Anion Exchange Membrane Electrolysis Research Articles

Best practices of modeling complex materials in electrocatalysis, exemplified by oxygen evolution reaction on pentlandites.

Pentlandites are natural ores with structural properties comparable to that of [FeNi] hydrogenases. While this class of transition-metal sulfide materials - (Fe,Ni)9S8 - with a variable Fe : Ni ratio has been proven to be an active electrode material for the hydrogen evolution reaction, it is also discussed as electrocatalyst for the alkaline oxygen evolution reaction (OER), corresponding to the bottleneck of anion exchange membrane electrolyzers for green hydrogen production. Despite the experimental evidence for the use of (Fe,Ni)9S8 as an OER catalyst, a detailed investigation of the elementary reaction steps, including consideration of adsorbate coverages and limiting steps under anodic polarizing conditions, is still missing. We address this gap in the present manuscript by gaining atomistic insights into the OER on an Fe4.5Ni4.5S8(111) surface through density functional theory calculations combined with a descriptor-based analysis. We use this system to introduce best practices for modeling this rather complex material by pointing out hidden pitfalls that can arise when using the popular computational hydrogen electrode approach to describe electrocatalytic processes at the electrified solid/liquid interface for energy conversion and storage.

A frogspawn inspired twin Mo2C/Ni composite with a conductive fibrous network as a robust bifunctional catalyst for advanced anion exchange membrane electrolyzers.

Anion exchange membrane water electrolysis (AEMWE) is considered one of the most cost-effective methods for producing green hydrogen. However, the performance of AEMWE is still restrained by the slow reaction kinetics and poor ion/electron transport of catalysts. Herein, inspired by frogspawn, Mo2C nanoparticles coupled with Ni were in situ embedded into a N-doped porous carbon nanofiber network (Mo2C/NCNTs@Ni) by chemical crosslinking electrospinning combined with carbonization. The unique bionic structure can guarantee favorable overall structural flexibility and fast ion/electron transport kinetics. As a result of the robust hydrogen binding energy of Mo2C, as well as the synergistic impact between Ni and Mo2C nanoparticles and the conductive network resembling frogspawn, the catalyst developed demonstrates excellent performance in both the HER and OER. When employed as a bifunctional catalyst in water electrolysis, Mo2C/NCNTs@Ni delivers overpotentials of 155 mV and 320 mV at 10 mA cm-2 for the HER and OER, respectively. In addition, the Mo2C/NCNTs@Ni also displays excellent long-term durability during a continuous operation test under different currents for 50 h. The assembled AEMWE electrolyzers with Mo2C/NCNTs@Ni as both the anode and cathode can achieve a current density of 82.5 mA cm-2 at 1.99 V, indicating great potential for industrial water splitting. These results give an insight for the development of advanced bifunctional electrocatalysts for the next generation of green and efficient H2 production by water electrolysis.

Advanced development of anion-exchange membrane electrolyzers for hydrogen production: from anion-exchange membranes to membrane electrode assemblies.

Anion-exchange membrane water electrolysis (AEMWE) has attracted attention owing to its operation in alkaline environments, which offers the advantage of not requiring the use of precious metals. Additionally, AEMWE exhibits higher kinetics in the hydrogen evolution reaction, enabling higher hydrogen production efficiency. The anion-exchange membrane (AEM) fabrication, catalyst design, and membrane electrode assembly (MEA) are crucial for enhancing the total water electrolysis performance. There is an urgent need to summarize the advances in the development of AEMWE to pave the way for the commercialization of AEMWE. In this review, first, the fundamental principles of AEMWE technology are introduced. Second, the optimization of AEM with high ion conductivity and high stability through innovative synthetic methods are discussed in detail. Third, the designs of catalysts to increase the reaction rates by regulating the OH-adsorption environment and relieving OH blockage are introduced. Last but not least, a systematic summary of the concepts of 3D-ordered MEA, 3D-unified MEA, and 3D-self-supported MEA is presented. This review would be helpful to enhance the overall performance of AEMWE and promote the development of green hydrogen energy.

