Figure 2.

Supramolecular cobalt porphyrin box organic cage shows superior electrochemical nitrate reduction (NO₃RR) activity relative to a parent cobalt tetraphenylporphyrin control analog. (A) Faradaic efficiency (FE) for electrochemical nitrate reduction to ammonia, plotted by NH₃ production, catalyzed by CoPB-C8 (red) and CoTPP (blue) over a range of applied potentials after 1 h electrolysis. (B) NH₃ yield rate for CoPB-C8 (red), and CoTPP (blue). (C) NH₃ production during 4 h electrolysis at −1.34 V vs. SCE for CoPB-C8 (red), and CoTPP (blue). (D) Comparison of turnover number (TON) values per Co over a range of applied potentials after 1 h electrolysis. (E) NH₃ production and TON for various amounts of CoPB-C8 loading at −1.54 V vs. SCE. (F) ¹H NMR spectra showing direct detection of NH₃ product with ¹⁵N labeling of substrate for electrolysis runs, after three independent nitrate reduction tests at −1.44 V vs SCE, 0.5 M Na₂SO₄/0.1 M NaNO₃, 0.5 M Na₂SO₄/0.1 M Na¹⁵NO₃, and 0.5 M Na₂SO₄. Maleic acid (C₄H₄O₄) was added as an internal standard.