Alkaline Anion Exchange Membrane Water Research Articles

Novel Large-scale Integrated Non-Precious Metal Electrodes for Efficient and Stable Oxygen Evolution Reaction at High Current Density in 2.5 kW Anion Exchange Membrane Water Electrolysis

The utilization of non-precious catalysts to substitute precious metal catalysts on anode side under high current density conditions and with long-term resistance is crucial for the implementation of alkaline anion-exchange membrane water electrolysis (AEMWE) applications. To accommodate industrial applications, a combination of chemical solution and electrodeposition was used to construct NiFeCo layered double hydroxide and NiS nanosheet heterostructures on Ni foam (NiFeCo LDH/NiS/NF). Both experiments and theoretical calculations show that the heterogeneous structure reduces the activation energy barrier of the catalytic reaction and provides an appropriate electronic structure. This not only guarantees the exposure of the active site but also adjusts the local coordination environment and chemisorption properties. Consequently, the reduction in energy barrier affects the rate-determining step (RDS) from *O to *OOH, as well as the energy barriers of all four steps in the oxygen evolution reaction (OER). Consequently, the optimized NiFeCo LDH/NiS/NF catalyst demonstrates a low voltage of 288mV to operate 1.0Acm-2. Additionally, the catalyst was conducted with commercial Pt/C coated onto carbon paper (Pt/C/CP) for 2×2 cm2 AEMWE exhibited 1.63V cell voltag to attain 1Acm−2 and operated for 2100h from 1Acm-2 to 2.5Acm-2 (1.69V to 1.92V). Further, the catalyst was prepared scalable to 15×15 cm2 for application into a 2.5kW AEMWE device, which required only 1.77V at 60 °C to catch 1Acm-2 for 1000h, which shows extremally promising application for stable AEMWE device.

The hybrid Pt nanoclusters/Ru nanowires catalysts accelerating alkaline hydrogen evolution reaction

Water electrolysis via alkaline hydrogen evolution reaction (HER) is a promising approach for large-scale production of high-purity hydrogen at a low cost, utilizing renewable and clean energy. However, the sluggish kinetics derived from the high energy barrier of water dissociation impedes seriously its practical application. Herein, a series of hybrid Pt nanoclusters/Ru nanowires (Pt/Ru NWs) catalysts are demonstrated to accelerate alkaline HER. And the optimized Pt/Ru NWs (10 ​% wt Pt) exhibits exceptional performance with an ultralow overpotential (24 ​mV at 10 ​mA ​cm−2), a small Tafel slope (26.3 ​mV dec−1), and long-term stability, outperforming the benchmark commercial Pt/C-JM-20 ​% wt catalyst. This amazing performance also occurred in the alkaline anion-exchange membrane water electrolysis devices, where it delivered a cell voltage of about 1.9 ​V at 1 ​A ​cm−2 and an outstanding stability (more than 100 ​h). The calculations have revealed such a superior performance exhibited by Pt/Ru NWs stems from the formed heterointerfaces, which significantly reduce the energy barrier of the decisive rate step of water dissociation via cooperative-action between Pt cluster and Ru substance. This work provides valuable perspectives for designing advanced materials toward alkaline HER and beyond.

Alleviating OH Blockage on the Catalyst Surface by the Puncture Effect of Single-Atom Sites to Boost Alkaline Water Electrolysis.

Nonprecious transition metal catalysts have emerged as the preferred choice for industrial alkaline water electrolysis due to their cost-effectiveness. However, their overstrong binding energy to adsorbed OH often results in the blockage of active sites, particularly in the cathodic hydrogen evolution reaction. Herein, we found that single-atom sites exhibit a puncture effect to effectively alleviate OH blockades, thereby significantly enhancing the alkaline hydrogen evolution reaction (HER) performance. Typically, after anchoring single Ru atoms onto tungsten carbides, the overpotential at 10 mA·cm-2 is reduced by more than 130 mV (159 vs 21 mV). Also, the mass activity is increased 16-fold over commercial Pt/C (MA100 = 17.3 A·mgRu-1 vs 1.1 A·mgPt-1, Pt/C). More importantly, such electrocatalyst-based alkaline anion-exchange membrane water electrolyzers can exhibit an ultralow potential (1.79 Vcell) and high stability at an industrial current density of 1.0 A·cm-2. Density functional theory (DFT) calculations reveal that the isolated Ru sites could weaken the surrounding local OH binding energy, thus puncturing OH blockage and constructing bifunctional interfaces between Ru atoms and the support to accelerate water dissociation. Our findings exhibit generality to other transition metal catalysts (such as Mo) and contribute to the advancement of industrial-scale alkaline water electrolysis.

