Recent Advances in Alkaline Exchange Membrane Water Electrolysis and Electrode Manufacturing

Effects of Structurally Different Tertiary Amines on the Properties of Quaternized Anionic Exchange Membranes Potentially Applicable for Water Electrolysis

In this work, two structurally different monoamines (trimethylamine [TMA] and N-methylpiperidine [N-MPip]) are used for the amination of a g-VBC-15 graft copolymer, obtained by the functionalization of a mechanically robust, commercially available styrene-butadiene block copolymer (SB) with vinylbenzyl chloride (VBC) via solution free-radical polymerization. Results demonstrate that g-VBC-15-based membranes quaternized with TMA have superior electrochemical performance than N-MPip counterparts; while, the mechanical properties are good and only slightly inferior to those of N-MPip. Therefore, TMA is the selected monoamine to be alternatively mixed with two polyamines (tetramethyl-1,3-propanediamine [TMPDA] and N,N,N',N'',N''-pentamethyldiethylenetriamine [PMDETA]) into different proportions, in order to modulate the average functionality of the amination mixture in terms of number of amine functional groups available for the quaternization reaction of the membranes. g-VBC-15-based membranes derived therefrom are extensively characterized to assess their thermal, mechanical, and ex situ electrochemical properties. Results indicate that membranes quaternized with a TMA/PMDETA mixture (90:10 in mole) display the highest conductivity among all the investigated membranes aminated with polyamine-based mixtures. Moreover, they have comparable mechanical and electrochemical properties to those quaternized with TMA, while exhibiting a reduced water uptake.

Highly Hydrophilic Zirconia Composite Anion Exchange Membrane for Water Electrolysis and Fuel Cells

To prepare anion exchange membranes with high water electrolysis and single fuel cell performance, an inorganic-organic composite (IOC) strategy with click cross-linked membranes coated with different contents of hydrophilic polar nanozirconia is proposed to fabricate composite membranes (CM) PBP-SH-Zrx. The performance test results showed that the CM PBP-SH-Zr4 not only has good through-plane ionic conductivity (167.7 mS cm-1, 80 °C), but also exhibits satisfactory dimensional stability (SR 16.5%, WU 206.4%, 80 °C), especially demonstrating excellent alkaline stability with only 16% degradation (2 M NaOH for 2200 h). In water electrolysis, the "microgap" between the membrane and catalyst layer (solid-solid interface) is alleviated, and the membrane electrode assembly (MEA) interfacial compatibility (liquid-solid-solid interface) is enhanced. The CM PBP-SH-Zr4 showed the lowest charge transfer resistance (Rct, 0.037 Ω cm2) and a high current density of 2.5 A cm-2 at 2.2 V, while the voltage drop was 0.361 mV h-1 after 360 h of endurance (six start-stop cycles) at 60 °C and 500 mA cm-2, proving a good water electrolysis durability. Moreover, an acceptable peak power density of 0.464 W cm-2 at 80 °C is achieved in a H2/O2 fuel cell with a PBP-SH-Zr4-AEM. Therefore, the IOC strategy can enhance the membrane's comprehensive performance and interface compatibility of MEA and may promote the development of anion exchange membranes (AEMs) for water electrolysis and fuel cells.

NiFe2O4 Material on Carbon Paper as an Electrocatalyst for Alkaline Water Electrolysis Module

NiFe2O4 material is grown on carbon paper (CP) with the hydrothermal method for use as electrocatalysts in an alkaline electrolyzer. NiFe2O4 material is used as the anode and cathode catalysts (named NiFe(+)/NiFe(-) hereafter). The results are compared with those obtained using CP/NiFe as the anode and CP/Ru as the cathode (named NiFe)(+)/Ru(-) hereafter). During cell operation with NiFe(+)/Ru(-), the current density reaches 500 mA/cm2 at a cell voltage of 1.79 V, with a specific energy consumption of 4.9 kWh/m3 and an energy efficiency of 66.2%. In comparison, for NiFe(+)/NiFe(-), the current density reaches 500 mA/cm2 at a cell voltage of 2.23 V, with a specific energy consumption of 5.7 kWh/m3 and an energy efficiency of 56.6%. The Faradaic efficiency is 96-99%. With the current density fixed at 400 mA/cm2, after performing a test for 150 h, the cell voltage with NiFe(+)/Ru(-) increases by 0.167 V, whereas that with NiFe(+)/NiFe(-) decreases by only 0.010 V. Good, long-term stability is demonstrated.

