The Electroreduction of Carbon Dioxide on Porous Copper Nanoparticles

Copper nanoparticles of porous, controlled structure were synthesized using the sacrificial support method (SSM). The precursor weight percent (wt%) of copper (Cu) and fumed silica (EH-5) was varied to determine the optimum ratio for this material. The precursors were reduced at i) 350°C in a 7% H2 atmosphere and ii) at 250°C in a 100% H2 atmosphere. The specific surface areas of the nanoparticles was measured by Brunauer-Emmett-Teller N2 absorption. The morphologies and widths of the nanoparticles were confirmed by imaging the nanoparticles by scanning electron microscopy (SEM). The bulk composition of the nanoparticles was determined by X-ray diffraction (XRD). Results of these characterizations are discussed in detail. The nanoparticles with a precursor Cu content of 5 and 10wt% exhibited the most controlled morphology with smallest particle widths when reduced at 250°C in 100% H2 (21.5 ± 6.7 nm and 29.3 ± 11.3 nm, respectively) and at 350°C in 7% H2 (29.8 ± 9.4 nm and 60.5 ± 21.5 nm, respectively). Carbon dioxide (CO2) electroreduction (CER) on the Cu nanoparticles synthesized by SSM was confirmed with rotating disk electrode experiments (RDE) using cyclic voltammetry at 25°C in CO2 saturated 0.1M potassium bicarbonate solution (KHCO3) at atmospheric pressure. The electrochemical stability of these nanoparticles was tested via bulk electrolysis for one hour at -1.2, -1.6, and -2.2 V vs. Ag/AgCl in kinetic and diffusion limited regimes. All nanoparticles exhibited activity towards CER and displayed excellent stability for at the potentials tested. The current densities observed during bulk electrolysis at -2.2 V vs. Ag/AgCl were between ca. -23 and -40 mA cm-2 for the nanoparticles reduced at 350 °C in 7% H2 atmosphere and ca. -12 and -20 mA cm-2 for the nanoparticles reduced at 250°C in 100% H2 atmosphere. The magnitude and stability of these particles makes them ideal candidates for further studies that will determine their relative efficiencies towards spec