Catalytic Proton–Hydroxide Recombination for Forward-Bias Bipolar Membranes

Mitchell, James B.; Chen, Lihaokun; Langworthy, Kurt; Fabrizio, Kevin; Boettcher, Shannon W.

doi:10.1021/acsenergylett.2c02043

Cited by 22 publications

(30 citation statements)

References 32 publications

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“…All BPMs in this work have the same monopolar layer (AEL and CEL) thicknesses (∼30 μm) and polymer compositions. The AEL (FAA-3/P4VP) permselectivity toward H + is low owing to the decline of BPM OCV and water formation voltage. , In addition, the composition of the BPM junction and catalysts contributes toward the OCV and water proton–hydroxide ion combination behavior in the BPM forward bias . An increase in the thickness of the 3D junction will lead to more contact area between the anion and cation polymers.…”

Section: Resultsmentioning

confidence: 99%

“… 38 , 39 In addition, the composition of the BPM junction and catalysts contributes toward the OCV and water proton–hydroxide ion combination behavior in the BPM forward bias. 40 An increase in the thickness of the 3D junction will lead to more contact area between the anion and cation polymers. However, this may be at the expense of more co-ion transport of protons and hydroxyl ions.…”

Section: Resultsmentioning

confidence: 99%

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Understanding the Impact of the Three-Dimensional Junction Thickness of Electrospun Bipolar Membranes on Electrochemical Performance

Al-Dhubhani

Post²,

Duisembiyev

et al. 2023

ACS Appl. Polym. Mater.

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The use of electrospun bipolar membranes (BPMs) with an interfacial three-dimensional (3D) junction of entangled nano-/microfibers has been recently proposed as a promising fabrication strategy to develop high-performance BPMs. In these BPMs, the morphology and physical properties of the 3D junction are of utmost importance to maximize the membrane performance. However, a full understanding of the impact of the junction thickness on the membrane performance is still lacking. In this study, we have developed bipolar membranes with the same composition, only varying the 3D junction thicknesses, by regulating the electrospinning time used to deposit the nano-/microfibers at the junction. In total, four BPMs with 3D junction thicknesses of ∼4, 8, 17, and 35 μm were produced to examine the influence of the junction thickness on the membrane performance. Current–voltage curves for water dissociation of BPMs exhibited lower voltages for BPMs with thicker 3D junctions, as a result of a three-dimensional increase in the interfacial contact area between cation- and anion-exchange fibers and thus a larger water dissociation reaction area. Indeed, increasing the BPM thickness from 4 to 35 μm lowered the BPM water dissociation overpotential by 32%, with a current efficiency toward HCl/NaOH generation higher than 90%. Finally, comparing BPM performance during the water association operation revealed a substantial reduction in the voltage from levels of its supplied open circuit voltage (OCV), owing to excessive hydroxide ion (OH–) and proton (H+) leakage through the relevant layers. Overall, this work provides insights into the role of the junction thickness on electrospun BPM performance as a crucial step toward the development of membranes with optimal entangled junctions.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Understanding the Impact of the Three-Dimensional Junction Thickness of Electrospun Bipolar Membranes on Electrochemical Performance

Al-Dhubhani

Post²,

Duisembiyev

et al. 2023

ACS Appl. Polym. Mater.

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“…Thus, strategies for operating an electrochemical cell with a pH gradient between the catholyte and anolyte are required to optimize the performance of many electrochemical devices. This pH gradient can be generated and maintained using a bipolar membrane (BPM), which consists of a cation exchange membrane (CEM) laminated onto an anion exchange membrane (AEM). − A catalyst layer is also typically included in the bipolar junction between the CEM and the AEM to accelerate dissociation or recombination reactions. BPMs display the property of ionic current rectification, allowing them to sustain differential pH and electrolyte environments optimized for cathodic and anodic half-reactions.…”

Section: Introductionmentioning

confidence: 99%

Neutralization Short-Circuiting with Weak Electrolytes Erodes the Efficiency of Bipolar Membranes