Triptycene Branched Poly(aryl-co-aryl piperidinium) Electrolytes for Alkaline Anion Exchange Membrane Fuel Cells and Water Electrolyzers.

Alkaline polymer electrolytes (APEs) are essential materials for alkaline energy conversion devices such as anion exchange membrane fuel cells (AEMFCs) and water electrolyzers (AEMWEs). Here, we report a series of branched poly(aryl-co-aryl piperidinium) with different branching agents (triptycene: highly-rigid, three-dimensional structure; triphenylbenzene: planar, two-dimensional structure) for high-performance APEs. Among them, triptycene branched APEs showed excellent hydroxide conductivity (193.5 mS cm-1 @80 °C), alkaline stability, mechanical properties, and dimensional stability due to the formation of branched network structures, and increased free volume. AEMFCs based on triptycene-branched APEs reached promising peak power densities of 2.503 and 1.705 W cm-2 at 75/100 % and 30/30 % (anode/cathode) relative humidity, respectively. In addition, the fuel cells can run stably at a current density of 0.6 A cm-2 for 500 h with a low voltage decay rate of 46 μV h-1 . Importantly, the related AEMWE achieved unprecedented current densities of 16 A cm-2 and 14.17 A cm-2 (@2 V, 80 °C, 1 M NaOH) using precious and non-precious metal catalysts, respectively. Moreover, the AEMWE can be stably operated under 1.5 A cm-2 at 60 °C for 2000 h. The excellent results suggest that the triptycene-branched APEs are promising candidates for future AEMFC and AEMWE applications.

Triptycene Branched Poly(aryl‐co‐aryl piperidinium) Electrolytes for Alkaline Anion Exchange Membrane Fuel Cells and Water Electrolyzers

AbstractAlkaline polymer electrolytes (APEs) are essential materials for alkaline energy conversion devices such as anion exchange membrane fuel cells (AEMFCs) and water electrolyzers (AEMWEs). Here, we report a series of branched poly(aryl‐co‐aryl piperidinium) with different branching agents (triptycene: highly‐rigid, three‐dimensional structure; triphenylbenzene: planar, two‐dimensional structure) for high‐performance APEs. Among them, triptycene branched APEs showed excellent hydroxide conductivity (193.5 mS cm−1@80 °C), alkaline stability, mechanical properties, and dimensional stability due to the formation of branched network structures, and increased free volume. AEMFCs based on triptycene‐branched APEs reached promising peak power densities of 2.503 and 1.705 W cm−2 at 75/100 % and 30/30 % (anode/cathode) relative humidity, respectively. In addition, the fuel cells can run stably at a current density of 0.6 A cm−2 for 500 h with a low voltage decay rate of 46 μV h−1. Importantly, the related AEMWE achieved unprecedented current densities of 16 A cm−2 and 14.17 A cm−2 (@2 V, 80 °C, 1 M NaOH) using precious and non‐precious metal catalysts, respectively. Moreover, the AEMWE can be stably operated under 1.5 A cm−2 at 60 °C for 2000 h. The excellent results suggest that the triptycene‐branched APEs are promising candidates for future AEMFC and AEMWE applications.

Hierarchical urchin-like CuxCo3−xO4 spinels as oxygen evolution reaction catalysts in alkaline anion exchange membrane water electrolyzers

Hierarchical urchin-like CuxCo3−xO4 spinels as oxygen evolution reaction catalysts in alkaline anion exchange membrane water electrolyzers

Boosting Oxygen Evolution Reaction of (Fe,Ni)Ooh via Defect Engineering for Anion Exchange Membrane Water Electrolysis Under Industrial Conditions.