Microwave Quasi‐Solid State to Construct Strong Metal‐Support Interactions with Interfacial Electron‐Enriched Ru for Anion Exchange Membrane Electrolysis

AbstractRegulating the metal‐support interaction of the anchored metal nanoclusters is recognized as valid approach to optimize the electrocatalytic performance through tuning the interfacial electronic structure. However, developing novel support and understanding the interfacial electron accumulation on modulating the reaction kinetics are still elusive. Herein, highly‐dispersed Ruthenium (Ru) nanoclusters anchored onto phosphorous doped molybdenum boride (Ru/P‐MoB) is developed through ultrafast microwave‐plasma (60 s) approach. The synthesized Ru/P‐MoB impressively promote the hydrogen evolution with low overpotentials of 34, 45, and 40 mV to drive 10 mA cm−2 in alkaline freshwater, alkaline seawater and acid media. Specially, it presents superior turnover frequency and mass/specific activity relative to Pt/C, Ru/C, and Ru/MoB. Moreover, the anion exchange membrane (AEM) electrolyzer cell based on Ru/P‐MoB can achieve 500 and 1000 mA cm−2 with small voltages of 1.71 and 1.78 V with good durability. Experimental and density functional theoretical (DFT) analysis reveal that the strong metal‐support interactions (Ru─Mo and Ru─P bonds) with generated interfacial electron‐enriched Ru, and then favoring the water‐molecule adsorption/dissociation and optimal H intermediate adsorption free energy. This work provides novel designing avenue to exploit electrocatalysts with outstanding catalytic performance under high current density at practical high‐temperature.

Influence of Contact Pressure and Flow Rate on the Performance of Anion Exchange Membrane Electrolysis

Hydrogen production by electrolysis is a key aspect of a climate-neutral economy. However, there are still weak points in the established low-temperature technologies such as high material costs in case of PEM electrolysis and poor dynamic operations in case of alkaline electrolysis. The emerging electrolysis technology, the anion exchange membrane (AEM) electrolysis, addresses these weaknesses and combines their advantages. Due to the solid polymer electrolyte and the alkaline environment, AEM water electrolysis is featured by a compact zero-gap cell design and inexpensive materials like non-noble metal catalysts. Hence, it offers the potential to a cost-effective and efficient electrolysis technology.To enable the breakthrough of this technology, we contribute by conducting performance evaluations of membrane electrode assemblies (MEAs) under application-oriented conditions. One focus is on non-noble metal MEAs with an active area of 25 cm2 operated with pure water and low concentrated potassium hydroxide solution.To ensure comparability of different MEAs, it is crucial to compare them at their performance optimum. This is achieved by determining the optimal set-up parameters like contact pressure and operation parameters like flow rate for each MEA type. Otherwise, deviation from the optimal operating point by up to 50 % may occur.The influence of the parameters contact pressure and flow rate on the MEA performance is discussed in this presentation. To investigate their impact, we analysed the MEAs in an electrolyser test station using polarisation curves, electrochemical impedance spectroscopy and load tests at constant current and constant voltage.Some of the results presented are obtained within the project “REVAL – reversible anion exchange membrane electrolysis” (funding code 03ZZ0732D) funded by the German Federal Ministry of Education and Research (BMBF).

(Invited) Current Status and Progress in Anion Exchange Membrane Electrolysis

Anion exchange membrane (AEM) electrolysis is a promising solution for large-scale hydrogen production from renewable energy resources. However, the performance of AEM electrolysis is still lower than what can be achieved with conventional technologies. Materials chemistry, MEA designs, and optimal operation conditions have driven recent advancements. Majority of the AEM research has focused on improving ionic conductivity and alkaline stability. Many AEMs exceed 0.1 S/cm (at 60–80 °C), however stability at temperatures above 60 °C needs improvement. Oxygen evolution reaction OER remains a bottleneck. The active-site mechanism of NiFe catalysts is disputed, and their long-term stability is unknown. Co boosts NiFe catalyst conductivity. Carbon-supported Pt dominates the hydrogen evolution process (HER), whereas PtNi alloys and clusters of Ni(OH)2 on Pt compete. Well-dispersed Ru nanoparticles on functionalized high-surface-area carbon substrates show promising HER actions. New in situ methods, AEMWE evaluation processes, and catalyst-structure designs could help the field advance faster. Nonetheless, single AEM water electrolyzer cells have operated for several thousand hours at 60 °C and 1 A/cm2.

