Membrane Electrode Assembly Research Articles

Carbon Nanocage Supported Asymmetrically Coordinated Nickle Single‐Atom for Enhanced CO2 Electroreduction in Membrane Electrode Assembly

AbstractDesigning efficient catalysts for operating CO2 electroreduction in membrane electrode assembly (MEA) faces significant obstacles. Herein, we propose an asymmetrically coordinated Ni single‐atom catalyst featuring axial Br coordination at NiN4Br sites anchoring onto hollow Br/N co‐doped carbon nanocages, achieved through a NaBr‐assisted confined‐pyrolysis strategy. The Ni‐NBr‐C catalyst exhibits a high CO Faradaic efficiency (FECO>97 %) over the current density range of 50 to 350 mA cm−2 in the MEA device. Furthermore, Ni‐NBr‐C shows a stable cell voltage of 2.66±0.2 V while delivering a large current density of 350 mA cm−2 over an 85‐hour long‐term operation, demonstrating its potential for industrial‐scale applications. Advanced characterization techniques and theoretical calculations reveal that the coordination and doping of Br not only enhance the intrinsic activity but also highlight that the unique pore structure improves mass transfer efficiency.

Roles of copper(I) in water-promoted CO2 electrolysis to multi-carbon compounds.

The membrane electrode assembly (MEA) is promising for practical applications of the electrocatalytic CO2 reduction reaction (CO2RR) to multi-carbon (C2+) compounds. Water management is crucial in the MEA electrolyser without catholyte, but few studies have clarified whether the co-feeding water in cathode can enhance C2+ formation. Here, we report our discovery of pivotal roles of a suitable nanocomposite electrocatalyst with abundant Cu2O-Cu0 interfaces in accomplishing water-promoting effect on C2+ formation, achieving a current density of 1.0 A cm-2 and a 19% single-pass C2+ yield at 80% C2+ Faradaic efficiency in MEA. The operando characterizations confirm the co-existence of Cu+ with Cu0 during CO2RR at ampere-level current densities. Our studies reveal that Cu+ works for water activation and aids C‒C coupling by enhancing formations of adsorbed CO and CHO species. This work offers a strategy to boost CO2RR to C2+ compounds in industrial-relevant MEA by combining water management and electrocatalyst design.

Toward revolutionizing PEMFC manufacturing for clean energy conversion: a review on the innovative contribution of 3D printing techniques

AbstractThree-dimensional printing (3DP) is a technology useful for fabricating both structural and energy devices. Of great concern to this review is promising nature of additive manufacturing (AM) for engineering fuel cells (FCs) for clean energy conversion. 3DP technique is useful for the fabrication of fuel cell components, and they offer waste minimization, low-cost, and complex geometric structures. In this review, significance of different 3DP techniques toward revolutionizing fuel cell fabrication is given. The aim is to unravel the importance and status of 3D-printed fuel cells and hence provides researchers and scientists with extensive opportunities of 3DP techniques for fuel cell engineering. After careful selection of state-of-the-art literatures, different kinds of 3DP techniques of relevance to electrolytes, electrodes, and other key components (e.g., gas diffusion layers (GDLs), bipolar plates (BPs), and membrane electrode assembly (MEA)) fabrication are explicitly discussed. Among the techniques, the best approaches are recommended for further studies. Advantages associated with these techniques are indicated for the benefit of those whose interests matter most on clean energy production. The challenges researchers are facing in the use of 3DP for fuel cell fabrications are identified. Possible solutions to the identified challenges are suggested as way forward to further development in this research area. It is expected that this review article will benefit engineers and scientists who have interest on clean energy conversion devices.

