Pairing oxygen vacancy-rich titanium (sub)oxides up with N-doped carbon electrodes for high-performance hybrid capacitive deionization (HCDI)

Capacitive deionization (CDI) technology’s potential for sustainable desalination is contingent on breakthroughs in electrode materials. Defect-rich titanium (sub)oxides (anatase TiO₂(A), Ti₂O₃, Ti₃O₅, Ti₄O₇) offer compelling advantages, including tunable capacity, low environmental impact, and robustness. This study provides a systematic comparison of their structural features, electrochemical responses, and desalination efficacy. Electrochemical characterization results show anatase TiO₂(A) leads in specific capacitance (252.5 F g⁻¹ at 0.3 A g⁻¹), while Ti₃O₅’s highest oxygen vacancy minimizes charge transfer resistance and maximizes ion migration rates. In desalination trials, TiO₂ delivers a maximum salt adsorption capacity of 37.1 mg g⁻¹ (500 mg L⁻¹ NaCl, 1.2 V). All electrodes exhibit outstanding cycling stability (capacity retentions > 83.5 %), affirming their practical potential. Correlation analysis discloses the oxygen vacancy-driven charge transfer mechanism inside these electrodes and establishes a structure-performance relationship. Overall, this work establishes fundamental structure-property relationships that underpin future electrode innovation via the oxygen vacancy-engineering strategy, which represents a promising pathway for advancing CDI performance boundaries.