Insights into the Structure Sensitivity of Fe-Based Materials for the Oxygen Evolution Reaction

The conversion of renewable energy into storable fuels is fundamental to the meeting of the net-zero CO2 emissions objective by 2050. However, the sluggish kinetics of the oxygen evolution reaction (OER) and the poor stability of electrocatalysts at industrial-level currents remain a problem for electrolyzers 1. Using platinum group metal-free electrocatalysts in anion exchange membrane electrolyzers is an appealing strategy to overcome some of the problems associated with PEM electrolyzers. Fe-based materials offer the possibility for the development of active, stable, and cost-effective electrocatalysts for the OER in alkaline media.In this work, we explore the influence of structure, composition, or crystalline phase on different Fe-based electrodes for the OER. Different fabrication procedures such as additive manufacturing 2, flame spray synthesis, or pulse laser ablation 3 allow us to have a wide range of Fe-based materials with a well-defined structure/composition/phase. The materials have been extensively characterized by physicochemical methods (XPS, Raman, XRD, ICP) and their electrocatalytic activity evaluates following careful procedures in order to obtain reliable results. The results show that the activity of Fe-rich electrodes is poor. However, if Fe is alloyed with other materials or its surface structure or crystallinity degree is modified, it results in a more active material. This information could guide the synthesis of more active and stable water-splitting materials. References S. Cherevko, S. Geiger, O. Kasian, N. Kulyk, J.-P. Grote, A. Savan, B. R. Shrestha, S. Merzlikin, B. Breitbach, A. Ludwig, and K. J. J. Mayrhofer, Catalysis Today, 262 170-180 (2016). J. Wegner, R. Martínez-Hincapié, V. Čolić, and S. Kleszczynski, Advanced Materials Interfaces, n/a (n/a), 2202499 (2023). J. Johny, Y. Li, M. Kamp, O. Prymak, S.-X. Liang, T. Krekeler, M. Ritter, L. Kienle, C. Rehbock, S. Barcikowski, and S. Reichenberger, Nano Research, 15 (6), 4807-4819 (2022).

Polymeric Anion Exchange Membranes for Green Hydrogen Production

Producing green hydrogen by using anion exchange membrane (AEM) water electrolysis is a promising approach to address the severe climate and energy crisis facing human society and aid the transition to net-zero emissions. AEM electrolysis can be integrated with renewable energy sources and utilizes cost-effective (Pt-free) electrocatalysts and other inexpensive components in stacks. To enable commercially viable hydrogen generation, improvement of the AEM component is imperative, and the goal of fabricating a membrane, in which the chemical, mechanical and electrochemical requirements are combined and optimized in a synergistic way, still represents a challenging task.The present work was, therefore, aimed at addressing several unique features of AEMs for implementation in an industrially scalable and sustainable energy-production process through a suitable synthetic strategy that involves the post-modification of a commercially available and relatively cheap poly(styrene-b-butadiene) (SB)-based block copolymer matrix by grafting vinylbenzyl chloride (VBC). The synthesized SB-g-VBC copolymers were, therefore, used for the fabrication of AEMs by solution casting followed by quaternization reaction with trimethylamine (TMA) for the quantitative conversion of –CH2Cl into –CH2(CH3)3N+ groups. Obtained AEMs were thermally, mechanically and electrochemically characterized. By varying the VBC functionalization degree of the copolymers it was possible to modulate the ionic exchange capacity, conductivity, water uptake and mechanical properties of the membranes derived therefrom. The most promising AEMs were selected for testing in electrolytic cells (Figure 1) and were found to resist to real operating conditions for more than 40 days. Acknowledgements. The authors thank the company Enapter s.r.l. for the contribution to the electrochemical characterization and the financial support.Figure.1 Polarization curves of the SB-g-VBC based AEM as a function of residence time in an electrolytic cell (KOH 1 wt % at 55 °C). Figure 1

