Bipolar membrane electrodialysis (BMED) efficiently transforms salts into acids and bases, with bipolar membranes (BPMs) playing a pivotal role. This study pioneers high-performance BPMs via a layer-by-layer casting/spraying technique, incorporating sulfonated polysulfone cation-exchange layers, polydopamine-modified MXene (PDA-Ti 3 C 2 T X ) interfacial layers, and quaternized polyphenylene oxide anion-exchange layers. PDA-Ti 3 C 2 T X exhibits remarkable catalytic activity, promoting water dissociation. The BPMs exhibit exceptional interfacial compatibility, alkali resistance, and long-term durability. At 80 mA · cm −2 , the BPMs manifest reduced transmembrane voltages (1.54 ∼ 2.80 V) compared to control samples (Blank BPM: 7.70 V; 0.75 %-Ti 3 C 2 T X -BPM: 5.51 V). Post-BMED salt conversion, the 1.00 %-PDA-Ti 3 C 2 T X -BPM displays the lowest final voltage drop (9.9 V), akin to the commercial SSBP-1 (9.8 V). The 0.75 %-PDA-Ti 3 C 2 T X -BPM attains the highest OH – concentration (0.094 mol·L -1 ) and current efficiency (98.79 %), surpassing SSBP-1 (0.090 mol·L -1 , 94.47 %). The BPMs demonstrate superior energy consumption (2.00 ∼ 2.49 kWh kg −1 ) compared to SSBP-1 (2.94 kWh kg −1 ). This investigation delineates efficient and stable BPMs for BMED applications.
The electrocatalytic reduction reaction of nitrate (NO3RR) is anticipated to convert nitrogen-containing pollutants into valuable ammonia products. Copper-based catalysts have received great attention because of their good performance in the NO3RR due to the strong binding energy with *NO3 intermediates. However, the poor H2O dissociation ability of Cu is unable to provide H• in time for the hydrogenation reaction of NOx, thus hindering the electroreduction of the NO3–. Herein, we designed a shell–core nanocube electrocatalyst Cu2O@Ni(OH)2-x (x represents the molar ratio of Ni/Cu) using the liquid phase reduction combined with the etching and precipitation method for electrocatalytic NO3RR. Due to the synergistic effect between the strong nitrate activation ability of Cu and the excellent H2O dissociation ability of Ni(OH)2, Cu2O@Ni(OH)2-3.3% shows an impressive ammonia yield rate (557.9 μmol h–1 cm–2) and Faradaic efficiency (97.4%) at −0.35 V vs. RHE. Operando Raman and Auger electron spectroscopy observe the reduction of Cu2O to Cu during the NO3RR process. Density functional theory calculations combined with electron paramagnetic resonance analysis reveals that Ni(OH)2 can lower the activation energy barrier of H2O dissociation, thereby promoting the generation of H• and accelerating the hydrogenation of *NO during the NO3RR. This research provides an efficient Cu-based catalyst for reducing NO3– and may motivate the development of effective ammonia electrocatalysts for further experimentation.
A promising membrane-free electrodeionization (MFEDI) process has been proposed for high purity water (HPW) production in our previous work. However, the employ of a large number of weak-acid resins in MFEDI limits this process for purifying the reverse osmosis (RO) permeate of tap water with a pH value below 6.0. In this work, a MFEDI system filled only with mixed strong-acid and strong-base resins was tested to desalinate the synthetic acidic RO permeate. Results demonstrated that the resins regeneration was achieved mainly by electrically enhancing water dissociation after a high current density was imposed to the resin layer. Both good purification and effective regeneration were achieved. The conductivity of effluent was 0.060–0.062 μS/cm only. The energy consumption fluctuated in the range of 0.35–0.41 kW h/m 3 water and the water recovery reached 93.1%. The mixed concentrate collected during regeneration, with an average conductivity of 145 μS/cm and a pH value of 6.5, could be returned to a pretreatment unit for recovery. No chemical was needed and no wastewater was produced. Repetitive experimental results showed the MFEDI system could work stably.
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