Electrolyte Membrane Research Articles

Physicochemical vs Electrochemical Technologies for Metal Recovery – Main Insights, Comparison, Complementarity and Challenges

AbstractThe quest toward the development of new, more eco‐friendly removal/recycling/recovery methods for a range of valuable elements is intense nowadays. In this Review we present and discuss in a critical way the best available physicochemical processes versus modern electrochemical approaches for metal recovery of elements which form part of spent catalysts or other sources such as wastewater, mining waste and spent batteries. These techniques include coagulation/flocculation, precipitation, electrocoagulation/electroflotation, membrane electrolysis, electrodeposition/electrowinning and gas‐diffusion electrocrystallization (GDEx). Several key performance indicators (KPIs) are utilized to facilitate the critical analysis of the different recovery methods. Such indicators have to do, for example, with the efficiency, the cost, the complexity, and the environmental friendliness of the methods used. In some cases, the recovered metals can be further used for specific applications, including the fabrication of electrocatalysts for reactions of interest. When possible, the more novel electrified technologies are benchmarked versus the state‐of‐the art approaches. This manuscript helps to summarize all types of approaches in a comparative manner. When the targeted metal cannot be recovered by any of the technologies explored, its removal can also be considered as satisfactory in some extent, especially if the element under discussion poses a risk of toxicity for the environment or for human health. Recovery technologies are sometimes combined for an optimum effect, exploiting the advantages of each approach and mitigating their drawbacks. Our review provides also some examples for ‘removal‐only’ possibilities of the studied methods, though its primary focus is the metal recovery aiming for metal reuse in the best possible scenarios.

Nonlinear modeling and control of hydrogen generating system

ABSTRACT This work attempts to develop a nonlinear control algorithm for a Proton Exchange Membrane (PEM) electrolyzer unit working as a hydrogen generating system. Initially, the system dynamics is studied using the model equations resulting from first principle balance at the anode and cathode. The system model is split into six ancillaries viz. anode, cathode, membrane, thermal, voltage, and storage. The first principles models are simulated using MATLAB/Simulink and verified with the data available in the open literature. This work is intended to analyze the performance of an observer-based controller for the system. The originality of this work lies in the integration of PEM electrolyzer and hydrogen storage system followed by controlling the electrolyzer temperature and storage system pressure. The system is automated with a nonlinear control strategy known as globally linearizing controller (GLC). An adaptive state observer (ASO) has been formulated to estimate unknown state variables. To select the optimal parameters, optimization algorithms, namely, particle swarm optimization (PSO) and Ali Baba and forty thieves (AFT) have been used. For the comparative controller performance, the closed-loop simulation of ASO-GLC has been performed. Upon comparing the closed-loop system response, the GLC performance is found better than a well-tuned PI controller.

Iron-Molybdenum Sulfide Electrocatalysts for the Hydrogen Evolution Reaction: An Operando XAS study

The comprehensive characterization of the structure-electrocatalytic activity relationships is of great interest to support the development of efficient catalysts for hydrogen evolution reaction (HER) in proton-exchange membrane (PEM) electrolyzers. The successful implementation of a bimetallic iron-molybdenum sulfide electrocatalyst for HER into a PEM electrolyzer has been reported. However, the precise nature of their active sites is still elusive. In this study, we employed X-ray absorption spectroscopy (XAS) to study iron-molybdenum and molybdenum sulfides obtained by a microwave irradiation synthetic approach. Operando XAS measurements in an acidic environment revealed sulfur-defective amorphous MoSx and FeS phases. Although the amount of dopant Fe is 10 times lower than that of Mo, the synergy between the two phases promotes the HER performance of iron-molybdenum sulfides.

A comparative analysis of ozone disinfection mainstream processes in wastewater treatment plants: Exergy and exergoeconomic viewpoints

Dielectric barrier discharge (DBD) and proton exchange membrane (PEM) electrolysis are widely recognized techniques for ozone disinfection. DBD, when using air, emits nitrogen oxides, posing environmental concerns, while an oxygen source elevates costs. Although PEM electrolysis can produce hydrogen and higher ozone concentrations, it demands greater energy and operational expenses. However, comparative assessments of their exergy efficiency and economic viability have been lacking. This study contrasted two ozone disinfection designs for secondary effluent from wastewater treatment plants using exergy and exergoeconomic analyses. The findings revealed that PEM electrolysis showed a higher total exergy efficiency (44.77%) when including hydrogen production, compared to DBD’s 33.16%. However, PEM also exhibited higher exergy destruction (746.6kW) versus DBD (317.0kW), mainly attributed to the ozone generator. Exergoeconomic analysis indicated that the unit product exergy cost of treated water for DBD was 2.62 times higher than for PEM. Considering the economic benefits of hydrogen production, PEM’s net cost is 83.39 USD/h, slightly higher than DBD’s 63.34 USD/h. Notably, the relative cost differences of ozone generators and exhaust gas treatment highlight the potential for optimizing economic benefits. Sensitivity analysis underscored the impact of interest rates and electricity prices. Overall, PEM electrolysis presents a promising alternative for ozone disinfection in wastewater treatment plants, offering higher exergy efficiency and potential economic benefits, especially with hydrogen production. The higher exergy destruction in PEM suggests room for further optimization, particularly in the ozone generator.