Materials Integration and Catalyst Interfaces in Anion Exchange Membrane, Low Temperature Electrolysis

As an energy carrier, hydrogen has unique advantages due to its high energy density, ability for long-term storage, and the ability to convert between chemical bonds and electricity. [1] Although hydrogen currently has a small role in energy pathways, low-cost renewable power sources can allow for significant growth. Anion exchange membrane (AEM) electrolyzers leverage several advantages, including a zero-gap approach that typically improves upon the efficiency of traditional alkaline systems. [2] Compared to proton exchange membrane (PEM) electrolyzers, the high pH also allows for platinum group metal-free (PGM-free) catalysts and component coatings (transport layers, separators) that can reduce system cost and improve long-term durability. In recent years, membrane advancements have further enabled higher AEM performance, particularly in supporting electrolytes. [3]This presentation includes an overview of efforts in AEM electrolysis and focuses on materials choices and their integration. While components are readily available that can achieve high performance, individual properties and their interactions create integration challenges. [4] In catalyst and transport layers, large particle sizes and lower catalyst conductivity coupled with the high distance between transport layer fibers can lead to lower catalyst utilization and high catalyst layer resistances. The ionomer, while critical for ionic transport in water, is primarily needed in supporting electrolytes for structural integrity, and changes to the ionomer content, type, and its distribution throughout the catalyst layer have been explored for its effect on performance and durability. These experiments demonstrate the complications of developing a single set of materials and test protocols for component evaluations.

Promoting AEM Water Electrolyzer Performance and Reproducibility by Tumbler Milling of Ni3fe-LDH OER Catalyst

Anion exchange membrane water electrolysis is an attractive clean energy technology for producing hydrogen for energy storage, transport 1,2 and numerous other applications. Rational choice of highly active and stable catalysts as well as the proper design of catalyst layers are crucial to achieve technical relevance of electrolyser systems. The establishment of clear understanding of optimal catalyst treatment and methods of implementation are key steps towards optimized electrolyzer performance and durability. One aspect of catalyst performance in catalyst layers is the catalyst size distribution. A multimodal size distribution of catalyst particles or agglomerates can jeopardize the layer homogeneity and thus electrode performance.In this work, the effect of high-energy ball tumbling milling on the promising Ni3Fe-LDH OER catalyst followed by catalyst dispersion control was correlated to the microstructure of the catalyst layer, the achieved catalyst activity and utilization, and the resulting single cell performance and stability. Physico-chemical characterization confirmed the stable layered double hydroxide structure of the catalyst. By milling, a 300-fold reduction of catalyst agglomerate size, and an 8.8-fold increase of the geometrical surface was achieved. The optimized solvent compositions effectively increased the catalyst ink stability. We found that a significantly decreased catalyst agglomerate size resulted in very homogeneous mixtures of catalyst and ionomer. By tailoring the electrode structure design, lower internal electronic resistances of the electrodes, decreased charge-transfer resistances (Rct) of the membrane electrode assembly, and stable single cell durability of 1000 h with a minor degradation rate of 57 µV h-1 were accomplished.This work presents a facile and scalable approach of NiFe-LDH catalyst treatment and dispersion control and provides a guideline to follow for further electrode development and increased AEM water electrolyzer performances. References (1) Hydrogen Applications. Hydrogen Europe. 2020. https://hydrogeneurope.eu/hydrogen-applications (accessed Jan 7, 2022).(2) Vincent, I.; Bessarabov, D. Low Cost Hydrogen Production by Anion Exchange Membrane Electrolysis: A Review. Renew. Sustain. Energy Rev. 2018, 81 (August 2016), 1690–1704. https://doi.org/10.1016/j.rser.2017.05.258. This work has been performed in the frame of the CHANNEL project. This project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking (now Clean Hydrogen Partnership) under grant agreement No 875088. This Joint undertaking receives support from the European Union's Horizon 2020 Research and Innovation program, Hydrogen Europe and Hydrogen Europe Research.

