Sigracet 39 bc

The cathode GDE were prepared by airbrushing catalyst inks with a carrier gas of nitrogen. The catalyst ink was prepared with 30 mL ethanol (Greenfield Global Inc., >99.8%), 150 μL Nafion (Fuel Cell Store D521 Alcohol based 1100 EW, 5 wt%) and catalytic material. The catalytic material quantities varied by sample. For example, the sample containing only CuPc was made with 14 mg of CuPc (Sigma–Aldrich 546682, >99%). Similarly, The catalytic materials for CNP:CuPc ratios of 1:1, 2:1, 4:1, 7:1 and CNP only were made with 14 mg CNP (Alfa Aesar 39724, 75 m² g⁻¹) + 14 mg of CuPc, 14 mg CNP + 7 mg CuPc, 14 mg CNP + 3.5 mg CuPc, 14 mg CNP + 2 mg CuPc and 14 mg CNP + no CuPc, respectively. The catalyst ink mixtures were sonicated for 5 h, and then sprayed on a gas diffusion carbon paper (Fuel Cell Store Sigracet 39 BC, with microporous layer) with a spray density of 0.22 mL cm⁻². After airbrushing, the GDE was dried for 24 h at room temperature (~20 °C). The anode electrode was prepared by dip-coating iridium chloride (Alfa Aesar, IrCl3·xH2O 99.8%) on titanium support (0.002” thickness, Fuel Cell Store). Then, IrO_x was formed on the coated electrode by thermal decomposition in air^{50 (link)}.

Cu powder (<45 μm, 99.7% trace metals basis), sodium hydroxide (semiconductor grade, 99.9% trace metals basis), sodium carbonate (99.99% trace metals basis), phosphoric acid (trace metals basis), Chelex 100 sodium form, isopropanol (99.999% trace metal basis), and Nafion solution (5 wt %) were purchased from Sigma-Aldrich. Carbon monoxide (99.999%) and argon (99.999%) were purchased from Air Liquide. The carbon fiber paper support (Sigracet 39 BC) was purchased from the Fuel Cell Store. The electrolyte solutions were prepared using Milli-Q water (18.2 MΩ cm).

Cu nanoparticles (25 nm, 99.99%), Cu microparticles (0.5–1.5 µm) were purchased from Sigma Aldrich. Oxide-derived Cu (OD-Cu) was prepared through electrochemical deposition of Cu₂O film on porous carbon paper (see details in the Supporting information). The as-deposited Cu₂O was reduced at 10 mA cm⁻² in 1 M NaOH for 15 min to form OD-Cu. Ag (20 nm, 99.99%), Bi (80 nm, 99%), and In (80 nm, 99%) were purchased from US Research Nanomaterials, Inc. Sn (<150 nm, 99.99%), Pd/C (5 wt%, 99.99% metal basis), and Pt/C (5 wt%, 99.99% metal basis) was purchased from Alfa Aesar. For a typical Cu nanoparticles electrode, 25 mg Cu nanoparticles were dispersed in 3 ml isopropanol, and 20 µl Nafion ionomer (5 wt% in H₂O) was added as a binder. The catalyst ink was sonicated for 20 min and drop-casted onto a 2.5 cm² porous carbon paper (Sigracet 39BC, Fuel Cell Store). The loading was controlled at 0.5 mg cm⁻² based on the metal mass. A similar procedure was applied to other metal catalysts.