Developing non-precious catalysts with long-term catalytic durability and structural stability under industrial conditions is the key to practical alkaline anion exchange membrane (AEM) water electrolysis. Here we propose an energy-saving approach to synthesize defect-rich iron nickel oxyhydroxide for stability and efficiency toward the oxygen evolution reaction (OER). Benefiting from in situ cation exchange, the nanosheet-nanoflake-structured catalyst is homogeneously embedded in, and tightly bonded to, its substrate, making it ultrastable at high current densities. Experimental and theoretical calculation results reveal that the introduction of Ni in FeOOH reduces the activation energy barrier for the catalytic reaction and that the purposely created oxygen defects not only ensure the exposure of active sites and maximize the effective catalyst surface but also modulate the local coordination environment and chemisorption properties of both Fe and Ni sites, thus lowering the energy barrier from *O to *OOH. Consequently, the optimized d-(Fe,Ni)OOH catalyst exhibits outstanding catalytic activity with long-term durability under both laboratory and industrial conditions. The large-area d-(Fe,Ni)OOH||NiMoN pair requires 1.795V to reach a current density of 500mA cm-2 at an absolute current of 12.5 A in an AEM electrolyzer for overall water electrolysis, showing great potential for industrial water electrolysis. This article is protected by copyright. All rights reserved.

Metallic Glass Nanofoam Anode Catalysts for Anion-Exchange Membrane Water Electrolyzers

Alkaline anion-exchange membrane water electrolyzers (AEMWEs) for hydrogen production are now receiving intensive attention due to their feasibility to use sustainable, low-cost platinum group metal (PGM-free) catalysts. Although a variety of highly efficient PGM-free catalysts for the oxygen evolution reaction (OER) have been explored, few of them demonstrated satisfied performance in real AEMWEs due to the insufficient electrical conductivity and unfavorable interfaces with ionomers in 3D porous electrodes. Herein, we report a series of highly porous ternary NiFeM (M: Cu, Co, and Mn) metallic glassy catalysts featured with nanofoam network morphologies, which are composed of amorphous OER active metal oxide shells and highly electrically conductive metallic glass alloy cores. Due to these unique properties, these NiFeM nanofoam catalysts demonstrated promising OER activities and stabilities in the half-cell with aqueous alkaline electrolytes, especially at high potentials. We also examined their magnetic properties and found no direct correlation with measured OER activity. These ternary NiFeM catalysts are further integrated with unique ionomers and AEMs to fabricate AEMWEs, showing superior performance to binary NiFe and commercial IrO2 catalysts when utilizing diluted KOH electrolytes. A different trend was identified when directly using desirable but challenging pure water, and the NiFeCu catalyst performed the best comparable to IrO2 especially at high current densities. Although deep understanding on limiting factor of pure water AEMWEs is still required, these NiFeM catalysts with favorable catalytic and morphological properties representing a new class of highly efficient PGM-free anode catalysts for viable AEMWEs toward clean hydrogen generation.

Dithiol cross-linked polynorbornene-based anion-exchange membranes with high hydroxide conductivity and alkaline stability

Vinylic-addition polynorbornenes possess high thermal stability, excellent mechanical integrity, and chemically inert backbones. Herein, we conveniently synthesize a series of vinylic-addition polynorbornene copolymers containing pendant alkenes from commercial vinyl-substituted norbornene (VNB) and alkyl-bromide-substituted norbornene (BrNB). Subsequently, the copolymers are photo-crosslinked with dithiol reagents through UV-initiated thiol-ene click reactions followed by quaternization to prepare the cross-linked anion-exchange membranes (AEMs). The extent of cross-linking and the hydrophobicity of the cross-linkers can be easily controlled, so that the absorption of excess water can be inhibited with enhanced membrane strength. The resultant AEMs have ultrahigh hydroxide conductivities (up to 199 mS/cm at 90 °C under humidified conditions) and excellent alkaline stability in 1 M KOH at 80 °C for 1200 h. The vinylic-addition AEMs are also successfully applied in alkaline anion-exchange membrane water electrolyzers with commercial noble-metal-free electrocatalysts.

