Nafion 117

Copper sulfates (CuSO₄, 99%), silver nitrate (AgNO₃, 99%), ammonium sulfate(99%, ethylenediamine(NH₂CH₂CH₂NH₂, 99.5%), potassium hydroxide (KOH, 90%) potassium bicarbonate(KHCO₃, 99.7%), sulfuric acid(H₂SO₄, 99.99%), Iridium (III) chloride hydrate (IrCl₃·xH₂O, 99.9%), 5-Amino-1,3,4-thiadiazole-2-thiol(C₂H₃N₃S₂,95%), 3-amino-1,2,4-triazole-5-thiol(C₂H₄N₄S,99%), cysteamine(C₂H₇NS,99%) and 1-Propanethiol (C₃H₈S, 99%) were purchased from Sigma Aldrich. Nafion 117 and anion exchange membrane (Fumapem FAA-3-50), gas diffusion layer (Freudenberg, H23C6), and titanium mesh were obtained from Fuel Cell Store. All chemicals were used as received. All aqueous solutions were prepared using deionized water with a resistivity of 18.2 MΩ cm⁻¹.

The cathodes for the acidic MEA were based on either CuPc/CNP or EDTA decorated CuPc/CNP electrodes with the catalyst loading of 0.15 mg cm^-2. The anodes were based on Ti felt (0.3 mm thickness) loaded with 1 mg cm^-2 IrO₂. 0.005 M H₂SO₄ was used as anolyte circulated with a flow rate of 5 mL min^-1. A microchanneled cation exchange membrane (Nafion 117, Fuel Cell Store) facing the anodic side was used for transporting proton and locally regenerated CO₂. The channeled CEM was prepared by hot embossing under a temperature of 220 °F and a pressure of 1.25 MPa for 5min^{31 (link)}. An anion exchange membrane (Sustainion X37-50 Grade RT, Dioxide Materials, USA) facing the cathodic side was used to facilitate CO₂R activation. DI water was circulated in the middle channel layer at a constant flow rate of 0.5 mL min^-2 using a syringe pump.

The following chemicals were used for platinum
nanoparticles (Pt NPs) synthesis and flocculation: hexa-chloroplatinic
(IV) acid hexahydrate (H₂PtCl₆·6H₂O, 99.9%, Alfa Aesar), ethylene glycol (EG, 99%, Alfa Aesar), sodium
hydroxide (NaOH, 99.99%, Merck), 37% hydrochloric acid (HCl, Suprapur,
Merck), and acetone (for HPLC, VWR Chemicals BDH). Vulcan XC72R carbon
black was employed as support for the metal nanoparticle deposition.
37% hydrochloric acid (HCl, Suprapur, Merck) and 65% nitric acid (HNO₃, Suprapur, Merck) were used for the dissolution of the metal
nanoparticles for inductively coupled plasma mass spectrometry analysis.
Isopropanol (IPA, for HPLC, VWR Chemicals BDH), Milli-Q water (resistivity
> 18.2 MΩ·cm, total organic carbon (TOC) < 5 ppb),
and Nafion (D1021, 10 wt %, Fuel Cell Store) were used for catalyst
ink preparation. 70% perchloric acid (HClO₄, Suprapur,
Merck) and formic acid (FA, ≥95%, Sigma-Aldrich) were used
for the preparation of the electrolyte and reactant during the electrochemical
measurements. Gas diffusion layers (GDL) with microporous layer (H23C8,
Freudenberg) and without microporous layer (H23, Freudenberg) as well
as Nafion membranes (Nafion 117, Fuel Cell Store) were used for the
catalyst layer assemblies. Ar (99.999%, Air Liquide) and CO (99.97%,
Air Liquide) were used for the electrochemical measurements.