Nafion

Oleylamine (OAm, >70%) and hexane (99.5%), were both purchased from Tokyo Chemical Industry Co. Ltd., Shanghai. Pt(acac)₂ (99.99%), Nafion (5% w/w solution) were all obtained from Alfa Aesar. Ammonium fluoride (≥96%), Ammonium chloride (≥99.5%), Ammonium bromide (≥99%), chloroform (≥99%) and ethanol (≥99.5%) were all purchased from Sinopharm Chemical Reagent Co. Ltd. All the chemicals were of analytical grade and used as received without further purification.

The improved gas diffusion cathodes (GDCs) were made by adopting method previously reported in the literature^{34 (link)}. Similarly, GDC comprised of catalytic carbon and Ni mesh for current collector. A paste for catalyst layer was produced from 25 mg carbon black and 125 mg FeCl₂. Ultrasonic bath (XUBA3, Grant Instruments, UK) was used to sonicate the mixture of carbon black and FeCl₂ for 10 min in 5 wt% Nafion^® from Alfa Aesar, UK (D-520 dispersion). The resulting sonicated paste of Nafion, carbon black, and FeCl₂ was rolled over 40 mm × 40 mm × 0.4 mm on a piece of carbon cloth pre-treated with 25 wt% PTFE as shown in Fig. 1. The catalyst loading was found around 5 mg cm⁻² on the electrode.Figure 1

GDC electrodes geometry and experimental arrangement of the undivided electrochemical flow cell.

Finally, electrode hot-pressed by using Carver 3851-0 Hydraulic Press (Cole Palmer, UK) for 2 min at 140 °C under a pressure of 5 MPa by arranging a 0.02 mm thick nickel mesh (current collector) as a top cover for the layered carbon cloth with carbon black and FeCl₂ layer. The GDC electrodes were recovered from the hydraulic press and allowed to spontaneously cool down in air for 10 min.

Commercial Pt/C (60 wt% Pt, Johnson Matthey, England) was used as the catalyst for both anode and cathode. The catalysts were dispersed in Nafion^® binder (Nafion^® D521 dispersion, Alfa Aesar, China), where the mass ratio of Nafion^® to the catalyst was 20 wt%. The resulting dispersion was sprayed by an air gun (Iwata, Japan) onto carbon paper (Toray 250, Japan) to achieve 0.4 mg cm⁻² catalyst loadings (0.24 mg Pt cm⁻²) on both anode and cathode with an effective area of 4 cm². Membrane electrode assembly was fabricated from the anode–membrane–cathode sandwich by hot press under a pressure of 4.0 MPa at 120 °C for 3 min. Single-cell PEMFC tests were conducted on a Fuel Cell Test System 850e (Scribner Associates, USA). The hydrogen and oxygen were supplied at selected RH values to the anode and cathode at flow rates of 120 and 160 sccm (standard atmospheric pressure without back pressure), respectively. The cell was activated at the selected test temperature for 3 h before the polarization curves were recorded. A 10 mV AC signal was included to the PEMFC to acquire EIS information, with the scanning frequency varied from 0.1 to 10⁵ Hz.

Material dispersions used for further GR electrode modification were prepared in i-propanol prior to use. One milligram of PANI nanostructures was dissolved in 100 μL of i-propanol solution containing 0.5% Nafion (Alfa Aesar, Kandel, Germany). Prior to use, the dispersion was stirred vigorously in an ultrasonic bath for 15 min. The rGO solution was prepared in the same manner as the PANI dispersion. Then, the PANI and rGO dispersions were mixed and added to the ultrasonic bath for an additional 15 min to prepare PANI and rGO mixtures of the required (5:1, 1:1, 1:5, 1:10, and 1:15) ratios.

Melamine (99%), Terethalaldehyde (98%), and dimethyl sulphoxide (99%) were received from Aladdin reagents (Shanghai) Co., LTD. Ferric chloride hexahydrate (FeCl₃.6H₂O), 99.0%), hydrochloric acid (36%), ethanol (99.7+%), Superpur Sulfuric acid (96.0%), Calcium Hydride (CaH₂) and sodium hydroxide (98.0%) were obtained from China Chemical Reagent Corporation Aladin and Macklin. The commercial Pt/C (Pt 20 wt%) and Nafion (5%) were purchased from Alfa Aesar. The carbon black (Ketjenblack EC600J) was bought from Akzo Nobel, Japan. The deionized water (18.2 MΩ) was used during all experimental work.