Water Transport and Salt Precipitation in Anion-Exchange Membrane Electrolyzers

The hydrophilic nature of hydrocarbon ionomers and membranes presents a major challenge in anion-exchange membrane (AEM) electrolysis, despite improved stability from reinforcements and modified polymer chemistry. Durability and performance are still highly influenced by the operation mode and water management within the membrane-electrode-assembly (MEA).Dry cathode operation in AEM water electrolysis, where only the anode is supplied with liquid electrolyte (KOH), offers increased hydrogen purity but poses challenges for non-fluorinated anion-exchange polymers that are sensitive to water content. In-situ neutron imaging with high resolution (~6 µm effective resolution) revealed that adjusting the anion-exchange capacity of the cathode binder ionomer can retain membrane humidification (Fig. 1)1.In the electrochemical reduction of CO2 using AEM, water management and salt precipitation are significant challenges. High-resolution neutron imaging of a zero-gap CO2 electrolyzer operating at 200 mA cm-² and 2.8 V showed salt precipitates penetrating the cathode gas diffusion layer, leading to blocked CO2 gas transport and a decay in Faraday efficiency. Salt accumulation was higher under the cathode channel of the flow field than the land2.Both studies demonstrate the substantial impact of water management and salt precipitation on the operation of AEM-based electrolyzers and how neutron imaging can assist in addressing these challenges. References (1) Koch, S.; Disch, J.; Kilian, S. K.; Han, Y.; Metzler, L.; Tengattini, A.; Helfen, L.; Schulz, M.; Breitwieser, M.; Vierrath, S. Water management in anion-exchange membrane water electrolyzers under dry cathode operation. RSC Adv 2022, 12, 20778–20784.(2) Disch, J.; Bohn, L.; Koch, S.; Schulz, M.; Han, Y.; Tengattini, A.; Helfen, L.; Breitwieser, M.; Vierrath, S.; High-resolution neutron imaging of salt precipitation and water transport in zero-gap CO2 electrolysis. Nat Commun 2022, 13, 6099. Figure 1

Benchmarking Activity and Stability of Layered Double Hydroxides (LDHs) Electrocatalysts for Alkaline Water Electrolysis

In order to reduce the cost of producing hydrogen through water electrolysis, novel technologies must be improved. Recently, the merging of conventional alkaline electrolysis (AEL) and proton exchange membrane electrolysis (PEM) has led to the development of anion exchange membrane electrolysis (AEMWE), which offers several advantages over AEL and PEM. In a nutshell, this technique employs cheap, abundant, and easily available (non-geostrategic) transition metals with anionic exchange membranes, overcoming the drawbacks of AEL and PEM.[1]To reach the readiness level of this technology, new and scalable synthetic routes for catalysts that lower the overpotential of the sluggish oxygen evolution reaction (OER) are required. Amongst all the OER catalysts reported in the literature, Layered Double Hydroxides (LDHs) have gained increasing attention due to their low overpotentials and stabilities.[2] Besides, electrochemical protocols to determine the activity and stability of these catalysts in different electrochemical cells must be established to understand their properties. Thus, this work focuses on the advantages and limitations of different electrochemical techniques, such as rotating disk electrode (RDE), three-electrode cells, and single-cell tests, to determine the activity and stability of two different LDHs. Unlike laboratory scale LDHs ‒prepared by hydrothermal treatment (HT-LDH)‒ room temperature synthesized LDHs (RT-LDH) can be prepared in kilogram quantities and present chemical structure and morphology differences. In this work, the LDHs have been characterized with spectroscopic techniques to correlate the chemical structure and morphology of the materials to their electrochemical response by RDE, three-electrode cells, and single-cell measurements.All in all, the scalable RT-LDH presents higher activity compared to HT-LDH in all three techniques. On the one hand, small current densities can only be reached by RDE, and the short-term stability of the materials is affected by the catalyst layer interface. On the other side, single-cell test measurements require long operational times, and the contribution of the membrane degradation to the overall cell voltage is still unclear. Thus, three-electrode cell measurements offer the possibility of characterizing LDHs at relevant current densities in a fast and straightforward manner, without membrane contributions, and are further employed in this work to study the stability of these systems.

