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Description
Titanium oxide is a promising corrosion-resistant catalyst support for the oxygen reduction reaction (ORR) in proton exchange membrane (PEM) fuel cells; however, its intrinsically low electrical conductivity limits its performance. In this study N-doped TiO2 (TiO_x N_y) was synthesized via a hydrothermal route using titanium ethoxide, followed by thermal calcination at 750 °C with systematically increasing nitrogen doping percentages (from 8.5N to 30.2N). Structural, textural, and optical characterizations revealed a clear dopant-dependent tuning mechanism across the material series. While structural over-saturation at the 26.5N threshold induced severe lattice distortions, a UV-Vis blue shift (364 nm; 2.98 eV), and a charge-transfer resistance ( Rct = 22.46Ω), the 23.9N-TiO₂ configuration emerged as the optimized structural electrocatalyst. The 23.9N-TiO₂ catalyst successfully stabilized a balanced crystallite size of 46.8 ± 4.5 nm, a controlled microstrain of 1.36 x 10⁻³, and a moderately accessible 9.37 nm mesoporous channel network. Further, the 23.9N-TiO₂ catalyst achieved a higher red shift of 268nm, narrowing the optical bandgap down to a minimum of 2.82 eV to overcome the intrinsic conductivity challenge of Pristine-TiO2. Electrochemical evaluations are in agreement with these findings, where the 23.9N-TiO₂ matrix displayed a uniform double layer capacitance, Cdl of 0.76 μFcm-2 and a low charge-transfer resistance Rct of 16.90 Ω. Consequently, the 23.9N-TiO₂ catalyst support delivered the outstanding electrocatalytic performance of the series, yielding the lowest polarization onset potential of 0.82 V vs. RHE and higher current retention of 0.00844 mA/cm² under continuous chronoamperometric durability stress. These findings show that optimizing the nitrogen substitution density to the 23.9N optimum represents a solution to the charge-transport bottlenecks, presenting a robust, high-performance, and corrosion-resistant support framework for sustainable fuel cell electrocatalysis.
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Keywords: Titanium oxynitride; Hydrothermal synthesis; ORR; PEM fuel cells; Catalyst supports, Charge transfer kinetics.