CATALYST BASED ON PALLADIUM‐MODIFIED MIL‐53(AL) PYROLYSATE FOR ORR IN ALKALINE MEDIA

A catalyst for the oxygen reduction reaction (ORR) based on the metal‐organic framework material MIL‐53(Al) modified with palladium was synthesized. Its textural and morphological characteristics were studied using the method of adsorption porosimetry, SEM, TEM, energy dispersive X‐ray analysis (EDAX) , X‐ray diffraction (XRD), Raman –spectroscopy, X‐ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA‐DSC). The electrocatalytic properties of the synthesized material in ORR were studied by voltammetry using a rotating disk electrode. Corrosion resistance was studied in the CV mode. It was found that the synthesized catalyst is characterized by high corrosion resistance. The tolerance of synthetized catalyst Pyr_MIL‐53(Al)_Pd to the methanol was studied. The obtained catalyst was studied in a membrane electrode assembly (MEA) formed by spraying an ionomer suspension onto a gas diffusion layer (GDL). The synthesized Pyr‐MIL‐53 (Al)_Pd and commercial platinum (60% Pt) (HiSPEC 9100) catalysts were compared in the cathode composition, and 10% PtM (M = Ni, Mo)/CNT catalysts were used on the anode. The power density of the FC (P) was calculated based on the obtained current‐voltage curves. Based on the set of characteristics, the synthesized catalyst based on MIL‐53 (AL) doped with palladium is superior in efficiency to the commercial platinum catalyst.

Prompting CO2 Electroreduction to Ethanol by Iron Group Metal Ion Dopants Induced Multi‐sites at the Interface of SnSe/SnSe2 p–n Heterojunction

AbstractThe development of non‐copper‐based materials for CO2 electroreduction to ethanol with high selectivity at large current density is highly desirable, but still a great challenge. Herein, we report iron group metal ions of M2+ (M=Fe, Co, or Ni)‐doped amorphous/crystalline SnSe/SnSe2 nanorod/nanosheet hierarchical structures (a/c‐SnSe/SnSe2) for selective CO2 electroreduction to ethanol. Iron group metal ions doping induces multiple active sites at the interface of M2+‐doped SnSe/SnSe2 p‐n heterojunction, which strengthens *CO intermediate binding for further C−C coupling to eventual ethanol generation. As a representative, Fe9.0%‐a/c‐SnSe/SnSe2 exhibits an ethanol Faradaic efficiency of 62.7 % and a partial current density of 239.0 mA cm−2 at −0.6 V in a flow cell. Moreover, it can output an ethanol Faradaic efficiency of 63.5 % and a partial current density of 201.2 mA cm−2 with a full‐cell energy efficiency of 24.1 % at 3.0 V in a membrane electrode assembly (MEA) electrolyzer. This work provides insight into non‐Cu based catalyst design for stabilizing the key intermediates for selective ethanol production from CO2 electroreduction.

Prompting CO2 Electroreduction to Ethanol by Iron Group Metal Ion Dopants Induced Multi-sites at the Interface of SnSe/SnSe2 p-n Heterojunction.

The development of non-copper-based materials for CO2 electroreduction to ethanol with high selectivity at large current density is highly desirable, but still a great challenge. Herein, we report iron group metal ions of M2+ (M=Fe, Co, or Ni)-doped amorphous/crystalline SnSe/SnSe2 nanorod/nanosheet hierarchical structures (a/c-SnSe/SnSe2) for selective CO2 electroreduction to ethanol. Iron group metal ions doping induces multiple active sites at the interface of M2+-doped SnSe/SnSe2 p-n heterojunction, which strengthens *CO intermediate binding for further C-C coupling to eventual ethanol generation. As a representative, Fe9.0%-a/c-SnSe/SnSe2 exhibits an ethanol Faradaic efficiency of 62.7 % and a partial current density of 239.0 mA cm-2 at -0.6 V in a flow cell. Moreover, it can output an ethanol Faradaic efficiency of 63.5 % and a partial current density of 201.2 mA cm-2 with a full-cell energy efficiency of 24.1 % at 3.0 V in a membrane electrode assembly (MEA) electrolyzer. This work provides insight into non-Cu based catalyst design for stabilizing the key intermediates for selective ethanol production from CO2 electroreduction.

Concentrated C2+ Alcohol Production Enabled by Post-Intermediate Modulation and Augmented CO Adsorption in CO Electrolysis.