In-Depth Study on the Effects of Impurity Ions in Saline Wastewater Electrolysis

Concentration followed by electrolysis is one of the most promising ways for saline wastewater treatment, since it could produce H₂, Cl_2, and an alkaline solution with deacidification potential. However, due to the diversity and difference of wastewater, knowledge on the suitable salt concentration for wastewater electrolysis and the effects of mixed ions are still lacking. In this work, electrolysis experiments of mixed saline water were conducted. The salt concentration for stable dechlorination was explored, with in-depth discussions on the effects of typical ions such as K⁺, Ca²⁺, Mg²⁺, and SO₄^2-. Results showed that K⁺ had a positive effect on the H₂/Cl₂ production of saline wastewater through accelerating the mass transfer efficiency in the electrolyte. However, the existence of Ca²⁺ and Mg²⁺ had negative effects on the electrolysis performance by forming precipitates, which would adhere to the membrane, reduce the membrane permeability, occupy the active sites on the cathode surface, and also increase the transport resistance of the electrons in the electrolyte. Compared to Mg²⁺, the damaging effect of Ca²⁺ on the membrane was even worse. Additionally, the existence of SO₄^2- reduced the current density of the salt solution by affecting the anodic reaction while having less of an effect on the membrane. Overall, Ca²⁺ ≤ 0.01 mol/L, Mg²⁺ ≤ 0.1 mol/L and SO₄^2- ≤ 0.01 mol/L were allowable to ensure the continuous and stable dechlorination electrolysis of saline wastewater.

Recent Advancements of Polymeric Membranes in Anion Exchange Membrane Water Electrolyzer (AEMWE): A Critical Review

Water electrolysis coupled with renewable energy is one of the principal methods for producing green hydrogen (or renewable hydrogen). Among the different electrolysis technologies, the evolving anion exchange membrane water electrolysis (AEMWE) shows the utmost promise for the manufacture of green hydrogen in an inexpensive way. In the present review, we highlight the most current and noteworthy achievements of AEMWE, which include the advancements in increasing the polymer anionic conductivity, understanding the mechanism of degradation of AEM, and the design of the electrocatalyst. The important issues affecting the AEMWE behaviour are highlighted, and future constraints and openings are also discussed. Furthermore, this review provides strategies for producing dynamic and robust AEMWE electrocatalysts.

Synthesis and Characterization of a Composite Anion Exchange Membrane for Water Electrolyzers (AEMWE)

Anion exchange membranes (AEM) have gained attention recently as a promising candidate for low-cost water electrolysis systems to produce hydrogen, linked with renewable energy resources as a sustainable alternative to fossil fuels. The development of potential materials for producing and analyzing AEM is an imperative step towards commercialization and plays a competitive role in the hydrogen production industry. In this article, we developed a composite anion exchange membrane prepared by activating a commercial support structure (Celgard^® 3401) with a commercially available functional group (Fumion^® FAA-3) through a phase-inversion process. Fourier-transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) analysis demonstrated the phase-inversion procedure as an effective methodology. Furthermore, the cell performance test result (with Celgard/Fumion) was very promising and even better in comparison with a commercial membrane commonly applied in alkaline electrolysis (Fumasep). We also developed a testing procedure for membrane performance evaluation during electrolysis which is very critical considering the effect of CO₂ absorption on membrane conductivity.

NiFeOx and NiFeCoOx Catalysts for Anion Exchange Membrane Water Electrolysis

Hydrogen production using an Anion exchange membrane (AEM) electrolyzer allows the use of non-platinum group metal catalysts for oxygen evolution reaction (OER). Nickel and Cobalt-based oxides are active in an alkaline environment for OER and are relatively inexpensive compared to IrO2 catalysts used in Polymer electrolyte membrane (PEM) electrolysis. Mixed metal oxide catalysts NiFeOx and NiFeCoOx catalysts were synthesized by the coprecipitation method using NaOH. X-ray diffraction results showed mainly NiO diffraction peaks for the NiFeOx catalyst due to the low concentration of Fe, for the NiFeCoOx catalyst, NiCo2O4 diffraction peaks were observed. NiFeCoOx catalysts showed a higher Anion exchange membrane water electrolysis (AEMWE) performance compared to NiFeOx and commercial NiO, the highest current density at 2 V was 802 mA cm−2 at 70 °C using 1 M KOH as an electrolyte. The effect of electrolyte concentration was studied by using 0.01 M, 0.1 M and 1 M KOH concentrations in an electrolysis operation. Electrochemical Impedance spectroscopy was performed along with the equivalent circuit fitting to calculate ohmic and activation resistances, the results showed a decrease in ohmic and activation resistances with the increase in electrolyte concentration. Commercially available AEM (Fumasep FAA-3-50 and Sustainion dioxide membrane X-37-50 grade T) were tested at similar conditions and their performance was compared. EIS results showed that X-37-50 offered lower ohmic resistance than the FAA-3-50 membrane.