The influence of electrode crack dimensions on the durability of polymer electrolyte membrane fuel cells

Electrode cracks in polymer electrolyte membrane fuel cells (PEMFCs) are correlated with early onset failures. In this work we investigate the influence of cracked gas diffusion electrodes (GDEs) on the durability of the membrane electrode assembly (MEA) using a combined chemical-mechanical accelerated stress test (AST). Electrode crack dimensions were systematically tuned using ink formulations and material selection strategies. A parameter to describe the crack width areal density (ΦCW) was used to quantify the degree of discontinuity in the electrode surfaces. Open circuit voltage (OCV) transient analyses were used to benchmark and characterize the failure mechanisms in the MEAs as a function of the ΦCW. While smaller electrode-level cracks, on the order of microns, yielded a 28 % decrease in operating lifetime, larger cracks that propagated from a discontinuous, microporous layer (MPL) coating, decreased the operating lifetime by 56 %. This work emphasizes the need for material processing strategies that consider defect tolerances to limit membrane failures in PEMFCs.

Gel polymer electrolyte membranes consisted of solvate ionic liquid and crosslinked network polymers bearing different main chains: Fabrication and lithium battery application

Gel polymer electrolyte membranes consisted of solvate ionic liquid and crosslinked network polymers bearing different main chains: Fabrication and lithium battery application

In situ establishment of rapid lithium transport pathways at the electrolytes-electrodes interface enabling dendrite-free and long-lifespan solid-state lithium batteries

Composite solid-state electrolytes (CSEs) exhibit the high ionic conductivity of ceramic electrolytes and the facile processing and good flexibility of polymer electrolytes, representing the most promising class of solid-state electrolytes for the industrialization of lithium batteries. Nevertheless, CSEs continue encountering substantial interfacial resistance, which impedes their practical deployment. In response to these issues, a Li6.4La3Zr1.4Ta0.6O12/poly(vinylidene fluoride) (LLZTO/PVDF) solid electrolyte membranes with a thickness of 25 μm were prepared by the doctor blade method. In situ polymerization of 1,3-dioxolane (DOL) at the electrolyte–electrode interface was initiated by lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalate)borate (LiDFOB) dual-salts to produce poly(1,3-dioxolane) (PDOL). The presence of PDOL in LLZTO/PVDF@PDOL results in a high room temperature ionic conductivity of 3.578 mS cm−1. Moreover, the Li||LLZTO/PVDF@PDOL||LiFePO4(LFP) battery exhibits a discharge-specific capacity of 143 mAh g−1 and capacity retention of 81.7 % after 1000 cycles at 2 C, and the pouch cell with LLZTO/PVDF@PDOL achieved a high energy density of 190 Wh kg−1. The findings of this study may facilitate the industrial application of CSEs.

Phosphorylated cerium functionalized Nafion for superior radical scavenging and enhanced proton conductivity in polymer electrolyte membrane fuel cells

Phosphorylated cerium functionalized Nafion for superior radical scavenging and enhanced proton conductivity in polymer electrolyte membrane fuel cells

Polyvinyl butyral solid electrolyte membrane and its electrochromic laminated safety glass

Polyvinyl butyral solid electrolyte membrane and its electrochromic laminated safety glass

Improved chemical durability in polymer electrolyte membranes with nanocellulose-based gas barrier interlayers