Dinh

Toh

Chu

et al. 2023

ACS Appl. Mater. Interfaces

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Bipolar membranes (BPMs) are critical components of a variety of electrochemical energy technologies. Many electrochemical applications require the use of buffers to maintain stable, nonextreme pH environments, yet the impact of buffers or weak acids/bases on the electrochemical behavior of BPMs remains poorly understood. Our data for a cell containing weak electrolytes is consistent with internal pH gradients within the anion exchange membrane (AEM) or cation exchange membrane (CEM) component of the BPM that form via ionic short-circuiting processes at open-circuit. Short-circuiting results from the coupling of co-ion crossover and parasitic neutralization and leads to buffering of the bipolar interface. This phenomenon, which we term neutralization short-circuiting, serves to erode BPM efficiency by attenuating the open-circuit membrane voltage and introducing parasitic reverse bias currents associated with weak acid/base dissociation at the interface. These findings establish a mechanistic basis for the operation of BPM cells in the presence of weak acid/ base electrolytes.

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“…The BPM equation also does not explicitly separate the forward WD reaction and reverse H + /OH − recombination reaction, which may proceed via different mechanisms or with different ratedetermining steps. For this, temperature-dependence and kinetic-isotopic-effect experiments for different WD catalysts in both forward and reverse bias (to obtain full polarization curves) is needed, probably using a hydrogen-pump cell instead of a water electrolyzer platform 74 .…”

Section: Discussionmentioning

confidence: 99%

Kinetics and Mechanism of Heterogeneous Voltage-Driven Water-Dissociation Catalysis

Chen¹,

Boettcher³

2023

Preprint

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The water-dissociation reaction (WD, H2O → H+ + OH−) affects the rates of electrocatalytic reactions and the performance of bipolar membranes (BPMs). How catalyzed interfacial WD is driven by voltage, however, is not understood. We designed a BPM electrolyzer with two reference electrodes attached laterally to each layer/side (here, poly(arylpiperidinium) and perfluorosulfonic-acid ionomers) to measure WD current and overpotential (ηwd), without soluble electrolyte and as a function of temperature and catalyst-layer properties. Using TiO2-P25 nanoparticles as a model WD catalyst, Arrhenius-type analysis yields a WD activation energy Ea of 25–30 kJ mol−1, only weakly dependent ηwd. The pre-exponential factor is unexpectedly proportional to ηwd. With D2O, ηwd is ~2 to 4 times larger than in H2O, largely due to a lower pre-exponential factor. Without catalyst, ηwd is ~10-fold larger and Ea decreases from 34 to 24 kJ mol−1 as ηwd goes from 0.1 to 1 V. To explain these data, we propose a new WD mechanism where metal-oxide nanoparticles, polarized by the voltage across the BPM junction, serve as i) proton acceptors (from water) on the negative sides of the particle to generate free OH−, ii) proton donors on the positive sides to generate H3O+, and iii) surface proton conductors that connect spatially separate donor/acceptor sites. Increasing electric-field strength with overpotential orients water for proton-transfer elementary steps comprising WD, increasing the pre-exponential factor and hence rate, but is insufficient to lower Ea. This understanding will accelerate development of electrocatalysis, electrodialysis, carbon-capture, and carbon-utilization technologies that require efficient WD.

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Catalytic Proton–Hydroxide Recombination for Forward-Bias Bipolar Membranes

Cited by 22 publications

References 32 publications

Understanding the Impact of the Three-Dimensional Junction Thickness of Electrospun Bipolar Membranes on Electrochemical Performance

Understanding the Impact of the Three-Dimensional Junction Thickness of Electrospun Bipolar Membranes on Electrochemical Performance

Neutralization Short-Circuiting with Weak Electrolytes Erodes the Efficiency of Bipolar Membranes

Kinetics and Mechanism of Heterogeneous Voltage-Driven Water-Dissociation Catalysis

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