Anion-Exchange Membrane Water Electrolyzers

This Review provides an overview of the emerging concepts of catalysts, membranes, and membrane electrode assemblies (MEAs) for water electrolyzers with anion-exchange membranes (AEMs), also known as zero-gap alkaline water electrolyzers. Much of the recent progress is due to improvements in materials chemistry, MEA designs, and optimized operation conditions. Research on anion-exchange polymers (AEPs) has focused on the cationic head/backbone/side-chain structures and key properties such as ionic conductivity and alkaline stability. Several approaches, such as cross-linking, microphase, and organic/inorganic composites, have been proposed to improve the anion-exchange performance and the chemical and mechanical stability of AEMs. Numerous AEMs now exceed values of 0.1 S/cm (at 60-80 °C), although the stability specifically at temperatures exceeding 60 °C needs further enhancement. The oxygen evolution reaction (OER) is still a limiting factor. An analysis of thin-layer OER data suggests that NiFe-type catalysts have the highest activity. There is debate on the active-site mechanism of the NiFe catalysts, and their long-term stability needs to be understood. Addition of Co to NiFe increases the conductivity of these catalysts. The same analysis for the hydrogen evolution reaction (HER) shows carbon-supported Pt to be dominating, although PtNi alloys and clusters of Ni(OH)2 on Pt show competitive activities. Recent advances in forming and embedding well-dispersed Ru nanoparticles on functionalized high-surface-area carbon supports show promising HER activities. However, the stability of these catalysts under actual AEMWE operating conditions needs to be proven. The field is advancing rapidly but could benefit through the adaptation of new in situ techniques, standardized evaluation protocols for AEMWE conditions, and innovative catalyst-structure designs. Nevertheless, single AEM water electrolyzer cells have been operated for several thousand hours at temperatures and current densities as high as 60 °C and 1 A/cm2, respectively.

Alcohol Diffusion in Alkali-Metal-Doped Polymeric Membranes for Using in Alkaline Direct Alcohol Fuel Cells

The alcohol permeability of anion exchange membranes is a crucial property when they are used as a solid electrolyte in alkaline direct alcohol fuel cells and electrolyzers. The membrane is the core component to impede the fuel crossover and allows the ionic transport, and it strongly affects the fuel cell performance. The aim of this work is to compare different anion exchange membranes to be used as an electrolyte in alkaline direct alcohol fuels cells. The alcohol permeability of four commercial anion exchange membranes with different structure were analyzed in several hydro-organic media. The membranes were doped using different types of alkaline doping agents (LiOH, NaOH, and KOH) and different conditions to analyze the effect of the treatment on the membrane behavior. Methanol, ethanol, and 1-propanol were analyzed. The study was focused on the diffusive contribution to the alcohol crossover that affects the fuel cell performance. To this purpose, alcohol permeability was determined for various membrane systems. The results show that membrane alcohol permeability is affected by the doping conditions, depending on the effect on the type of membrane and alcohol nature. In general, heterogeneous membranes presented a positive correlation between alcohol permeability and doping capacity, with a lower effect for larger-size alcohols. A definite trend was not observed for homogeneous membranes.

What is Next in Anion-Exchange Membrane Water Electrolyzers? Bottlenecks, Benefits, and Future

As highlighted by the recent roadmaps from the European Union and the United States, water electrolysis is the most valuable high-intensity technology for producing green hydrogen. Currently, two commercial low-temperature water electrolyzer technologies exist: alkaline water electrolyzer (A-WE) and proton-exchange membrane water electrolyzer (PEM-WE). However, both have major drawbacks. A-WE shows low productivity and efficiency, while PEM-WE uses a significant amount of critical raw materials. Lately, the use of anion-exchange membrane water electrolyzers (AEM-WE) has been proposed to overcome the limitations of the current commercial systems. AEM-WE could become the cornerstone to achieve an intense, safe, and resilient green hydrogen production to fulfill the hydrogen targets to achieve the 2050 decarbonization goals. Here, the status of AEM-WE development is discussed, with a focus on the most critical aspects for research and highlighting the potential routes for overcoming the remaining issues. The Review closes with the future perspective on the AEM-WE research indicating the targets to be achieved.

Anion Exchange Membranes for Fuel Cell Application: A Review

The fuel cell industry is the most promising industry in terms of the advancement of clean and safe technologies for sustainable energy generation. The polymer electrolyte membrane fuel cell is divided into two parts: anion exchange membrane fuel cells (AEMFCs) and proton exchange membrane fuel cells (PEMFCs). In the case of PEMFCs, high-power density was secured and research and development for commercialization have made significant progress. However, there are technical limitations and high-cost issues for the use of precious metal catalysts including Pt, the durability of catalysts, bipolar plates, and membranes, and the use of hydrogen to ensure system stability. On the contrary, AEMFCs have been used as low-platinum or non-platinum catalysts and have a low activation energy of oxygen reduction reaction, so many studies have been conducted to find alternatives to overcome the problems of PEMFCs in the last decade. At the core of ensuring the power density of AEMFCs is the anion exchange membrane (AEM) which is less durable and less conductive than the cation exchange membrane. AEMFCs are a promising technology that can solve the high-cost problem of PEMFCs that have reached technological saturation and overcome technical limitations. This review focuses on the various aspects of AEMs for AEMFCs application.