MXene/Polydopamine as interfacial layers for enhancing the water dissociation within bipolar membranes

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-Ti₃C₂T_X) interfacial layers, and quaternized polyphenylene oxide anion-exchange layers. PDA-Ti₃C₂T_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 %-Ti₃C₂T_X-BPM: 5.51 V). Post-BMED salt conversion, the 1.00 %-PDA-Ti₃C₂T_X-BPM displays the lowest final voltage drop (9.9 V), akin to the commercial SSBP-1 (9.8 V). The 0.75 %-PDA-Ti₃C₂T_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.