Activation of Commercial Stainless-Steel Electrodes for Highly Efficient and Stable Anion-Exchange Membrane Electrolysis

Commercial stainless steel (SS) is gaining interest as a promising electrode material to be widely used for green hydrogen production from alkaline water electrolysis. Herein, low-cost 304-type SS meshes (SM) were engineered through a simple 2-step activation process, i.e., chemical etching and electrochemical activation. The modified electrodes exhibited comparable hydrogen and oxygen evolution reaction properties with commercially, noble metal-based electrodes available. The modified stainless steel-based electrodes were assembled and tested in an AEM electrolyzer cell, which displays more than 300 mV-voltage drops compared to the bare stainless steel-based cells. The in-situ impedance spectroscopy revealed a significant decrease in the resistances due to interfacial contact, charge transfer, and mass transport. In addition, we identified nanocrystalline Fe-NiCr2O4 and nanocrystalline Ni(OH)2/Fe(OH)2 active species for SS used in hydrogen and oxygen evolution side respectively which could explain the significantly higher performance. In addition, we also developed an electrolyzer system to assess the long-term durability of our cell reactors in which our cells exhibited exceptional durability at 5.0 A (1.0 A cm-2) for 250 h. Our results exemplify that such an approach has the potential for upscaling and deployment in the next-generation, low-cost AEM electrolysis for green hydrogen production.

Anion Exchange Ionomers: Design Considerations and Recent Advances - An Electrochemical Perspective.

Alkaline-based electrochemical devices, such as anion exchange membrane (AEM)fuel cells and electrolyzers, are receiving increasing attention. However, while the catalysts and membrane are methodically studied, the ionomer is largely overlooked. In fact, most of the studies in alkaline electrolytes are conducted using the commercial proton exchange ionomer Nafion. The ionomer provides ionic conductivity; it is also essential for gas transport and water management, as well as for controlling the mechanical stability and the morphology of the catalyst layer. Moreover, the ionomer has distinct requirements that differ from those of anion-exchange membranes, such as a high gas permeability, and that depend on the specific electrode, such as water management. As a result, it is necessary to tailor the ionomer structure to the specific application in isolation and as part of the catalyst layer. In this review, an overview of the current state of the art for anion exchange ionomers is provided, summarizing their specific requirements and limitations in the context of AEM electrolyzers and fuel cells.

Environmental and material criticality assessment of hydrogen production via anion exchange membrane electrolysis

The need to drastically reduce greenhouse gas emissions is driving the development of existing and new technologies to produce and use hydrogen. Anion exchange membrane electrolysis is one of these rapidly developing technologies and presents promising characteristics for efficient hydrogen production. However, the environmental performance and the material criticality of anion exchange membrane electrolysis must be assessed. In this work, prospective life cycle assessment and criticality assessment are applied, first, to identify environmental and material criticality hotspots within the production of anion exchange membrane electrolysis units and, second, to benchmark hydrogen production against proton exchange membrane electrolysis. From an environmental point of view, the catalyst spraying process heavily dominates the ozone depletion impact category, while the production of the membrane represents a hotspot in terms of the photochemical ozone formation potential. For the other categories, the environmental impacts are distributed across different components. The comparison of hydrogen production via anion exchange membrane electrolysis and proton exchange membrane electrolysis shows that both technologies involve a similar life-cycle environmental profile due to similar efficiencies and the leading role of electricity generation for the operation of electrolysis. Despite the fact that for proton exchange membrane electrolysis much less material is required due to a higher lifetime, anion exchange membrane electrolysis shows significantly lower raw material criticality since it does not rely on platinum-group metals. Overall, a promising environmental and material criticality performance of anion exchange membrane electrolysis for hydrogen production is concluded, subject to the expected technical progress for this technology.

