Single cell tests

The membrane electrode assembly (MEA) includes cathode gas diffusion layer (GDL), cathode catalyst layer, anode GDL, anode catalyst layer and proton exchange membranes. The GDL on both electrodes was polytetrafluoroethylene (PTFE)-treated carbon paper (Toray TGP-H-060) covered with 0.4 mg cm⁻² carbon powder containing 40 wt% PTFE. The cathode catalyst Pt₁-N/BP was mixed with Nafion solution (DuPont, 5 wt %) and ethanol with a mass ratio of 1:20:30 to obtain a uniform ink, which was then brushed onto the cathode GDL to obtain the cathode. The loading of Pt₁-N/BP on the electrode was 2.5 mg cm⁻². The anode catalyst layer was prepared by a catalyst-coated-membrane procedure. Specifically, 20 wt% Pt/C (Johnson Matthey), Nafion solution and absolute ethanol with a mass ratio of 1:5:200 were mixed uniformly to obtain catalyst ink, which was directly sprayed on one side of the Nafion212 membrane until the Pt loading is 0.08 mg cm⁻²to obtain the anode catalyst layer after dried. Then, the MEA components were stacked up in the order of anode GDL, Nafion membrane with the anodic catalyst layer facing down and cathode GDE with the cathodic catalyst layer facing down, and then placed on a hot plate at 130 °C for 120 s without pressure. The obtained MEA was sandwiched between two Au-plating stainless steel bi-polar plate-embedded graphite plates with flow fields. The active area of the MEA is 1 cm². The single cell was evaluated on a fuel cell test station (Green Light Inc.) at a cell temperature of 80 °C. The anode supply was pure H₂ and the flow rate was 100 sccm with 100% humidity. The cathode supply was pure O₂ and the flow rate was 200 ml min⁻¹ with 100% humidity. The discharging curve was recorded at the back pressure of 0.2 bar. The durability or the lifetime of the single cell was tested at 0.5 V and the back pressure of 0.2 bar, with the other conditions unchanged. The fuel cell with commercial Pt/C as both cathode and anode was prepared and tested in the same way as described above.