Ni3S2@NiFePx electrode with dual-anion-modulated layer for efficient and stable oxygen evolution

The rational construction of high-performance and stable electrocatalyst for oxygen evolution reaction (OER) is a prerequisite for efficient water electrolysis. Herein, we develop a broccoli-like Ni3S2@NiFePx (Ni3S2@NFP) catalyst on nickel foam (NF) via a sequential two-step layer-by-layer assembly electrodeposition method. X-ray diffraction, in situ Raman and Fourier-transform infrared spectra have mutually validated the element segregation and phase refusion during OER condition. The reconstruction of double layer Ni3S2@NFP facilitates the formation of the active (oxy)hydroxides, which is modulated by the dual anionic layer with mixed sulfate and phosphate ions. As a result, the obtained Ni3S2@NFP electrode exhibits low overpotential (329 mV) and long-term durability (∼500 h) for OER at current density of 500 mA/cm2. Moreover, the self-supported Ni3S2@NFP can act as an efficient and durable anode in alkaline anion exchange membrane water electrolysis device (AEMWE). This work provides a facile and scaled-up strategy to construct self-supported electrocatalyst and emphasizes the crucial role of anions in pre-catalyst reconstruction and enhancing OER performance.

Optimizing the Electronic Structure of Atomically Dispersed Ru Sites with CoP for Highly Efficient Hydrogen Evolution in both Alkaline and Acidic Media.

Developing efficient and stable electrocatalysts for hydrogen evolution reaction (HER) over a wide pH range and industrial large-scale hydrogen production is critical and challenging. Here, a tailoring strategy is developed to fabricate an outstanding HER catalyst in both acidic and alkaline electrolytes containing high-density atomically dispersed Ru sites anchored in the CoP nanoparticles supported on carbon spheres (NC@RuSA -CoP). The obtained NC@RuSA -CoP catalyst exhibits excellent HER performance with overpotentials of only 15 and 13 mV at 10 mA cm-2 in 1 m KOH and 0.5 m H2 SO4 , respectively. The experimental results and theoretical calculations indicate that the strong interaction between the Ru site and the CoP can effectively optimize the electronic structure of Ru sites to reduce the hydrogen binding energy and the water dissociation energy barrier. The constructed alkaline anion exchange membrane water electrolyze (AAEMWE) demonstrates remarkable durability and an industrial-level current density of 1560 mA cm-2 at 1.8 V. This strategy provides a new perspective on the design of Ru-based electrocatalysts with suitable intermediate adsorption strengths and paves the way for the development of highly active electrocatalysts for industrial-scale hydrogen production.

Freestanding μm-thin nanomesh electrodes exceeding 100x current density enhancement for high-throughput electrochemical applications

Nanomeshes (NMs), regularly interconnected 3D nanowire-networks, obtained from electroplating in rationally designed alumina templates, are attractive for numerous fields due to their extremely high surface area and porosity. Until now, non-porous support substrates were required to provide sufficient mechanical robustness to the highly porous NM. However, to exploit these compelling nano-architectures as freestanding electrodes in electrochemical flow cells, e.g. water electrolysis, it is essential that the nanowire-network is accessible from all sides requiring a porous support structure. To demonstrate the advantage of the high volumetric NM surface area of 26 m2/cm3 for water electrolysis up to 1 A/cm2, we monolithically integrated a nickel NM with an open support grid in a facile and up-scalable fabrication flow. The freestanding NM electrodes show beyond state-of-the-art performance for the alkaline hydrogen- and oxygen evolution reaction (HER and OER), with over 100x enhanced current densities in respect to planar nickel. Interestingly, the regular nano-architecture of the electrodes causes an intrinsic catalytic effect for the HER. The high potential of these novel 4 μm thin electrodes toward high-throughput electrochemical applications is shown by the significant 400 mV lower overpotential compared to commercial 1.6 mm thick nickel foams (<0.01 m2/cm3) in the alkaline anion-exchange membrane water electrolysis.

