Titanium-, Nitrogen-Doped Carbon Flowers Catalyze Electrochemical Nitrate Reduction Reaction to Ammonia

An emerging design heuristic for electrochemical nitrate reduction (NO₃RR) catalysts is synthesizing electron-deficient sites to facilitate binding of electron-rich NO₃^-. However, this rule has rarely been applied to metal-, nitrogen-doped carbon (MNC) catalysts. Titanium (Ti), with low electronegativity and high NO₃RR reactivity, is a compelling MNC candidate. To date, atomically dispersed TiN_x motifs have eluded synthesis due to the strong oxophilicity of Ti. Here, we leverage nitrogen-rich carbon flowers (CF) to overcome synthetic challenges and produce Ti-, N-doped carbon flower (TiCF) catalysts. Advanced materials characterization demonstrates that TiCF catalysts are a mixed phase material with 3/4 of Ti atoms in TiO₂-like nanoparticles and 1/4 of Ti atoms in novel, atomically dispersed TiN_x sites. TiCF achieves 61 ± 7% NH₃-selectivity at -0.70 V vs RHE and 14 ± 5 mA/cm² to NH₃ formation (|j_NH3|) at -0.85 V vs RHE in (0.1 M NaOH + 0.1 M NaNO₃ + 0.45 M Na₂SO₄) electrolyte. Control studies show both CF morphology and Ti sites are essential for high NO₃RR activity. Density functional theory calculations attribute the NO₃RR reactivity to TiN_x, which facilitates multiple bond formation with surface intermediates to promote favorable NH₃ synthesis pathways. Thus, TiCF exhibits 60× higher |j_NH3| values than bulk Ti and NH₃ yield rates (>0.06 mmol NH₃/h/cm²) that are competitive with state-of-the-art MNC catalysts (e.g., FeNC, CuNC). TiCF introduces a new class of Ti electrocatalysts, advancing the MNC design space and sustainable NH₃ production.