Suppression of current-induced membrane discharge of bipolar membranes by regulating ion crossover transport

Bipolar membranes(BPMs)exhibit the unique capability to regulate the operating environment of electrochemical system through the water dissociation-combination processes.However,the industrial utilization of BPMs is limited by instability and serious energy consumption.The current-induced membrane discharge(CIMD)at high-current conditions has a negative influence on the performance of anion-exchange membranes,but the underlying ion transport mechanisms in the BPMs remain unclear.Here,the CIMD-coupled Poisson-Nernst-Planck(PNP)equations are used to explore the ion transport mechanisms in the BPMs for both reverse bias and forward bias at neutral and acid-base conditions.It is demonstrated that the CIMD effect in the reverse-bias mode can be suppressed by enhancing the diffusive transport of salt counter-ions(Na^(+)and Cl^(−))into the BPMs,and that in the forward-bias mode with acid-base electrolytes can be suppressed by matching the transport rate of water counter-ions(H_(3)O^(+)and OH^(−)).Suppressing the CIMD can promote the water dissociation in the reverse-bias mode,as well as overcome the plateau of limiting current density and reduce the interfacial blockage of salt co-ions(Cl^(−))in the anion-exchange layer in the forward-bias mode with acid-base electrolytes.Our work highlights the importance of regulating ion crossover transport on improving the performance of BPMs.

Preparation of CS-CMC Bipolar Membrane and its Application in Electro-generated FeO_4^(2-)

CS-CMC bipolar membrane was prepared and the cross-section photograph of CS-CMC BM was observed by SEM. FT-IR spectrum indicated that CS-CMC BM contained -N=CRH2^＋ and -COO^- functional groups. The charge density of -N--CRH2^＋ in CS membrane was about 14.13 mmol/g and the charge density of -COO in CMC membrane was about 9.01 mmol/g. The electrochemistry properties of CS-CMC BM were also studied. CS-CMC BM not only can effectively stop FeO4^2- from diffusing into the cathode chamber, but also plays an important role in the supply of OH＂ consumed during the electro-generated FeO4^2- process.

A Simple Model to Determine the Trends of Electric Field Enhanced Water Dissociation in a Bipolar Membrane

This work is concentrated on elucidating the mechanism of the electric field enhanced water dissociation. A simple model was established for the theoretical current-voltage characteristics in water dissociation process on a bipolar membrane based on the existence of a depletion layer and Onsager's theory. Particular attention was given to the influence of applied voltage on depletion thickness and the dissociation constant. The factors on the water splitting process, such as water diffusivity, water content, ion exchange capacity, temperature, relative permittivity, etc. Were adequately analysed based on the derived model equations and several suggestions were proposed for decreasing the applied voltage in practical operation. The water dissociation tests were conducted and compared with both the theoretical calculation and the measured current-voltage curves reported in the literature, which showed a very good prediction to practical current-voltage behavior of a bipolar membrane at high current densities when the splitting of water actually commenced.

Using bipolar membrane electrodialysis to synthesize di-quaternary ammonium hydroxide and optimization design by response surface methodology

Bipolar membrane electrodialysis(BMED) has already been described for the preparation of quaternary ammonium hydroxide. However, compared to quaternary ammonium hydroxide, di-quaternary ammonium hydroxide has raised great interest due to its high thermal stability and good oriented performance.In order to synthesize N,N-hexamethylenebis(trimethyl ammonium hydroxide)(HM(OH)_2) by EDBM,experiments designed by response surface methodology were carried out on the basis of single-factor experiments. The factors include current density, feed concentration and flow ratio of each compartment(feed compartment: base compartment: acid compartment: buffer compartment). The relationship between current efficiency and the above-mentioned three factors was quantitatively described by a multivariate regression model. According to the results, the feed concentration was the most significant factor and the optimum conditions were as follows: the current efficiency was up to 76.2%(the hydroxide conversion was over 98.6%), with a current density of 13.15 m A·cm^(-2), a feed concentration of 0.27 mol·L^(-1) and a flow ratio of 20 L·h^(-1):26 L·h^(-1):20 L·h^(-1):20 L·h^(-1) for feed compartment, base compartment, acid compartment, and intermediate compartment, respectively. This study demonstrates the optimized parameters of manufacturing HM(OH)_2 by direct splitting its halide for industrial application.