Self-Supported Bimetallic Phosphide Heterojunction-Integrated Electrode Promoting High-Performance Alkaline Anion-Exchange Membrane Water Electrolysis

Self-Supported Bimetallic Phosphide Heterojunction-Integrated Electrode Promoting High-Performance Alkaline Anion-Exchange Membrane Water Electrolysis

Self-Supporting NiFe Layered Double Hydroxide “Nanoflower” Cluster Anode Electrode for an Efficient Alkaline Anion Exchange Membrane Water Electrolyzer

The development of an efficient and durable oxygen evolution reaction (OER) electrode is needed to solve the bottleneck in the application of an anion exchange membrane water electrolyzer (AEMWE). In this work, the self-supporting NiFe layered double hydroxides (NiFe LDHs) “nanoflower” cluster OER electrode directly grown on the surface of nickel fiber felt (Ni fiber) was synthesized by a one-step impregnation at ambient pressure and temperature. The self-supporting NiFe LDHs/Ni fiber electrode showed excellent activity and stability in a three-electrode system and as the anode of AEMWE. In a three-electrode system, the NiFe LDHs/Ni fiber electrode showed excellent OER performance with an overpotential of 208 mV at a current density of 10 mA cm−2 in 1 M KOH. The NiFe LDHs/Ni fiber electrode was used as the anode of the AEMWE, showing high cell performance with a current density of 0.5 A cm−2 at 1.68 V and a stability test for 200 h in 1 M KOH at 70 °C. The electrocatalytic performance of NiFe LDHs/Ni fiber electrode is due to the special morphological structure of “nanoflower” cluster petals stretching outward to produce the “tip effect,” which is beneficial for the exposure of active sites at the edge and mass transfer under high current density. The experimental results show that the NiFe LDHs/Ni fiber electrode synthesized by the one-step impregnation method has the advantages of good activity and low cost, and it is promising for industrial application.

Electrochemical integration of amorphous NiFe (oxy)hydroxides on surface-activated carbon fibers for high-efficiency oxygen evolution in alkaline anion exchange membrane water electrolysis

Designing a high-efficiency and low-cost three-dimensional (3D) OER electrode via electrochemical integration of amorphous NiFeOOH on surface activated carbon fibers.

Next-generation anion exchange membrane water electrolyzers operating for commercially relevant lifetimes

Alkaline anion exchange membrane (AEM) water electrolysis has gained increasing attention due to its potential to achieve low-cost, high performance hydrogen production. However, most existing membranes are not durable in industrial settings. Here, we demonstrate good performance relative to industrial parameters using Sustainion® anion exchange membranes. Long-duration tests showed stable performance of 1 A/cm2 at 1.85 V with a degradation rate of less than 1 μV/h over 10,000 h. The projected lifetime is thus over 20 years. Daily on/off cycling performance over the course of 30 years was simulated experimentally through accelerated voltage shock tests, resulting in a performance loss of only 0.15 μV/cycle over 11,000 cycles. As shown through impact and crossover testing, an improvement in performance is achieved by the addition of zirconia to the polymer matrix and mechanically reinforcing the membrane.

(Invited) Performance and Stability of Radiation Grafted Based Anion Exchange Membrane Electrolysers

