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Advanced bipolar membranes (BPMs) with low water-dissociation overpotential (ηwd) may enable new electrochemical technologies for electrolysis, fuel cells, acid–base synthesis, brine remediation, lithium-battery recycling, and cement production. However, these advanced BPMs have only been demonstrated in BPM water electrolysis (BPMWE) configurations where the BPM is under static compression by the porous-transport layers. It is important to study these BPMs in applications like electrodialysis where large degrees of static compression are not possible. We present a BPM electrodialysis (BPMED) platform to measure water-dissociation overpotential (ηwd) and compare BPMWE and BPMED systems. We show advanced BPMs with half the ηwd compared tomore » commercial BPMs for BPMED while maintaining ∼90% current efficiency from 0.05–0.5 A cm–2. The BPMED ηwd values are, however, about 0.2 V higher at 0.5 A cm–2 than those for BPMWE. Regardless, these results show that BPMs developed and optimized in BPMWE applications are well-suited for next-generation high-current-density BPMED technologies.« less

Ion-selective membranes are necessary components of many electrochemical systems including fuel cells, electrolyzers, redox flow batteries, and electrodialyzers. Perfluorinated sulfonated membranes (PFSMs) dominate these applications due to their excellent combination of fast ion transport, stability, and processability. However, perfluorinated cation exchange membranes (CEMs) are expensive, and their production process involves chemistry that generates toxic perfluorinated chemicals. The development of affordable, nonfluorinated membranes with a competitive combination of high ion selectivity, transport, and stability could help enable the widespread use of the technologies listed above while hastening the development of emerging electrochemical systems, including aqueous alkaline CO₂ sorbent regeneration. To thismore » end, we pursue the use of thin-film composite polyamide (PA-TFCs) membranes–those that typically find application in reverse osmosis and nanofiltration desalination–as cation-selective exchange membranes. Given their negative surface charge under neutral-to-alkaline conditions, PA-TFCs can serve as effective CEMs in these pH regimes. We prepared a series of PA-TFCs from traditional monomers (trimesoyl chloride and piperazine) and compared their thicknesses, charge densities, water transport properties, ion transport properties, and long-term stability in a high pH environment to traditional CEMs (Nafion and FKE) and commercial nanofiltration and reverse osmosis membranes. We find that some of the best-performing PA-TFC membranes have similar resistances and Na⁺ transference numbers compared to Nafion 117 in Na₂SO₄ and NaHCO₃-containing solutions. This proof-of-principle study suggests that further optimization of PA-TFCs could enable cost-effective ion exchange membrane alternatives to PFSMs.« less

Electrochemical nitrate reduction (NO₃ RR) has attracted attention as an emerging approach to mitigate nitrate pollution in groundwater. Here, we report that a highly ordered PdCu alloy-based electrocatalyst exhibits selective (91% N₂), stable (480 h), and near complete (94%) removal of nitrate without loss of catalyst. In situ and ex situ XAS provide evidence that structural ordering between Pd and Cu improves long-term catalyst stability during NO₃RR. In contrast, we also report that a disordered PdCu alloy-based electrocatalyst exhibits non-selective (44% N₂ and 49% NH₄⁺), unstable, and incomplete removal of nitrate. The copper within disordered PdCu alloy is vulnerable tomore » accepting electrons from hydrogenated neighboring Pd atoms. This resulted in copper catalyst losses which were 10× greater than that of the ordered catalyst. The design of stable catalysts is imperative for water treatment because loss of the catalyst adds to the system cost and environmental impacts.« less

Electrocatalytic conversion of nitrate in waste can enable efficient waste remediation (NO₃^- to N₂) or waste valorization (NO₃^- to NH₄⁺) depending on the selectivity of the catalyst. Palladium and copper electrocatalysts typically exhibit ideal nitrate and nitrite binding properties, allowing for effective destruction of nitrate. However, rational steering of selectivity through material design remains a critical challenge for PdCu electrocatalyst. Here, we use the electrochemical underpotential deposition method to synthesize palladium nanocube electrocataysts with controlled copper surface coverage (e.g., partial and full copper coatings). We then examine the potential for NO₃^- destruction (conversion) and NO₂^- reduction reaction. We identify thatmore » partial copper-coated Pd nanocubes not only effectively facilitate the reduction of 95% of NO₃^- but also increase the reduction of NO₂^- to N₂ with 89% selectivity over 20 consecutive cycles (80 h). We also show that under these conditions, the Pd(100) surface facet is exposed. Complete copper-covered Pd nanocubes effectively facilitate the reduction of ~99% of NO₃^-. Complete coverage of copper; however, prevented exposure of Pd(100) surface facet, promoting the selective reduction of NO₂^- to NH₄⁺ with a 70% selectivity over 20 consecutive cycles (80 h). Density functional theory (DFT) calculations show that NO₃^- and NO₂^- adsorb more strongly on the Cu(100) surface compared to the Pd(100) surface, while the NO* intermediate generated from NO₃^- or NO₂^- reduction adsorbs more strongly on the Pd surface. Furthermore, barrier calculations show that NO* can readily migrate from the Cu domain to the Pd domain and that the N–N coupling barrier on Pd is significantly diminished at high NO* coverage. Together, these results suggest that the high N₂ selectivity observed on the PdCu electrocatalyst is caused by the spillover of NO* from the Cu domains to the Pd domains.« less