Stable overall water splitting in an asymmetric acid/ alkaline electrolyzer comprising a bipolar membrane sandwiched by bifunctional cobalt-nickel phosphide nanowire electrodes

Water splitting has been proposed to be a promising approach to producing clean hydrogen fuel.The two half-reactions of water splitting,that is,the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),take place kinetically fast in solutions with completely different pH values.Enabling HER and OER to simultaneously occur under kinetically favorable conditions while using exclusively low-cost,earth-abundant electrocatalysts is highly desirable but remains a challenge.Herein,we demonstrate that using a bipolar membrane(BPM)we can accomplish HER in a strongly acidic solution and OER in a strongly basic solution,with bifunctional self-supported cobaltnickel phosphide nanowire electrodes to catalyze both reactions.Such asymmetric acid/alkaline water electrolysis can be achieved at 1.567 V to deliver a current density of 10 mA/cm2 with ca.100%Faradaic efficiency.Moreover,using an“irregular”BPM with unintentional crossover the voltage needed to afford 10 mA/cm2 can be reduced to 0.847 V,due to the assistance of electrochemical neutralization between acid and alkaline.Furthermore,we show that BPM-based asymmetric water electrolysis can be accomplished in a circulated single-cell electrolyzer delivering 10 mA/cm2 at 1.550 V and splitting water very stably for at least 25 hours,and that water electrolysis is enabled by a solar panel operating at 0.908 V(@13 mA/cm2),using an“irregular”BPM.BPMbased asymmetric water electrolysis is a promising alternative to conventional proton and anion exchange membrane water electrolysis.

Electro-generation of TGA by Ni-mSA-mCS bipolar membrane

Ni-mSA-mCS bipolar membrane （BM） was prepared by sodium alginate （SA） and chitosan （CS）, which were modified by Ca^2＋ and glutaraldehyde as linking reagents, respectively, mSA-mCS membrane was characterized by FTIR, SEM, TG and used as a separator in the electrolysis cell to produce thioglycolic acid （TGA）. The experiment results show that TGAwas prepared effectively by electro-reduction of dithiodiglycolic acid （DTDGA） with the mixture of TGA and DTDGA in the cathodic chamber. The current efficiency was up to 66.7% at the room temperature （25 ℃） during the current density of 10 mA/cm^2. Compared with the traditional metal reduction method, the electro-reduction technology saves the zinc powder and eliminates the pollution to environment.

Water Dissociation Phenomena on a Bipolar Membrane──Current-voltage Curve in Relation with IonicTransport and Limiting Current Density

The water dissociation mechanism on a bipolar membrane under the electrical field was investigated and characterized in terms of ionic transport and limiting current density. It is considered that the depletion layer exists at the junction of a bipolar membrane, which is coincided with the viewpoint of the most literatures, but we also consider that the thickness and conductivity of this layer is not only related with the increase of the applied voltage but also with the limiting current density. Below the limiting current density, the thickness of the depletion layer keeps a constant and the conductivity decreases with the increase of the applied voltage; while above the limiting current density, the depletion thickness will increase with the increase of the applied voltage and the conductivity keeps a very low constant. Based on the data reported in the literatures and independent determinations, the limiting current density was calculated and the experimental curves Ⅰ-Ⅴ in the two directions were com

Bipolar membrane electrodialysis integrated with in-situ CO_(2)absorption for simulated seawater concentrate utilization,carbon storage and production of sodium carbonate

In the context of carbon capture,utilization,and storage,the high-value utilization of carbon storage presents a significant challenge.To address this challenge,this study employed the bipolar membrane electrodialysis integrated with carbon utilization technology to prepare Na_(2)CO_(3)products using simulated seawater concentrate,achieving simultaneous saline wastewater utilization,carbon storage and high-value production of Na_(2)CO_(3).The effects of various factors,including concentration of simulated seawater concentrate,current density,CO_(2)aeration rate,and circulating flow rate of alkali chamber,on the quality of Na_(2)CO_(3)product,carbon sequestration rate,and energy consumption were investigated.Under the optimal condition,the CO_(3)^(2-)concentration in the alkaline chamber reached a maximum of 0.817 mol/L with 98 mol%purity.The resulting carbon fixation rate was 70.50%,with energy consumption for carbon sequestration and product production of 5.7 k Whr/m^(3)CO_(2)and1237.8 k Whr/ton Na_(2)CO_(3),respectively.This coupling design provides a triple-win outcome promoting waste reduction and efficient utilization of resources.

