Mw 40000

Ionic liquid 1-hexylpyridinium hexafluorophosphate (HPPF₆, >99%, Lanzhou Yulu Fine Chem. Ltd., Co., Lanzhou, China), HRP (MW. 40000, Sinopharm Chem. Reagent Co., Shanghai, China), black phosphorus nanoplates dispersion (BPNPs, Nanjing XFNANO Materials Tech. Ltd., Co., Nanjing, China), trichloroacetic acid (TCA, Tianjin Kemiou Chem. Co., Tianjin, China), graphite powder (particle size 30 μm, Shanghai Colloid Chem. Co., Shanghai, Shanghai, China), potassium bromate (KBrO₃, Shanghai Aladdin Regent Ltd., Co., Shanghai, China), potassium hexacyanoferrate (III) (K₃[Fe(CN)₆], Guangzhou Chem. Reagent Co., Guangzhou, China), Nafion ethanol solution (5.0%, Beijing Honghaitian Tech. Co., Beijing, China), and 1-methyl-2-pyrrolidinone (NMP, 99.5%, Shanghai Aladdin Regent Ltd., Co., Shanghai, China) were used directly.
The supporting electrolyte was 0.1 mol/L phosphate buffer (PB) solution with various pH values and deoxygenated by using pure nitrogen for 30 min before the experiments. All the other chemicals were of analytical grade, and ultra-pure water from a Mill-Q water purification system (Milli-Q IQ7000, Boston, MA, USA) was used throughout the experiments.

The following were used as received: 1-hexylpyridinium hexafluorophosphate (HPPF₆, Lanzhou Yulu Fine Chem. Co., Lanzhou, China), HRP (MW. 40000, Sinopharm Chem. Reagent Co., Shanghai, China); black phosphorus nanoplates (BPNPs, Nanjing XFNANO Materials Tech. Ltd. Co., Nanjing, China), purified amio single-walled carbon nanotubes (SWCNTs, diameter: 1–2 nm, length: 5–30 nm, special surface area: 380 m²/g, Nanjing XFNANO Materials Tech. Ltd. Co., Nanjing, China), trichloroacetic acid (TCA, Tianjin Kemiou Chem. Co., Tianjin, China), NaNO₂ (Shanghai Chem. Plant, Shanghai, China), H₂O₂ (Xilong Scientific Ltd. Co., Guangzhou, China), 1-methyl-2-pyrrolidinone (NMP, 99.5%, Shanghai Aladdin Regent Ltd. Co., Shanghai, China), and Nafion (5.0%, Dupont, Wilmington, NC, USA). The supporting electrolyte was 0.1 mmol/L PBS. All other reagents were of analytical grade. Ultrapure water was obtained from a Milli-Q water purification system (Milli-Q IQ7000, Merck, Billerica, MA, USA) throughout the experiments.