The electrocatalytic synthesis of multicarbon products from CO2/CO feedstock represents a sustainable method for chemical production with a reduced carbon footprint. Traditional copper catalysts predominantly produce alkenes, but generating valuable and versatile C2+ alcohols, especially high-energy-density C3 alcohols, has been challenging due to issues with selectivity, activity, and stability. Here, we present the construction of Ru-doped Cu nanowires that enhance the selectivity of n-PrOH and C2+ alcohols. In situ Raman spectroscopy shows that our approach promotes both *CO binding and availability, particularly facilitating the formation of high-frequency-bound *CO (*COHFB) and maintaining multiple *CO adsorption modes on Ru-modified and bare low-coordinated Cu nanowires. Density-functional theory (DFT) simulations illustrate that introducing Ru species onto a low-coordinated Cu step surface simultaneously stabilizes CO and alcohol-related intermediates, shifting the dominant reaction pathway toward alcohols and facilitating CO-C2 coupling at the expense of ethylene selectivity. In an alkaline gas-diffusion electrolyzer, we attained a maximum Faradaic efficiency (FE) of 35.9% for n-PrOH and 62.4% for the total C2+ alcohols. Optimizing parameters in the membrane electrode assembly (MEA) system enabled the one-pot generation and separation of C2+ alcohols, achieving a record concentration of 18.8 wt % (4.2 wt % n-PrOH and 14.6 wt % EtOH) with nearly 100% purity at 200 mA/cm2 over 100 h. This work not only provides new insights and guidance for the development of future catalysts from the perspectives of surface science and mechanisms but also highlights the importance of coupling material engineering with reactor engineering to optimize the production process of high-value alcohol products.

Polymeric Lithium Battery using Membrane Electrode Assembly

Alternative configuration lithium cell exploits electrode and polymer electrolyte cast all‐in‐one to form a membrane electrode assembly (MEA), in analogy to fuel cell technology. The electrolyte is based on polyethylene oxide (PEO), lithium bis‐trifluoro sulfonyl imide (LiTFSI) conducting salt, LiNO3 sacrificial film‐forming agent to stabilize the lithium metal, and fumed silica (SiO2) to increase the polymer amorphous degree. The membrane has conductivity ranging from ~5×10−4 S cm‐1 at 90 °C to 1×10−4 S cm‐1 at 50 °C, lithium transference number of ~0.4, and relevant interphase stability. The MEA including LiFePO4 (LFP) cathode is cycled in polymer lithium cells operating at 3.4 V and 70 °C, with specific capacity of ~155 mAh g‐1 (1C = 170 mA gLFP‐1) for over 100 cycles, without signs of decay or dendrite formation. The cell exploiting the MEA shows enhanced electrochemical performance as compared with the one using simple polymeric membrane stacked between cathode and anode. Furthermore, the MEA reveals the key advantage of possible scalability and applicability in roll‐to‐roll systems for achieving high‐energy lithium metal battery, as demonstrated by pouch‐cell application. These data may trigger new interest on this challenging battery exploiting the polymer configuration for achieving environmentally/economically sustainable, and safe energy storage.

Honeycomb‐Structured IrOx Foam Platelets as the Building Block of Anode Catalyst Layer in PEM Water Electrolyzer

AbstractAchieving robust long‐term durability with high catalytic activity at low iridium loading remains one of great challenges for proton exchange membrane water electrolyzer (PEMWE). Herein, we report the low‐temperature synthesis of iridium oxide foam platelets comprising edge‐sharing IrO6 octahedral honeycomb framework, and demonstrate the structural advantages of this material for multilevel tuning of anodic catalyst layer across atomic‐to‐microscopic scales for PEMWE. The integration of IrO6 octahedral honeycomb framework, foam‐like texture and platelet morphology into a single material system assures the generation and exposure of highly active and stable iridium catalytic sites for the oxygen evolution reaction (OER), while facilitating the reduction of both mass transport loss and electronic resistance of catalyst layer. As a proof of concept, the membrane electrode assembly in single‐cell PEMWE based on honeycomb‐structured IrOx foam platelets, with a low iridium loading (~0.3 mgIr/cm2), is demonstrated to exhibit high catalytic activity at ampere‐level current densities and to remain stable for more than 2000 hours.

Insights of the Proton Transport Efficiency of a Membrane Electrode Assembly by Operando Monitoring of the Local Proton Concentration during Water Oxidation

Insights of the Proton Transport Efficiency of a Membrane Electrode Assembly by Operando Monitoring of the Local Proton Concentration during Water Oxidation

Honeycomb-Structured IrOx Foam Platelets as the Building Block of Anode Catalyst Layer in PEM Water Electrolyzer.