Review on electrochemical carbon dioxide capture and transformation with bipolar membranes

Anthropogenic carbon dioxide(CO_(2))emission from the combustion of fossil fuels aggravates the global greenhouse effect.The implementation of CO_(2)capture and transformation technologies have recently received great attention for providing a pathway in dealing with global climate change.Among these technologies,electrochemical CO_(2)capture technology has attracted wide attention because of its environmental friendliness and flexible operating processes.Bipolar membranes(BPMs)are considered as one of the key components in electrochemical devices,especially for electrochemical CO_(2)reduction and electrodialysis devices.BPMs create an alkaline environment for CO_(2)capture and a stable pH environment for electrocatalysis on a single electrode.The key to CO_(2)capture in these devices is to understand the water dissociation mechanism occurring in BPMs,which could be used for optimizing the operating conditions for CO_(2)capture and transformation.In this paper,the references and technologies of electrochemical CO_(2)capture based on BPMs are reviewed in detail,thus the challenges and opportunities are also discussed for the development of more efficient,sustainable and practical CO_(2)capture and transformation based on BPMs.

Multistage-batch bipolar membrane electrodialysis for base production from high-salinity wastewater

Bipolar membrane electrodialysis(BMED)is considered a state-of-the-art technology for the conversion of salts into acids and bases.However,the low concentration of base generated from a traditional BMED process may limit the viability of this technology for a large-scale application.Herein,we report an especially designed multistage-batch(two/three-stage-batch)BMED process to increase the base concentration by adjusting different volume ratios in the acid(Vacid),base(Vbase),and salt compartments(Vsalt).The findings indicated that performance of the two-stage-batch with a volume ratio of Vacid:Vbase:Vsalt=1:1:5 was superior in comparison to the threestage-batch with a volume ratio of Vacid:Vbase:Vsalt=1:1:2.Besides,the base concentration could be further increased by exchanging the acid produced in the acid compartment with fresh water in the second stage-batch process.With the two-stage-batch BMED,the maximum concentration of the base can be obtained up to 3.40 mol∙L^(-1),which was higher than the most reported base production by BMED.The low energy consumption and high current efficiency further authenticate that the designed process is reliable,cost-effective,and more productive to convert saline water into valuable industrial commodities.

Preparation and Performance of Bipolar Membranes with Liquid Ion-Exchange Medium

The current density is rather low in solid bipolar membranes, because the water transfer rate is relatively slow across solid bipolar membranes made of solid ion-exchange materials. This paper describes the use of polymer solutions, such as phosphatic poly(vinyl alcohol) solution, poly(acrylic acid) solution and poly(vinyl alcohol) solutions with dispersed cation/anion-exchange resin particles to prepare bipolar membranes. The 0.1 mol/L NaOH and the 0.05 mol/L H 2SO 4 were used to test the performance of the bipolar membranes. For a fixed liquid layer thickness, both the current density and the selectivity increase with the concentration increase of a polyelectrolyte solution. The maximum current density measured in the experiment was 1497 A/m 2 with a selectivity of 96.8%.

Bipolar ionomer electrolytes with desirable self-discharge suppression for supercapacitors

Supercapacitors based on electric double layers are prone to serious self-discharge due to electrolyte ion desorption and the resulting energy loss severely limits the application range of supercapacitors.Rational design of polymer electrolyte systems to address this problem shows considerable generality and high feasibility.Herein,we reported a quasi-solid-state bipolar ionomer electrolyte prepared by an in-situ layer-by-layer ultraviolet-curing method,which has an integrated Janus structure with an intermediate binding layer.Based on the synergistic effect of confining impurity ions by ionizable groups and electrostatic repulsion to stabilize the electric double layers and superimposing synergies on both sides,the assembled device not only possesses ideal supercapacitor characteristics,but also exhibits an ultrahigh voltage retention of 71% after being left to stand for 100 h after being fully charged.Furthermore,through the quasi-in-situ energy dispersive X-ray spectroscopy linear scanning,the characteristics of ion diffusion in this ionomer electrolyte are revealed,suggesting its correlation with self-discharge behavior.

