From parasitic to productive: Leveraging ORR-generated alkalinity for electrochemical lithium recovery via...

This study elucidates the overlooked role of cathodic (Oxygen reduction reaction, ORR) in electrochemical lithium extraction via HCDI. Traditionally viewed as a parasitic side process, ORR is redefined as a performance-enhancing reaction when properly regulated. By engineering a hybrid electrode via the in situ growth of lithium titanate on Ti₃C₂T_x MXene, we construct vertically aligned transport channels that promote Li⁺ and OH^-diffusion kinetics, simultaneously. This architecture minimizes concentration polarization, enabling rapid Li⁺ intercalation capacity (44.55 mg g^-1) and excellent Mg²⁺/Li⁺ selectivity (389.8) in real brine. Tuning the cathode potential to -1.0 V vs. Ag/AgCl directs ORR via a four-electron pathway, achieving an optimal balance between ORR and Li⁺ intercalation (Faradaic efficiency: 53 %). Electrochemical and computational analyses reveal that ORR-generated hydroxide ions (OH^-) creates a localized alkaline microenvironment at the cathode, which enhances lithium selectivity by (i) promoting H⁺ expulsion from Li₄Ti₅O₁₂ lattice for faster Li⁺ intercalation, (ii) suppressing the migration of competing multivalent ions through precipitation as their corresponding hydroxides and (iii) facilitating electrostatic pairing between OH^- and Li⁺ to guide selective migration. This work introduces a microenvironmental strategy that harnesses controlled ORR to enhance ion selectivity and transport, guiding rational electrode design for lithium recovery.