Optimization of Ionomer Content in Anode Catalyst Layer for Improving Performance of Anion Exchange Membrane Water Electrolyzer

Anion exchange membrane (AEM) water electrolyzers, which are considered next-generation hydrogen production energy devices, generate hydrogen using a nonprecious metal as the electrocatalyst. However, most current studies tend to focus on the development of highly active electrocatalysts based on nonprecious metals, and there have been few attempts to develop improved electrodes for these devices. In particular, the catalyst layer of the electrode is the key component that directly affects the performance of AEM electrolyzers. In this study, we developed a high-performance anode for the AEM water electrolyzer by optimizing the ionomer content of the anode catalyst layer. In particular, the electrochemical behavior of the AEM electrolyzer was systematically analyzed while varying the amount of ionomer present within the anode catalyst layer. The ionomer content significantly affects the ohmic and mass transport losses of the AEM electrolyzer and consequently plays an important role in determining its performance. Upon employing the optimized ionomer, a current density of 1.44 A/cm2 was achieved at 1.8 V, representing a 25% improvement compared to using a nonoptimized ionomer. In addition, the ionomer content also significantly affects the durability of the system. Thus, this study highlights the importance of developing improved electrodes for the realization of high-performance AEM water electrolyzers.

Feasibility of CO2 desorption and electrolytic regeneration of potassium carbonate solution in an anion exchange membrane cell

In this work, an electrolytic process was introduced for coupled regeneration of potassium carbonate (K2CO3) solution and water electrolysis by using an anion exchange membrane cell. The process made the CO2 separation from O2 much easier with respect to the existing cationic exchange membrane process. The solution of K2CO3 was used in the cathode chamber to simulate the solution after absorbing CO2. The solution of sulfuric acid (0.1 mol/L H2SO4) was charged in the anode chamber. The feasibility of the process was discussed. The effects of various operation parameters, including temperature, current density, and electrolysis time, were studied. The results indicate that both the yield rate of CO2 and the current efficiency increase initially and decrease afterward with temperature. The yield rate of CO2 increases while the current efficiency decreases with the current density. A low current density can reduce the energy consumption for producing the same amount of CO2. The processes using anion exchange membrane electrolysis can regenerate the absorbent solution to achieve 89% current efficiency, and the simultaneous production of three pure gases, CO2, H2, and O2, makes this method promising.

Alkaline-Stable, In Situ Menshutkin Coat and Curable Ammonium Network: Ion-Solvating Membranes for Anion Exchange Membrane Water Electrolyzers

Anion exchange membranes fabricated through a one-step Menshutkin reaction with down-selected multifunctional alkyl halides and multifunctional tertiary amines within an ion-solvating matrix, poly(ethylene-co-vinyl alcohol), yielded alkaline-stable ammonium network polymers. Due to the vast simplicity in fabrication due to the quaternization/Menshutkin reaction between tertiary amine and alkyl bromides, which does not evolve any by-products that require purification, alkaline-stable membranes were fabricated in one step through facile mixing and curing of alkaline-stable ammonium network forming monomers. Prepared membranes showed controllable ion exchange capacity (IEC), conductivity, and mechanical strength by controlling of poly(ethylene-co-vinyl alcohol) amount which is an ion-solvating polymer. The selection of ammonium network chemical structure allowed for flawless retention of IEC and conductivity under conditions of 70°C, 1M KOH of over 300 h. Anion exchange membrane electrolysis membrane electrode assembly tests with optimized membranes showed a greater performance (1.78 A/cm2 at 2.0 V) and more enhanced water electrolyzer durability than that of commercial anion exchange membrane.