Enhancing the lifetime of polymer electrolyte fuel cells (PEFCs) is a key factor in accelerating their application in heavy-duty vehicles (HDVs). A major contributing factor to their worsening performance over time is chemical degradation of the polymer electrolyte membrane (PEM). This is largely caused by the generation of reactive oxygen species such as hydroxyl radicals (•OH) or hydrogen peroxide (H2O2), which break down the polymer structure. This radical attack results in a loss of ionic conductivity and thus an increase in cell resistance over the operational lifetime. Here we show that adding an interlayer with suitable gas barrier properties can effectively suppress the generation of reactive oxygen species, slow the rate of membrane thinning, and extend the lifetime of the cell. We found that cellulose nanocrystals (CNC) blends with poly(vinyl sulfonic acid) (PVS) are suitable composite materials for the interlayer, combining low oxygen permeability with reasonable proton conductivity. Accelerated degradation of the PEMs was investigated via open circuit voltage (OCV) holding tests, in which the device lifetime was reproducibly extended by the incorporation of the CNC/PVS interlayer. Post-mortem analysis revealed that the rate of membrane thinning at the anode side of the PEM after 100 h test was just 30 nm/h, compared with 80 nm/h without an interlayer. Our results clearly confirm that the incorporation of CNC/PVS interlayers with low oxygen permeability into PEMs can suppress chemical degradation and significantly improve the durability of PEFCs. The obtained results also indicate that the concept of the gas barrier PEM for the improved chemical durability of PEMs can be widely and universally applied. We anticipate that this will contribute to the development of next-generation devices with sufficient lifetime for efficient use in fuel cell electric vehicles (FCEVs), including heavy-duty FCEVs.

Electro-upcycling polyethylene glycol aqueous solutions in a proton exchange membrane electrolyser

Electro-upcycling polyethylene glycol aqueous solutions in a proton exchange membrane electrolyser

Comparative techno-economic evaluation of alkaline and proton exchange membrane electrolysis for hydrogen production amidst renewable energy source volatility

Comparative techno-economic evaluation of alkaline and proton exchange membrane electrolysis for hydrogen production amidst renewable energy source volatility

Enhancement of Hydrogen Production Using an Integrated Evacuated Tube Solar Collector and PEM Electrolyzer With Al2O3 and SiO2 Hybrid Nanofluids

ABSTRACTThe motivation for this study stems from the global demand for clean energy solutions and the limitations of conventional fluids in hydrogen production systems. By exploring hybrid nanofluids, this research aims to enhance efficiency and sustainability in solar‐thermal energy applications. An evacuated tube solar collector (ETSC) with a polymer electrolyte membrane (PEM) electrolyzer efficiently harnesses solar energy for hydrogen production. The ETSC's vacuum design minimizes heat loss, providing consistent thermal performance. This system enables clean hydrogen generation, reducing emissions. This study investigated the integration of an ETSC with a PEM electrolyzer and organic Rankine cycle (ORC) for efficient hydrogen production. Water as the working fluid in the ETSC circuit resulted in lower hydrogen production rates, prompting the introduction of Al2O3 and SiO2 hybrid nanoparticles at a 50:50 ratio to form an enhanced hybrid nanofluid. The resulting various volume concentrations (0.5%, 1%, 1.5%, and 2%) of the hybrid nanofluid were tested, yielding energy gains of 13.22%, 21.37%, 30.38%, and 48.52%, respectively, compared to water. The ORC efficiency enhanced by 12.29% at 0.5 vol.%, 23.10% at 1 vol.%, 34.15% at 1.5 vol.%, and 48.40% at 2 vol.%. The PEM electrolyzer produced a maximum hydrogen yield of 3105.6 g, with an overall system efficiency of 71.3% and hydrogen production of 2156.7 g at 2 vol.%, demonstrating the significant performance enhancements achieved with hybrid nanofluids. The results demonstrated the effectiveness of hybrid nanofluids in enhancing system efficiency and hydrogen output, underscoring their importance in promoting sustainable hydrogen production technologies.

Dynamic performance prediction of PEM electrolyzers combining an electrochemical neural network model and a lumped thermal capacitance model

ABSTRACT The proton exchange membrane (PEM) electrolyzer electrochemical models based on conventional analytical and empirical approaches require numerous parameters, which are difficult to obtain accurately, leading to lower dynamic performance prediction accuracy while the parameters of the lumped thermal capacitance model are relatively simple and easily identifiable. This study proposes an integrated modeling framework, which combines a backpropagation (BP) neural network model for electrochemical performance and a lumped thermal capacitance model for the assessment of thermal performance. The neural network model is trained on polarization data collected from 44°C to 76°C. The BP neural network, optimized through iterative hyperparameter tuning, achieves high predictive accuracy with three hidden layer nodes and tansig and purelin activation functions, exhibiting less than 1% error in polarization curve predictions at four additional temperatures and current densities from 0.04 to 2.6 A/cm2. The thermal model, calibrated with experimental data, predicts thermal-balance temperatures with root mean square error (RMSE) of 0.08°C to 0.52°C under four different operating conditions. The dynamic performance of the integrated model is validated under three different operating conditions. This comprehensive model enables detailed analysis of critical operating variables, providing actionable insights for selecting and optimizing operating conditions in practical applications.

