PEMWE using different input parameters. These input parameters include cell voltage, temperature, torque, and water flowrate. SVM was detected to be the best technique in predicting all output parameters with a Mean Absolute Error (MAE) of 0.0317 and 0.0671 for current density and hydrogen flowrate predictions in the test set, respectively. The study results show that machine-learning algorithms can optimize operational parameters in electrolyzer control systems.

An inquiry into transport phenomena and artificial intelligence-based optimization of a novel bio-inspired flow field for proton exchange membrane fuel cells

Achieving an effective flow field configuration is requisite to ensure the optimal performance of a proton exchange membrane fuel cell (PEMFC). Herein, an unprecedented bio-inspired flow field is offered to improve species transport and enhance the power density of PEMFCs in order to provide a pathway for effective utilization of them. The flow field consists of two twin parts, resembling the lung structure, and a repeating converging-diverging pattern, so-called “converging-diverging lung-inspired serpentine (CDLIS).” Utilizing multiphase computational fluid dynamics, this study delves into the transport phenomena and evaluates the comprehensive efficacy of a three-dimensional PEMFC. The CDLIS flow field considerably enhances both crosswise and lengthwise mass transfer by inducing several favorable flow mixing phenomena and improving reactant's velocity distribution. The output power of CDLIS exhibits a substantial increase of 10.87%, 43.63%, 12.22%, 12.83%, 12.52%, and 13.8% compared with the simple serpentine, parallel, two-path serpentine, four-path serpentine, lung-inspired serpentine, and combined parallel-serpentine flow fields, respectively. Due to its highly efficient mass transfer capabilities, enhanced convective mass flow, and outstanding current density, CDLIS possesses the most effective water management and the lowermost flooding risk. To further improve the performance of the PEMFC, artificial intelligence codes based on the non-sorting genetic algorithm II (NSGA II) and a surrogate analytical model are developed to optimize the operating conditions of CDLIS at the limiting current density situation where concentration losses impede the mass transfer of reactants. The target parameters for optimization are current density, water saturation (WS), and oxygen transport resistance (OTR). Under optimum conditions, a remarkable current density of 6.35 A cm−2, a low WS of 0.043, and a reduced OTR of 5.06 s m−1 are obtained.

A Lyapunov-based adaptive control strategy with fault-tolerant objectives for proton exchange membrane fuel cell air supply systems

Proton exchange membrane fuel cells (PEMFCs) are being extensively studied for large-scale applications. The need for reliable and safe system integration processes emphasizes the importance of health-conscious control research. Considering their high-frequency operation and load variations, the reliability of PEMFCs can be compromised by mechanical failures within air supply systems. Therefore, this paper proposes an adaptive control strategy with fault-tolerant objectives for regulating the oxygen excess ratio (OER). Specifically, it addresses two common faults within air compressors, namely compressor overheating and increased mechanical friction. While these faults have been studied in fault diagnosis research, their treatment within the context of fault-tolerant control is relatively uncommon. To ensure reliable OER regulation under multiple fault occurrences, estimator-based parameter adaptation laws are firstly derived using Lyapunov theory during the stability demonstration process. Then, the baseline controller is designed using an extended state observer and feedback linearization, with a clear presentation of the existence and stability of the state transformation. Furthermore, extensive numerical tests are conducted to demonstrate the effectiveness of the proposed control strategy. The proposed adaptive control strategy ensures consistent regulation outcomes without compromising performance under healthy conditions, highlighting its potential for large-scale application as a standard control approach in practical applications.

Experimental study on the cold-start performance of a gas heating assisted air-cooled proton exchange membrane fuel cell stack

Air-cooled proton exchange membrane fuel cells (PEMFCs) have the advantages of simple structure, low parasitic power, and flexible application scenarios. However, it is difficult to warm up the stack under subzero temperatures because excessive air is used as the cooling medium. In this study, the thermal balance inside an air-cooled PEMFC stack during cold start was theoretically analyzed to explore the relationship between the heating power and ambient temperature. Subsequently, the cold-start performance was tested in a climatic chamber. The results showed that the combination of endplate heating and gas heating is a feasible cold-start measure. The theoretical analysis indicated that only 14 % of the stack rated power for preheating can promote a successful cold start at −30 °C, which has also been validated in the ensuing tests. The test results showed that the temperature uniformity and the cell voltage consistency deteriorate as the ambient temperature decreases, while these two indicators can be improved by increasing the gas heating power. As the ambient temperature decreases, the heating power may become too high, resulting in poor cold-start performance. Therefore, if an air-cooled stack is to be started at extreme low temperatures, further research is needed in terms of flow fields and materials.