Conductive and corrosion behaviors of silver-doped carbon-coated stainless steel as PEMFC bipolar plates

Ni–Cr enrichment on stainless steel SS316 L resulting from chemical activation enabled the deposition of carbon by spraying a stable suspension of carbon nanoparticles; trace Ag was deposited in situ to prepare a thin continuous Ag-doped carbon film on a porous carbon-coated SS316 L substrate. The corrosion resistance of this film in 0.5 mol·L^（-1） H_2SO_4 solution containing 5 ppm F- at 80°C was investigated using polarization tests. The results showed that the surface treatment of the SS316 L strongly affected the adhesion of the carbon coating to the stainless steel. Compared to the bare SS316 L, the Ag-doped carbon-coated SS316 L bipolar plate was remarkably more stable in both the anode and cathode environments of proton exchange membrane fuel cell（PEMFC） and the interface contact resistance between the specimen and Toray 060 carbon paper was reduced from 333.0 m？·cm^2 to 21.6 m？·cm^2 at a compaction pressure of 1.2 MPa.

Asymmetric acidic/alkaline N_(2)electrofixation accelerated by high-entropy metal-organic framework derivatives

High-entropy materials are composed of five or more metal elements with equimolar or near-equimolar concentrations within one crystal structure,which offer remarkable structural properties for many applications.Despite previously reported entropy-driven stabilization mechanisms,many high-entropy materials still tend to decompose to produce a variety of derivatives under operating conditions.In this study,we use transition-metal(Ni,Co,Ni,Zn,V)-based high-entropy metal-organic frameworks(HE-MOFs)as the precursors to produce different derivatives under acidic/alkaline treatment.We have shown that HE-MOFs and derivatives have shown favorable kinetics for N_(2)electrofixation in different pH electrolytes,specifically cathodic nitrogen reduction reaction in acidic media and anodic oxygen evolution reaction in alkaline media.To buffer the pH mismatch,we have further constructed an asymmetric acidic/alkaline device prototype by using bipolar membranes.As expected,the prototype showed remarkable activities,with an NH_(3)yield rate of 42.76μg h^(−1)mg^(−1),and Faradaic efficiency of 14.75%and energy efficiency of 2.59%,which are 14.4 and 4.4 times larger than those of its symmetric acidic and alkaline counterparts,respectively.

Ion Exchange Membrane“ABC”–A Key Material for Upgrading Process Industries

Ion exchange membrane plays a crucial role in transforming and upgrading traditional chemical manufacturing procedures and boosting a multitude of new applications.Due to the strict regulations on wastewater discharge and increasing demands of renewable energy,anion exchange membrane(“A”membrane),bipolar membrane(“B”membrane)and cation exchange membrane(“C”membrane)have become a key material for upgrading various process industries.Herein,we summarized several novel synthetic routes for“ABC”membranes fabrication from the viewpoints of designing novel membrane synthetic routes,regulating the ionic transport channels,imparting dynamic transfer regions,introducing intrinsic micro-porosity into the membrane and among others.The account includes a brief introduction to membrane structure designs and fabrications,emerging and industrial applications,and perspectives on ion exchange membranes.

Suppressing the liquid product crossover in electrochemical CO_(2)reduction

Coupling electrochemical CO_(2)reduction(CO_(2)R)with a renewable energy source to create high‐value fuels and chemicals is a promising strategy in moving toward a sustainable global energy economy.CO_(2)R liquid products,such as formate,acetate,ethanol,and propanol,offer high volumetric energy density and are more easily stored and transported than their gaseous coun-terparts.However,a significant amount(~30%)of liquid products from electrochemical CO_(2)R in a flow cell reactor cross the ion exchange membrane,leading to the substantial loss of system‐level Faradaic efficiency.This severe crossover of the liquid product has—until now—received limited attention.Here,we review promising methods to suppress liquid product crossover,including the use of bipolar membranes,solid‐state electrolytes,and cation‐exchange membranes‐based acidic CO_(2)R systems.We then outline the re-maining challenges and future prospects for the production of concentrated liquid products from CO_(2).