Unlocking Peak Efficiency in Anion-Exchange Membrane Electrolysis with Iridium-Infused Ni/Ni2P Heterojunction Electrocatalysts.

Developing cost-effective, highly efficient, and durable bifunctional electrocatalysts for water electrolysis remains a significant challenge. Nickel-based materials have shown promise as catalysts, but their efficiency in alkaline electrolytes is still lacking. Fascinatingly, Mott-Schottky catalysts can fine-tune electron density at interfaces, boosting intermediate adsorption and facilitating desorption to reduce the energy barrier. In this study, iridium-implanted Mott-Schottky Ni/Ni2P nanosheets (IrSA-Ni/Ni2P) is introduced, which are delivered from the metal-organic framework and employ them as the bifunctional catalysts for water electrolysis devices. This catalyst requires a small 54mV overpotential for hydrogen evolution reaction (HER) and 192mV for oxygen evolution reaction (OER) to reach 10 mA·cm-2 in a 1.0m KOH electrolyte. Density functional theory (DFT) calculations reveal that the incorporation of Ir atoms with enriched interfaces between Ni and Ni2P can promote the active sites and be favorable for the HER and OER. This discovery highlights the most likely reactive sites and offers a valuable blueprint for designing highly efficient and stable catalysts tailored for industrial-scale electrolysis. The IrSA-Ni/Ni2P electrode exhibits exceptional current density and outstanding stability in a single-cell anion-exchange membrane electrolyzer.

Bias-Induced Ga-O-Ir Interface Breaks the Limits of Adsorption-Energy Scaling Relationships for High-Performing Proton Exchange Membrane Electrolyzers.

Rationally manipulating the in-situ formed catalytically active surface of catalysts remains a significant challenge for achieving highly efficient water electrolysis. Herein, we present a bias-induced activation strategy to modulate in-situ Ga leaching and trigger the dynamic surface restructuring of lamellar Ir@Ga2O3 for the electrochemical oxygen evolution reaction. The in-situ reconstructed Ga-O-Ir interface sustains high water oxidation rates at OER overpotentials. We found that OER at the Ga-O-Ir interface follows a bi-nuclear adsorbate evolution mechanism with unsaturated IrOx as the active sites, while GaOx atoms play an indirect role in promoting water dissociation to form OH* and transferring OH* to Ir sites. This breaks the scaling relationship of the adsorption energies between OH* and OOH*, significantly lowering the energy barrier of the rate-limiting step and greatly increasing reactivity. The Ir@Ga2O3 catalyst achieves lower overpotentials, a current density of 2 A cm-2 at 1.76 V, and stable operation up to 1 A cm-2 in scalable PEM electrolyzers at 1.63 V, maintaining stable operation at 1 A cm-2 over 1000 hours with a degradation rate of 11.5 μV h-1. This work prompted us to jointly address substrate-catalyst interactions and catalyst reconstruction, an underexplored path, to improve activity and stability in Ir PEMWE anodes.

Bias‐Induced Ga‐O‐Ir Interface Breaks the Limits of Adsorption‐Energy Scaling Relationships for High‐Performing Proton Exchange Membrane Electrolyzers

Rationally manipulating the in‐situ formed catalytically active surface of catalysts remains a significant challenge for achieving highly efficient water electrolysis. Herein, we present a bias‐induced activation strategy to modulate in‐situ Ga leaching and trigger the dynamic surface restructuring of lamellar Ir@Ga2O3 for the electrochemical oxygen evolution reaction. The in‐situ reconstructed Ga‐O‐Ir interface sustains high water oxidation rates at OER overpotentials. We found that OER at the Ga‐O‐Ir interface follows a bi‐nuclear adsorbate evolution mechanism with unsaturated IrOx as the active sites, while GaOx atoms play an indirect role in promoting water dissociation to form OH* and transferring OH* to Ir sites. This breaks the scaling relationship of the adsorption energies between OH* and OOH*, significantly lowering the energy barrier of the rate‐limiting step and greatly increasing reactivity. The Ir@Ga2O3 catalyst achieves lower overpotentials, a current density of 2 A cm‐2 at 1.76 V, and stable operation up to 1 A cm‐2 in scalable PEM electrolyzers at 1.63 V, maintaining stable operation at 1 A cm‐2 over 1000 hours with a degradation rate of 11.5 μV h−1. This work prompted us to jointly address substrate‐catalyst interactions and catalyst reconstruction, an underexplored path, to improve activity and stability in Ir PEMWE anodes.

