Potassium bicarbonate

All chemicals were analytical grade and used without further purification. Ketjenblack EC‐600 JD (CB) was purchased from AkzoNobel. Nickel hexahydrate nitrate (Ni(NO₃)₂ ⋅ 6H₂O, 98 %) was obtained from Sigma‐Aldrich. Urea (CH₄N₂O, 99 %), thiourea (CH₄N₂S, 99 %) and nitric acid (HNO₃, 65 wt%) were from VMR chemicals. Potassium bicarbonate (KHCO₃, 98 %), Nafion D‐521 dispersion (5 % w/w in water and 1‐propanol) and Nafion‐117 ionic exchange membrane were purchased from Alfa Aesar. Deionized (DI) water was produced by a Milli‐Q (18.2 MΩ cm) system.

Potassium citrate monohydrate (K₃C₆H₅O₇·H₂O, 99+%, Alfa Aesar Co., Ltd.), copper nitrate trihydrate (Cu (NO₃)₂·3H₂O, 99%, Alfa Aesar Co., Ltd.), α-D-glucose (C₆H₁₂O₆, 99%, Alfa Aesar Co., Ltd.), melamine (C₃H₆N₆, 99%, Alfa Aesar Co., Ltd.), copper phthalocyanine (CuPc, Alfa Aesar Co., Ltd.), potassium bicarbonate (KHCO₃, 99.7%–100.5%, Alfa Aesar Co., Ltd.). Sulfuric acid (H₂SO₄, 95%–98%, Sinopharm Chemical Reagent Co. Ltd.), N, N-dimethylformamide (DMF, 99.9%, Sinopharm Chemical Reagent Co. Ltd.).

Ammonia 25%, ammonium sulfate (≥ 99.0%), and silver nitrate (≥ 99.0%) were obtained from Sigma Aldrich. Potassium bicarbonate (99%) was obtained from Alfa Aesar. The brass alloys of different compositions were cut into 1.5 × 3.0 cm sheets. All reagents were used without further purification. MilliQ ultrapure water was applied throughout the study.

CuCl₂·2H₂O (A.R. grade), chitosan (low viscosity, 100–200 mPa s), polyvinylpyrrolidone (PVP, K30), acetone (A.R. grade), hydrogen chloride (HCl, 37%), Ni foam, Al foil (2 mm) were provided by Sinopharm Chemical Reagent Co., Ltd, China. Potassium bicarbonate (KHCO₃, >99.7%), potassium hydroxide (KOH, A.R. grade, 85%) were purchased from Acros. Sodium borohydride (NaBH₄, 98%), polytetrafluoroethylene-hydrophobized carbon paper (PTFE-CP, Toray, YLS-30T GDL), and Nafion D-521 dispersion (5% w/w in water and 1-propanol, ≥0.92 meg/g exchange capacity) were purchased from Alfa Aesar China Co., Ltd. Anion-exchange membrane (3PK-130-100 × 100) was purchased from Gaoss Union Company. CO₂ (99.999%) was provided by Beijing Analytical Instrument Company.

All chemicals were purchased from commercial suppliers and used as received. 2,2,2-Trichloroethoxycarbonyl chloride (Troc-Cl), ammonium hydroxide and dichloromethane were purchased from Sigma-Aldrich (St. Louis, MO.). Potassium bicarbonate was purchased from Acros Organics (Westchester, PA.). Autosampler vials were purchased from Agilent Technologies (Santa Clara, CA.). Fentanyl and acetylfentanyl were synthesized using published protocols [11 (link)]. Thin layer chromatography (TLC) was used to monitor the production of amine-containing intermediates leading to the synthesis of fentanyl and acetylfentanyl using Merck 60-F254 sheets and detection accomplished with UV light (λ = 254 nm) in conjunction with CAM [36 (link), 37 (link)] and iodine vapor [38 (link), 39 (link)]. All fentanyls as well as the Troc-norfentanyl and Troc-noracetylfentanyl standards were purified by flash column chromatography using a Biotage Isolera purification system.