Recovery and Utilization of Lead in Lead–Containing Waste Residue from Electrolytic Manganese Production

As a metallurgical and chemical raw material, electrolytic manganese is an important strategic resource. However, with the rapid development of the electrolytic manganese industry, the correct disposal of anode slime has become a serious problem. The purpose of this experiment was to reduce the occupation of land resources by the lead–containing waste residue of electrolytic manganese, reduce the pollution caused by the lead–containing waste residue to the environment and provide a reference for the research on the treatment technology and resource utilization of lead–containing waste residue in China. In this experiment, a special process was studied for the composition characteristics of lead–containing waste residues produced by electrolytic manganese. The acid leaching–enrichment–membrane electrolysis process was used to recover the lead in the lead–containing waste residues of electrolytic manganese and to recover the acid, so as to maximize the utilization of resources. In this experiment, the pretreated lead–containing waste residue was leached, enriched and concentrated, and then the enriched Pb2+ solution was used as cathode solution and dilute nitric acid as anode solution to recover lead by membrane electrolysis. The membrane electrolysis experiment uses lead plate as cathode, selects the best anion exchange membrane and anodic electrolysis material, and then takes lead recovery, acid recovery, current efficiency, voltage and power consumption as investigation indexes to explore and analyze the influence of many factors such as Pb2+ concentration and current density on the experiment, so as to determine the best membrane electrolysis process parameters. The optimum process parameters of lead recovery by membrane electrolysis were determined as follows: Pb2+ concentration was 40 g/L, current density was 30 mA/cm2, reaction temperature was 60 °C, cathodic pH value was 4.0, anodic HNO3 concentration was 0.5 mol/L, and cathodic ammonium nitrate concentration was 50 g/L. Under the optimal conditions, the current efficiency was 85.6%, the acid recovery was 73.03%, the lead recovery was 99.2%, the voltage was 3.8 V, and the power consumption was 1148.4 kW·h·t−1. Through the three steps of acid leaching–enrichment–membrane electrolysis, 78.53% of the Pb2+ in the original lead–containing waste residue can be recovered in the form of metal lead element, and the HNO3 recovered in the anode chamber can also be used again in the acid leaching process, which can not only solve the problem of environmental pollution caused by lead–containing waste residue but also achieve the recovery and utilization of resources, with good social and economic benefits.

Mo2C nanocrystalline coupling with Ni encapsulated in N-doped fibrous carbon network as bifunctional catalysts towards advanced anion exchange membrane electrolyzers

Anion exchange membrane water electrolysis (AEMWE) has been considered to be the promising approach for cost-effective hydrogen production. However, the noble metal catalysts of AEM enable it still under the early stage of development. Herein, Mo2C nanocrystalline coupling with Ni have been successfully encapsulated into robust carbonaceous network (Mo2C/NC@0.5Ni) as inexpensive transition metal catalysts for AEM electrolyzers. The Mo2C nanocrystals are uniformly confined in N doped porous carbon network which is derived from the decomposition of PVP and urea during carbonation process. Importantly, rational designed Ni layers are also coated on the surface of the network structure. When utilized as bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the Mo2C/NC@ 0.5Ni can achieve desirable overpotentials of 103 mV and 307 mV at a current density of 10 mA cm−2 in 1 M KOH, respectively. Furthermore, the Mo2C/NC@ 0.5Ni‖Mo2C/NC@ 0.5Ni AEM electrolyzers requires only a voltage of 1.9 V to reach a current density of 110.5 mA cm−2 with remarkable durability over 50 h. Numerous interconnected porous structure and defects caused by N doping can provide abundant active sites, facilitate electrons transportations and suppress the aggregation of inner Mo2C. Particularly, the conductive Ni layers could effectively improve the structural strength and induce the synergistic effect with Mo2C component, thereby, improving the catalytic activity and stability. In addition, the DFT calculation results indicate that the Mo2C/NC@ 0.5Ni catalyst has a lower Gibbs free energy of hydrogen adsorption (ΔGH*=−0.21 eV), which is beneficial to its HER catalytic activity. This work provides an insight in developing advanced AEMWE for high efficient and green hydrogen production.