Achieving robust long-term durability with high catalytic activity at low iridium loading remains one of great challenges for proton exchange membrane water electrolyzer (PEMWE). Herein, we report the low-temperature synthesis of iridium oxide foam platelets comprising edge-sharing IrO6 octahedral honeycomb framework, and demonstrate the structural advantages of this material for multilevel tuning of anodic catalyst layer across atomic-to-microscopic scales for PEMWE. The integration of IrO6 octahedral honeycomb framework, foam-like texture and platelet morphology into a single material system assures the generation and exposure of highly active and stable iridium catalytic sites for the oxygen evolution reaction (OER), while facilitating the reduction of both mass transport loss and electronic resistance of catalyst layer. As a proof of concept, the membrane electrode assembly in single-cell PEMWE based on honeycomb-structured IrOx foam platelets, with a low iridium loading (~0.3 mgIr/cm2), is demonstrated to exhibit high catalytic activity at ampere-level current densities and to remain stable for more than 2000 hours.

Continuous Electrosynthesis of Pure H2O2 Solution with Medical-Grade Concentration by a Conductive Ni-Phthalocyanine-Based Covalent Organic Framework.

Electrosynthesis of H2O2 provides an environmentally friendly alternative to the traditional anthraquinone method employed in industry, but suffers from impurities and restricted yield rate and concentration of H2O2. Herein, we demonstrated a Ni-phthalocyanine-based covalent-organic framework (COF, denoted as BBL-PcNi) with a higher inherent conductivity of 1.14 × 10-5 S m-1, which exhibited an ultrahigh current density of 530 mA cm-2 with a Faradaic efficiency (H2O2) of ∼100% at a low cell voltage of 3.5 V. Notably, this high level of performance is maintained over a continuous operation of 200 h without noticeable degradation. When integrated into a scale-up membrane electrode assembly electrolyzer and operated at ∼3300 mA at a very low cell voltage of 2 V, BBL-PcNi continuously yielded a pure H2O2 solution with medical-grade concentration (3.5 wt %), which is at least 3.5 times higher than previously reported catalysts and 1.5 times the output of the traditional anthraquinone process. A mechanistic study revealed that enhancing the π-conjugation to reduce the band gap of the molecular catalytic sites integrated into a COF is more effective to enhance its inherent electron transport ability, thereby significantly improving the electrocatalytic performance for H2O2 generation.

Enhancing the performance of unitized regenerative proton exchange membrane fuel cells through microwave-synthesized chitosan based nanocomposites

The membrane electrode assembly (MEA) is a core component of unitized regenerative proton exchange membrane fuel cells (UR-PEMFCs). The studies aimed to improve the cell performance and reduce the cost of the MEAs for the widespread adoption of UR-PEMFCs. The present study focuses on modifications of MEA. For this purpose, an innovative nanocomposite electrocatalyst was developed by using a carbon-based support material containing platinum nanoparticles with a diameter of approximately 20–30 nm via microwave synthesis technique. The electrocatalyst was developed by a single-step process, consist of multi-walled carbon nanotubes (MWCNT), graphitic carbon nitride (g-C3N4), chitosan (Chi), and platinum nanoparticles (MWCNT/g-C3N4/Chi/Pt nanocomposite). With the development of this support material, a relatively economical and effective electrocatalyst was obtained by large surface area and using the platinum on this surface at the nano level. The prepared catalyst was applied to commercially available membrane electrode assemblies with an active area of 100 cm2. Single-cell and triple-stack performance tests were conducted, and an increase of 17.13 % in the electrolyzer mode and 16.98 % in the fuel cell mode was achieved in single-cell performance with this applied electrocatalyst. Furthermore, an enhancement of 16.96 % in the electrolyzer mode and 16.81 % in the fuel cell mode was discerned in the UR-PEMFC stack. Beside the experimental studies, a numerical model of the modified membrane properties has been developed and validated through experimental data.

