Titanium-, nitrogen-doped carbon flowers catalyze the 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 TiNx 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 ¾ of Ti atoms in TiO2-like nanoparticles and ¼ of Ti atoms in novel atomically-dispersed TiNx sites. TiCF achieves 61 ± 8% NH3-selectivity of at −0.70 V vs. RHE and 14 ± 5 mA/cm2 to NH3 formation (|jNH3|) 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 TiNx, which facilitates multiple bond formation with surface intermediates to promote favorable NH₃ synthesis pathways. Thus, TiCF exhibits 60x higher |jNH3| values than bulk Ti and NH₃ yield rates (> 0.06 mmol NH₃/hr/cm²) 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.