Micro-CT structures facilitated lattice Boltzmann simulations on the water dynamics in PEMFCs GDL-Gas channel

This study employed Micro X-ray computed tomography (Micro-CT) to reconstruct the gas diffusion layer (GDL) in proton exchange membrane fuel cells (PEMFCs) and used lattice Boltzmann method (LBM) simulations to investigate the dynamic behavior of liquid water in the multiscale space of the GDL and gas channel (GC). The results showed that the transport of liquid water from GDL to GC through the interface of GDL-land and GDL-GC were divided into four stages: large pore filling, through-plane breakthrough, in-plane diffusion, and rapid transport into GC. The wettability of GC wall and GDL affects the transport and distribution of liquid water. When the contact angle on the GC wall was less than 90°, it promoted liquid water transport to the top GC wall, resulting in faster internal flow formation. Conversely, contact angles exceeding 90° caused liquid water to break through the GDL-GC interface from pores away from the GC wall. When the contact angle of the GDL was in the range of 110°–150°, both excessively large and excessively small contact angles hindered water transport and management. Maintaining the contact angle of the GDL around 130° enhanced the breakthrough path and transport speed of liquid water into the GC, and it also reduces localized liquid water accumulation.

A directional electrode separator improves anodic biofilm current density in a well-mixed single-chamber bioelectrochemical system

In this study, a directional electrode separator (DES) was designed and incorporated into a single-chamber bioelectrochemical system (BES) to reduce migration and reoxidation of hydrogen. This issue arises when H2, generated at the cathode, travels to the anode where anodic biofilms use H2. To test the feasibility of our design, a 3D-printed BES reactor equipped with a DES was inoculated with anaerobic digestor granules and operated under fed-batch conditions using fermented corn stover effluent. The DES equipped reactor achieved significantly higher current densities (∼53 A/m²) compared to a conventional single-chamber BES without a separator (∼16 A/m²), showing a 3.3 times improvement. Control abiotic electrochemical experiments revealed that the DES exhibited significantly higher proton conductivity (456±127 µS/mm) compared to a proton exchange membrane (67±21 µS/mm) with a statistical significance of P=0.03. The DES also effectively reduced H2 migration to the anode by 21-fold relative to the control. Overall, incorporating a DES in a single-chamber BES enhanced anodic current density by reducing H2 migration to the anode.

Self-supported porous carbon decorated with coralline RuCo alloy for efficient OER in acid

Developing an OER electrocatalyst that combines high performance with low cost represents a crucial challenge to address for the widespread adoption and implementation of PEM water electrolyzers. The Ru-based catalyst has garnered significant interest owing to its cost-effectiveness and high activity, positioning it as one of the prime contenders to replace Ir-based catalysts. Nevertheless, Ru-based catalysts are easily corrupted by oxidation at high potential, leading to poor catalyst durability. In this work, we used a simple method to synthesize an electrode material which was a carbon framework-supported coralline RuCo alloy catalyst on the CC surface. The porous and highly conductive carbon framework in RuCo@C/CC effectively anchors the RuCo alloy, preventing its aggregation and detachment from the CC. And the carbon framework also facilitates enhanced mass and charge transfer processes, thereby greatly improving catalytic performance. Additionally, charge transfer and redistribution occur within the RuCo alloy, thereby efficiently reducing the activation energy barrier (via the AEM mechanism) of the OER, consequently enhancing OER performance. Therefore, RuCo@C/CC exhibits outstanding performance in acidic OER, achieving a current density of 10 mA/cm2 at a remarkably low overpotential of 200 mV, significantly surpassing commercial RuO2 (which requires 280 mV), owing to its exceptional OER kinetics, while also demonstrating exceptional stability in practical PEMWE test. This research introduces a convenient route for creating a highly efficient and durable alloy electrocatalyst, showcasing its promise for Proton Exchange Membrane Water Electrolysis.