Numerical Model for Investigating Effects of Cracks and Perforation on Polymer Electrolyte Fuel Cell Performance

The presence of cracks in the microporous layer (MPL) of polymer electrolyte fuel cells (PEFCs), often occurring during the membrane electrode assembly manufacturing process, has a significant impact on cell performance. However, the exact influence of crack presence, density, and patterns within MPLs on cell performance and transport behaviors remains unclear. This study introduces a three-dimensional macroscale model of PEFCs aimed at investigating the effects of MPL cracks and gas diffusion layer (GDL) perforations on cell performance and transport behavior. This model offers several advantages, including the ability to potentially integrate the effects of flow channel design in future. Additionally, the model can seamlessly incorporate electrochemical reactions and explore phenomena within the catalyst layers (CLs), expanding simulation capabilities beyond water transport alone. The findings suggest that MPL cracks contribute positively to performance by facilitating water drainage. Furthermore, when combined with perforations in GDLs, MPL cracks can significantly enhance performance by providing pathways for water transport. Overall, this study provides valuable insights into developing models for optimizing PEFC performance and underscores the need for further research and development in this area.

Continuous lattice oxygen participation of NiFe stack anode for Sustainable water Splitting

Non-noble anode catalysts exhibit insufficient activity and stability for anion exchange membrane water electrolysis (AEMWE). Accordingly, we propose an electrolyte additive strategy involving NiFe-layered double hydroxide. In situ Raman spectroscopy and 18O isotope labeling experiments reveal that Fe ions in the electrolyte change the oxygen evolution reaction mechanism from adsorbate evolution to the lattice oxygen participation mechanism (LOM). These Fe ions continuously refill Fe vacancies owing to facile metal dissolution via the LOM. In a unit cell, we achieve an excellent cell voltage of 1.73 V and energy conversion efficiency (ECE) of 69.4 % at 3.0 A cm−2, meeting the target set by the U.S. Department of Energy (1.80 V and 69.0 % ECE). Our optimized membrane electrode assembly enhances the cell activity (1.567 V at 1.0 A cm−2; ECE = 76.5 %) and stability (0.125 mVcell h−1 at 0.5 A cm−2 for 500 h) with a 100 cm2 AEMWE stack.

Tracking the Early-life of PtNi/C Shape-Controlled Catalysts upon their Integration in PEMFC

Abstract The integration of promising bimetallic electrocatalytic active materials for oxygen reduction reaction (ORR) into practical and functional proton-exchange membrane fuel cell (PEMFC) electrodes remains largely impeded by the poor performances that these exhibit at high current loads. The early life of PtNi/C catalysts presenting either structurally faceted/ordered or defective/disordered surface morphology is compared to that of both spherical PtNi/C and Pt/C catalysts. Different single-cell operating conditions were studied. At low current density, in the kinetically limited region, a good agreement between liquid electrolyte and single-cell configuration is reported and the kinetic benefit of PtNi/C catalysts compared to Pt/C is (at least partially) maintained. However, PtNi/C catalysts show severe limitations in the O2 mass transport limited region. Morphological and compositional changes were monitored at each stage showing that Ni atoms are leached at every step from ink formulation to the first PEMFC test. We show that Ni is already redistributed in the membrane in the fresh membrane electrode assembly (MEA) state. Ni2+ cationic contamination of the ionomer/membrane contributes to the disappointing results obtained in MEA configuration. In addition, for shaped-controlled PtNi/C, the surface faceting loss combined with restructuring via coalescence and crystallite growth further compromise their transfer in technological devices.

Membrane-Free Water Electrolysis for Hydrogen Generation with Low Cost.

Conventional water electrolysis relies on expensive membrane-electrode assemblies and sluggish oxygen evolution reaction (OER) at the anode. Here, we develop an innovative and efficient membrane-free water electrolysis system to overcome these two obstacles simultaneously. This system utilizes the thermodynamically more favorable urea oxidation reaction (UOR) to generate clean N2 over a new class of Cu-based catalyst (CuXO), fundamentally eliminating the explosion risk of H2 and O2 mixing while removing the need for membranes. Notably, this membrane-free electrolysis system exhibits the highest H2 Faradaic efficiency among reported membrane-free electrolysis work. In situ spectroscopic studies reveal that the new N2Hy intermediate-mediated UOR mechanism on the CuXO catalyst ensures its unique N2 selectivity and OER inertness. More importantly, an industrial-type membrane-free water electrolyser (MFE) based on this system successfully reduces electricity consumption to only 3.87 kWh Nm-3, significantly lower than the 5.17 kWh Nm-3 of commercial alkaline water electrolyzers (AWE). Comprehensive techno-economic analysis (TEA) suggests that the membrane-free design and reduced electricity input of the MFE plants reduce the green H2 production cost to US$1.81 kg-1, which is lower than those of grey H2 while meeting the technical target (US$2.00-2.50 kg-1) set by European Commission and United States Department of Energy.

