Potassium hydroxide

Analytical-grade chemicals were used as received, without any further purification. Coconut shell (from Ping-Tong, Taiwan), potassium hydroxide (98% purity, Showa, Tokyo, Japan), HCl (Showa, Tokyo, Japan) and ammonium persulfate (98% purity, Honeywell, Hannover, Germany) were utilized to prepare activated carbon powder. Nickel foam (NF) (98% purity, Fluka, Tokyo, Japan), carbon black and polyvinylidene fluoride (PVDF) (Showa, Tokyo, Japan) was used to prepare AC/NF electrode. Sodium sulfate (≥98% purity, Honeywell, Hannover, Germany) was used as the electrolyte.

Tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl), PEI (branched, MW 800 Da), chloramine-T hydrate, and phenol red sodium salt were purchased from Sigma-Aldrich (St. Louis, MO, USA). Dopamine hydrochloride (DA-HCl) was purchased from Acros Organic (Geel, Belgium). Potassium hydroxide, hydrochloride, sodium thiosulfate, and potassium bromide were purchased from SHOWA (Gunma, Japan). Ethylenediamine (En), anhydrous cobalt chloride, silver nitrite, and anhydrous copper chloride were purchased from Alfa Aesar (Tewksbury, MA, USA). Sodium chloride was purchased from Fluka (Munich, Germany). Sodium acetate was purchased from Vetec (St. Louis, MO, USA). All these chemicals were of analytical grade and were used without further purification. The PPMM (catalog number: 201PP-47-045-50; diameter of 47 mm; pore size of 450 nm; thickness of 200 µm) was purchased from Rone Scientific Inc. (New Taipei City, Taiwan).