Vulcan xc 72

Iron(II) chloride (>98%),
tin(II) chloride dihydrate, Nafion (5 wt % in a mixture of lower aliphatic
alcohols and water), diethyl ether (>99.8%), ethanol (HPLC grade
>99.8%), THF (HPLC grade > 99.9%), acetone (HPLC grade > 99.9%),
acetic
acid (>99.8%), methanol (HPLC grade > 99.9%), potassium hydroxide
(assay 86.7%), HCl (37%), sodium acetate trihydrate, and sodium nitrite
were purchased from Sigma-Aldrich and Carlo Erba reagents and used
without any purification. Vulcan XC72 was purchased from Fuel Cell
Store (USA), and 1,10-phenanthroline (>99%) was purchased from
Alfa-Aesar.
Highly pure H₂SO₄ (Fluka, 93–98%, TraceSELECT)
was employed for electrochemical characterization. Carbon paper with
PTFE treatment and Nafion 117 membrane were purchased from Hydro2Power
SRL.

Carbon paper electrodes (SGL 39BC, thickness: 340 μm, Sigracet^®) were modified with silk. Given the hydrophobic nature of the surface of the PTFE, freeze dried sponges of AmelF3 were dissolved in hexafluoro isopropanol (HFIP) rather than the protein being prepared in water^{47 (link)}. Given that CoPPIX is not soluble in HFIP, the macrocycle was incorporated into a precast silk film by soaking the film in a 70:30 v/v methanol:water solution with CoPPIX (1 mg mL⁻¹). The effect of using carbon black (Vulcan XC 72, Fuel Cell Store, USA; 0.5 mg cm⁻²) to increase the surface area was also tested. The optimum procedure was found using 5 wt% PTFE with carbon black in HFIP (10 mg mL⁻¹) dispersed by sonication for 45 min. The carbon black solution could either be cast as a film prior to the silk or mixed with a solution of silk dissolved in HFIP.

The electrodes were prepared by air-bushing the CuPc/CNP or EDTA/CuPc/CNP inks onto hydrophobic carbon papers. The spray density was kept at 0.1 mL cm^-2. The CuPc/CNP catalyst inks were prepared by dispersing 64 mg CuPc ( > 99.5%, Sigma-Aldrich) and 42 mg CNP (Vulcan XC 72, Fuel Cell Store) mixture in 30 mL methanol (>99.5%, Fisher chemical) with 150 µL 5 wt% PiperIon (Fuel Cell Store) anion exchange ionomer as the binder. We obtained different CuPc/CNP ratios by varying the CNP quantity in the mixture, and the CuPc/CNP ratio was ranged from 1:4 to 5:1. The molecule (ED, EDDA and EDTA) decorated CuPc/CNP inks were prepared by adding 16 mg decoration molecule (ED > 99.5% Sigma-Aldrich; EDDA > 98% Sigma-Aldrich; EDTA > 99.5%, Sigma-Aldrich) into 2 mL fully dispersed CuPc/CNP solutions, followed by sonicating for 24 h. The EDTA and CuPc ratio were optimized from 16:1 to 2:1 by tuning the EDTA weight in the CuPc/CNP dispersed solution.