Performance constraints of high temperature polymer electrolyte membrane fuel cells by varying the Pt/C ratio of the catalyst

Electrodes prepared from catalysts with Pt weight percentages on the carbon support (Pt/C nanoparticles) ranging from 10 up to 60 wt% are used as cathodes of membrane electrode assemblies (MEAs) and tested in high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). For each Pt/C percentage in the catalyst, the cathode Pt-loading (which become proportional to the thickness of the electrode formed by the catalyst nanoparticles) is stepwise scanned from low to high loadings. Results show that when the Pt load increases, the MEA performance (measured by its power density at 0.6 V) rises initially (due to the increase in the number of active sites in the cathode) up to a maximum value limited by the mass transport of oxygen, associated to an optimum Pt-loading (different for each Pt/C ratio). Noteworthy, the peak performance is significantly different depending on the catalyst used (60 > 40 >> 20 > 10 wt% Pt/C), a fact that restricts the catalyst choice according to the performance required by the application. Furthermore, higher amounts of Pt in the cathode lead to a large catalyst waste as the FC performance even decreases as the cathode thickness increases.

Optimization design of assembly sequence for the proton exchange membrane fuel cell stacks with dimensional errors

Proton exchange membrane fuel cell (PEMFC) stacks are assembled by numerous bipolar plates (BPPs) and membrane electrode assemblies (MEAs). Component manufacturing errors are inevitably caused during the production process and brought into the stack, affecting the mechanical consistency of every cell. Aiming to improve the uniformity of the assembled stack effectively, this paper establishes a novel assembly deviation model based on the asymptotic homogenization (AH) method and proposes an assembly sequence optimization approach for the stack with dimensional errors using the genetic algorithm. The results reveal that dimensional errors significantly affect the equivalent mechanical properties of the stack. Reasonable matching of components with different types of dimensional errors is an effective method to avoid the cumulative negative impacts on the mechanical behavior of the stack. Statistically, the optimization of the assembly sequence can improve contact pressure uniformity in a 10-cell stack by more than 9.00%, while reducing the maximum contact pressure by 15.55%. This methodology is also applicable to improving the assembly uniformity of other stacked structures.

Nickel-Doped Facet-Selective Copper Nanowires for Activating CO-to-Ethanol Electrosynthesis.

Ethanol isa promising energy vector for closing the anthropogenic carbon cycle through reversible electrochemical redox. Currently, ethanol electrosynthesissuffers from low product selectivity due to the competitive advantage of ethylene in CO2/CO electroreduction. Here, a facet-selective metal-doping strategy is reported, tuning the reaction kinetics of CO reduction paths and thus enhancing the ethanol selectivity. The theoretical calculations reveal that nickel (Ni)doped Cu(100) surface facilitates water dissociation to form adsorbed hydrogen, which promotesselective electrochemical hydrogenation of a key C2 intermediate (*CHCOH) toward ethanol path over ethylene path. Experimentally, a solution-phase synthesis of a Ni-doped {100}-dominated Copper nanowires (Cu NWs) catalyst is reported, enabling an ethanol Faradaic efficiency of 56% and a selectivity ratio of ethanol to ethylene of 2.7, which are ≈4 and 15 times larger than those of undoped Cu NWs, respectively. The operando spectroscopic characterizationsconfirm that Ni-doping in Cu NWs can alter the interfacial water activity and thus regulate the C2 product selectivity. With further electrode engineering, a membrane electrode assembly electrolyzer using Ni-doped Cu NWs catalysts demonstrates an ethanol Faradaic efficiency over 50% at 300mA cm-2 with a full cell voltage of ≈2.7V and operates stably for over 300 h.