Hydrogen is a promising renewable fuel and energy storage solution, due to its highly efficient conversion with electricity and good energy density in comparison to most batteries. However, 95 % of the produced hydrogen globally is generated from non-renewable sources and only 5% is generated from electrolysis due to high systems cost [1,2]. Around 50% of the cost of the electrolyser system comes from the precious metal catalyst used in proton exchange membrane system [3,4]. Alkaline anion exchange membrane water electrolyser AAEM-WE allow the use of non-precious metals as: effective electro-catalyst and affordable flow fields and bipolar plates, reducing the cost significantly. It is estimated that replacement of PEM electrolysers with AAEM electrolysers could offer a 43% reduction in stack cost [5]. We look here at advantages and limitations of AAEM-WE and their ideal operating range.Higher performances can be achieved using high alkaline feed concentration but this in turn reduces the lifetime of the system due to degradation of AEM membrane/ionomers. Thus, in order to reduce the degradation and improve the lifetime, low alkaline concentration should be used as feed solution for AEMWE i.e. deionised water. We have shown previously [4] that an electrolyser current density of 100 mA cm-2 at 1.65V using NiCo2O4 for Oxygen Evolution Reaction (OER) could be achieved at 60 °C [4]. We present here a binary-catalyst based on manganese oxides MnOx as very efficient electro-catalyst for OER with Tafel slope of 30 mV dec-1. Using low cost LDPE based membranes radiation grafted AEM, a very promising performance electrolyser was obtained of 1.59 V at 100 mA cm-2 and a current density of 1 A cm-2 at a potential of 1.78 V in 0.01 M NaOH at 60 °C. The current highest performance reported for Ni based catalysts (2.7 mg cm-2) in the AEM system is 500 mA cm-2 at a potential of 1.9 V in 1% K2CO3 solution(pH 10-11) at 60 °C [6,7] which is ca. a third of the current density reported here. This performance is comparable to PEM electrolysers performances with the reported operating voltage is in the range of 1.6-1.7 V [8] at 1 A cm-2. However, the long-term stability of these systems remains a challenge. Keywords : AEM, water electrolysis, alkaline, non-precious metal catalyst,

Novel Electrocatalyst for Alkaline Membrane Water Electrolysis

AbstractThe production of H2 has aroused considerable attention worldwide as a renewable and sustainable energy source for domestic, industrial, and automotive purposes. Currently, about 95 % of H2 is produced from the steam reforming of methane. However, this process leads to the burning of fossil fuels and emits greenhouse gases into the atmosphere. Water electrolysis is an effective strategy to produce H2 in high purity. Alkaline anion exchange membrane water electrolysis (AAEMWE) is preferred to proton exchange membrane water electrolysis (PEMWE) because of the flexibility to be able to use cheaper membranes as separators and non‐noble electrocatalysts. However, the sluggish oxygen evolution reaction (OER) kinetics in AAEMWE is a bottleneck for water splitting efficiency and decreases the overall performances. Now, a novel nickel and iron graphene‐nanoplatelets‐supported metal‐organic framework‐based electrocatalyst has been developed that shows excellent durability and record‐high current density for alkaline electrolysis that outperforms the state‐of‐the‐art OER electrocatalysts.

The effects of morphology, microstructure and mixed-valent states of MnO2 on the oxygen evolution reaction activity in alkaline anion exchange membrane water electrolysis

In this work, we focused on the evaluation of oxygen evolution reaction (OER) activity of three different shapes of α-MnO2 nanowires (NWs), nanorods (NRs) and nanotubes (NTs) in alkaline anion exchange water electrolyser. We have attempted to separate the effect of shape, surface area, Mn3+ content and crystal facets on OER activity and stability. X-ray Photoelectron Spectroscopy (XPS) measurements showed that NTs had the highest surface concentration of Mn3+ on the as prepared samples with average Mn oxidation state of 3.33. However, after activation an increase in the average oxidation state of all three shapes to 3.9 was confirmed by XPS. X-Ray Diffraction (XRD) showed surface restructuring after testing. MnO2 NWs showed the highest OER mass activity of 60.6 A g−1 (10 mA cm−2 at 1.67 V (RHE)) due to the higher surface area of 72.2 m2 g−1. While NTs showed the highest specific activity due to highest content of 211 facet, high Mn3+ surface concentration/surface defects. Similar trend was observed in electrolyser testing with 2 mg cm−2 loading. Poor electronic conductivity of MnO2 resulted in decrease in performance with increased loading to 4 mg cm−2. All the studied shapes showed good stability over 36 h of electrolyser testing.

Graphene-nanoplatelets-supported NiFe-MOF: high-efficiency and ultra-stable oxygen electrodes for sustained alkaline anion exchange membrane water electrolysis

A simple and effective strategy for fabricating high-stability alkaline anion exchange membrane water electrolyzers for large-scale hydrogen production.