Transition Metal-Coordinated Polymer Achieves Stable Seawater Oxidation over NiFe Layered Double Hydroxide.

Seawater electrolysis has emerged as a promising approach for the generation of hydrogen energy, but the production of deleterious chlorine derivatives (e.g., chloride and hypochlorite) presents a significant challenge due to the severe corrosion at the anode. Transition metal-coordinated polymers have garnered attention as promising electrocatalysts for alkaline seawater oxidation (ASO), attributed to their remarkable chlorine corrosion resistance, high conductivity, and facile synthesis. In this study, we employ an anodic oxidation-electrodeposition strategy to grow NiFe-polyaniline on NiFe layered double hydroxide supported on Ni foam (NiFe LDH@NiFe-PANI/NF) as a highly efficient catalyst for ASO. We demonstrate stable ASO at industrial-level current densities (j) by employing a synergistic strategy that integrates NiFe-PANI, which offers resistance to chlorine-induced corrosion, and molybdate, which effectively repels chloride anions. In alkaline seawater, NiFe LDH@NiFe-PANI/NF requires 380 mV to sustain a j of 1000 mA cm-2, and it exhibits continuous operation for 500 h at a j of 1000 mA cm-2. Besides, the anion-exchange membrane electrolyzer consisting of NiFe LDH@NiFe-PANI/NF requires a voltage of 2.16 V to drive 300 mA cm-2. Notably, it can operate stably for 120 h, highlighting its potential for sustainable energy applications.

A Super‐Chlorophobic Yet Weak‐Reconstructed Electrocatalyst by Fluorination Engineering toward Chlorine Oxidation‐Free and High‐Stability Seawater Electrolysis

AbstractDirect seawater electrolysis is key for achieving sustainable green‐hydrogen production and transitioning toward a decarbonized energy system. However, its performance is limited by significant challenges, mainly catalyst instability, which is caused by excessive reconstruction, low catalytic activity, and aggressive chlorine‐corrosion. Herein, high‐electronegativity F is introduced into NiFe layered double‐hydroxide (F‐NiFe‐LDH) through fluorination engineering to induce electron‐deficient regions around Ni, thus creating abundant intrinsic high‐valence Ni sites. Correspondingly, the features of weak reconstruction accompanied by high stability, chlorophobic surface, and high‐activity lattice oxygen are produced on the F‐NiFe‐LDH, confirmed detailedly by experiment and theory. Consequently, the F‐NiFe‐LDH exhibits a superior oxygen evolution reaction (OER) activity with low overpotentials of 306 and 375 mV to reach 500 mA cm−2 at alkaline simulated seawater and alkaline seawater, respectively. Also, it demonstrates a chlorine‐corrosion resistance, along with ultra‐stability seawater electrolysis for over 1000 h at 1000 mA cm−2 without performance degradation, structural collapse, or chlorine oxidation reaction. Furthermore, an anion exchange membrane electrolyzer assembled by the F‐NiFe‐LDH anode shows an energy consumption of only 4.87 kWh Nm−3 for hydrogen production. This work provides an inspiration for designing corrosion‐resistance electrocatalysts aimed at chlorine oxidation‐free seawater electrolysis, which simultaneously achieve high stability and OER activity.

Isomeric Poly(arylene piperidinium) Electrolyte Membranes with High Alkaline Durability

AbstractThe isomerization strategy is employed to enhance the alkaline stability of poly(arylene piperidinium)s (PAP) while maintaining the monomer commerciality and polymer architecture tunability. Isomeric poly(arylene piperidinium) (i‐PAP) exhibits improved alkali resistance relative to conventional PAP, as evidenced by ex situ alkaline stability and in situ cell durability tests. Following treatment in 10 m aqueous NaOH at 80 °C for 360 h or operation at 0.4 A cm−2 for 100 h in an anion exchange membrane fuel cell (AEMFC) prototype, the decomposition of the piperidinium moieties in i‐PAP is ≈50% of that observed in PAP. Moreover, through a copolymerization strategy, the i‐PAP‐88 membrane, which has suppressed water absorption, reaches a peak power density of 1.44 W cm−2 and demonstrates an in situ durability of 310 h. Furthermore, a noble metal‐free (anode) AEM water electrolyzer (AEMWE) achieves a high current density of 6.43 A cm⁻2 at 2.0 V and an excellent Faradaic efficiency of 98.3%. This study highlights a strategy for designing alkali‐stable polyelectrolytes that mitigate degradation during the operation of alkaline electrochemical devices.